SSADM

The methodology of SSADM is created in the early eighties and accepted in 1993 as the national standard of Great Britain for development of information systems. Its undoubted advantage is existence of the mutually agreed techniques regulating the initial stages of system development central of which the stage of iterative determination of requirements is. At the same time SSADM does not extend to the stages connected with implementation, implementation and maintenance of a system, sending the developer to other public methodologies recommended by the British state agency on information science and ADP equipment.

In SSADM the descending approach to creation of the integrated function, information and event models is applied. When modeling, functions classical DFD are used (the including only basic objects: process, a data stream, the data warehouse, an external entity) with minispecifications in the structured natural language. Data modeling is performed using a notation of LDS (Logical Data Structure) which is an ER model dialect. For event modeling the charts of a life story of entities of ELN (Entity Life History) supporting indicators of statuses, events with the actions tied to them, an opportunity to set consecutive, parallel and iterative constructions and also choice constructions are used.

IT system development stages on SSADM

According to the standard when developing an automated system the next stages are selected:

Stage 0. Estimation of feasibility (optional).

• Define a framework and make the development plan.
• Define the original version of requirements.
• Select option of estimation of feasibility.
• Issue the report on a possibility of creation.

Stage 1. Preproject research.

• Define a framework of a preproject research.
• Define the main requirements.
• Study processing of information in the existing system.
• Study the data processed in the existing system.
• Develop the logical description of the existing system.
• Generalize results of a preproject research.

Stage 2. Choice of option of automation.

Stage 3. Development of technical specifications.

• Develop general requirements to the automated functions.
• Develop a required logical data model.
• Specify requirements and functional tasks.
• Specify a logical data model.
• Develop a demonstration prototype.
• Develop requirements to data processing.
• Specify the development purposes.
• Issue technical specifications on creation of AS.

Stage 4. Choice of option of technical implementation.

• Develop options of technical implementation,
• Select option of technical implementation.

Stage 5. Development of the logical project.

• Define an order of dialogue interaction.
• Develop problem definitions of modification of databases.
• Develop settings of information tasks.
• Complete development of the logical project.

Stage 6. Physical design.

• Prepare the plan of physical design.
• Develop physical implementation of databases.
• Develop requirement specifications to program components.
• Optimize physical structure of databases.
• Specify requirement specifications to program components.
• Approve the interface between tasks and databases.
• Issue the physical project.

Comments

Initial data collect in the special document – "The directory of requirements".

At a stage 3 make other documents supplementing the directory of requirements. Determination of requirements – iterative process.

At a stage 0 the directory of requirements can appear if stage 0 is not carried out, it is entered at a stage 1.

At a stage 1 the model in terms of tasks, information flows, the processed data is formed. All revealed shortcomings of the existing system are made out in the directory of requirements. If a system is created for no reason, then all requirements register according to wishes of users. The main objective of stage 1 to make the list of functions of a system.

At a stage 2 develop from three to six options of automation and select one of them. At a stage 3 requirements are reviewed taking into account the selected automation option. If any requirements are not met, then specify the reason.

At stages 301-303 build the formalized model.

The model of information flows, logical data model, the description of functions enter it.

After stage 3 it is forbidden to add new requirements to a system, however their refining is allowed.

At a stage 4 are requirements concerning technical and program implementation. Ways of their satisfaction are reflected in "options of technical implementation". Other part of requirements – requirements to dialogue interaction, are implemented at stage 501. Document requirements – the main objective of the designer. Its tasks also include collecting of primary requirements.

In the course of collecting it is necessary to receive the answer to many questions, such as: what is required from a system why it is necessary, who needs it as far as it is important, than it is possible to measure degree of compliance to requirements.

To a stage 3 all requirements are not final.

Requirements of again developed documents can be added to them. Types of requirements are divided into functional and nonfunctional (that needs to be done and with what quality).

Sources

• Case-technologies