How to choose the right diagram to draw

The next time you take out your pencils and post-it notes, ask yourself the question: Why am I drawing a diagram? What and who will it be used for? You will be able to choose to follow (or not) a standard and avoid wasting your time by doing the right thing from the first time! A draft is always useful, but should not take too much time.

A picture is worth a thousand words, OK, but what picture to draw? I have drawn many diagrams during my professional life. I am often asked how I choose the type of diagram to present. It is true that there are many standards and nomenclatures. The first question to ask is: technical or functional? Then it is possible to choose more precisely the standard to follow.

Although this is a fundamental issue, it is often forgotten. What is usually chosen is the standard most used or known in the organization or by the person who draws, without ensuring that it is the most appropriate. Even worse, the drawing begins, without really thinking about it. In the majority of cases, you will then have to start over.

So a functional or technical diagram?

When you decide to draw, it’s for one (or more) reason(s). As a general rule, if you want to understand (or explain) a system, service or product, it is the functional diagram that is most effective. If you are at a stage of programming, industrialization or production, you need a technical diagram. The functional diagram is a communication tool, for an expert in a field to share with non-experts. On the other hand, the technical diagram is a working tool between professionals in the same sector or field.

The functional diagram

It prioritizes understanding. It can therefore simplify, or even omit certain aspects in favor of a more global view. Exceptions are rarely documented. Scales are not always respected, whether they are of time or space.

For example, a flowchart might have boxes that represent activities lasting a few minutes or several hours in the same drawing to simplify while emphasizing what you want to explain.

A functional diagram is in general understandable by people who are in the context. They know the vocabulary of the organization as well as the immediate environment.

The technical diagram

It is generally more complex, it includes technical information, not understandable for neophytes. On the other hand, it may be understood by other professionals in the same field in other sectors of activity or geographical areas. In this sense, it is more universal. It can serve as a contractual basis for the realization, as it documents the operation and exceptions.

In the building sector, for example, 3D views as well as plans with furniture are functional diagrams. They help customers or partners understand the concept, and have an overview. On the other hand, the execution plans contain information and measures that are only useful to builders, plumbers and electricians.

Some examples of standards for making diagrams

The best known technical diagram is the BPMN (Business Process Model and Notation). Depending on your needs, you might also encounter VSM (Value Stream Mapping), Service Blueprint,UML , Petri nets or Gantt, which are also technical charts.

The ultimate functional diagram is the flowchart. However, all technical diagrams can become a basis or inspiration for creating functional diagrams. The standard will be respected in part, abandoning rigor in favor of understanding.

The most common adaptation of a technical diagram into a functional one is BPMN. Corridors are used, but users omit the many symbols and codes and settle for rectangles and diamonds. It is an improved flowchart, to make it easier to understand.

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