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This is probably the most complex stage in SSADM. Using the requirements developed in stage 1 and working within the framework of the selected business option, the analyst must develop a full logical specification of what the new system must do. The specification must be free from error, ambiguity and inconsistency. By logical, we mean that the specification does not say how the system will be implemented but rather describes what the system will do.
To produce the logical specification, the analyst builds the required logical models for both the [[Data flow diagram|data-flow diagrams]] (DFDs) and the [[Logical Data Model]] (LDM), consisting of the Logical Data Structure (referred to in other methods as [[Entity-relationship model|entity relationship diagrams]]) and full descriptions of the data and its relationships. These are used to produce function definitions of every function which the users will require of the system, Entity Life-Histories (ELHs) which describe all events through the life of an entity, and Effect Correspondence Diagrams (ECDs) which describe how each event interacts with all relevant entities. These are continually matched against the requirements and where necessary, the requirements are added to and completed.
The product of this stage is a complete requirements specification document which is made up of:
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