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©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 1 Chapter 4 Software Processes Modified by Randy K. Smith Additional Material.

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Presentation on theme: "©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 1 Chapter 4 Software Processes Modified by Randy K. Smith Additional Material."— Presentation transcript:

1 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 1 Chapter 4 Software Processes Modified by Randy K. Smith Additional Material taken from: Object-Oriented and Classical Software Engineering, Fifth Edition, WCB/McGraw- Hill, 2002, Stephen R. Schach Software Engineering A Practitioner’s Approach, Fifth Edition, WCB/McGraw-Hill, 2001, Roger S. Pressman

2 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 2 Software Processes l Coherent sets of activities for specifying, designing, implementing and testing software systems l Objectives To introduce software process models To describe a number of different process models and when they may be used To describe outline process models for requirements engineering, software development, testing and evolution To introduce CASE technology to support software process activities

3 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 3 The software process l A structured set of activities required to develop a software system Specification Design Validation Evolution l A software process model is an abstract representation of a process. It presents a description of a process from some particular perspective

4 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 4 System/information engineering Generic software process model analysis design code test Software Engineering A Practitioner’s Approach, Fifth Edition, WCB/McGraw-Hill, 2001, Roger S. Pressman

5 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 5 Generic software process models l The waterfall model Separate and distinct phases of specification and development l Evolutionary development Specification and development are interleaved l Formal systems development A mathematical system model is formally transformed to an implementation l Reuse-based development The system is assembled from existing components

6 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 6 Waterfall model

7 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 7 Waterfall model phases l Phases Requirements analysis and definition System and software design Implementation and unit testing Integration and system testing Operation and maintenance The drawback of the waterfall model is the difficulty of accommodating change after the process is underway l Problems Inflexible partitioning of the project into distinct stages Makes it difficult to respond to changing customer requirements Model is appropriate when requirements are well-understood

8 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 8 Waterfall model (Another View) Object-Oriented and Classical Software Engineering Fifth Edition, WCB/McGraw-Hill, 2002 Stephen R. Schach

9 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 9 Evolutionary Models Build/Revise mock-up Listen to Customer Customer test drives mock-up Prototyping Evolutionary Build to keep Throwaway Built not to keep Sommerville

10 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 10 Evolutionary development l Exploratory development Objective is to work with customers and to evolve a final system from an initial outline specification. Should start with well-understood requirements l Throw-away prototyping Objective is to understand the system requirements. Should start with poorly understood requirements Build/Revi se mock- up Listen to Customer Customer test drives mock-up

11 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 11 Evolutionary development

12 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 12 Evolutionary development Build-and-Fix Object-Oriented and Classical Software Engineering Fifth Edition, WCB/McGraw-Hill, 2002, Stephen R. Schach

13 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 13 Evolutionary development l Problems Lack of process visibility Systems are often poorly structured Special skills (e.g. in languages for rapid prototyping) may be required l Applicability For small or medium-size interactive systems For parts of large systems (e.g. the user interface) For short-lifetime systems

14 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 14 Process iteration l System requirements ALWAYS evolve in the course of a project so process iteration where earlier stages are reworked is always part of the process for large systems l Iteration can be applied to any of the generic process models l Two (related) approaches Incremental development Spiral development

15 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 15 Incremental development l Do not deliver the system as a single delivery development and delivery broken down into increments each increment delivering part of the required functionality l User requirements are prioritized (highest first) l Once an increment is started, requirements are frozen requirements for later increments can continue to evolve

16 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 16 Incremental development Object-Oriented and Classical Software Engineering, Fifth Edition, WCB/McGraw-Hill, 2002 Stephen R. Schach

17 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 17 The Incremental Model analysis designcodetest System/information engineering analysis designcodetest analysis designcodetest analysis designcodetest increment 2 increment 3 increment 4 increment 1 delivery of 1st increment delivery of 2nd increment delivery of 3rd increment delivery of 4th increment calendar time

18 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 18 Incremental development advantages l Customer value can be delivered with each increment so system functionality is available earlier l Early increments act as a prototype to help elicit requirements for later increments l Lower risk of overall project failure l The highest priority system services tend to receive the most testing

19 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 19 Spiral development l Process is represented as a spiral rather than as a sequence of activities with backtracking l Each loop in the spiral represents a phase in the process. l No fixed phases such as specification or design - loops in the spiral are chosen depending on what is required l Risks are explicitly assessed and resolved throughout the process

20 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 20 Spiral model of the software process

21 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 21 Spiral model sectors l Objective setting Specific objectives for the phase are identified l Risk assessment and reduction Risks are assessed and activities put in place to reduce the key risks l Development and validation A development model for the system is chosen which can be any of the generic models l Planning The project is reviewed and the next phase of the spiral is planned

22 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 22 The Rational Unified Process l A modern process model derived from the work on the UML and associated process. l Normally described from 3 perspectives A dynamic perspective that shows phases over time; A static perspective that shows process activities; A perspective that suggests good practice.

23 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 23 The (Rational) Unified Process

24 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 24 RUP good practice l Develop software iteratively l Manage requirements l Use component-based architectures l Visually model software l Verify software quality l Control changes to software

25 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 25 Formal systems development l Based on the transformation of a mathematical specification through different representations to an executable program l Transformations are ‘correctness-preserving’ so it is straightforward to show that the program conforms to its specification l Embodied in the ‘Cleanroom’ approach to software development

26 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 26 Formal systems development l Problems Need for specialised skills and training to apply the technique Difficult to formally specify some aspects of the system such as the user interface l Applicability Critical systems especially those where a safety or security case must be made before the system is put into operation

27 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 27 Synchronize-and Stabilize Model l Microsoft’s life-cycle model l Requirements analysis—interview potential customers l Draw up specifications l Divide project into 3 or 4 builds l Each build carried out by small teams in parallel l At the end of the day—synchronize (test and debug) l At the end of the build—stabilize (freeze build) l Components always work together Get early insights into operation of product Object-Oriented and Classical Software Engineering, Fifth Edition, WCB/McGraw-Hill, 2002 Stephen R. Schach

28 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 28 Agile Methods l Effective (rapid and adaptive) response to change l Effective communication among all stakeholders l Drawing the customer onto the team l Organizing a team so that it is in control of the work performed Yielding … l Rapid, incremental delivery of software l Extreme Programming (XP) Test First, Pair Programming

29 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 29 System/information engineering Generic software process model analysis design code test Software Engineering A Practitioner’s Approach, Fifth Edition, WCB/McGraw-Hill, 2001, Roger S. Pressman

30 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 30 Software specification l The process of establishing what services are required and the constraints on the system’s operation and development l Requirements engineering process Feasibility study Requirements elicitation and analysis Requirements specification Requirements validation

31 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 31 The requirements engineering process

32 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 32 System/information engineering Generic software process model analysis design code test Software Engineering A Practitioner’s Approach, Fifth Edition, WCB/McGraw-Hill, 2001, Roger S. Pressman

33 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 33 Software design and implementation l The process of converting the system specification into an executable system l Software design Design a software structure that realises the specification l Implementation Translate this structure into an executable program l The activities of design and implementation are closely related and may be inter-leaved

34 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 34 Design process activities l Architectural design l Abstract specification l Interface design l Component design l Data structure design l Algorithm design

35 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 35 The software design process l Systematic approaches to developing a software design l The design is usually documented as a set of graphical models l Possible models Data-flow model Entity-relation-attribute model Structural model Object models (UML)

36 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 36 System/information engineering Generic software process model analysis design code test Software Engineering A Practitioner’s Approach, Fifth Edition, WCB/McGraw-Hill, 2001, Roger S. Pressman

37 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 37 Programming and debugging l Translating a design into a program and removing errors from that program l Programming is a personal activity - there is no generic programming process l Programmers carry out some program testing to discover faults in the program and remove these faults in the debugging process

38 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 38 System/information engineering Generic software process model analysis design code test Software Engineering A Practitioner’s Approach, Fifth Edition, WCB/McGraw-Hill, 2001, Roger S. Pressman

39 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 39 Software validation l Verification and validation is intended to show that a system conforms to its specification and meets the requirements of the system customer l Involves checking and review processes and system testing l System testing involves executing the system with test cases that are derived from the specification of the real data to be processed by the system

40 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 40 The testing process

41 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 41 Testing stages l Unit testing Individual components are tested l Module testing Related collections of dependent components are tested l Sub-system testing Modules are integrated into sub-systems and tested. The focus here should be on interface testing l System testing Testing of the system as a whole. Testing of emergent properties l Acceptance testing Testing with customer data to check that it is acceptable

42 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 42 Testing phases

43 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 43 Software evolution l Software is inherently flexible and can change. l As requirements change (changing business circumstances), software must evolve and change l The demarcation between development and evolution (maintenance) is increasingly irrelevant as fewer and fewer systems are completely new

44 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 44 Automated process support (CASE) l Computer-aided software engineering (CASE) is software to support software development and evolution processes l Activity automation Graphical editors for system model development Data dictionary to manage design entities Graphical UI builder for user interface construction Debuggers to support program fault finding Automated translators to generate new versions of a program

45 Activity-based classification

46 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 46 Key points l Software processes are the activities involved in producing and evolving a software system. They are represented in a software process model l General activities are specification, design and implementation, validation and evolution l Generic process models describe the organisation of software processes l Iterative process models describe the software process as a cycle of activities

47 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 4 Slide 47 Key points l Requirements engineering is the process of developing a software specification l Design and implementation processes transform the specification to an executable program l Validation involves checking that the system meets to its specification and user needs l Evolution is concerned with modifying the system after it is in use l CASE technology supports software process activities


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