Even though the purpose of technical software documentation isn't to explain what the software does in detail, it can be useful to expand on the context and summarise what the major functions of the software are.
This section allows you to summarise what the key functions of the system are (use cases, user stories, etc). A functional overview should answer the following types of questions:
- Is it clear what the system actually does?
- Is it clear who the important users are (roles, actors, personas, etc) and how the system caters for their needs?
Alternatively, if your software automates a business process or workflow, a functional view should answer questions like the following:
- Is it clear what the system does from a process perspective?
- What are the major processes and flows of information through the system?
By all means refer to existing documentation if it's available, whether that's in the form of functional specifications, use case documents, lists of user stories, etc. However, it's often useful to summarise the business domain and the functionality provided by the system. Again, diagrams can help, and you could use a UML use case diagram or a collection of simple wireframes showing the important parts of the user interface. Either way, the purpose of this section is to provide a functional overview.
Alternatively, if your software automates a business process or workflow, you could use a flow chart or UML activity diagram to show the smaller steps within the process and how they fit together. This is particularly useful to highlight aspects such as parallelism, concurrency, where businesses processes fork or join, etc.
This doesn't necessarily need to be a long section, with diagrams being used to provide an overview. Where a context section summarises how the software fits into the existing environment, this section describes what the system actually does. Again, this is about providing a summary and setting the scene rather than comprehensively describing every user/system interaction.
Technical and non-technical people, inside and outside of the immediate software development team.
Yes, all software documentation should include a summary of the functionality provided by the software.