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SSADM - Stage 5 |
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Logical Design
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Once the user option has been selected, the analysis phase is complete and the design process can begin. It is important that for as long as possible the design should consider only logical design with a detailed logical model being produced.
Stages 4 and 5 of SSADM are carried out in parallel and interact at all times. Stage 4 looks at the data design and is concerned with developing two products: optimized 3rd normal form (TNF) relations and a composite logical data model (CLDD). Stage 5 on the other hand develops more detailed process outlines. The Objectives of stage 5 are to design the menu structure and dialogues of the system and to specify the update/enquiry process modules.
This step is normally done after the CLDD (composite logical data model) has been produced.
While expanding the detail of some enquiry functions it may be found that they change the state of the database or file record.
In which case they should be transferred to the update function catalogue(s) produced in the step 3 of stage 2 and dealt with in the update-processing step of this stage. It may be convenient to specify output formats at this point. Each entry remaining in the retrievals function catalogue should result in a logical enquiry process outline being produced.
Tasks
Create a Logical enquiry process outline for each function listed in the retrievals function catalogue.
Create output formats for each output identified on the enquiry process outlines.
Update the data dictionary.
Update logical dialogue outlines to be consistent with the CLDD.
Techniques
- Process outlines.
- Dialogue design.
Outputs
- Logical enquiry process outlines. Which goes to section 4 (Validation and review of design).
- Output formats. Which also go to section 4.
- Logical dialogue outlines and controls.
This step can only be done after the CLDD (composite logical data design) has been produced.
It involves updating the ELH's (entity life histories) and all other products of the required system specification to take account of the differences between the CLDD and the LDS (logical data structure). Having identified all the events with which the system has to deal, creating a logical update outline for each event.
Tasks
Update the event catalogue with events that have been identified as a result of creating the CLDD.
Create an entity life history for each entity that appears on the CLDD but was not on the LDS.
Remove entity life histories for entities that do not appear on the CLDD.
Review the remaining entity life histories and amend as necessary.
Amend the other products of the required system specification to reflect changes identified as a result of updating the entity life histories.
Update logical dialogue outlines to be consistent with the CLDD.
Create logical dialogue outlines for new events identified as a result of updating the entity life histories.
Create a logical update process outline for each event catalogue.
Update the CLDD, entity descriptions and data dictionary with any changes found as a result of the creation/updating of logical update process outlines.
Techniques
- Entity life histories.
- Process outlines.
- Dialogue design.
Outputs
- Logical update process outlines.
- Updated entity life histories and entity descriptions.
- Update CLDD.
- Update data flow diagrams, function's descriptions and function catalogues.
- Logical design outlines. All to section 4.
This step involves validating the logical design by submitting all products of the process and data design activities to the formal quality assurance review in order that authorization for continuance to the physical design stage can be obtained.
This step also represents the point at which the detailed logical design is completed.
Tasks
Plan and carry out a quality assurance review of all relevant products.
Amend the logical system design and data dictionary to reflect any changes necessary as a result of the review.
Obtain formal authorization to continue to Stage 6.
Techniques
- Quality assurance.
Outputs
- Validated logical system design
- Formal authorization to continue. Both go to stage 6.