Software Engineering – University of Tampere, CS DepartmentJyrki Nummenmaa SOFTWARE LIFECYCLE MODELS These slides contain a few different software lifecycle models.

Software Engineering – University of Tampere, CS DepartmentJyrki Nummenmaa THE BASIC WATERFALL MODEL Requirement specification Maintenance Testing Implementation Analysis & Design

Software Engineering – University of Tampere, CS DepartmentJyrki Nummenmaa 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 Validation: Are we building the right product? Verification: Are we building the product right?

Software Engineering – University of Tampere, CS DepartmentJyrki Nummenmaa 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 – University of Tampere, CS DepartmentJyrki Nummenmaa 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 – University of Tampere, CS DepartmentJyrki Nummenmaa INCREMENTAL DEVELOPMENT It is useful to divide the development so that the subsequent releases are based on the previous releases. 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. The previous releases should be independent of the following ones.

Software Engineering – University of Tampere, CS DepartmentJyrki Nummenmaa EVOLUTIONARY 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. May work well with a really small development team (just 1-2 people)

Software Engineering – University of Tampere, CS DepartmentJyrki Nummenmaa HIGHER-LEVEL VIEW Maintenanc e 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 – University of Tampere, CS DepartmentJyrki Nummenmaa 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 and to acknowledge the fact that it is so hard to get the requirements right.