The water drop model marks a procedural model in the software development, with which the software development process in phases is organized. The phase results are received as always with a Wasserfall as binding defaults for the next deeper phase.

First it was suggested in a paper from the year 1970 of Winston Royce with the title Managing the development OF Large software of system: Concepts and Techniques. In the water drop model each phase has well-defined starting and terminator points with clearly defined results. In milestone meetings at the respective phase end the result documents are discharged. Among the most important documents thereby the work statement as well as product requirement specifications rank. In operational practice there are many variants of the pure model. It is however traditionally the furthest common procedural model.

The name "“Wasserfall"” comes from the frequently selected diagram of the five to six points into cascade extensions of the simple model (water drop model with return) permits a gradual "“upward running"” to the cascade, if in the current phase somewhat should go wrong, in order to be able to eliminate the error on the next higher stage.

The water drop model is used favourably generally, where requirements, achievements and expirations in the planning phase relatively precisely to be described to be able.

Phases

1. Requirement analysis and - specification (English requirement analysis and specification)
2. System Design and - specification (English system Design and specification)
3. Programming and module test (English Coding and of modules testing)
4. Integration and systematical test (English integration and system testing)
5. Distribution, employment and maintenance (English Delivery, and maintenance deployment)

Another variant makes from it six steps:

1. Planning (with production of the work statement, project calculation and project plan) (of English system engineering)
2. Definition (with production of product requirement specifications, product model, GUI model and possibly already user manual) (English analysis)
3. Draft (UML, program structure charts) (English Design)
4. Implementation (English Coding)
5. Tests (English Testing)
6. Employment and maintenance (English maintenance)

"“Definition and draft"” correspond thereby approximately to the subdivided point "“system Design and - specification"” in the first variant, while the second variant together-throws the two possible levels software of the Testing (on module and overall system level).

Problems

1. Delimitation problem-clearly phases from each other defined are unrealistic - the transition between them is flowing into reality: Divide a system can still under the planning be itself, while others already are in the execution or the used.
2. Succession-problem-individual phases run off in the theory successively, in practice are however backward steps often inevitable.
3. AngemessenheitsproblemJe a pattern is more general, on the more projects is applicable it - however the less information is in him contained. The more concrete/more detailed a pattern is, the fixed is it and on the fewer projects is it to be used.

Disadvantages

1. The model is applicable only to simple projects.
2. Early fixing of the requirements very problematic possibly expensive changes (repeatedly repeated going through of the process when changes)
3. Introduction of the system after beginning of the development cycle return on investment later very late

Since it is difficult to specify already at the start of the project everything finally and in the detail the risk exists that the finally finished software does not correspond to the actual requirements. In order to meet, a disproportionately high expenditure in the analysis and conception phase is often operated. Besides the water drop model does not permit and/or only very reduced to take up in the course of the project changes. Therefore the finished software forms not the current, but the requirement conditions at the start of the project again. Since larger software projects have usually also a very long running time, it can occur that a new software already became outdated at the time of its introduction contentwise.

Other procedural models

Because of the partly engraving disadvantages of the water drop model with partial substantial economic consequences the IT-industry developed variety of alternative or supplementing proceedings, software technologies, suggestions and aids. Examples for this are:

• The spiral model (advancement)
• The Unified Process
• Extreme Programming
• Agile software development
• Iterative prototyping and evolutionary prototyping
• Large use of configurable standard software, e.g. for the Workflow management, the user administration u.v.a.
• Universal Application
• On the development phase expanded CHANGE management
• Paging fewer priorisierter subtasks at power user, see also under END user Computing
• Pronounced modularity, up to splitting up more largely into smaller, better visible projects with short running time
• V-model

See also

• Generik

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