IFC, IDS and BCF: what each open format is for
Three open standards come up in almost every conversation about openBIM, and they are regularly treated as interchangeable. They are not. Each one answers a different question, and a project that uses all three is doing something quite different from a project that only exchanges files.
IFC describes the thing
IFC is a vendor-neutral schema for describing a built asset: the elements, their properties, their relationships and the spatial structure that holds them. It is maintained by buildingSMART International and published as an ISO standard. An IFC file is the model, expressed in a way that does not depend on the application that produced it.
What IFC does not do is say whether a given model is any good. A file can be perfectly valid IFC and still be missing every property somebody downstream needs.
IDS states the requirement
Information Delivery Specification is the machine-readable way of writing down what a model has to contain. Instead of a written brief that says fire ratings are required on all walls, IDS expresses that as a rule software can check: for this class of object, in this context, these properties must be present, and their values must fall within these limits.
The practical consequence is that acceptance stops being a matter of opinion. The same specification that is issued at the start of a project is the one that is run against the model at the end, and it produces the same answer for everyone.
BCF states the issue
BIM Collaboration Format carries the conversation rather than the model. A BCF issue holds a description, a status, an assignment, a camera viewpoint and a reference to the objects concerned. It travels between tools without moving the model itself.
This matters because coordination comments are otherwise trapped in whichever application produced them, and the reasoning behind a decision is lost the moment the project moves on to the next platform.
How they fit together
Read in order, the three standards describe a complete loop. IDS says what is required. IFC carries what was produced. BCF carries what was found and what was agreed about it. Any one of them on its own leaves a gap that somebody has to close by hand.
- IFC - the description of the asset, independent of authoring software
- IDS - the requirement, written so that it can be checked automatically
- BCF - the issue and the decision, portable between tools
None of this requires a particular vendor, and none of it requires abandoning the tools a team already uses. It requires agreeing, at the start, what the model has to be able to answer, and then checking that it does.