Pflichtenheft

What is a functional specification?

The functional specification is the vendor's response document to a requirements specification. While the requirements specification describes what a system or solution should do, the functional specification defines how the vendor intends to fulfill those requirements. It is typically created after the tender and before the contract award – serving as the central document for the contractual basis and subsequent project implementation.

In intralogistics projects – such as the introduction of a warehouse management system, a conveyor system, or an automated picking solution – the functional specification is particularly important because many requirements can only be fully defined through dialogue between the client and the vendor.

Typical structure and contents

A complete functional specification typically contains the following components:

• Solution concept: How will the required functionality be realized technically and procedurally?
• System architecture: Which components, modules, and technologies will be used?
• Interfaces: How will the system communicate with ERP, WMS, control systems, or external services?
• Process descriptions: Which workflows will be covered, and which are outside the scope?
• Testing and acceptance criteria: Which performance parameters must be demonstrated during FAT and SAT?
• Project plan: Milestones, responsibilities, resources, and timelines.
• Open items: Requirements that have not yet been fully clarified should be explicitly flagged.

Relevance for warehouse planning, IT, and procurement

For logistics management and warehouse planning, the functional specification is the central tool for ensuring that all procedural and technical requirements are actually included in the project scope. It creates transparency around which functions are delivered as standard and which require individual customization – a point that can have a significant impact on costs and timelines.

For IT managers, the interface definition is often the most critical part: this is where it becomes clear whether the vendor has truly understood the existing system landscape and how data flows, protocols, and responsibilities are governed.

In procurement, the functional specification serves as the basis for comparing proposals, managing change requests during implementation, and defining the contractually agreed acceptance conditions. An incomplete or vague functional specification is frequently the root cause of subsequent amendment negotiations.

What to look for when evaluating a functional specification

The quality and level of detail of a functional specification vary considerably from vendor to vendor. Make sure that open requirements are explicitly identified rather than simply overlooked. Check whether testing and acceptance criteria are formulated in measurable terms – vague language such as "adequate performance"