Requirements - functional perspective, structural perspective, behavioural perspective

IREB, the International Requirements Engineering Board, makes a distinction between three types of modeling perspectives:

• Structural perspective
• Functional perspective
• Behavioral perspective

Each of these views can be modeled in a view, which are aptly named:
* Structural view
* Functional view
* Behavioral view

At first sight the latter of the two may look as overlapping. Let's have a look at these three perspectives.

The structural perspective concerns itself with the structure of the elements which make up the system.
In UML it is supported by the following types of diagrams:
* class diagram
* component diagram
* composite structure diagram

For the functional perspective, typical UML diagrams are:
* Activity diagram
* Use Case diagram

For the behavioral perspective, i think a typical UML diagrams is:
* machine state diagram


In the above text I used the word 'modelling'. I know that this word is sensitive, as some requirements specifiers maintain that modelling is part of design, not of requirements elicitation. That discussion is quite another topic, and I only used the word because the IREB uses it in this context.