Functional Specification (Pflichtenheft)
Document created by the supplier that describes the concrete technical implementation for every requirement listed in the requirements specification.
The functional specification, known in German as Pflichtenheft, is the supplier's answer to the requirements specification. Where the requirements specification defines what needs to be achieved, the functional specification describes how the supplier intends to implement each requirement, including the chosen solution, approach, and timeline.
A well-built functional specification takes up every requirement from the requirements specification and assigns it a concrete implementation, including technical specifications, the components or methods used, and planned dates. This makes it possible to later verify whether a requirement was actually met.
Once both parties agree, the functional specification usually becomes part of the contract and thus a binding description of scope. Any further changes typically go through a formal change request process, since they can affect scope, cost, or schedule.
Practical Example
In response to the coating line requirements specification, an equipment builder answers in the functional specification with concrete figures: a conveyor rated at 45 parts per hour, an automated nozzle cleaning system enabling a 150-second colour change, a standardised interface to the customer's ERP system, and commissioning within twelve weeks.
How Leanshift Helps
The functional specification makes visible how a requirement turns into a concrete solution, a core idea behind any improvement work: first understand what is needed, then deliberately develop what delivers it.
Frequently Asked Questions
Is a functional specification mandatory for every project?
It is not legally required, but it is common and advisable for more complex technical projects to avoid misunderstandings.
Can the functional specification deviate from the requirements specification?
It should address every requirement from the requirements specification, but may propose alternative technical solutions as long as the goal is met.