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SSADM - Stage 1 |
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Requirement Analysis
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This Stage establishes the basis for subsequent work by focusing on the existing system and thereby identifying the needs of the people and the requirements of the future system.
Step 121 Establish Analysis Framework
The First Step is to establish an Analysis Framework; here we look at the Nature of the problem with a view to customizing the approach to ensure it meets the needs of the system. It is assumed the some work has taken place previous to this stage but this is not always so. Depending on what has been covered in the previous stages decides the amount of work required in this step.
Essentially This step checks that the preceding work is satisfactory and allows us to establish the scale and nature of the project.
Inputs
New/Modified Outputs
The Second Step is to Investigate and Define Requirements. The requirement catalogue will become the backbone of the project. Entering Requirements may only be partly carried out during this stage. During this stage descriptions of the current system are established. The Third Step is to Investigate Current Processes.
This step also establishes a complete list of users and their activities so that all potential users may be consulted. This list must be made available to all other steps which require it such as Investigate Current Processing And Investigate Current Data.
Inputs
Context Diagram
Level One Data Flow Diagram
Outputs
Context Diagram
Current Physical Data Flow Modeling
This step simply describes the existing systems. Here we record the existing system as a set of Data Flow Diagrams. All current processes and data flows are documented regardless if they are right or wrong. We simply want a clear picture of what the system currently does. This allows us to identify the problems in the current system and also identify the aspects we want to keep.
We also create a Data Flow Model which is the combination of one or more levels of Dfd's plus their supporting detail, i.e. External Entity Descriptions, Elementary Process Descriptions and I/O Descriptions.
The Detailed Information relating to data items is recorded in the Data Catalogue, i.e. attributes (fields)
Inputs
Context Diagram
Level One Data Flow Diagram
Outputs
Context Diagram
Current Physical Data Flow Modeling
During this stage it is sufficient to identify major entities. Details of there content is normally limited to major attributes such as keys and other highly significant items. Identifying entities is frequently difficult especially trying to reach a consensus agreement of them so the use of relational data analysis on documents usually will help.
Inputs
Overview LDS
Outputs
Current Environment LDM
This Step brings together all the work done so far on the current system. One purpose of this stage is to check for consistency between the steps. E.g. the Logical Data Store/Entity cross-reference is created in this step.
During this step we also convert the Physical DFM into a logical DFM by eliminating external physical factors, duplication and redundancy. The LDM which is already by definition, Logical, is used for reference and validation.
Processes and data stores that are purely to service the physical implementation of the current system are deleted. After these updates some DFD may no longer be viable in their own right and can be combined with other diagrams.
It is good practice to record the reasons, if any, why particular decisions were taken in case the situation changes and they need to be revised.
Inputs
User Catalogue
Requirements Catalogue
Context Diagram
Current Physical DFM
Current Environment LDM
Outputs
Context Diagram
Logical Data Store/Entity cross-reference
Logical DFM
Requirements Catalogue
Current Environment LDM
Step 126 Assemble Investigation Results
This Step concludes the stage and is concerned with quality. This review concentrates on coherence and consistency of the whole stage of products. This does not mean that quality reviewing only takes place at the end of the stage.
This Step requires links with the external Quality Assurance set up by the Project Board and mediated through the Project Procedures for quality control. In contrast to the assembly steps there are no results to be formally published by this step.
Inputs
User Catalogue
Context Diagram
Logical Data Store/Entity Cross-Reference
Logical DFM
Requirements Catalogue
Current Environment LDM
Outputs
Current Services Description
Requirements Catalogue
User Catalogue