Lecture Objectives. Software Life Cycle. Software Engineering Layers. Software Process. Common Process Framework. Umbrella Activities

Transcription

1 Software Life Cycle Lecture Objectives What happens in the life of software To look at the life cycle of a software To understand the software process and its related elements To relate to the different software engineering paradigms TCS2411 Software Engineering 1 TCS2411 Software Engineering 2 Software Engineering Layers Software Process tools methods process model a quality focus Activities in software projects Characterised by a common process framework Framework activities - task sets Umbrella activities Process maturity enables development of quality software products TCS2411 Software Engineering 3 TCS2411 Software Engineering 4 Common Process Framework Umbrella Activities Common process framework Framework activities work tasks work products milestones & deliverables QA checkpoints Umbrella Activities Software project management Formal technical reviews Software quality assurance Software configuration management Document preparation and production Reusability management Measurement Risk management TCS2411 Software Engineering 5 TCS2411 Software Engineering 6 1

2 Process as Problem Solving The Process : Adaptability status quo problem definition solution integration technical development the framework activities will always be applied on every project... BUT the tasks (and degree of rigor) for each activity will vary based on: the type of project (an entry point to the model) characteristics of the project common sense judgment; concurrence of the project team TCS2411 Software Engineering 7 TCS2411 Software Engineering 8 The Primary Goal: High Quality The Systematic Process Remember: High quality = project timeliness Why? Less rework! Analysis Design Development Problem s Testing Solution TCS2411 Software Engineering 9 TCS2411 Software Engineering 10 Generic Phases Definition Phase Focus on what the software is Development Phase Focus on how the software works Maintenance Phase Focus on change to the software TCS2411 Software Engineering 11 Definition Phase Identify information to be processed Identify system behaviour - functions and performance Determine constraints, interfaces, validation criteria Major tasks: System engineering Software project planning Requirements analysis TCS2411 Software Engineering 12 2

3 Development Phase Maintenance Phase Define data structures, function implementation, procedural details, interfaces Translate design to programming language How testing is performed Major tasks: Software design Code generation Software testing TCS2411 Software Engineering 13 Reapplies definition and development phases to existing software Types of changes: Correction Adaptation Enhancement Prevention TCS2411 Software Engineering 14 Waterfall Waterfall System Engineering Analysis Design Code Testing Maintenance The classic life cycle - oldest and most widely used paradigm Activities flow from one phase to another If there are corrections, return to a previous phase and flow from there again Major advantages: Good for planning and well-defined/repeated projects TCS2411 Software Engineering 15 TCS2411 Software Engineering 16 Problems of Waterfall Prototyping Real projects often follow the sequence All requirements may not be stated explicitly by customer Customer only sees the results after some time Developers are often delayed at certain phases Start Requirements gathering and refinement Engineer product Stop Quick design Refining prototype Building prototype Customer evaluation listen to customer customer test-drives mock-up build/revise mock-up TCS2411 Software Engineering 17 TCS2411 Software Engineering 18 3

4 Prototyping Developer and customer determine objectives and draft requirements Prototype quickly produced and evaluated by customer Prototype then refined, and re-evaluated Process iterated, before final product development Advantages: Customer participation and better requirements TCS2411 Software Engineering 19 Problems of Prototyping Problem 1: Customer may see prototype as working model and expects fast results Problem 2: Developer compromised when producing prototype quickly, e.g. different operating system or programming language TCS2411 Software Engineering 20 Rapid Application Development (RAD) Team #1 Business Data Process Time period Team #2 Business Data Process Application Application Generation Testing & Turnover Generation Testing & Turnover TCS2411 Software Engineering 21 RAD High-speed version of waterfall model Primarily for information systems applications Requirements well-understood, fully functional system produced in short time The application modularised - major functions can be completed in 3 months Separate teams complete the functions, then integrated as a whole Requires human resource and commitment TCS2411 Software Engineering 22 Incremental Incremental System/information increment 1 engineering analysis design code test delivery of 1st increment increment 2 analysis design code test delivery of 2nd increment increment 3 analysis design code test delivery of 3rd increment increment 4 analysis design code test delivery of 4th increment Software separated into different increments - complete working portions Focus on delivery of operational product with each increment - can be evaluated Useful when insufficient staff and can be planned to manage technical risks, e.g. waiting for new hardware calendar time TCS2411 Software Engineering 23 TCS2411 Software Engineering 24 4

5 Spiral Spiral Customer Communication Customer Evaluation Planning Risk Analysis Construction & Release Engineering Originally proposed by Boehm, couples iterative nature of prototyping and the systematic aspects of waterfall model Software is developed in series of incremental releases Each iteration produces a more complete product Better management through risk analysis TCS2411 Software Engineering 25 TCS2411 Software Engineering 26 Problems of Spiral Component Assembly May be difficult to convince customers that evolution is controllable Demands risk assessment expertise - major risk will cause problems if not identified Relatively new and not widely used - cannot determine performance Identify candidate Look up in library Available? Extract yes no Build Construct System TCS2411 Software Engineering 27 TCS2411 Software Engineering 28 Component Assembly Fourth Generation Techniques (4GT) Use of object-oriented technology Components - classes that encapsulate both data and algorithms Components developed to be reusable Paradigm similar to spiral model, but engineering activity involves System produced by assembling the correct TCS2411 Software Engineering 29 Requirements gathering "Design" Strategy Implementation using 4GL Testing TCS2411 Software Engineering 30 5

6 4GT Use of software tools that allow software engineer to specify s/w characteristics at higher level The tools generate codes based on specification More time in design and testing - increase productivity Tools may not be easy to use, codes generated may not be efficient TCS2411 Software Engineering 31 Other Process s Component assembly model the process to apply when reuse is a development objective Concurrent process model recognizes that different part of the project will be at different places in the process Formal methods the process to apply when a mathematical specification is to be developed Cleanroom software engineering emphasizes error detection before testing TCS2411 Software Engineering 32 Conclusion The paradigm used for development of software depends on a number of factors People - staff & users Software product Tools available Environment Existing models makes development process clearer, but they can be evolved to become new paradigms END References TCS2411 Software Engineering 33 TCS2411 Software Engineering 34 6