Software Engineering 2003 Jyrki Nummenmaa 1 SOFTWARE ENGINEERING - SOFTWARE LIFECYCLE MODELS These slides contain a few different software lifecycle models.

Software Engineering 2003 Jyrki Nummenmaa 2 THE BASIC WATERFALL MODEL Requirement specification Maintenance Testing Implementation Analysis & Design

Software Engineering 2003 Jyrki Nummenmaa 3 A MODIFIED WATERFALL MODEL Requirement spec. - V&V Maintenance - V&V Testing - V&V Implementation - V&V Analysis & Design - V&V V&V = Verification and Validation

Software Engineering 2003 Jyrki Nummenmaa 4 PROTOTYPING FOR REQUIREMENT ANALYSIS Requirement spec. - V&V Maintenance - V&V Testing - V&V Quick Implementa- tion - V&V Analysis & Design - V&V V&V = Verification and Validation Quick Analysis & Design - V&V Implementation - V&V

Software Engineering 2003 Jyrki Nummenmaa 5 THE SPIRAL (ITERATIVE) MODEL A0 A1 D1 C1 B0 B1 A2B2 D2 D3 C2 C3 Planning Risk analysis Prototyping Client evaluation and input Model simulation Operational prototype Verification for next level

Software Engineering 2003 Jyrki Nummenmaa 6 INCREMENTAL SOFTWARE DEVELOPMENT It is useful to divide the development so that the subsequent releases are based on the previous releases. Here it is important to choose the increments in such a way, that the feedback from the previous increments shows if the development is going right. Also, the previous releases should be independent of the following ones.

Software Engineering 2003 Jyrki Nummenmaa 7 EVOLUTIONARY SOFTWARE DEVELOPMENT In evolutionary software development different activities (design, implementation, testing, and even requirements specification) may all progress at the same time. In this type of a situation controlling the project can be very difficult. Evolutionary software development may take place because it is not really known what is needed or how it can be achieved. Evolutionary software development may also be a sign of lack of control over the development process.

Software Engineering 2003 Jyrki Nummenmaa 8 THE MANAGEMENT VIEW Maintenance and audit Installation Build new system: requirement specification, analysis & design, implementation, testing Do a feasibility study to find out whether it is feasible to implement a new system.

Software Engineering 2003 Jyrki Nummenmaa 9 NEW DEVELOPMENTS Special considerations for distributed software and web-based software Availability of Commercial Off-The-Shelf (COTS) components. Many companies now work as integrators – they use COTS and subcontractors and maybe only write a minor part of the software themselves. “Lightweight” process models to get more flexibility.