1 Non-Functional Requirements Lawrence Chung Department of Computer Science The University of Texas at Dallas Non-Functional Requirements Practices and Recommendations: A Brief Synopsis
Why
What
Some Classification Schemes
NFRs and RE Processes
Some Individual NFRs
With Rational Unified Process and UML
With Volere Requirements Specification Templates Lawrence Chung Why Non-Functional Requirements (NFRs)? • Consider a brochure from an automobile manufacturer: – When you buy our car, you can now drive to a store… • Consider a brochure from a cellular phone manufacturer: – When you buy our cellular phone, you can now call your friend. – Well, … Lawrence Chung Why NFRs? • With automobiles: – The basic function is transportation from one location to another. – “With premium luxury, outstanding safety features and superior off-pavement capability, … continues to exceed the high expectations of its owners, …continue to set the standard for premium luxury in its segment." • With cellular phones: – The basic function is communication with another party – “… enhancements enable the best possible operation of your mobile … in various conditions. … The earpiece fits in either ear allowing for convenient and discreet access to all basic call controls. ... To maximize call security, the headset also supports encryption of the wireless connection for compatible … models. • With home networking: “… is the total home networking solution … linking variety of digital home appliances as one. It enables you to enjoy convenient, pleasant, and comfortable living environment at any time and any place. • With CASE tool software: – The basic function is provision of some services – “… is a powerful, easy-to- use application definition platform used by business experts to quickly assemble functionally rich simulations of Web-based applications in a matter of hours. … Using the easy to learn, drag-and-drop paradigm …, business people can quickly lay out the page flow of simulations and create high fidelity pages that precisely mimic not only the look and feel of the final application, …” 2 Lawrence Chung NFRs: IEEE definition “non functional requirement – in software system engineering, a software requirement that describes not what the software will do, but how the software will do it, for example, software performance requirements, software external interface requirements, design constraints, and software quality attributes. Nonfunctional requirements are difficult to test; therefore, they are usually evaluated subjectively.” General Observations General Observations “non functional requirement – generally informally stated, often contradictory, difficult to enforce during development and evaluate for the customer prior to delivery” Lawrence Chung What are Non-Functional Requirements? • -ilities: understandability, usability, modifiability, interoperability, reliability, portability, maintainability, scalability, (re-)configurability, customizability, adaptability, variability, volatility, traceability, … • -ities: security, simplicity, clarity, ubiquity, integrity, modularity, nomadicity, … • -ness: user-friendliness, robustness, timeliness, responsiveness, correctness, completeness, conciseness, cohesiveness, … • …and many other things: performance, efficiency, accuracy, precision, cost, development time, low coupling, … Lawrence Chung NFRs: Some classification schemes - 1 • Interface requirements: describe how the system is to interface with its environment, users and other systems. E.g., user interfaces and their qualities (e.g., user-friendliness) • Performance requirements: describe performance constraints involving – time/space bounds, such as workloads, response time, throughput and available storage space. E.g., “system must handle 100 transactions/second” – reliability involving the availability of components and integrity of information maintained and supplied to the system. E.g., “system must have less than 1hr downtime/3 months” – security, such as permissible information flows – survivability, such as system endurance under file, natural catastrophies • Operating requirements: include physical constraints (size, weight), personnel availability, skill level considerations, system accessibility for maintenance, etc. • Lifecycle requirements: can be classified under two subcategories: – quality of the design: measured in terms such as maintainability, enhanceability, portability. – limits on development, such as development time limitations, resource availability, methodological standards, etc. • Economic requirements: immediate and/or long-term costs • Political requirements   [Roman, IEEE Computer 1985] [Roman, IEEE Computer 1985] Lawrence Chung NFRs: Some classification schemes - 2  Process, Product and External considerations [Sommerville 1992] 3 Lawrence Chung NFRs: Some classification schemes - 3 Lawrence Chung F Functionality Feature set capabilities, security, generality U Usability Human factors aesthetics, consistency, documentation R Reliability Frequency/severity of failure, recoverability, predictability, accuracy, MTBF P Performance Speed efficiency, resource usage, throughput, response time S Supportability Testability Extensibility Adaptability Maintainability Compatibility Configurability Serviceability Installability Localizability Robustness NFRs: Some classification schemes - 4  Dimensions of Quality –Components of FURP+ [Grady1992] Lawrence Chung NFRs: Some classification schemes - 5  Software Quality Tree [Boehm 1976] Lawrence Chung NFRs & RE Processes: Why? Quality of product Quality of Process Product P r o c e s s
Garbage in garbage out, so get the right requirements
Garbage thru garbage out, so get the right process Evolution is inevitable – traceability is a virtue 4 Lawrence Chung Approaches to NFRs • Product vs. Process? PPrroodduucctt vvss.. PPrroocceessss?? Product vs. Process? – Product-oriented Approaches • Focus on system (or software) quality • Aim is to have a way of measuring the product once it’s built –metrics – Process-oriented Approaches • Focus on how NFRs can be used in the design process • Aim is to have a way of making appropriate design decisions • Quantitative vs. Qualitative? QQuuaannttiittaattiivvee vvss.. QQuuaalliittaattiivvee?? Quantitative vs. Qualitative? – Quantitative Approaches • Find measurable scales for the quality attributes • Calculate degree to which a design meets the quality targets – Qualitative Approaches • Study various relationships between quality goals • Reason about trade-offs etc. Lawrence Chung NFRs & RE Processes:  Before FRs?  After FRs?  At the same time with FRs?  … and what about Business objectives/goals, system architectures, system models, SS, SRS, … ? But, should we perhaps better know about the various relationships between NFRS and such and such, before answering these questions, more clearly, understandably, concisely, precisely, agreeably, … ? So, where are NFRs in an RE Process? So, where are NFRs in an RE Process? Lawrence Chung Product-oriented approaches Lawrence Chung Product-oriented approaches 5 Lawrence Chung NFRs: Portability • The degree to which software running on one platform can easily be converted to run on another platform • E.g., number of target statements (e.g., from Unix to Windows) • Hard to quantify, since it is hard to predict what a “next generation” platform might be like • Can be enhanced by using languages, OSs and tools that are universally available and standardized. E.g., C/C++/C#/Java J2EE/J2ME/.NET Lawrence Chung • the ability of the system to behave consistently in a user-acceptable manner when operating within the environment for which the system was intended. • theory and practice of hardware reliability are well established; some try to adopt them for software • one popular metric for hardware reliability is mean-time-to-failure (MTTF) "Bathtub" curve characterizes MTTF: • Infant mortality: Given a large population of a particular component, many will fail soon after development due to inaccuracies in the manufacturing process; • Issues: Do 2 different software copies have different characteristics? Does software wear & tear by decomposition? Does software obey physical laws? NFRs: Reliability time # of failures Infant motility Constant operation Wear & tear MTBF MTBF MTTF MTTFMTTR MTTR Availability = [MTTF/(MTTF + MTTR)] x 100% Lawrence Chung • Sometimes reliability requirements take the form: "The software shall have no more than X bugs/1K LOC" But how do we measure bugs at delivery time? • Bebugging Process - based on a Monte Carlo technique for statistical analysis of random events. 1. before testing, a known number of bugs (seeded bugs) are secretly inserted. 2. estimate the number of bugs in the system 3. remove (both known and new) bugs. # of detected seeded bugs/ # of seeded bugs = # of detected bugs/ # of bugs in the system # of bugs in the system = # of seeded bugs x # of detected bugs /# of detected seeded bugs Example: secretely seed 10 bugs an independent test team detects 120 bugs (6 for the seeded) # of bugs in the system = 10 x 120/6 = 200 # of bugs in the system after removal = 200 - 120 - 4 = 76 • But, deadly bugs vs. insignifant ones; not all bugs are equally detectable; ( Suggestion [Musa87]: "No more than X bugs/1K LOC may be detected during testing" "No more than X bugs/1K LOC may be remain after delivery, NFRs: Reliability original original seeded seeded seeded seeded original original = = : :: : 6 6 10 10 114 114 ? ? 190 190 - 114 114 Lawrence Chung • refers to the level at which a software system uses scarce computational resources, such as CPU cycles, memory, disk space, buffers and communication channels • can be characterized along a number of dimensions: Capacity: maximum number of users/terminals/transactions ... Degradation of service: what happens when a system with capacity X widgets per time unitreceives X+1 widgets? - Let the system handle the load, perhaps with degraded performance - Let the system crash Timing constraints: Let stimulus refer to an action performed by the user/environment, and response refer to an action generated by the system. NFRs: Efficiency response response stimulus stimulus - stimulus stimulus-response response: : e.g., "the system will generate a dial tone within 10 e.g., "the system will generate a dial tone within 10 secs secs from the time the phone is picked up" from the time the phone is picked up" - response response-response response: : e.g., "the system will record that the phone is in use no later e.g., "the system will record that the phone is in use no later than 1 micro than 1 micro-second after it had second after it had generated a dial tone" generated a dial tone" - stimulus stimulus-stimulus stimulus: : e.g., "the user will type her password within 15 e.g., "the user will type her password within 15 secs secs from typing her login name" from typing her login name" - response response-stimulus stimulus: : e.g., "the user will start dialing the phone number within 1 min e.g., "the user will start dialing the phone number within 1 minute from getting the dial tone" ute from getting the dial tone" 6 Lawrence Chung NFRs: Usability • broadly – quality; fit to use narrowly - good UI • Usability inspection: finding usability problems in UI design, making recommendations for fixing them, and improving UI design. • Heuristics: a set of criteria against which usability of UI design is evaluated • "9 usability heuristics" [Nielsen90] • Promptness no undue delay in accepting info items and responding to requests • Tolerance no hang-ups against errors, delays, unexpected behavior, etc. • Guidance providing guidance for correcting errors, generating reminders, etc. • Coherence ... ... • "10 usability heuristics" [Molich and Nielsen90] • Simple and natural dialogue; Speak the user ’ s language • Minimize the user ’ s memory; Consistency; Feedback • Clearly makred exits; Shortcuts • Precise and constructive error messages; Prevent errors • Help and documentation Lawrence Chung NFRs: Usability • All users will be satisfied with the usability of the product. • 95% of all users will be satisfied with the usability of the product. • 95% of the users will be able to complete representative tasks without requiring assistance (e.g., modifying exclusion date set) • 95% of the users will be able to complete representative tasks by the third attempt without requiring assistance • 95% of the users will be able to complete tasks X Y Z by the third attempt without requiring assistance • 95% of the users will be able to complete tasks X Y Z in less than 10 minutes without requiring assistance • 95% of the users will be able to complete task X in less than 10 minutes without requiring assistance • 80% of the users will be able to complete task Y in less than 10 minutes • 77% of the users will be able to complete task Z in less than 5 minutes Lawrence Chung Dependability • Dimensions of Dependability – Availability - The ability of the system to deliver services when requested – Reliability - The ability of the system to deliver services as specified – Safety - The ability of the system to operate without catastrophic failure – Security - The ability of the system to protect itself against accidental or deliberate intrusion• Cost of development - Geometric rise in cost from low dependability to highest • Effects of low dependability – Often unused – Failure recovery costs may be high – Difficult to retrofit dependability – Loss of information • Repeatable improvement process helps – CMM -SEI – More later • Critical Systems – Safety critical – Mission critical – Business critical • Dependability a key aspect – A system failure causes • Significant economic loss • Physical damage • Threat to or loss of human life Lawrence Chung Dependability • Cost of failure – direct • Loss of life / Injury • Loss of business – Indirect • Litigation • Good will • Availability and Reliability – Factors effecting • Environment office versus university • Perception (frequency of occurrence) • Degrees – Failure - service that is expected is not delivered – Error – behavior that does not conform to the specification – Fault – incorrect state – unanticipated – Human error • Improve reliability – Fault avoidance – Fault detection and removal – testing and debugging – Fault tolerance - self checking and redundancy • Errors of this type are random – Remain after testing due to unforeseen combinations of input or use – Random based on user methods • Not all inputs done the same • Learn to avoid • Therefore removal of some faults will not improve perception 7 Lawrence Chung Dependability - Safety • Ability to operate normally or abnormally without threat to life or environment • Classes – Primary safety critical • Embedded as controller – Secondary • There output could effect indirectly other processes (CAD) • Reasons for less than 100% certainty of fault tolerant/free – Incomplete specification – Hardware malfunction – causing exceeded limits in software – Incorrect input • Methods to lessen chance of safety failure – Hazard avoidance • Added control features (I.e. two man rule) – Hazard detection and removal • Scans for known causes and cause preventive action – Damage limitation (control) • Firewalls and other protective reactions to results • Terms – Accident – Hazard – Damage – Hazard Severity – Hazard Probability – Risk Lawrence Chung Specification • Safety – IEC 61508 safety life cycle • Concept to death – Hazard analysis – Safety requirements definition – Planning , validation, development, external risk reduction – Separate safety validation – installation and commissioning – O&M – Decommissioning – Hazard and Risk Analysis • Iterative process – Hazard Identification » Hazard description – Risk analysis and hazard classification » Risk assessment – Hazard decomposition » Analysis as to potential causes (fault-tree analysis) – Risk reduction analysis – Preliminary safety requirements • Fault tree – Deductive – start with a hazard – Inductive – start with failure – Fault tree starts with the failure and works backwards to potential causes • Risk assessment – Classifications • Intolerable • As low as reasonably practical (ALARP) • Acceptable – For each hazard • Probability • Severity • Estimated risk • Risk reduction – Avoidance – Detection and removal – Damage limitation Lawrence Chung Dependability - Security • Lack of security comprise to availability and reliability • Types – Denial of service – Corruption of programs or data – Unauthorized disclosure • Terms – Exposure – Vulnerability – Attack – Threats – Controls • Methods – Vulnerability avoidance – Detection and neutralization – Damage limitation • Security Specification – Similar to safety – Impractical to specify – Usually are “shall not” • Cycle in General – Asset ID and evaluation • Degree of importance – Threat analysis and risk assessment – Threat assignment lists all threats against each asset – Technology analysis what is available to counteract – Security specification Lawrence Chung Specification • Requirements specification – Functional for error detection and recovery – Non functional for reliability and availability – Shall not requirements • Reliability specification – Hardware – Software – Operator • Decrease probability of failure – For a series of dependent components Pt = sum of P1 to Pn – But if there are n replicated (redundant) and independent components then the Pt=pa to the nth • Metrics for reliability – POFD probability of failure on demand .0001 = 1 on 10000 • Systems with unpredictable demand over long time periods – emergency systems – ROCOF Rate of failure occurrence 2/1000 • Systems with a regular demand atm/airline reservations – MTTF Mean time to Failure avg time between observed failures 500 = avg of 1 in 500 time units • Systems with long transactions (auto save) – AVAIL probability system is available at any given time .999 equals in every given 1000 time units system is • Non-functional reliability requirements – ID type of failure to occur – Partition them into • Transient • Permanent • Recoverable • Unrecoverable • Non-corrupting • Corrupting – Define the appropriate requirement (metric) • E.g. recoverable w/intervention – POFOD • If automatic the ROCOF 8 Lawrence Chung NFRs: With Rational Unified Process and UML Home Appliance Control System Vision Version 1.2 Revision History DescriptionAuthorDateVersion Table of Contents 1. Introduction 5 1.1 Purpose 5 1.2 Scope 5 1.3 Definitions, Acronyms, and Abbreviations 5 1.4 References 5 2. Positioning 5 2.1 Business Opportunity 5 2.2 Problem Statement 5 2.3 Product Position Statement 6 3. Stakeholder and User Descriptions 6 3.1 Market Demographics 6 3.2 Stakeholder Summary 6 3.3 User Summary 7 3.4 User Environment 7 3.5 Stakeholder Profiles 7 3.5.1 Homeowner 7 3.5.2 Business Owner 8 3.5.3 Customer Care 8 3.6 User Profiles 9 3.7 Key Stakeholder or User Needs 9 3.8 Alternatives and Competition 9 3.8.1 House Sitter 9 4. Product Overview 9 4.1 Product Perspective 9 4.2 Summary of Capabilities 10 4.3 Assumptions and Dependencies 11 4.4 Cost and Pricing 11 4.5 Licensing and Installation 11 5. Product Features 11 5.1 Start system 11 5.2 Shutdown system 11 5.3 View status of system 11 5.4 Add a new group of sequences 12 … 6. Constraints 14 6.1 Security 14 6.2 Usability 15 6.3 Responsiveness 15 6.4 Capacity 15 Appendix A. COTS Components 15 Lawrence Chung 6. Constraints 6.1 Security Security for the HACS includes authentication, access control, data integrity, and data privacy. Authentication of the user is by identifier and password. Homeowners and Business Owners can monitor and change the state of the system. Customer Care users can only monitor the system and manually place a medical alert 911 emergency request for an ambulance. Transmissions should be encrypted for privacy 6.2 Usability Easy to use (especially safety related features) Request for an ambulance, police or fire truck needs to be at the push of a button or voice activated 6.3 Responsiveness System responds quickly to user requests or changes in the environment. System responds within 2 seconds on average to local user requests and changes in the environment. System responds within 4 seconds on average to remote user requests and changes in the environment. 6.4 Capacity Maximum number of sequences for indoor lights is twenty (20) Maximum number of indoor lights that can be controlled is fifty (50) Maximum number of sequences for outdoor lights is twenty (20) Maximum number of outdoor lights that can be controlled is fifty(50) Maximum number of sequences for radios, CD players, televisions is twenty (20) Maximum number of radios, CD players, televisions that can be controlled is ten (10) Maximum number of sequences for safety and security equipment istwenty (20) Maximum number of sensors, security cameras, security VCRs, emergency notifications, that can be controlled is fifty NFRs: With Rational Unified Process and UML Lawrence Chung NFRs: With Volere Requirements Specification Template The Atlantic Systems Guild Limited Table of Contents (http://www.volere.co.uk/template.htm) NON-FUNCTIONAL REQUIREMENTS: 10. Look and Feel 11. Usability and Humanity 12. Performance 13. Operational 14. Maintainability and Support 15. Security 16. Cultural and Political 17. Legal PROJECT ISSUES: 18. Open Issues 19. Off-the-shelf Solutions 20. New Problems 21. Tasks 22. Cutover 23. Risks 24. Costs 25. User Documentation and Training 26. Waiting Room 27. Ideas for Solutions PROJECT DRIVERS: 1. The Purpose of the Project 2. Client, Customer, Stakeholders 3. Users of the Product PROJECT CONSTRAINTS: 4. Mandated Constraints 5. Naming Conventions and Definitions 6. Relevant Facts and Assumptions FUNCTIONAL REQUIREMENTS: 7. The Scope of the Work 8. The Scope of the Product 9. Functional and Data Requirements Lawrence Chung NFRs: With Volere Requirements Specification Template 10 Look and Feel Requirements 10a. The interface Content The section contains requirements relating to spirit of the interface. Your client may have given you particular demands such as corporate branding, style, colors to be used, degree of interaction and so on. This section captures the requirements for the interface rather than the design for the interface. Motivation To ensure that the appearance of the product conforms to the organizationÕsexpectations. Examples The product shall comply with corporate branding standards. The product shall be attractive to a teenage audience. The product shall appear authoritative. Considerations Interface design may overlap the requirements gathering process.This particularly true if you are using prototyping as part of your requirements process. As prototypes develop it is important to capture the requirements that relate to the look and feel. In other words, be sure that you understand your client's intentions for the product's look and feel. Record these as requirements instead of merely having a prototype to which the client has nodded his approval. 10b. The style of the product Content A description of salient features of the product that are related to the way a potential customer will see the product. For example, if your client wants the product to appealto the business executive, then a look and feel requirement is that the product has a conservative and professional appearance. Similarly if the product is for sale to children, then the look and feel requirement is that it be colorful and look like it's intended for children. … Motivation Given the state of today's market and people's expectations, … Once the functional requirements are satisfied, it is often the appearance of products that determines whether theyare successful or not. … Considerations 9 Lawrence Chung NFRs: With Volere Requirements Specification Template 11 Usability and Humanity Requirements 11a. Ease of use. Content This section describes your client's aspirations for how easy itwill be for the intended users of the product to operate it. The product's usability is derived from the abilities of the expected users of the product and the complexity of its functionality. The usability requirements should cover such things as: Efficiency of use - how quickly or accurately the user can use the product. Ease of remembering - how much is the casual user expected to remember about using the product Error rates - for some products it is crucial that the user commits very few, or no, errors. Overall satisfaction in using the product - this is especially important for commercial, interactive products where there is a lot of competition. Web sites are good example of this. Feedback - how much feedback does the user need in order to feel confident that the product is actually accurately doing what the user expects. The necessary degree of feedback will be higher for some products (eg: safety critical) than in others. Motivation To guide the product's designers into building a product that will meet the expectations of its eventual users. Examples The product shall be easy for 11 year-old children to use. The product shall help the user to avoid making mistakes. The product shall make the users want to use it. The product shall be used by people with no training, and possibly no understanding of English. Fit Criterion These examples may seem simplistic, but they do express the intention of the client. To completely specify what is meant by the requirement it is necessary to add a measurement ofacceptance. We call this a fit criterion. The fit criterion for the above examples would be: [An agreed percentage, say 90%] of a test panel of 11 year olds shall be able to successfully complete [list of tasks] within [specified time] One month's use of the product shall result in a total error rate of less than [an agreed percentage, say 2%] An anonymous survey shall show that [an agreed percentage, say 75%] of the users are regularly using the product after [an agreed time] familiarization period.
Why
What
Some Classification Schemes
NFRs and RE Processes
Some Individual NFRs
With Rational Unified Process and UML
With Volere Requirements Specification Templates Non-Functional Requirements Practices and Recommendations: A Brief Synopsis Non-Functional Requirements What - Essential Concepts softgoal satisficing Lawrence Chung NFRs: functional vs. non-functional: a mathematical perspective • (mathematical) function: f1: I -> O f2: I1 X I2 -> O e.g.: sum: R X R -> R • non-functional: – How fast can it be done? – How precise is the answer? – How easy is it to figure out how to use it? – How robust is it concerning the 2nd input of f2? – Who can use it? – Can it be changed easily? – How much would it cost to design and implement it? 10 Lawrence Chung • (mathematical) function: f(x, y) = f1(f2(x), f3(y)) • non-functional: nf(x, y) = nf1(nf2(x), nf3(y)) nf(x, y) = nf1(nf2(n(x)), nf3(n(y))) Global nature NFRs: functional vs. non-functional: a mathematical perspective Lawrence Chung NFRs: subjective, graded, interacting • Subjective vs. objective: subjective objective • Graded: worse better expensive cheaper slower faster • Interacting: – Conflicting: the whole is less than the sum of its parts – Synergistic: the whole is more than the sum of its parts Lawrence Chung NFRs: subjective in both definitions & solutions Classification 2 - Process, Product and External considerations [Sommerville 1992] Classification 5 - Software Quality Tree [Boehm 1976] Classification 1 Classification 1 [Roman, IEEE Computer 1985] [Roman, IEEE Computer 1985] Lawrence Chung NFRs: subjective in both definitions & solutions  Consider “security” – problem is subjective • Protection of data alone, fine with Chris • Protection of data, and data availability, fine with Pat • Protection of data, and data availability, and data accuracy, fine with Alex • Protection of data, and data availability, and data accuracy, and filtering of viruses, fine with Neo • Protection of data, and data availability, and data accuracy, and filtering of viruses, and blocking adware, fine with Gail  Consider “security” – solutions are subjective • A password authentication fine with Chris • A password authentication, with periodic change, fine with Pat • A password, together with a fingerprint verification, fine with Alex • A password, with a fingerprint verification rechecked every hour, fine with Neo • A password, with a fingerprint verification rechecked every hour, and copresence of two people, fine with Gail 11 Lawrence Chung NFRs: subjective – and also relative in priorities security performance reliability usability security safety reliability reliability security Lawrence Chung NFRs: graded in both definitions and solutions – and relative very bad bad good very good worse better expensive cheaper slower faster

Protection of data alone good Protection of data alone good

A password authentication alone bad A password authentication alone bad

Protection of data alone << Protection of data, and data availa Protection of data alone << Protection of data, and data availability bility

A password authentication << A password authentication << A password, together with a fingerprint verification A password, together with a fingerprint verification Lawrence Chung – Conflicting: the whole is less than the sum of its parts  A password, with a fingerprint verification rechecked every hour, fine for security  Simplicity is the key for ease-of-use – Synergistic: the whole is more than the sum of its parts NFRs: interacting   A password, with a fingerprint verification rechecked every hour A password, with a fingerprint verification rechecked every hour, fine for security , fine for security   Restricted access is good for data accuracy Restricted access is good for data accuracy Non-Functional Requirements What - Essential Concepts
non-functional,
subjective,
graded,
interacting
– and relative
- in both definitions & solutions 12 Non-Functional Requirements How 1 - Essential Tasks softgoal satisficing Lawrence Chung NFRs: functional vs. non-functional: a mathematical perspective • (mathematical) function: f1: I -> O f2: I1 X I2 -> O e.g.: sum: R X R -> R • non-functional: – How fast can it be done? Fast, Fast(f), Fast(f2) – How precise is the answer? Precise, Precise(f), Precise(O) – How easy is it to figure out how to use it? Easy-to-learn, Easy-to-learn(f), Easy-to-learn(f2), Easy-tolearn(x) – How robust is the input? Robust, Robust(I1) , Robust(I2) – Who can use it? Security, Security(f), Security(I), Security(O), Security (f2), Accessibility, Accessibility(f), Accessibility(O) – Can it be changed easily? Changeability, Changeability(f), Changeability(f2) – How much would it cost? Cost, Design-cost(f), Implementation-cost(f), Testing-cost(f2) f(x, y) = f f(x, y) = f1 1(f (f2 2(x), f (x), f3 3(y)) (y)) n n f(x f(x, y) = , y) = n n f f1 1( ( n n f f2 2(x), (x), n n f f3 3(y)) (y)) n n f(x f(x, y) = , y) = n n f1( f1( n n f2( f2( n n (x)), (x)), n n f3( f3( n n (y))) (y))) Lawrence Chung The NFR Framework • Based on traditional framework for problem solving in AI [Nilsson] – Establish the goals – Introduce sub-goals to satisfy the goal where the relationship is AND or OR • AND goal is satisfied when all of sub goals are satisfied • OR goal is satisfied when any of the sub goals are met – Continue until you cannot decompose further • Softgoal Softgoal Softgoal Softgoal : no clear-cut definition and or criteria as to whether it is satisfied or not , since NFRs are subjective, relative, and interdependent – Introduce concept of satisficing – Provide basis for saying the softgoal can contribute positively or negatively, fully or partially , to some degree in satisfying other softgoals (i.e., achieved not absolutely but within acceptable limits). • Softgoal Interdependency Graphs (SIGs) – For modeling non-functional requirements and interdependencies between them • Introduces Catalogues of NFRs much like patterns for design are built [Sullivan07 lecture notes] [Sullivan07 lecture notes] Qualitative in nature, Process oriented {Chung et.al.} Non-functional Requirements in Software Engineering Lawrence Chung The NFR Framework Secure Accounts Integrity of Accounts Confidentiality of Accounts Availability of Accounts Integrity of Accounts Confidentiality of Accounts Availability of Accounts Complete Accounts Accurate Accounts Secure Accounts Sub-goals U Make Make >> >> Help Help >> >> Hurt Hurt >> >> Break Break Qualitative in nature, Process oriented NFR softgoal Sub-goals 13 Lawrence Chung Make Make >> >> Help Help >> >> Hurt Hurt >> >> Break Break U The NFR Framework Softgoal Interdependency Graph (SIG) Lawrence Chung Operationalize OOppeerraattiioonnaalliizzee Operationalize The NFR Framework Softgoal Interdependency Graph (SIG): Three types of refinements Lawrence Chung The NFR Framework [J. Mylopoulos, L. Chung, E. Yu, "From object-oriented to goal-oriented requirements analysis ", CACM, pp31-37.ACM Press] Object Model Example: A small portion of a hospital model for requirements analysis Softgoal Interdependency Graph (SIG) From Softgoals to Use Cases Lawrence Chung NFRs: subjective in both definitions & solutions  Know at least what you mean decompose decompose decompose decompose security Integrity Confidentiality Availability performance Time-P Space-P Responsive 14 Lawrence Chung NFRs: subjective in both definitions & solutions  Know at least what you mean as precisely as possible - as many decompositions as needed security Integrity Confidentiality Availability performance Time-P Space-P Responsive Accuracy Completeness Response-T Throughput +Coverage -Coverage Lawrence Chung NFRs: subjective in both definitions & solutions  Know at least what you mean as precisely as possible - as many decompositions as needed authentication password fingerprint Password+ fingerprint indexing Single-level indexing Multi-level indexing Single password Multiple passwords Category-based indexing Single password multiple checks Several different passwords Keyword-based indexing Lawrence Chung NFRs: subjective in both definitions & solutions  Know at least what you mean as precisely as possible - as many decompositions as needed security Integrity Confidentiality Availability performance Time-P Space-P Responsive Accuracy Completeness Response-T Throughput +Coverage -Coverage authentication password fingerprint Password+ fingerprint indexing Single-level indexing Multi-level indexing Single password Multiple passwords Category-based indexing Single password multiple checks Several different passwords Keyword-based indexing Operationalize OOppeerraattiioonnaalliizzee Operationalize Lawrence Chung NFRs: non-functional …and…functional  Know at least what you mean – decompose  Relate Functional and Non-functional sides security Integrity Confidentiality Availability performance Time-P Space-P Responsive Home networking Home networking authentication password fingerprint Password+ fingerprint indexing Single-level indexing Multi-level indexing 15 Lawrence Chung NFRs: non-functional …and…functional  Know at least what you mean – decompose  Relate Functional and Non-functional sides  Be as specific about the scope/topic/parameter: from global to local security Integrity Confidentiality Availability Home networking authentication password fingerprint Password+ fingerprint Garage Door Oven Home Networking Contoller Home Security Lighting  Security Security [Home Networking] Security [Garage Door, Home Networking]  Authentication authentication [Home Networking] authentication [Garage Door, Home Networking] Lawrence Chung NFRs: non-functional …and…subjective in both definitions & solutions  Know at least what you mean – decompose  Relate Functional and Non-functional sides  Different functional Different functional Different functional Different functional operationalizations operationalizations operationalizations o p e r a t i o n a l i z a t i o n s c o n t r i b u t e d i f f e r e n t l y contribute differently contribute differently contribute differently Information security Integrity Confidentiality Availability Home networking authentication password fingerprint Password+ fingerprint Garage Door Oven Home Networking Contoller Home Security Lighting Fixed Lighting Variable Lighting Physical security Make Make >> >> Help Help >> >> Hurt Hurt >> >> Break Break “ “ Satisficing Satisficing ” ” (cf. Nilsson (cf. Nilsson ’’ s) s) Lawrence Chung NFRs: graded in both definitions and solutions – and relative  Explore alternatives – some are better/worse than others security Integrity Confidentiality Availability authentication password fingerprint Password+ fingerprint Confidentiality Lawrence Chung NFRs: graded in both definitions and solutions – and relative  Explore alternatives – some are better/worse than others  Different alternatives may have different degrees o f contributions security Integrity Confidentiality Availability authentication password fingerprint Password+ fingerprint Confidentiality Indivisual password Shared password ++ + ++ + Make Make >> >> Help Help >> >> Hurt Hurt >> >> Break Break “ “ Satisficing Satisficing ” ” (cf. Nilsson (cf. Nilsson ’’ s) s) 16 Lawrence Chung NFRs: interacting – Conflicting: the whole is less than the sum of its parts – Synergistic: the whole is greater than the sum of its parts security Integrity Confidentiality Availability performance Time-P Space-P Responsive Home networking Home networking authentication password fingerprint Password+ fingerprint indexing Single-level indexing Multi-level indexing ease-of-use Lawrence Chung NFRs: interacting – graded/relative – Different techniques thru nfr-operationalizations have different impacts (cf. fr-operationalizations) security Integrity Confidentiality Availability performance Time-P Space-P Responsive Home networking Home networking authentication password fingerprint Password+ fingerprint indexing Single-level indexing Multi-level indexing ease-of-use Indivisual password Shared password ++ + ++ + Lawrence Chung NFRs: interacting – graded and relative –Through functional choices ( fr-operationalizations ) Information security Integrity ConfidentialityAvailability Home networking authentication password fingerprint Password+ fingerprint Garage Door Oven Home Networking Contoller Home Security Lighting Fixed Lighting Variable Lighting Physical security ease-of-use Lawrence Chung NFRs: interacting – graded/relative – Different techniques have different impacts – Prioritize Prioritize Prioritize Prioritize security Integrity Confidentiality Availability performance Time-P Space-P Responsive Home networking Home networking authentication password fingerprint Password+ fingerprint indexing Single-level indexing Multi-level indexing ease-of-use Indivisual password Shared password ++ + ++ + ! + 17 Lawrence Chung NFRs: interacting – graded and relative – Through functional choices – Prioritize Prioritize Prioritize Prioritize Information security Integrity ConfidentialityAvailability Home networking authentication password fingerprint Password+ fingerprint Garage Door Oven Home Networking Contoller Home Security Lighting Fixed Lighting Variable Lighting Physical security ease-of-use!!   Claims Claims Ordinary people experience difficulties with the sequencing No reported break-in incidents Due to fixed lighting   Evaluate Evaluate thru propagation of labels (satisficed, denied) thru propagation of labels (satisficed, denied) Lawrence Chung Softgoal Interdependency Graph (SIG): Evaluation Thru Label Propagation Make Make >> >> Help Help >> >> Hurt Hurt >> >> Break Break AND OR U UU U Lawrence Chung Softgoal Interdependency Graph (SIG): Summary of Modeling Concepts  Softgoals: NFR Softgoals, Operationalizing Softgoals, Claim Softgoals Integrity password Garage Door

Make Make >> >> Help Help >> >> Hurt Hurt >> >> Break Break No reported break-in incidents due to fixed lighting Softgoals ::= Priority Type [topic list] Label  Contributions:

“ “Satisficing Satisficing” ” AND OR ! U Lawrence Chung Softgoal Interdenpency Graph (SIG): Semantics  Proposition = Softgoal U Contribution 18 Lawrence Chung Softgoal Interdenpency Graph (SIG): Semantics MAKE MAKE HELP HELP If satisficed(HELP(G0, G1)) then there exist propositions G2, …, Gn such that HELP BREAK BREAK HURT HURT HURT HURT HURT Und(G0, G1) = MAKE(G0, G1) HELP(G0, G1) HURT(G0, G1) BREAK(G0,G1) Lawrence Chung Softgoal Interdenpency Graph (SIG): Process of Construction An iterative, interleaving process!!!  Post NFR Softgoals:  Refine NFR Softgoals as many times until the meaning is clear  Refine the type  Refine the topic list  Refine the priority  Operationalize NFR Softgoals  Refine Operationalizing Softgoals as many times until all the parts and relationships are designed (N.B: recall “one person’s floor is another person’s ceiling”)  Refine the type  Refine the topic list  Refine the priority  Provide justifications in terms of Claim Softgoals, for any kindof softgoals  Evaluate the degree to which each softgoal is satisficed. Non-Functional Requirements How 2 – Dos and Don’ts softgoal satisficing Lawrence Chung NFRs – Dos & Don’ts  Dos • Relate to FRs • Clarify scope/topic • Identify agents, whenever useful • Discover relationships between definitions of NFRs • Discover relationships between solutions to NFRs • Refine definitions as many times as needed • Refine solutions as many times as needed • Prioritize • Discover conflicts • Safeguard against conflicts • Discover synergies • Discover operationalizations as reasons for conflicts/synergies • Determine strengths of contributions • Justify strengths of contributions • Explore alternatives • Discover solutions from requirements • Discover requirements from solutions • Consider use of multiple solutions • Consider scenarios • If necessary, quantify • Evaluate, …subjectively, …objectively • Establish traceability  Don ’ ts • Absolute security, absolute reliabilty, absolute safety, …. • One definition fits all • One solution solves all problems • The contribution is such and such, since I say so • Refine the definition only once • They are falling down from the sky • Dissociate from FRs • May be more important than FRs, but should consume less resources • You name it; our system does it • No quantification, no existence • Everybody needs the same • Be only pessimistic • Asking why “+” reveals ignorance • Beg the question • Evaluate & only evaluate • Brainwash nothing but objectivity 19 Lawrence Chung Conflict resolution 1 – Delete email w. any zip file attachment -> misunderstanding betw. sender and receiver <- move email w. any zip file attachment into a junk file folder -> If the receiver does not check the junk file folder, still misunderstanding <- at the time the file is moved, notify this to the receiver -> if the receiver still does not check the junk file folder or checks it late, still misunderstanding <- at the time the file is moved, notify the sender too -> If the receiver checks the junk file folder and opens it and the file is an attack, still a security breach Delete email w. any zip file attachment and block any future email from the same sender Lawrence Chung Conflict resolution 2 – If the receiver opens email w. zip file and the file is an attack, a security breach – Delete email any w. zip file attachment -> misunderstanding betw. sender and receiver <- move email w. any zip file attachment into a junk file folder -> If the receiver does not check the junk file folder, still misunderstanding <- at the time the file is moved, notify this to the receiver -> if the receiver still does not check the junk file folder or checks it late, still misunderstanding <- at the time the file is moved, notify the sender too -> If the receiver checks the junk file folder and opens it and the file is an attack, still a security breach
Delete email w. any zip file attachment and block any future email from the same sender
If the email is from a sender who is not in the list of allowed senders, delete it
Leave the email but delete the attachment only Lawrence Chung Conflict resolution 3 – Security[PC] -> S[email] -> S[sender] ^ S[recipient] ^ S[body] ^ S[attachment] – Denied (S[attachment]) -> denied (S[email]) -> denied (S[PC]) – Zip(attachment] ^ attack(attachment) ^ open(attachment) -> denied (S[attachment]) /* If the receiver opens email w. zip file and the file is an attack, a security breach */ ~ Zip(attachment] v ~attack(attachment) v ~open(attachment) -> ~ denied (S[attachment]) helps ~denied(S[email]) – Delete email w. any zip file attachment -> misunderstanding betw. sender and receiver <- move email w. any zip file attachment into a junk file folder -> If the receiver does not check the junk file folder, still misunderstanding <- at the time the file is moved, notify this to the receiver -> if the receiver still does not check the junk file folder or checks it late, still misunderstanding <- at the time the file is moved, notify the sender too -> If the receiver checks the junk file folder and opens it and the file is an attack, still a security breach
Leave the email, but delete the attachment only
Leave the email, but delete the attachment only if it is an attack
Leave the email but change the name of the attachment to “…renameToZip”
If the email is from a sender who is not in the list of allowed senders, delete it Lawrence Chung Conflict resolution 4 – Security[PC] -> S[email] -> S[sender] ^ S[recipient] ^ S[body] ^ S[attachment] – Denied (S[attachment]) -> denied (S[email]) -> denied (S[PC]) – Zip(attachment] ^ attack(attachment) ^ open(attachment) -> denied (S[attachment]) /* If the receiver opens email w. zip file and the file is an attack, a security breach */ ~ Zip(attachment] v ~attack(attachment) v ~open(attachment) -> ~ denied (S[attachment]) helps ~denied(S[email]) – Delete email w. any zip file attachment, at the time of reception -> misunderstanding betw. sender and receiver <- move email w. any zip file attachment into a junk file folder -> If the receiver does not check the junk file folder, still misunderstanding <- at the time the file is moved, notify this to the receiver -> if the receiver still does not check the junk file folder or checks it late, still misunderstanding <- at the time the file is moved, notify the sender too -> If the receiver checks the junk file folder and opens it and the file is an attack, still a security breach
Leave the email, but delete the attachment only
Leave the email, but delete the attachment only if it is an attack: detectable[attack(attachment)]
Leave the email but change the name of the attachment to “…renameToZip” 20 Lawrence Chung NFRs – Where  Wherever better/cheaper/faster/happier matters • Requirements Engineering • System Architecting • Software Architecting • Design • Implementation • Validation & Verification • Testing • Maintenance • Software Process • Project Planning and Management • Configuration Management • Decision making Lawrence Chung NFRs – How to represent  From informal to tabular to visual (a la html->xml->oo-xml/eb-xml/ … ; CRC cards->classes; use cases & use case templates)  Dos • Bring in FRs • Clarify scope/topic • Identify agents, whenever useful • Discover relationships between definitions of NFRs • Discover relationships between solutions to NFRs • Refine definitions as many times as needed • Refine solutions as many times as needed • Prioritize • Discover conflicts • Safeguard against conflicts • Discover synergies • Discover operationalizations as reasons for conflicts/synergies • Determine strengths of contributions • Justify strengths of contributions • Explore alternatives • Discover solutions from requirements • Discover requirements from solutions • Consider use of multiple solutions • Consider scenarios • If necessary, quantify • Evaluate • Evaluate subjectively • Evaluate objectively • Establish traceability Claim Viewpoint Affecting NFRs/Operationalizations Sat Status Affected NFRs Priority Agent Topic Type Description Name Lawrence Chung Appendix • RUP Specification • Volere Specification • How to Augment UML softgoal satisficing Lawrence Chung NFRs: With Rational Unified Process and UML Home Appliance Control System Vision Version 1.2 Revision History DescriptionAuthorDateVersion Table of Contents 1. Introduction 5 1.1 Purpose 5 1.2 Scope 5 1.3 Definitions, Acronyms, and Abbreviations 5 1.4 References 5 2. Positioning 5 2.1 Business Opportunity 5 2.2 Problem Statement 5 2.3 Product Position Statement 6 3. Stakeholder and User Descriptions 6 3.1 Market Demographics 6 3.2 Stakeholder Summary 6 3.3 User Summary 7 3.4 User Environment 7 3.5 Stakeholder Profiles 7 3.5.1 Homeowner 7 3.5.2 Business Owner 8 3.5.3 Customer Care 8 3.6 User Profiles 9 3.7 Key Stakeholder or User Needs 9 21 Lawrence Chung NFRs: With Rational Unified Process and UML 4. Product Overview 9 4.1 Product Perspective 9 4.2 Summary of Capabilities 10 4.3 Assumptions and Dependencies 11 4.4 Cost and Pricing 11 4.5 Licensing and Installation 11 5. Product Features 11 5.1 Start system 11 5.2 Shutdown system 11 5.3 View status of system 11 5.4 Add a new group of sequences 12 5.5 Modify an existing group of sequences 12 5.6 Delete an existing group of sequences 12 5.7 Categorize a group 12 5.8 Schedule a group 12 5.9 Start a group 12 5.10 Stop a group 12 5.11 View the status of whole system 12 5.12 View the status of indoor lights 12 5.13 View the status of outdoor lights 12 5.14 View the status of entertainment equipment (radios, cd players, televisions) 12 5.15 View the status of the safety system 12 5.16 View the status of the security system 12 5.17 Make a new sequence 12 5.18 Modify an existing sequence 12 5.19 Delete an existing sequence 12 5.20 Schedule a sequence 12 5.21 Start a sequence 12 5.22 Stop a sequence turn on indoor lights (all) 12 Lawrence Chung 5.29 Schedule a sequence13 5.30 Start a sequence 13 5.31 Stop a sequence turn on outdoor lights (all) 13 5.32 Turn off outdoor lights (all) 13 5.33 Turn on selected outdoor lights 13 5.34 Turn off selected outdoor lights 13 5.35 Make a new sequence 13 5.36 Modify an existing sequence 13 5.37 Delete an existing sequence 13 5.38 Schedule a sequence13 5.39 Start a sequence 13 5.40 Stop a sequence 13 5.41 Turn on radios, cd players, televisions (all) 13 5.42 Turn off radio, cd player, television (all) 13 5.43 Turn on selected radio, cd player, television 13 5.44 Turn off selected radio, cd player, television 13 5.45 Automatic notification of emergency 14 5.46 Make a new sequence 14 5.47 Modify an existing sequence 14 5.48 Delete an existing sequence 14 5.49 Schedule a sequence14 5.50 Start a sequence 14 5.51 Stop a sequence 14 5.52 Turn on security system (all features) 14 5.53 Turn off security system (all features) 14 5.54 Turn on safety system (all features)14 5.55 Turn off safety system (all features)14 5.56 Turn on selected features of security system 14 5.57 Turn off selected features of security system 14 5.58 Turn on selected features of safety system 14 5.59 Turn off selected features of safety system 14 NFRs: With Rational Unified Process and UML Lawrence Chung NFRs: With Rational Unified Process and UML 6. Constraints 14 6.1 Security 14 6.2 Usability 15 6.3 Responsiveness 15 6.4 Capacity 15 Appendix A. COTS Components 15 Lawrence Chung 6. Constraints 6.1 Security Security for the HACS includes authentication, access control, data integrity, and data privacy. Authentication of the user is by identifier and password. Homeowners and Business Owners can monitor and change the state of the system. Customer Care users can only monitor the system and manually place a medical alert 911 emergency request for an ambulance. Transmissions should be encrypted for privacy 6.2 Usability Easy to use (especially safety related features) Request for an ambulance, police or fire truck needs to be at the push of a button or voice activated 6.3 Responsiveness System responds quickly to user requests or changes in the environment. System responds within 2 seconds on average to local user requests and changes in the environment. System responds within 4 seconds on average to remote user requests and changes in the environment. 6.4 Capacity Maximum number of sequences for indoor lights is twenty (20) Maximum number of indoor lights that can be controlled is fifty (50) Maximum number of sequences for outdoor lights is twenty (20) Maximum number of outdoor lights that can be controlled is fifty(50) Maximum number of sequences for radios, CD players, televisions is twenty (20) Maximum number of radios, CD players, televisions that can be controlled is ten (10) Maximum number of sequences for safety and security equipment istwenty (20) Maximum number of sensors, security cameras, security VCRs, emergency notifications, that can be controlled is fifty NFRs: With Rational Unified Process and UML 22 Lawrence Chung NFRs: With Volere Requirements Specification Template The Atlantic Systems Guild Limited Table of Contents (http://www.volere.co.uk/template.htm) NON-FUNCTIONAL REQUIREMENTS: 10. Look and Feel 11. Usability and Humanity 12. Performance 13. Operational 14. Maintainability and Support 15. Security 16. Cultural and Political 17. Legal PROJECT ISSUES: 18. Open Issues 19. Off-the-shelf Solutions 20. New Problems 21. Tasks 22. Cutover 23. Risks 24. Costs 25. User Documentation and Training 26. Waiting Room 27. Ideas for Solutions PROJECT DRIVERS: 1. The Purpose of the Project 2. Client, Customer, Stakeholders 3. Users of the Product PROJECT CONSTRAINTS: 4. Mandated Constraints 5. Naming Conventions and Definitions 6. Relevant Facts and Assumptions FUNCTIONAL REQUIREMENTS: 7. The Scope of the Work 8. The Scope of the Product 9. Functional and Data Requirements Lawrence Chung NFRs: With Volere Requirements Specification Template 10 Look and Feel Requirements 10a. The interface Content The section contains requirements relating to spirit of the interface. Your client may have given you particular demands such as corporate branding, style, colors to be used, degree of interaction and so on. This section captures the requirements for the interface rather than the design for the interface. Motivation To ensure that the appearance of the product conforms to the organizationÕsexpectations. Examples The product shall comply with corporate branding standards. The product shall be attractive to a teenage audience. The product shall appear authoritative. Considerations Interface design may overlap the requirements gathering process.This particularly true if you are using prototyping as part of your requirements process. As prototypes develop it is important to capture the requirements that relate to the look and feel. In other words, be sure that you understand your client's intentions for the product's look and feel. Record these as requirements instead of merely having a prototype to which the client has nodded his approval. 10b. The style of the product Content A description of salient features of the product that are related to the way a potential customer will see the product. For example, if your client wants the product to appealto the business executive, then a look and feel requirement is that the product has a conservative and professional appearance. Similarly if the product is for sale to children, then the look and feel requirement is that it be colorful and look like it's intended for children. You would also consider here the design of the package if this were to be a manufactured product. The package may have some requirements as to its size, style, and consistency with other packages put out by your organization, etc. Keep in mind the European laws on packaging. There is a requirement that the package Lawrence Chung 11 Usability and Humanity Requirements 11a. Ease of use. Content This section describes your client's aspirations for how easy itwill be for the intended users of the product to operate it. The product's usability is derived from the abilities of the expected users of the product and the complexity of its functionality. The usability requirements should cover such things as: Efficiency of use - how quickly or accurately the user can use the product. Ease of remembering - how much is the casual user expected to remember about using the product Error rates - for some products it is crucial that the user commits very few, or no, errors. Overall satisfaction in using the product - this is especially important for commercial, interactive products where there is a lot of competition. Web sites are good example of this. Feedback - how much feedback does the user need in order to feel confident that the product is actually accurately doing what the user expects. The necessary degree of feedback will be higher for some products (eg: safety critical) than in others. Motivation To guide the product's designers into building a product that will meet the expectations of its eventual users. Examples The product shall be easy for 11 year-old children to use. The product shall help the user to avoid making mistakes. The product shall make the users want to use it. The product shall be used by people with no training, and possibly no understanding of English. Fit Criterion These examples may seem simplistic, but they do express the intention of the client. To completely specify what is meant by the requirement it is necessary to add a measurement ofacceptance. We call this a fit criterion. The fit criterion for the above examples would be: [An agreed percentage, say 90%] of a test panel of 11 year olds shall be able to successfully complete [list of tasks] within [specified time] One month's use of the product shall result in a total error rate of less than [an agreed percentage, say 2%] NFRs: With Volere Requirements Specification Template Lawrence Chung NFRs: With Volere Requirements Specification Template 11b. Personalization and internationalization requirements Content This section describes the way in which the product can be altered or configured to take into account the user's personal preferences or choice of language. The personalization requirements should cover such things as: Languages, spelling preferences, language idioms Currencies including the symbols and decimal conventions Personal configuration options - there are a myriad of these Motivation To ensure that the product's users do not have to struggle with,or meekly accept, the cultural conventions of the builder. Examples The product shall retain the buyer's buying preferences. The product shall allow the user to select a chosen language. Considerations Consider the locations of the potential customers and users of your product. Any out of country users will welcome the opportunity to convert to their home spelling and expressions. By allowing users to customize the way in which they use the product, you are giving them the opportunity to participate more closely with your organization, as well as givethem their own personal user experience. You might also consider the configurability of the product. Thisallows different users to have different functional variations of the product. 23 Lawrence Chung NFRs: With Volere Requirements Specification Template 11c. Ease of learning. Content A statement of how easy it should be to learn to use the product. This will range from zero time for products intended for placement in the public domain (for example a parking meter or a web site) to a considerable time for complex, highly technical products. (We know of one product where it was necessary for graduate engineers to spend 18 months in training before being qualified to use the product.) Motivation To quantify the amount of time that your client feels is allowable before a user can successfully use the product. This requirement will guide designers in how users will learn the product. For example, the designers may build elaborate interactive help facilities into the product, orthe product may be packaged with a tutorial. Alternatively the product may have to be constructed so that allof its functionality is apparent upon first encountering it. Examples The product shall be easy for an engineer to learn. A clerk shall be able to be productive within a short time. The product shall be able to be used by members of the public who will receive no training before using it. The product shall be used by engineers who will attend 5 weeks of training before using the product. Fit Criterion Fit criterion for the above example requirements are: An engineer shall produce a [specified result] within [specifiedtime] of beginning to use the product, without needing to use the manual. After receiving [number of hours] training a clerk shall be ableto produce [quantity of specified outputs] per [unit of time]. [Agreed percentage] of a test panel shall successfully complete [specified task] within [specified time limit]. The engineers shall achieve [agreed percentage] pass rate from the final examination of the training. Considerations Refer back to Section 3, the Users of the System, to ensure thatyou have considered the ease of learning requirements from the perspective of all the different types of users. Lawrence Chung NFRs: With Volere Requirements Specification Template 11d. Understandability and Politeness requirements. This section is concerned with discovering requirements related to concepts and metaphors that are familiar to the intended end-users. Content This specifies the requirement for the product to be understood by its users. While usability refers to ease of use, efficiency etc., understanding determines whether the users instinctively know what the product will do for them. In other words, the product fits into their view of the world. You can think of this as the product being polite to its users and not expecting them to know or learn things that have nothing to do with their business problem. Motivation To avoid forcing the user to learn terms and concepts that are part of the productÕsinternal construction and are not relevant to the usersÕ world. To make the product more comprehensible and thus more likely to be adopted by its intended users. Examples The product shall use symbols and words that are naturally understandable by the user community. The product shall hide the details of its construction from the user. Considerations Refer back to Section 3, the Users of the Product, and consider the world from the point of view of each of the different types of users. 11e. Accessibility requirements. Content The requirements for how easy it should be for people with common disabilities to access the product. These disabilities might be to do with sight, physical disablement, hearing, cognitive, or others. Motivation In many countries it is required that some products are made available to the disabled. In any event, it seems selfdefeating to exclude this sizable community of potential customers. Examples The product shall be usable by partially-sighted users. Lawrence Chung NFRs: With Volere Requirements Specification Template 12 Performance Requirements 12a. Speed and latency requirements Examples Any interface between a user and the automated system shall havea maximum response time of 2 seconds The response shall be fast enough to avoid interrupting the user's flow of thought The product shall poll the sensor every 10 seconds The product shall download the new status parameters within 5 minutes of a change Fit Criterion - Unit of measurement, Required range of values 12b. Safety critical requirements Examples The product shall not emit noxious gases that damage people's health. The heat exchanger shall be shielded from human contact. Fit Criterion - Description of the perceived risk, Factors that could cause the damage Unit for measuring the factors that could cause the damage "The product shall be certified to comply with the Health Department's standard E110-98. This is to be certified by qualified testing engineers." "No member of a test panel of [specified size] shall be able to touch the heat exchanger. The heat exchanger must also comply with safety standard [specify which one].". 12c. Precision or accuracy requirements Examples All monetary amounts shall be accurate to 2 decimal places. Accuracy of road temperature readings shall be within + or -2 degrees centigrade. Fit Criterion - Unit of measure plus degree of precision Lawrence Chung NFRs: With Volere Requirements Specification Template 12d. Reliability and Availability requirements Examples The product shall be available for use 24 hours per day, 365 days per year. The product shall be available for use between the hours of 8:00am and 5:30pm. The escalator shall run from 6am until the last flight arrives at 10pm. The product shall achieve 99% up time. 12e. Robustness or Fault Tolerance requirements Examples The product shall continue to operate in local mode whenever it loses its link to the central server. The product shall provide 10 minutes of emergency operation should it become disconnected from the electricity source. 12f. Capacity requirements Examples The product shall cater for 300 simultaneous users within the period from 9:00am to 11:am. Maximum loading at other periods will be 150. During a launch period the product shall cater for up to 20 people to be in the inner chamber. Fit Criterion - quantified, and thus can be tested. 12g. Scalability requirements Examples The product shall be capable of processing the existing 100,000 customers. This number is expected to grow to 500,000 within three years. The product shall be able to process 50,000 transactions an hourwithin two years of its launch. 12h. Longevity requirements Examples The product shall be expected to operate within the maximum maintenance budget for a minimum of 5 years. 24 Lawrence Chung NFRs: With Volere Requirements Specification Template 13 Operational Requirements 13a. Expected physical environment Examples The product shall be used by a worker, standing up, outside in cold, rainy conditions. The product shall be used in noisy conditions with a lot of dust. 13b. Expected technological environment 13c. Partner applications Examples We must be able to interface with any html browser. The new version of the spreadsheet must be able to access data from the previous 2 versions. 13d. Productization Requirements Examples The product shall be distributed as a ZIP file. The product shall be able to be installed by an untrained user without recourse to separately-printed instructions. Lawrence Chung NFRs: With Volere Requirements Specification Template 14 Maintainability and Support Requirements 14a. Maintenance Requirements Examples New MIS reports must be available within one working week of thedate the requirements are agreed A new weather station must be able to be added to the system overnight 14b. Are there special conditions that apply to the maintenance of this product? Examples The maintenance releases will be offered to end-users once a year. Every registered user will have access to our help site via the Internet. Fit Criterion Description of type of maintenance + amount of effort budgeted 14c. Supportability Requirements 14d. Adaptability requirements Examples The product is expected to run under Windows 95 and Unix The product might eventually be sold to the Japanese market Fit Criterion Specification of system software on which the product must operate. Specification of future environments in which the product is expected to operate. 14e. Installation requirements Example The product shall be able to be installed in the specified environment within 2 working days. Lawrence Chung NFRs: With Volere Requirements Specification Template 15 Security Requirements 15a. Access requirements Examples Only direct managers can see the personnel records of their staff. Only holders of current security clearance can enter the building. Fit Criterion System function name or system data name User role/s and/or names of people who have clearance 15b. Integrity requirements Examples The product shall prevent its data from incorrect data being introduced. The product shall protect itself from intentional abuse. 15c. Privacy requirements Examples The product shall make its user aware of its information practices before collection data from them. The product shall notify customers of changes to its informationpolicy. 15d. Audit requirements 15e. Immunity requirements Content The requirements for what the product has to do to protect itself from infection by unauthorized or undesirable software programs, such as viruses, worms, Trojan horses and others. Motivation To build a product that is as secure as possible from malicious interference. Considerations Each day brings more malevolence from the unknown, outside world. People buying software, or any other kind of product, expect that it can protect itself from outside interference, Lawrence Chung NFRs: With Volere Requirements Specification Template 16 Cultural and Political Requirements 16a. Cultural requirements Examples The product shall not be offensive to religious or ethnic groups. The product shall be able to distinguish between French, Italianand British road numbering systems. 16b. Political requirements Examples The product shall be installed using component X. The product shall make all functionality available to the managing director. The product shall be developed using XYZ standards. Considerations Did you intend to develop the product on a Macintosh, when the office manager has laid down a edict that only Windows machines are permitted? Is a director also on the board of a company that manufactures products similar to the one that you intend to build? Whether you agree with these political requirements has little bearing on the outcome. The reality is that the system has to comply with political requirements even if you can find a better/more efficient/more economical solution. A few probing questions here may save some heartache later. The political requirements might be purely concerned with the politics inside your organization. However there are situations when you need to consider the politics inside your customersÕ organizations or the national politics of the country. 25 Lawrence Chung NFRs: With Volere Requirements Specification Template 17 Legal Requirements 17a. Compliance requirements Examples Personal information shall be implemented so as to comply with the data protection act. Fit Criterion Lawyers' opinion that the product does not break any laws. Considerations Consider consulting lawyers to help identify the legal requirements. Are there any copyrights/intellectual property that must be protected? Alternatively, do any competitors have copyrights that you might be in danger of infringing? 17b. Standards requirements Example The product shall comply with MilSpec standards. The product shall comply with insurance industry standards. The product shall be developed according to SSADM standard development steps. Fit Criterion The appropriate standard-keeper certifies that the standard has been adhered to. Considerations It is not always apparent that there are applicable standards because their existence is often taken for granted. Consider the following: Are there any industry bodies that have applicable standards? Has the industry a code of practice, watchdog or ombudsman? Are there any special development steps for this type of product? Lawrence Chung NFRs: With Rational Unified Process and UML UML – de facto standard for OOA; but FR-dominance! Web Presentation Pricing User Profile Data Access Supplier 1: prepare proposal 1.1: getRFP (user) 1.1.1: getCompany (user) 1.1.2: getRPF (company) 1.2: getLanguageLocale (user) 1.3: getTimeZone (user) 2: submitProposal (proposal) 2.1: submitProposal (proposal) 2.1.1: submitProposal (company, proposal) 2.1.1: getCompany (user) NFR Association Point Actor Actor-Use Case Assoication Use Case System Boundary NFR Goal (NG) System Bound. - NFR Assoc NFR Assoc Propagation Actor - NFR Assoc Propagation Actor - NFR Assoc Usecase - NFR Assoc Propagation Use Case - NFR Assoc AU-A - NFR Assoc Propagation AU-A - NFR Assoc R9 R11 R10 R1 R3 R2 R4 R5 R6 R7 R8 R12 R13R14 Use cases as primary tool for FRs elicitation and modeling Use cases are realized with interaction diagram showing interaction between components or objects Package Dependency Diagram or Class diagram to describe components/objects and their relationships A Meta-model for partial FRs and NFRs Integration Bill of Material System Update Bill of Material Pricing System Service Item Planner Create Service Item Supplier Send RFP extends Submit Price Proposal Procurement Manager Approve Price Proposal UserSupplier Perform On-line Function Lawrence Chung What Are Use Cases? System = the system in question that provides the functionality represented by use cases Use CaseActor Actor-Use Case Association System Use case details, including NFRs, are embedded textually using atemplate Use case = functionality (FRs) provided by the system Actor = an external entity (human or system) Actor-Use Case Association = an interface between an actor and the system Specialized Actor Generalized Actor Specialized Use Case Generalized Use Case Bill of Material System Update Bill of Material Pricing System Service Item Planner Create Service Item Supplier Send RFP extends Submit Price Proposal Procurement Manager Approve Price Proposal UserSupplier Perform On-line Function NFRs: With Rational Unified Process and UML Lawrence Chung Inadequate Handling of NFRs Supplier may not see other suppliers’ identity and submitted proposals.Special Requirements In step 3, Supplier may request to …Alternate Flows 1.Supplier selects an RFP and requests system to submit a proposalagainst the RFP. 2.System prompts the Supplier for proposal information. 3.Supplier provides the following proposal information… 4.… Basic Flow SupplierActors Supplier submits price proposal against a RFP (request for proposal).Description Submit Price ProposalTitle Textual description for NFRs embedded in the use case special requirements section – not 1st class citizens Problems: 1. NFRs not modeled and organized, and not visually 2. NFRs not traceable to architecture and design 3. Error prone if NFR applicable to multiple use cases NFRs: With Rational Unified Process and UML 26 Lawrence Chung Other Integration Schemes Specific to performance NFR. No organizational constructs. Informal annotation on diagrams Use cases, Sequence diagram, State chart, Activity diagram Dimitrov’s [4] Using use cases (FR constructs) to represent NFRs. Nonstandard usage of unnamed entity. No organizational constructs. Unnamed use cases with stereo type name indicating the NFR, e.g., <> Text (use case template) Moreira’s [3] Using use cases (FR constructs) to represent NFRs. No organizational constructs. Use casesUse casesLee’s [2] Not using the preferred use case modeling for FR elicitation Text (LEL)SIG, Class/ERD extensionsCysnerios’s [1] NFR Modeling ConstructsDrawbacksMethodIntegration Point No single scheme providing all of:  Use case driven  Modeling constructs for representing and organizing NFRs  Preserving underlying use case principles (e.g., ovals for FRsbut not for NFRs)  Generic for a wide range of NFRs NFRs: With Rational Unified Process and UML