Short for Structured Systems Analysis and Design Method, a set of standards developed in the early 1980s for systems analysis and application design widely used for government computing projects in the United Kingdom. SSADM uses a combination of text and diagrams throughout the whole life cycle of a system design, from the initial design idea to the actual physical design of the application.
SSADM uses a combination of three techniques:
- Logical Data Modeling -- the process of identifying, modeling and documenting the data requirements of the system being designed. The data is separated into entities (things about which a business needs to record information) and relationships (the associations between the entities.
- Data Flow Modeling -- the process of identifying, modeling and documenting how data moves around an information system. Data Flow Modeling examines processes (activities that transform data from one form to another), data stores (the holding areas for data), external entities (what sends data into a system or receives data from a system, and data flows (routes by which data can flow).
- Entity Behavior Modeling -- the process of identifying, modeling and documenting the events that affect each entity and the sequence in which these events occur.
Each of these three system models provides a different viewpoint of the same system, and each viewpoint is required to form a complete model of the system being designed. The three techniques are cross-referenced against each other to ensure the completeness and accuracy of the whole application.
SSADM application development projects are divided into five modules that are further broken down into a hierarchy of stages, steps and tasks:
- Feasibility Study -- the business area is analyzed to determine whether a system can cost effectively support the business requirements.
- Requirements Analysis -- the requirements of the system to be developed are identified and the current business environment is modeled in terms of the processes carried out and the data structures involved.
- Requirements Specification -- detailed functional and non-functional requirements are identified and new techniques are introduced to define the required processing and data structures.
- Logical System Specification -- technical systems options are produced and the logical design of update and enquiry processing and system dialogues.
- Physical Design -- a physical database design and a set of program specifications are created using the logical system specification and technical system specification.
Unlike rapid application development, which conducts steps in parallel, SSADM builds each step on the work that was prescribed in the previous step with no deviation from the model. Because of the rigid structure of the methodology, SSADM is praised for its control over projects and its ability to develop better quality systems.