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Functional Specification

What is a functional specification? Definition and meaning

A functional specification is the counterpart to the requirements specification. A requirements specification first lists the client’s requirements. These are necessary for the implementation of a project. A functional specification is then drawn up by potential contractors to explain how they would resolve or implement these requirements from the requirements specification.

Once the client accepts this functional specification, the respective contractor is obliged to implement these points.

Quality management with a functional specification

A functional specification is a quality management document and is standardised according to DIN 69901-5.

Contents of a functional specification

  • Description of the actual requirements.
  • Concept for implementing the requirements.
  • Prerequisites that are fulfilled.
  • Sequence of individual processes.
  • Date & schedule for when the implementations will be completed.
  • The groups of people/teams involved.
  • Documents, such as process plans & checklists, as an appendix.
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Frequently asked questions

What is the difference between a requirements specification and a functional specification?
In the requirements specification, the client lists their requirements for a project. In the functional specification, the contractor then describes how they would resolve and implement these requirements from the requirements specification.
Is a functional specification binding?
Yes. As soon as the client accepts the functional specification, the respective contractor is obliged to implement the points described in it.
What belongs in a functional specification?
A functional specification describes the requirements and the concept for implementation, the prerequisites, the sequence of processes, the schedule and the teams involved. As a document standardised under DIN 69901-5, it accompanies project management from planning through to acceptance.