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EE6421/ED5031Software Engineering Slide 1 Section # 2 (Read Sommerville Ch (3 or 4) and Pressman Ch 2) Software Processes.

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Presentation on theme: "EE6421/ED5031Software Engineering Slide 1 Section # 2 (Read Sommerville Ch (3 or 4) and Pressman Ch 2) Software Processes."— Presentation transcript:

1 EE6421/ED5031Software Engineering Slide 1 Section # 2 (Read Sommerville Ch (3 or 4) and Pressman Ch 2) Software Processes

2 EE6421/ED5031Software Engineering Slide 2 Objectives l To introduce software process models l To describe three generic process models and when they may be used l To describe outline process models for requirements engineering, software development, testing and evolution l To explain the Rational Unified Process model l To introduce CASE technology to support software process activities

3 EE6421/ED5031Software Engineering Slide 3 Topics covered 1.Software process models 2.Process iteration 3.Process activities 4.The Rational Unified Process 5.Computer-aided software engineering

4 EE6421/ED5031Software Engineering Slide 4 1. 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.

5 EE6421/ED5031Software Engineering Slide 5 Generic software process models l The waterfall model Separate and distinct phases of specification and development. l Evolutionary development Specification, development and validation are interleaved. l Reuse-oriented development The system is assembled from existing components. l There are many variants of these models e.g. formal development where a waterfall-like process is used but the specification is a formal specification that is refined through several stages to an implementable design.

6 EE6421/ED5031Software Engineering Slide 6 Waterfall model

7 EE6421/ED5031Software Engineering Slide 7 Waterfall model phases l Requirements analysis and definition Determine the systems services, constraints and goals – performed in consultation with system users. l System and software design The design Process – this is where the overall system is specified – it is where the main work of a software designer is performed.

8 EE6421/ED5031Software Engineering Slide 8 Waterfall model phases l Implementation and unit testing The programming phase – each code block is realised and tested to verify that it meets specifications. l Integration and system testing Integrate the individual program blocks and test them for completeness. l Operation and maintenance System is in use – maintenance involves fixing bugs and providing system enhancements.

9 EE6421/ED5031Software Engineering Slide 9 Waterfall model phases The main advantage of the waterfall model is that documentation is produced at each phase and other models can be interwoven with it as it proceeds. The main drawback of the waterfall model is the difficulty of accommodating change after the process is underway. One phase has to be complete before moving onto the next phase.

10 EE6421/ED5031Software Engineering Slide 10 Waterfall model problems l Inflexible partitioning of the project into distinct stages makes it difficult to respond to changing customer requirements. l Therefore, this model is only appropriate when the requirements are well-understood and changes will be fairly limited during the design process. l Few business systems have stable requirements. l The waterfall model is mostly used for large systems engineering projects where a system is developed at several sites.

11 EE6421/ED5031Software Engineering Slide 11 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 and add new features as proposed by the customer. l Throw-away prototyping Objective is to understand the system requirements. Should start with poorly understood requirements to clarify what is really needed. Prototypes are developed to see what the customer really wants and needs.

12 EE6421/ED5031Software Engineering Slide 12 Evolutionary development

13 EE6421/ED5031Software Engineering Slide 13 Evolutionary development l Problems Lack of process visibility; - deliverables are not clearly defined as documentation is poor. Systems are often poorly structured; - since changes are constantly being made the resultant code is often poorly written and formatted. Special skills (e.g. in languages for rapid prototyping) may be required;

14 EE6421/ED5031Software Engineering Slide 14 Evolutionary development l Applicability For small or medium-size interactive systems; - generally a design that has a limited number of programmers working on it (say up to 3 programmers) is more suited to this method. For parts of large systems (e.g. the user interface); - GUI development often benefits from many iterations and sample systems being developed before a final GUI is selected. For short-lifetime systems; - not suitable for products like Microsoft office as maintenance is very difficult.

15 EE6421/ED5031Software Engineering Slide 15 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 increasingly used as component standards have emerged.

16 EE6421/ED5031Software Engineering Slide 16 Reuse-oriented development

17 EE6421/ED5031Software Engineering Slide 17 Reuse-oriented development l The Reuse approach can mean that software modules that are not 100% useful may have to have extra functionality added to them. This approach still saves time and money, but requires some development and integration into the system. l Generally a full system development is not possible using total software reuse but the principle of some reuse can be applied to most system developments.

18 EE6421/ED5031Software Engineering Slide 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 Three (related) approaches Incremental delivery; Extreme Programming; Spiral development.

19 EE6421/ED5031Software Engineering Slide 19 Incremental delivery 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.

20 EE6421/ED5031Software Engineering Slide 20 Incremental development

21 EE6421/ED5031Software Engineering Slide 21 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.

22 EE6421/ED5031Software Engineering Slide 22 Extreme programming l An 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. l Often referred to as Rapid Application Development (RAD) l (Read ch 17 of Sommerville)

23 EE6421/ED5031Software Engineering Slide 23 Extreme programming

24 EE6421/ED5031Software Engineering Slide 24 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.

25 EE6421/ED5031Software Engineering Slide 25 Spiral model of the software process

26 EE6421/ED5031Software Engineering Slide 26 Spiral model sectors #1 l Objective setting Specific objectives for the phase are identified. Constraints are identified. Management plan is drafted. Risks are assessed Alternative strategies may be planned depending on risk assessments.

27 EE6421/ED5031Software Engineering Slide 27 Spiral model sectors #2 l Risk assessment and reduction Risks are assessed and activities put in place to reduce the key risks. For example: if there is a risk that the requirements are flawed or inappropriate then a prototype may be developed to asses them.

28 EE6421/ED5031Software Engineering Slide 28 Spiral model sectors #3 l Development and validation A development model for the system is chosen which can be any of the generic models. Examples: User interface development – Evolutionary Prototyping. Sub-system integrations – Waterfall model. Safety Critical code – Formal Transformations (This model is similar to the Waterfall model but is based on mathematical analysis and verifications) – not discussed further here.

29 EE6421/ED5031Software Engineering Slide 29 Spiral model sectors #4 l Planning The project is reviewed and the next phase of the spiral is planned. All spiral phases are similar and they develop on the previous phase in order to improve the design of the software product.

30 EE6421/ED5031Software Engineering Slide Process activities l Software specification l Software design and implementation l Software validation l Software evolution

31 EE6421/ED5031Software Engineering Slide 31 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. l The above process is not necessarily carried out in a strict sequence it is often interleaved.

32 EE6421/ED5031Software Engineering Slide 32 The requirements engineering process

33 EE6421/ED5031Software Engineering Slide 33 The requirements engineering process l Feasibility Study l Estimate if work is feasible with current technology. l Determine if it is a cost effective project. l Outputs: l Feasibility report. l Proceed with requirements phase.

34 EE6421/ED5031Software Engineering Slide 34 The requirements engineering process l Requirements Elicitation (extraction) and Analysis l Derive system requirements through observations and discussions. l May involve one or more system models and prototypes. l Outputs: l System Model. l Requirements specification.

35 EE6421/ED5031Software Engineering Slide 35 The requirements engineering process l Requirements Specification l Outputs: l User requirements – what the end user wants and needs. l System requirements – how the system will function.

36 EE6421/ED5031Software Engineering Slide 36 The requirements engineering process l Requirements Validation l Checks the requirements for completeness, consistency and realism. l Any errors in the requirements are corrected in the documentation at this stage and the specifications are reworked. l Output l Final requirements document.

37 EE6421/ED5031Software Engineering Slide 37 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 – as in the spiral model.

38 EE6421/ED5031Software Engineering Slide 38 Structured methods l Systematic approaches to developing a software design: build, test, verify and repeat until happy. l The design is usually documented as a set of graphical models – better for documentation and record keeping of the design – The UML (later)

39 EE6421/ED5031Software Engineering Slide 39 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.

40 EE6421/ED5031Software Engineering Slide 40 The debugging process

41 EE6421/ED5031Software Engineering Slide 41 Software validation l Verification and validation (V & V) 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.

42 EE6421/ED5031Software Engineering Slide 42 The testing process

43 EE6421/ED5031Software Engineering Slide 43 Testing stages l Unit testing Individual components are tested to ensure functionality 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 Linked and can be called component testing.

44 EE6421/ED5031Software Engineering Slide 44 Software evolution l Software is inherently flexible and can change. l As requirements change through changing business circumstances, the software that supports the business must also evolve and change. l Although there has been a demarcation between development and evolution (maintenance) this is increasingly irrelevant as fewer and fewer systems are completely new.

45 EE6421/ED5031Software Engineering Slide 45 System evolution

46 EE6421/ED5031Software Engineering Slide 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 practice perspective that suggests good practice.

47 EE6421/ED5031Software Engineering Slide 47 RUP phase model

48 EE6421/ED5031Software Engineering Slide 48 RUP phases l Inception Establish the business case for the system. What benefits it provides – if minimal then project may be cancelled. l Elaboration Develop an understanding of the problem domain, the system architecture and establish a project plan – requirements document and a management plan. l Construction System design, programming, testing & associated documentation l Transition Deploy the system in its operating environment.

49 EE6421/ED5031Software Engineering Slide 49 RUP good practice l Develop software iteratively l Manage requirements – good documentation l Use component-based architectures (A system design composed of separate components that can be connected together) l Visually model software – using the UML l Verify software quality l Control changes to software

50 EE6421/ED5031Software Engineering Slide Computer-aided software engineering l Computer-aided software engineering (CASE) is software to support software development and evolution processes. (Visual Paradigm for UML-Community edition)Visual Paradigm for UML l Activity automation Graphical editors for system model development; Data dictionary to manage design entities; Graphical User Interface (GUI) builder for user interface construction; Debuggers to support program fault finding; Automated translators to generate new versions of a program.

51 EE6421/ED5031Software Engineering Slide 51 Case technology l Case technology has led to significant improvements in the software process. However, these are not the order of magnitude improvements that were once predicted Software engineering requires creative thought - this is not readily automated; Software engineering is a team activity and, for large projects, much time is spent in team interactions. CASE technology does not really support these.

52 EE6421/ED5031Software Engineering Slide 52 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 – provide support for one or more process activities

53 EE6421/ED5031Software Engineering Slide 53 Functional tool classification

54 EE6421/ED5031Software Engineering Slide 54 Activity-based tool classification

55 EE6421/ED5031Software Engineering Slide 55 CASE integration - summary 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.

56 EE6421/ED5031Software Engineering Slide 56 Tools, workbenches, environments

57 EE6421/ED5031Software Engineering Slide 57 Key points l Software processes are the activities involved in producing and evolving a software system. l Software process models are abstract representations of these processes. l General activities are specification, design and implementation, validation and evolution. l Generic process models describe the organisation of software processes. Examples include the waterfall model, evolutionary development and component-based software engineering. l Iterative process models describe the software process as a cycle of activities.

58 EE6421/ED5031Software Engineering Slide 58 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 its specification and user needs. l Evolution is concerned with modifying the system after it is in use. l The Rational Unified Process is a generic process model that separates activities from phases. l CASE technology supports software process activities.

59 EE6421/ED5031Software Engineering Slide 59 Section # 3 (Read Sommerville Ch (4 or 5) and Pressman Ch 3) Project Management


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