Our Company uses as a basis similar principles of SSADM to produce Studies, Support and Training Courses. We have chosen as our process method Structured Systems Analysis and Design Method (SSADM), as all the objectives are linked with new technologies and are easily applied with some modifications to maritime industry.
Our method involves the application of a sequence of analysis, documentation and design tasks concerned with the following:
Stage 0 - Feasibility study
In order to determine whether or not a given project is feasible, there must 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.
In larger projects, the feasibility may be done but in an informal sense, either because there is no time for a formal study or because the project is a "must-have" and will have to be done one way or the other. When a feasibility study is carried out, there are four main areas of consideration:
• Technical - is the project technically possible?
• Financial - can the business afford to carry out the project?
• Organizational - will the new system be compatible with existing practices?
• Ethical - is the impact of the new system socially acceptable?
To answer these questions, the feasibility study is effectively a condensed version of a fully-blown systems analysis and design. The requirements and users are analysed to some extent, some business options and even some details of the technical implementation are drawn up.
The product of this stage is a formal feasibility study document. Our method specifies the sections that the study must contain, including any preliminary models that have been constructed and also details of rejected options and the reasons for their rejection.
Stage 1 - Investigation of the current environment
This is one of the most significant stages. The developers understood that though the tasks and objectives of a new system may be radically different from the old system, the underlying data will probably change very little. By coming to a full understanding of the data requirements at an early stage, the remaining analysis and design stages can be built up on a firm foundation.
In almost all systems there is some form bureaucracy. Through a combination of interviewing employees, circulating questionnaires and observing the current documentation, the analyst comes to full understanding of the system as it is at the beginning of the project.
This serves many purposes such as:
• The team learns the terminology of the business, what users do and how they do it
• The old system provides the core requirements for the new system
• Faults, errors and areas of inefficiency are highlighted and their correction added to the requirements
• The data model can be constructed
• The users become involved and learn the techniques and models of the analyst
• The boundaries of the system can be defined
The products of this stage are:
• Users Catalogue describing all the users of the system and how they interact with it
• Requirements Catalogues detailing all the requirements of the new system
• Current Services Description further composed of
• Current environment logical data structure (ERD)
• Context diagram (DFD)
• Levelled set of DFDs for current logical system
• Full data dictionary including relationship between data stores and entities
To produce the models, our team works through the construction of the models as we have described. However, the first set of data-flow diagrams (DFDs) are the current physical model, that is, with full details of how the old system is implemented. The final version is the current logical model which is essentially the same as the current physical but with all reference to implementation removed together with any redundancies such as repetition of process or data.
In the process of preparing the models, the analyst will discover the information that describes the users and requirements catalogues.
Stage 2 - Business system options
Having investigated the current system, the analyst must decide on the overall design of the new system. In order to accomplish this and by using the outputs of the previous stage, a set of business system options can be developed. There are different ways in which the new system can be produced varying from doing nothing to throwing out the old system entirely and building a completely new one. The analyst may hold a brainstorming session so that as many ideas as possible are generated.
The ideas are then collected to form a set of two or three different options which are presented to the user. The options consider the following:
• The degree of automation
• The boundary between the system and users
• The distribution of the system, for example: is it centralized to one office or spread out across several?
• Environmental 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 our team of experts together choose a single business option. This may be one of the already defined options or may be a synthesis of different aspects of the existing options. The output of this stage is a single selected business option together with all the outputs of stage 1.
Stage 3 - Requirements specification
This is probably the most complex stage. 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. Consequently, we mean that the specification does not express how the system will be implemented but rather describes what the system will do.
To produce an accurate specification, the analyst builds the required logical models for both the data-flow diagrams (DFDs) and the entity relationship diagrams (ERDs). These are used to produce function definitions of every function which the users will require from the system, entity life-histories (ELHs) and effect correspondence diagrams, these are models of the product of this stage is a complete Requirements Specification document which is made up of:
• The updated data catalogue
• The updated requirements catalogue
• The processing specification which in turn is made up of
• user role/function matrix,
• function definitions,
• required logical data model,
• entity life-histories and
• 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 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 honed down to two or three to present to the user which of the final option is chosen or synthesized.
However, some reasonably different considerations are the:
• Hardware architectures
• Software to use
• Cost of the implementation
• Staffing required
• Physical limitations such as a space occupied by the system
• Distribution including any networks which that may require
• Overall format of the human computer interface
All of these aspects must also conform to any constraints imposed by the business, such as money availability and 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 details of the implementation, the outputs of this stage are implementation-independent and concentrate on the requirements for the human computer interface. The logical design specifies the main methods of interaction in terms of menu structures and command structures.
One area of activity is the definition of user dialogues. These are the main interfaces with which the users will interact with the system. Other activities are concerned with analysing both the effects of scenarios in updating the system and the need to make inquiries about the data on the system. Both of these, use 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 catalogue
• Required logical data structure
• Logical process model -- includes dialogues and model for the update and inquiry processes
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 where necessary to meet size and performance requirements.
The product is a complete Physical Design which informs software engineers how to build the system in specific details of hardware and software and to the appropriate standards.
Advantages and disadvantages
Using this methodology involves a considerable undertaking which may not be suitable to all projects.
The main advantages are:
• Three different views of the system
• Separation of logical and physical aspects of the system
• Well-defined techniques and documentation
• User involvement
There is a large investment in cost and time in training people to use the techniques. The learning curve is considerable as there are not only several modelling techniques to come to terms with, but also a lot of standards for the preparation and presentation of documents.