Glossary Requirements & traceability
What is an interface control document?
An interface control document (ICD) defines how two systems or parts connect: what passes between them, in what form, and who is responsible for each side.
Also called ICD.
Interface control document
An interface control document, or ICD, records the agreed definition of an interface between systems, subsystems or components. It can cover mechanical connections, electrical power, data signals and protocols, timing and environmental limits, and it states who owns each side. Once agreed, it is placed under change control, so neither side changes the interface alone.
Why it matters
Integration problems tend to sit at boundaries, where each side made its own assumptions. An ICD turns those assumptions into a written agreement that both sides design and test against.
How it goes wrong
- Writing the ICD after the parts are built, so it records assumptions instead of agreeing them
- Letting the ICD drift from the requirements and tests that depend on it
- Leaving an interface with no owner on either side
In Cairn
Cairn models each interface as a record between two nodes, with a name, a protocol, a description and its signals, each signal with a direction, a data type and a rate. The Architecture lens shows interfaces as a diagram, an N² chart and an interface list, and Quality flags an interface with no signals, no protocol, a signal with no data type, or a repeated signal. That is the content an ICD starts from, but Cairn does not write a formal ICD document and does not record who owns each side.
Questions
- Is an ICD only for software interfaces?
- No. ICDs cover mechanical, electrical, data, thermal and other interfaces, and many interfaces are several of these at once.
- Does Cairn produce an ICD?
- No. Cairn holds the interface data an ICD is written from: each interface's ends, protocol and signals. Writing and controlling the formal document happens outside Cairn.
See it on your own system.
Describe what you are building and Cairn interviews you, then builds the first model with you.