![Part of an ATM specification
class ATM {
// declarations here
public static void main (String args[]) throws InvalidCard {
try {
thisCard.read () ; // may throw InvalidCard exception
pin = KeyPad.readPin () ; attempts = 1 ;
while ( !thisCard.pin.equals (pin) & attempts < 4 )
{ pin = KeyPad.readPin () ; attempts = attempts + 1 ;
}
if (!thisCard.pin.equals (pin))
throw new InvalidCard ("Bad PIN");
thisBalance = thisCard.getBalance () ;
do { Screen.prompt (" Please select a service ") ;
service = Screen.touchKey () ;
switch (service) {
case Services.withdrawalWithReceipt:
receiptRequired = true ;
34](https://image.slidesharecdn.com/lecture-5-requirementsanalysisandspecification-230526184827-2010aec0/85/Lecture-5-Requirements-Analysis-and-Specification-pptx-34-320.jpg)
Lecture-5-Requirements Analysis and Specification.pptx
- 1. Requirements Analysis and Specification By 1 Dr. JUNAID AKRAM ASSISTANT PROFESSOR, DEPARTMENT OF COMPUTER SCIENCE COMSATS (LAHORE)
- 2. Requirements engineering The process of establishing the services that the customer requires from a system and the constraints under which it operates and is developed The requirements themselves are the descriptions of the system services and constraints that are generated during the requirements engineering process 2
- 3. What is a requirement? It may range from a high-level abstract statement of a service or of a system constraint to a detailed mathematical functional specification This is inevitable as requirements may serve a dual function May be the basis for a bid for a contract - therefore must be open to interpretation May be the basis for the contract itself - therefore must be defined in detail Both these statements may be called requirements 3
- 4. Types of requirement User requirements Statements in natural language plus diagrams of the services the system provides and its operational constraints. Written for customers System requirements A structured document setting out detailed descriptions of the system services. Written as a contract between client and contractor Software specification A detailed software description which can serve as a basis for a design or implementation. Written for developers 4
- 5. Definitions and specifications 1. The software must provide a means of representing and 1. accessing external files created by other tools. 1.1 The user should be provided with facilities to define the type of 1.2 external files. 1.2 Each external file type may have an as sociated tool which may be 1.2 applied to the file. 1.3 Each external file type may be represented as a specific icon on 1.2 the user’s display. 1.4 Facilities should be provided for the icon representing an 1.2 external file type to be defined by theuser. 1.5 When a user selects an icon representing an external file, the 1.2 effect of that selection is to apply the tool associated with the type of 1.2 the external file to the file representedby the selected icon. Requirements definition Requirements specification 5
- 6. Requirements readers Client managers System end-users Client engineers Contractor managers System architects System end-users Client engineers System architects Software developers Client engineers (perhaps) System architects Software developers User requirements System requirements Software design specification 6
- 7. Functional and non-functional requirements Functional requirements Statements of services the system should provide, how the system should react to particular inputs and how the system should behave in particular situations. Non-functional requirements constraints on the services or functions offered by the system such as timing constraints, constraints on the development process, standards, etc. Domain requirements Requirements that come from the application domain of the system and that reflect characteristics of that domain 7
- 8. Functional requirements Describe functionality or system services Depend on the type of software, expected users and the type of system where the software is used Functional user requirements may be high-level statements of what the system should do but functional system requirements should describe the system services in detail 8
- 9. Examples of functional requirements The user shall be able to search either all of the initial set of databases or select a subset from it. The system shall provide appropriate viewers for the user to read documents in the document store. Every order shall be allocated a unique identifier (ORDER_ID) which the user shall be able to copy to the account’s permanent storage area. 9
- 10. Requirements imprecision Problems arise when requirements are not precisely stated Ambiguous requirements may be interpreted in different ways by developers and users Consider the term ‘appropriate viewers’ User intention - special purpose viewer for each different document type Developer interpretation - Provide a text viewer that shows the contents of the document 10
- 11. Requirements completeness and consistency In principle requirements should be both complete and consistent Complete They should include descriptions of all facilities required Consistent There should be no conflicts or contradictions in the descriptions of the system facilities In practice, it is impossible to produce a complete and consistent requirements document 11
- 12. Non-functional requirements Define system properties and constraints e.g. reliability, response time and storage requirements. Constraints are I/O device capability, system representations, etc. Process requirements may also be specified mandating a particular CASE system, programming language or development method Non-functional requirements may be more critical than functional requirements. If these are not met, the system is useless 12
- 13. Non-functional classifications Product requirements Requirements which specify that the delivered product must behave in a particular way e.g. execution speed, reliability, etc. Organisational requirements Requirements which are a consequence of organisational policies and procedures e.g. process standards used, implementation requirements, etc. External requirements Requirements which arise from factors which are external to the system and its development process e.g. interoperability requirements, legislative requirements, etc. 13
- 15. Non-functional requirements examples Product requirement 4.C.8 It shall be possible for all necessary communication between the APSE and the user to be expressed in the standard Ada character set Organisational requirement 9.3.2 The system development process and deliverable documents shall conform to the process and deliverables defined in XYZCo-SP-STAN-95 External requirement 7.6.5 The system shall not disclose any personal information about customers apart from their name and reference number to the operators of the system 15
- 16. Goals and requirements Non-functional requirements may be very difficult to state precisely and imprecise requirements may be difficult to verify. Goal A general intention of the user such as ease of use Verifiable non-functional requirement A statement using some measure that can be objectively tested Goals are helpful to developers as they convey the intentions of the system users 16
- 17. Examples A system goal The system should be easy to use by experienced controllers and should be organised in such a way that user errors are minimised. A verifiable non-functional requirement Experienced controllers shall be able to use all the system functions after a total of two hours training. After this training, the average number of errors made by experienced users shall not exceed two per day. 17
- 18. Requirements measures Property Measure Speed Processed transactions/second User/Event response tim e Screen refresh tim e Size K Bytes Number of RAM chips Ease of use Training time Number of help frames Reliability Mean time to failure Probability of unavailability Rate of failure occurrence Availability Robustness Time to restart after failure Percentage of events causing failure Probability of data corruption on failure Portability Percentage of target dependent statements Number of target system s 18
- 19. Requirements interaction Conflicts between different non-functional requirements are common in complex systems Spacecraft system To minimise weight, the number of separate chips in the system should be minimised To minimise power consumption, lower power chips should be used However, using low power chips may mean that more chips have to be used. Which is the most critical requirement? 19
- 20. Domain requirements Derived from the application domain and describe system characteristics and features that reflect the domain May be new functional requirements, constraints on existing requirements or define specific computations If domain requirements are not satisfied, the system may be unworkable 20
- 21. Domain requirements problems Understandability Requirements are expressed in the language of the application domain This is often not understood by software engineers developing the system Implicitness Domain specialists understand the area so well that they do not think of making the domain requirements explicit 21
- 22. User requirements Should describe functional and non-functional requirements so that they are understandable by system users who don’t have detailed technical knowledge User requirements are defined using natural language, tables and diagrams 22
- 23. Problems with natural language Lack of clarity Precision is difficult without making the document difficult to read Requirements confusion Functional and non-functional requirements tend to be mixed-up Requirements amalgamation Several different requirements may be expressed together 23
- 24. Database requirement The database shall support the generation and control of configuration objects; that is, objects which are themselves groupings of other objects in the database. The configuration control facilities shall allow access to the objects in a version group by the use of an incomplete name. 24
- 25. Requirement problems Database requirements includes both conceptual and detailed information Describes the concept of configuration control facilities Includes the detail that objects may be accessed using an incomplete name Grid requirement mixes three different kinds of requirement Conceptual functional requirement (the need for a grid) Non-functional requirement (grid units) Non-functional UI requirement (grid switching) 25
- 26. Guidelines for writing requirements Invent a standard format and use it for all requirements Use language in a consistent way. Use shall for mandatory requirements, should for desirable requirements Use text highlighting to identify key parts of the requirement 26
- 27. System requirements More detailed specifications of user requirements Serve as a basis for designing the system May be used as part of the system contract System requirements may be expressed using system models discussed in Chapter 7 27
- 28. Requirements and design In principle, requirements should state what the system should do and the design should describe how it does this In practice, requirements and design are inseparable A system architecture may be designed to structure the requirements The system may inter-operate with other systems that generate design requirements The use of a specific design may be a domain requirement 28
- 29. Problems with NL (Natural Language) specification Ambiguity The readers and writers of the requirement must interpret the same words in the same way. NL is naturally ambiguous so this is very difficult Over-flexibility The same thing may be said in a number of different ways in the specification Lack of modularisation NL structures are inadequate to structure system requirements 29
- 30. Alternatives to NL specification Notation Description Structured natural language This approach depends on defining standard forms or templates to express the requirements specification. Design description languages This approach uses a language like a programming language but with more abstract features to specify the requirements by defining an operational model of the system. Graphical notations A graphical language, supplemented by text annotations is used to define the functional requirements for the system. An early example of such a graphical language was SADT (Ross, 1977; Schoman and Ross, 1977). More recently, use-case descriptions (Jacobsen, Christerson et al., 1993) have been used. I discuss these in the following chapter. Mathematical specifications These are notations based on mathematical concepts such as finite-state machines or sets. These unambiguous specifications reduce the arguments between customer and contractor about system functionality. However, most customers don’t understand formal specifications and are reluctant to accept it as a system contract. I discuss formal specification in Chapter 9. 30
- 31. Structured language specifications A limited form of natural language may be used to express requirements This removes some of the problems resulting from ambiguity and flexibility and imposes a degree of uniformity on a specification Often bast supported using a forms-based approach 31
- 32. Form-based specifications Definition of the function or entity Description of inputs and where they come from Description of outputs and where they go to Indication of other entities required Pre and post conditions (if appropriate) The side effects (if any) 32
- 33. Form-based node specification ECLIPSE/Workstation/Tools/DE/FS/3.5.1 Function Add node Description Addsa node to an existing design. The user selects the type of node, and its position. When added to the design, the node becomes the current selection. The user chooses the node position by moving the cursor to the area where the node is added. Inputs Node type, Node position, Design identifier. Source Node type and Node position are input by the user, Design identifier fromthe database. Outputs Design identifier. Destination The design database. The design is com mitted to the database on com pletion of the operation. Requires Design graph rooted at input design identifier. Pre-condition The design is open and displayed on the user's screen. Post-condition The design is unchanged apart fromtheaddition of a node of the specified type at the given position. Side-effects None Definition: ECLIPSE/Workstation/Tools/DE/RD/3.5.1 33
- 34. Part of an ATM specification class ATM { // declarations here public static void main (String args[]) throws InvalidCard { try { thisCard.read () ; // may throw InvalidCard exception pin = KeyPad.readPin () ; attempts = 1 ; while ( !thisCard.pin.equals (pin) & attempts < 4 ) { pin = KeyPad.readPin () ; attempts = attempts + 1 ; } if (!thisCard.pin.equals (pin)) throw new InvalidCard ("Bad PIN"); thisBalance = thisCard.getBalance () ; do { Screen.prompt (" Please select a service ") ; service = Screen.touchKey () ; switch (service) { case Services.withdrawalWithReceipt: receiptRequired = true ; 34
- 35. The requirements document The requirements document is the official statement of what is required of the system developers Should include both a definition and a specification of requirements It is NOT a design document. As far as possible, it should set of WHAT the system should do rather than HOW it should do it 35
- 36. Users of a requirements document Use the requirements to develop validation tests for the system Use the requirements document to plan a bid for the system and to plan the system development process Use the requirements to understand what system is to be developed System test engineers Managers System engineers Specify the requirements and read them to check that they meet their needs. They specify changes to the requirements System customers Use the requirements to help understand the system and the relationships between its parts System maintenance engineers 36
- 37. Requirements document requirements Specify external system behaviour Specify implementation constraints Easy to change Serve as reference tool for maintenance Record forethought about the life cycle of the system i.e. predict changes Characterise responses to unexpected events 37
- 38. IEEE requirements standard Introduction General description Specific requirements Appendices Index This is a generic structure that must be instantiated for specific systems 38
- 39. Requirements document structure Introduction Glossary User requirements definition System architecture System requirements specification System models System evolution Appendices Index 39
- 40. Thanks for your attention! Any Question? 40 Email me on : junaidakram@cuilahore.edu.pk