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©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 1 Software Processes l Coherent sets of activities for specifying, designing,

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Presentation on theme: "©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 1 Software Processes l Coherent sets of activities for specifying, designing,"— Presentation transcript:

1 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 1 Software Processes l Coherent sets of activities for specifying, designing, implementing and testing software systems

2 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 2 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

3 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 3 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

4 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 4 Waterfall model

5 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 5 Waterfall model phases l Requirements analysis and definition l System and software design l Implementation and unit testing l Integration and system testing l Operation and maintenance l The drawback of the waterfall model is the difficulty of accommodating change after the process is underway

6 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 6 Waterfall model problems l Inflexible partitioning of the project into distinct stages l This makes it difficult to respond to changing customer requirements l Therefore, this model is only appropriate when the requirements are well-understood

7 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 7 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

8 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 8 Evolutionary development

9 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 9 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

10 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 10 Formal systems development

11 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 11 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

12 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 12 Reuse-oriented development l Based on systematic reuse where systems are integrated from existing components or COTS (Commercial-off-the-shelf) systems l Process stages Component analysis Requirements modification System design with reuse Development and integration l This approach is becoming more important but still limited experience with it

13 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 13 Reuse-oriented development

14 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 14 Incremental development l Rather than deliver the system as a single delivery, the development and delivery is broken down into increments with each increment delivering part of the required functionality l User requirements are prioritised and the highest priority requirements are included in early increments l Once the development of an increment is started, the requirements are frozen though requirements for later increments can continue to evolve

15 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 15 Incremental development

16 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 16 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

17 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 17 Extreme programming l New approach to development based on the development and delivery of very small increments of functionality l Relies on constant code improvement, user involvement in the development team and pairwise programming

18 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 18 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

19 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 19 The requirements engineering process

20 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 20 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

21 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 21 The software design process

22 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 22 Design methods 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

23 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 23 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

24 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 24 The testing process

25 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 25 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

26 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 26 Testing phases

27 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 27 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

28 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 28 Case technology l Case technology has led to significant improvements in the software process though not the order of magnitude improvements that were once predicted Software engineering requires creative thought - this is not readily automatable Software engineering is a team activity and, for large projects, much time is spent in team interactions. CASE technology does not really support these

29 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 29 CASE classification l Classification helps us understand the different types of CASE tools and their support for process activities l Functional perspective Tools are classified according to their specific function l Process perspective Tools are classified according to process activities that are supported l Integration perspective Tools are classified according to their organisation into integrated units

30 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 30 Functional tool classification

31 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 31 CASE integration l Tools Support individual process tasks such as design consistency checking, text editing, etc. l Workbenches Support a process phase such as specification or design, Normally include a number of integrated tools l Environments Support all or a substantial part of an entire software process. Normally include several integrated workbenches

32 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 1 Slide 32 Tools, workbenches, environments


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