# What is a diagram- Part 2

• Note di Apprendimento

### Systems Engineering - What is a diagram- Part 2

• Revisione degli argomenti
Nigeria 07 aprile 2017
Emeana S.

Diagram can be defined as a representation of informations and ideas about complex situatuations

• Text Version

### Systems Engineering - What is a diagram- Part 2

As there is variety in the types of diagrams we can see and use we need to think more broadly about what diagrams are trying to represent. One distinction which follows on from the discussion above is:

• Analogue representations: these diagrams look similar to the object or objects they portray. At their simplest they are photographs of real objects and at their most complicated they are colourful, fully labelled drawings of the inner workings of organisms or machines.

• Schematic representations: these are plans or diagrams which represent the essence of ‘real world’ objects or phenomena, but do not look similar to them. Maps and plans are prime examples.

• Conceptual representations: these diagrams largely try to describe interrelationships between ideas or processes that cannot be readily observed, but are put forward as a model for acceptance by others. They are mostly used to represent non-visual features where the emphasis can be as much on emotional or abstract relationships as with rational and real relationships. These interpretations may not always be shared by others (because they are based on our internal models) but are essential elements of the diagrammer's own view of the world.

A second distinction arising from this discussion relates to which building blocks (words, lines, symbols, pictures, numbers) that we use to represent things dominate the diagram:

• Pictorial diagrams: pictures and symbols dominate;
• Non-pictorial diagrams: words and lines dominate.

There are also the diagrams where numbers or mathematical relationships dominate, but in this module we deal mainly with non-mathematical relationships and so exclude the charts and graphs most commonly found in scientific and technological texts.

Diagrams are normally intended to describe either structure or process and not both. Table 1 gives a classification of diagram types by structure or process. Another way to view this is to note that there are diagram types that represent largely static relationships and those that represent situations over a period of time.

Though some, like the influence diagram, may appear to contain both structure and process, the emphasis is on the static relationships, not the temporal processes, in the situation.
Another classification of diagram types is shown as Figure 2. This orders diagrams by the two main features introduced above: namely, whether they emphasise thoughts, things or processes and whether they show static or dynamic relationships.
This does distinguish between many of the diagram types, but some are found in more than one category. However this is not the only way to group diagram types as you will see later in module. It is also my view on how to group them. You may have other ideas when you have finished reading the module.
You should now read the document "Figure 2- A classification tree showing all the types of diagrams mentioned in this unit arranged by what relationships they try to represent over what time period", in the section titled 'Extra reading materials' .
This brief outline of the types of diagrams you will meet gives you some idea of their main features, but how and when do you use them?
We will be looking at both these questions in this module, although the emphasis will be on the non-pictorial schematic and conceptual diagrams.

Before we do so I want to re-emphasise that whenever we take in, think and express new ideas, we describe and represent the ‘reality’ we perceive (in words, lines, pictures, symbols or numbers) by making simplifications for some purpose.