Software Requirements Objectives To introduce the concepts of user in addition to system re
Daniels, Tommy, Morning On-Air Personality has reference to this Academic Journal, PHwiki organized this Journal Software Requirements Objectives To introduce the concepts of user in addition to system requirements To describe functional in addition to non-functional requirements To explain how software requirements may be organised in a requirements document Topics covered Functional in addition to non-functional requirements User requirements System requirements Interface specification The software requirements document
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Requirements engineering The process of establishing the services that the customer requires from a system in addition to the constraints under which it operates in addition to is developed. The requirements themselves are the descriptions of the system services in addition to constraints that are generated during the requirements engineering process. 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 as long as a bid as long as a contract – there as long as e must be open to interpretation; May be the basis as long as the contract itself – there as long as e must be defined in detail; Both these statements may be called requirements. Requirements abstraction (Davis)
Types of requirement User requirements Statements in natural language plus diagrams of the services the system provides in addition to its operational constraints. Written as long as customers. System requirements A structured document setting out detailed descriptions of the systems functions, services in addition to operational constraints. Defines what should be implemented so may be part of a contract between client in addition to contractor. Definitions in addition to specifications Requirements readers
Functional in addition to non-functional requirements Functional requirements Statements of services the system should provide, how the system should react to particular inputs in addition to 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, st in addition to ards, etc. Domain requirements Requirements that come from the application domain of the system in addition to that reflect characteristics of that domain. Functional requirements Describe functionality or system services. Depend on the type of software, expected users in addition to 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. The LIBSYS system A library system that provides a single interface to a number of databases of articles in different libraries. Users can search as long as , download in addition to print these articles as long as personal study.
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 as long as 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 accounts permanent storage area. Requirements imprecision Problems arise when requirements are not precisely stated. Ambiguous requirements may be interpreted in different ways by developers in addition to users. Consider the term appropriate viewers User intention – special purpose viewer as long as each different document type; Developer interpretation – Provide a text viewer that shows the contents of the document. Requirements completeness in addition to consistency In principle, requirements should be both complete in addition to 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 in addition to consistent requirements document.
Non-functional requirements These define system properties in addition to constraints e.g. reliability, response time in addition to storage requirements. Constraints are I/O device capability, system representations, etc. Process requirements may also be specified m in addition to ating 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. 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 in addition to procedures e.g. process st in addition to ards used, implementation requirements, etc. External requirements Requirements which arise from factors which are external to the system in addition to its development process e.g. interoperability requirements, legislative requirements, etc. Non-functional requirement types
Non-functional requirements examples Product requirement 8.1 The user interface as long as LIBSYS shall be implemented as simple HTML without frames or Java applets. Organisational requirement 9.3.2 The system development process in addition to deliverable documents shall con as long as m to the process in addition to deliverables defined in XYZCo-SP-STAN-95. External requirement 7.6.5 The system shall not disclose any personal in as long as mation about customers apart from their name in addition to reference number to the operators of the system. Goals in addition to requirements Non-functional requirements may be very difficult to state precisely in addition to 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. Examples A system goal The system should be easy to use by experienced controllers in addition to 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.
Requirements measures 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 Domain requirements Derived from the application domain in addition to describe system characteristics in addition to features that reflect the domain. Domain requirements be new functional requirements, constraints on existing requirements or define specific computations. If domain requirements are not satisfied, the system may be unworkable.
Library system domain requirements There shall be a st in addition to ard user interface to all databases which shall be based on the Z39.50 st in addition to ard. Because of copyright restrictions, some documents must be deleted immediately on arrival. Depending on the users requirements, these documents will either be printed locally on the system server as long as manually as long as warding to the user or routed to a network printer. Train protection system The deceleration of the train shall be computed as: Dtrain = Dcontrol + Dgradient where Dgradient is 9.81ms2 compensated gradient/alpha in addition to where the values of 9.81ms2 /alpha are known as long as different types of train. Domain requirements problems Underst in addition to ability Requirements are expressed in the language of the application domain; This is often not understood by software engineers developing the system. Implicitness Domain specialists underst in addition to the area so well that they do not think of making the domain requirements explicit.
User requirements Should describe functional in addition to non-functional requirements in such a way that they are underst in addition to able by system users who dont have detailed technical knowledge. User requirements are defined using natural language, tables in addition to diagrams as these can be understood by all users. Problems with natural language Lack of clarity Precision is difficult without making the document difficult to read. Requirements confusion Functional in addition to non-functional requirements tend to be mixed-up. Requirements amalgamation Several different requirements may be expressed together. LIBSYS requirement 4 5 LIBSYS shall provide a financial accounting system that maintains records of all payments made by users of the system. System managers may configure this system so that regular users may receive discounted rates.
Requirements document structure Preface Introduction Glossary User requirements definition System architecture System requirements specification System models System evolution Appendices Index Key points Requirements set out what the system should do in addition to define constraints on its operation in addition to implementation. Functional requirements set out services the system should provide. Non-functional requirements constrain the system being developed or the development process. User requirements are high-level statements of what the system should do. User requirements should be written using natural language, tables in addition to diagrams. Key points System requirements are intended to communicate the functions that the system should provide. A software requirements document is an agreed statement of the system requirements. The IEEE st in addition to ard is a useful starting point as long as defining more detailed specific requirements st in addition to ards.
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