SSADM Introduction

On December 7, 2008

Introduction

In the early days of large scale information systems development many organisations used the Cobol programming language together with indexed sequential files to build systems for customer billing, payroll, stock control and a variety of other business areas. Developments at this time were characterised by :-

limited user involvement;
inadequate requirements elicitation;
use of ad hoc analysis and design techniques;
absence of CASE support for analysis and design;
time consuming use of 3GL tools;
inflexible file and 3rd generation database management systems.

Frequently the results of this approach were systems which, on delivery, did not satisfy business requirements. This caused extensive maintenance requirements and thus an increase in the applications backlog. A variety of problems may have caused the mis-match between system functionality and business requirements :-

a lack of ownership of and commitment to the system from users as a result of the low level of involvement;
business requirements may have changed between inception and delivery;
requirements may have been mis-understood;
inadequate analysis and design tools and techniques may have been used;
or more likely a combination of these problems.

The response from the information systems community to these problems was the development of structured methodologies for ISE. The purpose of these methodologies seems to have been to (a) formalise the requirements elicitation process to reduce the chances of mis-understanding the requirements and (b) to introduce best practice techniques to the analysis and design process

SSADM (in common with other structured methodologies) adopts a precriptive approach to information systems development in that it specifies in advance the modules, stages and tasks which have to be carried out, the deliverables to be produced and furthermore the techniques used to produce the deliverables. SSADM adopts the Waterfall model of systems development, where each phase has to be completed and signed off before subsequent phases can begin. SSADM is one example of a structured methodologies, a variety of others are widely used in ISE, including :

STRADIS: (Structured Analysis, Design and Implementation of Information Systems) a methodology developed by Gane and Sarson (1979). The methodology is based on the philosophy of top down functional decomposition and relies on the use of Data Flow Diagrams.

YSM: (Yourdon Systems Method,Yourdon, 1993). YSM is similar to STRADIS in its use of functional decomposition, however a middle-out approach is dopted and slightly more emphasis is placed on the importance of data structures.

MERISE: (Quang and Chartier-Kastler, 1991)The methodology is widely used in ISE in France, Spain and Switzerland. MERISE consists of three ‘cycles’, the decision cycle, the life cycle and the abstraction cycle. The abstraction cycle is the key, in this cycle both data and processes are viewed firstly at the conceptual level, then the logical or organisational level and finally at the physical or operational level.

EUROMETHOD: (CCTA, 1994) Euromethod could be described as a framework for the integration of existing european methodologies rather than as a methodology in its own right.

What is SSADM?

SSADM (Structured Systems Analysis and Design Methodology) is a methodology (Def. a system of ways of doing things especially regular and orderly procedures), used in the analysis and design stages of systems development. SSADM does not cover SITP issues or the construction, testing and implementation of software.

“SSADM has been used by the government in computing since its launch in 1981. It was commissioned by the CCTA (Central Computing and Telecommunications Agency) in a bid to standardise the many and varied IT projects being developed across government departments. The CCTA investigated a number of approaches before accepting a tender from Learmonth & Burchett Management Systems to develop a method.”

Since 1981 SSADM has been further refined and version 4 was launched in 1990. SSADM is an open standard, i.e. it is freely available for use in industry and many companies offer support, training and Case tools for it.

Why is SSADM Used?

Within government departments SSADM has to be used. External contractors producing software for the government also have to use SSADM. SSADM is used by other companies because they expect the use of a disciplined ‘engineering approach will eventually improve the quality of the systems they produce. many companies have been willing to incur the considerable expense of implementing SSADM (e.g. staff training) with this expectation in mind.

How is SSADM Controlled in the UK?

SSADM is managed by the CCTA, however the Design Authority Board (DAB) is responsible for maintaining and developing SSADM and the NCC (National Computing Centre) produce and maintain the definitive SSADM documentation.

What are the Major Tools of SSADM?

SSADM revolves around the use of three key techniques, namely Logical Data Modelling, Data Flow Modelling and Entity/Event Modelling.

Logical Data Modelling; This is the process of identifying, modelling and documenting the data requirements of a business information system. A Logical Data Model consists of a Logical Data Structure (LDS – The SSADM terminology for an Entity-Relationship Model) and the associated documentation. LDS s represent Entities (things about which a business needs to record information) and Relationships (necessary associations between entities).
Data Flow Modelling; This is the process of identifying, modelling and documenting how data flows around a business information system. A Data Flow Model consists of a set of integrated Data Flow Diagrams supported by appropriate documentation. DFDs represent processes (activities which transform data from one form to another), data stores (holding areas for data), external entities (things which send data into a system or receive data from a system and finally data flows (routes by which data can flow).
Entity Event Modelling; This is the process of identifying, modelling and documenting the business events which affect each entity and the sequence in which these events occur. An Entity/Event Model consists of a set of Entity Life Histories (one for each entity) and appropriate supporting documentation.

Three Interdependent Views

The success of SSADM may lie in the fact that it does not rely on a single technique. Each of the three system models provides a different viewpoint of the same system, each of which are required to form a complete model of the system. Within SSADM each of the three techniques are cross reference against each other to ensure the completeness and accuracy of the complete model.

Framework

A brief explanation of a framework for comparing methodologies developed by Avison and Fitzgerald (1995) is followed by its application to the SSADM and DSDM methodologies. The framework consists of 7 elements :-

Philosophy: In their terms a philosophy is a principle or set of principles that underlie a methodology. In fact they define a methodology as a set of techniques underpinned by a philosophy.

Model: The model is the basis of the methodology’s view of the world, e.g. the Waterfall and Spiral models of Information Systems Engineering.

Techniques and Tools: Typically a methodology adopts a set of integrated techniques, such as Entity-Relationship Modelling and Data Flow Modelling and may use CASE tools to support the techniques.

Scope: The scope of a methodology defines its start and end points within the ISE lifecycle.

Outputs: The outputs define the deliverables to be produced during the phases of the methodology.

Practice: This element looks at the use of the methodology in terms of the differences between the theory and the practice.

Product: This element looks at the nature of the product itself, in terms of documentation, CASE tool support, training courses etc.

The forthcoming evaluation addresses each of these elements, however it concentrates on the philosophy, models, techniques and tools and scope areas. The framework is also extended to enable comparison on the basis of the suitability of the methodologies for use within a Corporate Information Management Strategy.