The analysis is done in two stages. The first task done by the developer is to create the Requirements Specification - this is really a statement of what we are to do with the current system in order to produce the required system. Stage 2 then develops a range of options that meet the defined requirements, and selects one option as the basis for the desired system.
SSADM revolves around the use of three key techniques, namely Logical Data Modelling, Data Flow Modelling and Entity/Event Modelling.
- Logical Data Modelling: this is the process of identifying, modelling and documenting the data requirements of a system. A Logical Data Model consists of a Logical Data Structure (LDS - also known as an Entity-Relationship Model) and the associated documentation. LDS represents Entities (things about which a business needs to record information, and usually proper nouns) and Relationships (links between entities).
- Data Flow Modelling: this is the process of modelling and documenting how data flows around a system. A Data Flow Model consists of a set of connected Data Flow Diagrams (DFDs) supported by appropriate documentation. Data Flow Diagrams represent processes and functions of the system (activities that transform data from one form to another), data stores (files or data storage), external entities (things that send data into a system or receive data from a system) and finally data flows (show the flow of data around the system).
- Entity Event Modelling: This is the process of identifying, modelling and documenting the business events that affect each entity and the sequence in which these events occur. An Entity/Event Model consists of a set of Entity Life Histories (one for each entity) and appropriate supporting documentation.
Next: SSADM Views