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software engineering
- 1. Software Engineering B.Tech IT/II Sem-II Term: 2008-2009 Unit-2 PPT SLIDES Text Books:1.Software Engineering, A practitioner’s approach Roger s. Pressman 6th edition McGraw- Hill 2.Software Engineering Somerville 7th edition 1
- 2. UNIT 2 SYLLABUS •Process models : The waterfall model, Incremental process models, Evolutionary process models, The Unified process. • Software Requirements : Functional and non-functional requirements, User requirements, System requirements, Interface specification, the software requirements document. 2
- 3. INDEX Unit-2 PPTS S.No Topic Lecture No PPTSlides 1 Process Models:Waterfall L1 4 Model 2 The incremental Model L2 8 The RAD Model 3 Evolutionary Process Models: L3 14 prototype 4 spiral model, Concurrent L4 19 development model 5 The unified Process History, L5 25 Phases 6 The unified process work L6 28 products 7 Software Requirements L7 30 -Functional Requirements -User Requirements 8 System Requirement, Interface L8 38 3 Specification
- 4. PROCESS MODELS • Helpin the software development • Guide the software team through a set of framework activities • Process Models may be linear, incremental or evolutionary 4
- 5. THE WATERFALL MODEL •Used when requirements are well understood in the beginning • Also called classic life cycle • A systematic, sequential approach to Software development • Begins with customer specification of Requirements and progresses through planning, modeling, construction and deployment 5
- 6. The Waterfall Model ThisModel suggests a systematic, sequential approach to SW development that begins at the system level and progresses through analysis, design, code and testing Communication Project initiation requirement gathering Planning Estimating Scheduling tracking Modeling Analysis design Construction Code test Deployment Delivery Support feedback 6
- 7. PROBLEMS IN WATERFALL MODEL • Real projects rarely follow the sequential flow since they are always iterative • The model requires requirements to be explicitly spelled out in the beginning, which is often difficult • A working model is not available until late in the project time plan 7
- 8. THE INCREMENTAL PROCESS MODEL • Linear sequential model is not suited for projects which are iterative in nature • Incremental model suits such projects • Used when initial requirements are reasonably well-defined and compelling need to provide limited functionality quickly • Functionality expanded further in later releases • Software is developed in increments 8
- 9. The Incremental Model Communication Software functionality and features Increment # n Planning Modeling Communication Planning Modeling Construction Analysis design Construction Code test Deployment Delivery Support feedback Deployment delivery of nth increment Increment#2 Communication Planning Modeling Construction Deployment Increment # 1 Analysis design Code test Delivery Support Delivery of feedback 2nd increment Communication Planning Modeling Analysis Construction Deployment design delivery of Code Delivery test Support feedback 1ST increment Project calendar time 9
- 10. THE INCREMENTAL MODEL •Software releases in increments • 1st increment constitutes Core product • Basic requirements are addressed • Core product undergoes detailed evaluation by the customer • As a result, plan is developed for the next increment Plan addresses the modification of core product to better meet the needs of customer • Process is repeated until the complete product is produced 10
- 11. THE RAD MODEL (Rapid Application Development) • An incremental software process model • Having a short development cycle • High-speed adoption of the waterfall model using a component based construction approach • Creates a fully functional system within a very short span time of 60 to 90 days 11
- 12. The RAD Model Team # n Modeling Business modeling Data modeling Process modeling Construction Team # 2 Component reuse automatic code generation Communication Modeling testing Business modeling Data modeling Process modeling Construction Planning Team # 1 Component reuse automatic code generation testing Modeling Business modeling Deployment Data modeling integration Process modeling delivery feedback Construction Component reuse automatic code generation testing 12
- 13. THE RAD MODEL •Multiple software teams work in parallel on different functions • Modeling encompasses three major phases: Business modeling, Data modeling and process modeling • Construction uses reusable components, automatic code generation and testing • Problems in RAD Requires a number of RAD teams Requires commitment from both developer and customer for rapid-fire completion of activities Requires modularity Not suited when technical risks are high 13
- 14. EVOLUTIONARY PROCESS MODEL • Software evolves over a period of time • Business and product requirements often change as development proceeds making a straight-line path to an end product unrealistic • Evolutionary models are iterative and as such are applicable to modern day applications • Types of evolutionary models – Prototyping – Spiral model – Concurrent development model 14
- 15. PROTOTYPING • Mock upor model( throw away version) of a software product • Used when customer defines a set of objective but does not identify input,output,or processing requirements • Developer is not sure of: – efficiency of an algorithm – adaptability of an operating system – human/machine interaction 15
- 16. Evolutionary Models: Prototype Quick Communication Plan Modeling Quick design Construction Deployment of prototype delivery & feedback 16
- 17. STEPS IN PROTOTYPING •Begins with requirement gathering • Identify whatever requirements are known • Outline areas where further definition is mandatory • A quick design occur • Quick design leads to the construction of prototype • Prototype is evaluated by the customer • Requirements are refined • Prototype is turned to satisfy the needs of customer 17
- 18. LIMITATION OF PROTOTYPING •In a rush to get it working, overall software quality or long term maintainability are generally overlooked • Use of inappropriate OS or PL • Use of inefficient algorithm 18
- 19. THE SPIRAL MODEL •An evolutionary model which combines the best feature of the classical life cycle and the iterative nature of prototype model • Include new element : Risk element • Starts in middle and continually visits the basic tasks of communication, planning,modeling,construction and deployment 19
- 20. Evolutionary Models: TheSpiral 20
- 21. THE SPIRAL MODEL • 1.COMMUNICATION *Tasks required are establish effective communication between developer • 2.PLANNING *Estimation *Scheduling *Risk analysis • MODELING *Analysis *Design • CONSTRUCTION *Code *Test • DEPLOYMENT *Delivery *Feedback 21
- 22. THE SPIRAL MODEL •Realistic approach to the development of large scale system and software • Software evolves as process progresses • Better understanding between developer and customer • The first circuit might result in the development of a product specification • Subsequent circuits develop a prototype • And sophisticated version of software 22
- 23. THE CONCURRENT DEVELOPMENT MODEL •Alsocalled concurrent engineering •Constitutes a series of framework activities, software engineering action, tasks and their associated states •All activities exist concurrently but reside in different states •Applicable to all types of software development •Event generated at one point in the process trigger transitions among the states 23
- 24. A FINAL COMMENTON EVOLUTIONARY PROCESS • Difficult in project planning • Speed of evolution is not known • Does not focus on flexibility and extensibility (more emphasis on high quality) • Requirement is balance between high quality and flexibility and extensibility 24
- 25. THE UNIFIED PROCESS •Evolved by Rumbaugh, Booch, Jacobson • Combines the best features their OO models • Adopts additional features proposed by other experts • Resulted in Unified Modeling Language(UML) • Unified process developed Rumbaugh and Booch • A framework for Object-Oriented Software Engineering using UML 25
- 26. PHASES OF UNIFIEDPROCESS • INCEPTION PHASE • ELABORATION PHASE • CONSTRUCTION PHASE • TRANSITION PHASE 26
- 27. The Unified Process(UP) 27
- 28. UNIFIED PROCESS WORKPRODUCTS • Tasks which are required to be completed during different phases • Inception Phase *Vision document *Initial Use- Case model *Initial Risk assessment *Project Plan • Elaboration Phase *Use-Case model *Analysis model *Software Architecture description *Preliminary design model *Preliminary model 28
- 29. UNIFIED PROCESS WORKPRODUCTS • Construction Phase *Design model *System components *Test plan and procedure *Test cases *Manual • Transition Phase *Delivered software increment *Beta test results *General user feedback 29
- 30. SOFTWARE REQUIREMENTS • IEEEdefines Requirement as : 1. A condition or capability needed by a user to solve a problem or achieve an objective 2. A condition or capability that must be met or possessed by a system or a system component to satisfy constract,standard, specification or formally imposed document 3. A documented representation of a condition or capability as in 1 or 2 30
- 31. SOFTWARE REQUIREMENTS • Encompassesboth the User’s view of the requirements( the external view ) and the Developer’s view( inside characteristics) • User’s Requirements --Statements in a natural language plus diagram, describing the services the system is expected to provide and the constraints • System Requirements • --Describe the system’s function, services and operational condition 31
- 32. SOFTWARE REQUIREMENTS • System Functional Requirements --Statement of services the system should provide --Describe the behavior in particular situations --Defines the system reaction to particular inputs • Nonfunctional Requirements - Constraints on the services or functions offered by the system --Include timing constraints, constraints on the development process and standards --Apply to system as a whole • Domain Requirements --Requirements relate to specific application of the system --Reflect characteristics and constraints of that system 32
- 33. FUNCTIONAL REQUIREMENTS • Shouldbe both complete and consistent • Completeness -- All services required by the user should be defined • Consistent -- Requirements should not have contradictory definition • Difficult to achieve completeness and consistency for large system 33
- 34. NON-FUNCTIONAL • REQUIREMENTS Types of Non-functional Requirements • 1.Product Requirements -Specify product behavior -Include the following • Usability • Efficiency • Reliability • Portability 2.Organisational Requirements --Derived from policies and procedures --Include the following: Delivery Implementation Standard • 3.External Requirements -- Derived from factors external to the system and its development process --Includes the following Interoperability Ethical Legislative 34
- 35. Different types ofnon-functional requirements Non-functional requirements Product Organisational External requirements requirements requirements Efficiency R bility elia Porta bility Interoper a bility Ethical requirements requirements requirements requirements requirements Usa bility Deli very Implementa tion Standar ds Legislative requirements requirements requirements requirements requirements Performance Space Pri vacy Safety requirements requirements requirements requirements 35
- 36. PROBLEMS FACED USINGTHE NATURAL LANGUAGE • 1. Lack of clarity -- Leads to misunderstanding because of ambiguity of natural language 2. Confusion -- Due to over flexibility,sometime difficult to find whether requirements are same or distinct. 3. Amalgamation problem -- Difficult to modularize natural language requirements 36
- 37. STRUCTURED LANGUAGE SPECIFICATION • Requirements are written in a standard way • Ensures degree of uniformity • Provide templates to specify system requirements • Include control constructs and graphical highlighting to partition the specification 37
- 38. SYSTEM REQUIREMENTS STANDARD FORM • Function • Description • Inputs • Source • Outputs • Destination • Action • Precondition • Post condition • Side effects 38
- 39. Interface Specification • Workingof new system must match with the existing system • Interface provides this capability and precisely specified • Three types of interfaces 1.Procedural interface -- Used for calling the existing programs by the new programs 2.Data structures --Provide data passing from one sub-system to another 3.Representations of Data -- Ordering of bits to match with the existing system --Most common in real-time and embedded system 39
- 40. The Software Requirementsdocument • The requirements document is the official statement of what is required of the system developers. • Should include both a definition of user requirements and a specification of the system 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 40
- 41. The Software Requirementsdocument • Heninger suggests that there are 6 requirements that requirement document should satisfy. It should specify only external system behavior specify constraints on the implementation. Be easy to change Serve as reference tool for system maintainers Record forethought about the life cycle of the system. Characterize acceptable responses to undesired events 41
- 42. Purpose of SRS •communication between the Customer, Analyst,system developers, maintainers, .. • firm foundation for the design phase • support system testing activities • Support project management and control • controlling the evolution of the system 42
- 43. IEEE requirements standard •Defines a generic structure for a requirements document that must be instantiated for each specific system. – Introduction. – General description. – Specific requirements. – Appendices. – Index. 43
- 44. IEEE requirements standard 1.Introduction 1.1 Purpose 1.2 Scope 1.3 Definitions, Acronyms and Abbreviations 1.4 References 1.5 Overview 44
- 45. 2. General description 2.1 Product perspective 2.2 Product function summary 2.3 User characteristics 2.4 General constraints 2.5 Assumptions and dependencies 3. Specific Requirements - Functional requirements -External interface requirements - Performance requirements - Design constraints - Attributes eg. security, availability,maintainability, transferability/conversion - Other requirements 45
- 46.