Structured systems analysis and design method

Structured systems analysis and design method ( SSADM ), originally released as methodology , is a systems approach to the analysis and design of information systems. SSADM was produced for the Central Computer and Telecommunications Agency , a UK government office concerned with the use of technology in government, from 1980 onwards.

Overview

SSADM is a waterfall method for the analysis and design of information systems . SSADM can be thought to represent a pinnacle of the rigorous document-led approach to system design, and contrasts with more contemporary agile methods such as DSDM or Scrum .

SSADM is one Particular implementation and builds on the work of different schools of structured analysis and development methods, Such As Peter Checkland’s soft systems methodology , Larry Constantine’s structured design , Edward Yourdon’s Yourdon Structured Method Michael A. Jackson’s Jackson Structured Programming , and Tom DeMarco’s Structured analysis .

The names “Structured Systems Analysis and Design Method” and “SSADM” are registered trademarks of the Office of Government Commerce (OGC), which is an office of the United Kingdom’s Treasury. [1]

History

The main stages of the development of SSADM were: [2]

  • 1980: Central Computer and Telecommunications Agency (CCTA) evaluate analysis and design methods.
  • 1981: Consultants working for Learmonth & Burchett Management Systems, led by John Hall, chosen to develop SSADM v1.
  • 1982: John Hall and Keith Robinson, LBMS later developed LSDM, their proprietary version.
  • 1983: SSADM made mandatory for all new information system developments
  • 1984: Version 2 of SSADM released
  • 1986: Version 3 of SSADM released, adopted by NCC
  • 1988: SSADM Certificate of Proficiency launched, SSADM promoted as ‘open’ standard
  • 1989: Moves towards Euromethod , launch of CASE products certification scheme
  • 1990: Version 4 launched
  • 1993: SSADM V4 Standard and Tools Conformance Scheme
  • 1995: SSADM V4 + announced, V4.2 launched
  • 2000: CCTA renamed SSADM as “Business System Development”. The method was repackaged into 15 modules and another 6 modules were added. [3] [4]

SSADM techniques

The three most important techniques that are used in SSADM are as follows:

Logical data modeling
The process of identifying, modeling and documenting the data requirements of the system being designed. The result is a data model containing entities (associations about the entities).
Data Flow Modeling
The process of identifying, modeling and documenting how data moves around an information system. Data Flow Modeling (Data Processing), data holdings, data entities, data entities, and data flows. Which data can flow).
Entity Event Modeling
A two-stranded process: Entity Behavior Modeling, identifying, modeling and documenting the events that affect each entity and the sequence (or life history) .

Stages

The SSADM method involves the application of a sequence of analysis.

Stage 0 – Feasibility study

In order to determine whether or not a given project is feasible, there should be some form of investigation into the goals and implications of the project. For very small scale projects this may not be necessary at all as the scope of the project is easily understood. If you are looking for a great place to stay, then this is the place for you.

When a feasibility study is carried out, there are four main areas of consideration:

Technical – is the project technically possible?
Financial – Can the business take the project?
Organizational – will the new system be compatible with existing practices?
Ethical – is the impact of the socially acceptable new system?

To answer these questions, the feasibility study is a condensed version of a fully blown systems analysis and design. The requirements and users are analyzed to some extent, some business options are drawn up and even some details of the technical implementation. The product of this stage is a formal feasibility study document. SSADMs are the most commonly used rejected and rejected options.

Stage 1 – Investigation of the current environment

The developers of SSADM, which is the most widely used in the world, Through a combination of interviewing employees, circulating questionnaires, observations and existing documentation, the analyst comes to full understanding of the system as it is at the start of the project. This serves many purposes.

Stage 2 – Business system options

Having investigated the current system, the analyst must decide on the overall design of the new system. To do this, he or she, using the outputs of the previous stage, develops a set of business system options. These are the first steps to be taken in the new system. The analyst may hold a brainstorming session so as many as possible are generated.

The ideas are presented to the user. The options consider the following:

  • The degree of automation
  • The boundary between the system and the users
  • The distribution of the system, for example, is it centralized to one office or spread out across several?
  • cost / benefit
  • Impact of the new system

Where necessary, the option will be documented with a logical data structure and a level 1 data-flow diagram.

The users and analyst together choose a single business option. This may be one of a number of aspects of the existing options. The output of this stage is the single selected business option together with all the outputs of the feasibility stage.

Stage 3 – Requirements specification

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 diagrams (DFDs) and the Logical Data Model (LDM), consistant of the Logical Data Structure (Referred to in other methods as entity relationship diagrams ) and Full descriptions of the data and its relationships. 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 continuously matched against the requirements and where necessary, the requirements are added to and completed.

The product of this stage is a complete specification document which is made up of:

  • The updated data catalog
  • The specifications
  • The processing specification which in turn is made up of
  • User role / function matrix
  • Function definitions
  • Required logical data model
  • Entity life-histories
  • Effect correspondence diagrams

Though some of these items may be unfamiliar to you, it is beyond the scope of this unit to go into them in great detail.

Stage 4 – Technical system options

This stage is the first step towards a physical implementation of the new system. Like the Business System Options, in this stage a large number of options for the implementation of the new system are generated. This is narrowed down to two or more to the user of which the final option is chosen or synthesized.

However, the considerations are quite different being:

  • The hardware architectures
  • The software to use
  • The cost of the implementation
  • The staffing required
  • The physical limitations of the system
  • The distribution including any networks
  • The overall format of the human computer interface

All of these aspects should also be considered as standardization of hardware and software.

The output of this stage is a chosen technical system option.

Stage 5 – Logical design

Though the previous level specifies the details of the implementation, the outputs of this stage are implementation-independent and concentrate on the human computer interface. The logical design specifies the main methods of interaction in terms of structure and order structures.

One area of ​​activity is the definition of the user dialogues. These are the interfaces with which the users will interact with the system. Other activities are concerned with analyzing both the effects of events in updating the system and the need to make inquiries about the data on the system. Both of these uses the events, function descriptions and effect correspondence diagrams produced in stage 3 to determine precisely how to update and read data in a consistent and secure way.

The product of this stage is the logical design which is made up of:

  • Data Collection
  • Required logical data structure
  • Logical process model – includes dialogs and model for the update and inquiry processes
  • Stress & Bending moment.

Stage 6 – Physical design

This is the final stage where all the logical specifications of the system are converted to descriptions of the system in terms of real hardware and software. This is a very technical stage and a simple overview is presented here.

The logical data structure is converted into a physical architecture in terms of database structures. The exact structure of the functions and how they are implemented is specified. The physical data structure is optimized to meet size and performance requirements.

The product is a complete physical design that could be used to design and build a computer system.

References

  1. Jump up^ “OGC – Annex 1” . Office of Government Commerce (OGC) . Retrieved 2010-12-17 .
  2. Jump up^ Mike Goodland; Karel Riha (20 January 1999). “History of SSADM” . SSADM – an Introduction . Archived from the original on 2013-02-19 . Retrieved 2010-12-17 .
  3. Jump up^ “Model Systems and SSADM” . Model Systems Ltd. 2002. Archived from the original on April 2, 2009 . Retrieved 2009-04-02 .
  4. Jump up^ SSADM foundation . Business Systems Development with SSADM. The Stationery Office . 2000. p. v. ISBN  0-11-330870-1 

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