Actitudes Ambientales

This section will examine two system modelling techniques, Input - Output diagrams and the IDEF0 technique. Of the two techniques the Input - Output diagram technique is simpler so it will be examined first.

Hall and Jenkins, (Hall 1962, Jenkins 1969b), both introduced the reader to the concept of the system as a box with inputs to the left and outputs to the right as shown in Figure 20 below, adapted from Hall, (1962).

Figure 20: The Input - Output Diagram

O2 O1 O3 Om I2 I1 I3 In

Both Hall and Jenkins explain that systems analysts need to follow the following procedure to develop a system using Input - Output diagrams:

1. For the main system all Inputs and Outputs need to be defined as in Figure 20;

2. Next the main system should be split into its component sub-systems until all inputs and outputs are included and Input - Output diagrams drawn.

It is very possible that the ratios of inputs to outputs on any particular system or subsystem will not be 1:1 and that the outputs of one sub-system could be the inputs of another.

Each sub-system now should be considered to be a main system and the procedure above should be followed so that each sub-system is split into its own sub-systems.

Eventually using this procedure it will not be appropriate to form any more sub-systems and the definition procedure will be finished. The result of the exercise is that the systems analyst would have a full list of systems with inputs and outputs indicated. Using these diagrams the systems analyst can design and implement all the relevant systems.

The strength and weakness of the Input - Output diagrams technique is that it is very simple. Another technique was developed that allowed definition of controls and mechanisms for change for a system. The technique was the original “Information Definition” technique, (IDEF0).

IDEF0, developed from the Systems Analysis and Design Technique, SADT, was used by the United States Air Force to model their complex integrated information systems, (Doniavi et al 1997). The IDEF0 model looks like the Input - Output diagram but also includes the concept of controls, (process triggers) and mechanisms, (process enablers). This is illustrated in Figure 21 below, adapted from Doniavi et al, (1997).

Figure 21: The IDEF0 Diagram

Control

Input

Process

Just like the Input - Output technique, the IDEF0 technique considers a system to be the mechanism of converting inputs to outputs but structures the process of creation of sub- systems by a process called Functional Decomposition. This is shown in Figure 22.

Figure 22: IDEF0 Functional Decomposition

At the top level the main system is defined as system A-0. In this case there are three inputs and one output.

From the definition of level A-0 the component sub-systems are defined as level A0. In this case it is found that the output from the first stage is the control on the second and the output from the second is the control on the third, no mechanisms are needed.

From level A1 each stage is itself broken down into stages. In this case the outputs from each stage become the inputs to the next stage, the controls are now carried over from level A0. A useful check when creating an IDEF0 model is that level A0 should have exactly the same system inputs, outputs, mechanisms and controls as level A-0 and so on throughout the hierarchical structure.

A-0

A0

There are a number of different applications of the IDEF model. Nookabadi and Middle, (1996), highlight seven current types of model available:

1. IDEF0, (systems model); 2. IDEF2, (dynamic model); 3. IDEF1X, (data model);

4. IDEF3, (process description capture); 5. IDEF4, (object-oriented design); 6. IDEF5, (ontology description); 7. IDEF6, (design rationale capture).

The work done in this thesis has been with information systems and as a result the IDEF0 technique has been studied. IDEF0 is the basis for Figure 21 and Figure 22.

It can be seen that both IDEF0 and Input-Output diagrams can be of significant benefit to a systems analyst. One drawback to these methods is that they are complicated to draw and need to be constantly updated by the systems analyst as systems change throughout a systems development project, (though this is made easier by use of modern software packages to draw and maintain the IDEF0 charts).

Work has been done on the effectiveness of systems modelling techniques. It has been shown from a survey conducted by Baines et al, (1996), that modelling is only used in 25% of all systems development projects. The survey went on to show that IDEF0, one of the more complicated approaches, is mainly used by consultancies and academia, rather than in industry.

Small et al, (1997b), present a nine stage process to help with a business process change project, which comprises system analysis and system design. The stages, collectively called the Manufacturing Change Framework, are as follows, (Small et al 1997a, Small et al 1997b):

1. Diagnosis:

1.1. Diagnose Diagnosis, (Formulate problem boundaries);

1.2. Plan Diagnosis, (Gather data about the current system and problem areas); 1.3. Implement Diagnosis, (Create and verify analysis model using data gathered);

2. Planning:

2.1. Diagnose Planning, (Evaluate change solutions using analysis model); 2.2. Plan Planning, (Design new system model with new system details); 2.3. Implement Planning, (Use design model to seek company-wide approval);

3. Implementation:

3.1. Diagnose Implementation, (Use design model to create project task list); 3.2. Plan Implementation, (Produce implementation project plan);

3.3. Implement Implementation, (Implement new system).

An important step in the Manufacturing Change Framework is step 2.3, getting senior and lower level approval is vital to any change project.

The problem situations faced by the author within Ferodo were not complex enough to necessitate use of these modelling tools. It will be shown, however, that they may be applied in the systems development and documentation methodology presented in Chapter 3 of this thesis.