bSDD Explained: The Dictionary That Makes IFC Data Actually Mean Something

IFC gives every wall, window, and pipe in a BIM model a structured place to live. It does not, on its own, guarantee that "door" in a model built in Warsaw means the same thing as "doorset" in a model built in Munich, or that either one lines up with a national classification system. That is a different problem, a terminology problem, and it has its own standard: bSDD, the buildingSMART Data Dictionary.

What is bSDD?

bSDD stands for buildingSMART Data Dictionary. It is a free, open access platform that hosts interconnected dictionaries of definitions for describing the built environment, managed by buildingSMART International as a distribution platform rather than a place where new standards get invented. Organisations publish their own dictionaries into it, international classifications, national standards, company specific agreements, and bSDD hosts over 300 of them, including IFC 4.3, Uniclass 2015, ETIM 9.0, and CCI Construction among the notable ones.

The problem it solves: one word, many languages

Construction terminology is not consistent, not across languages, not across countries, and often not even within the same country's different classification systems. A door might be called a door in one dataset, a doorset in another, and its French or German equivalent in a third, all describing the same physical object. Without something tying those terms together, a piece of software has no way to know they mean the same thing, and information gets lost or misread every time a project crosses a language or classification boundary.

bSDD solves this by giving each concept, not each word, a single identity. "Door," "doorset," and their equivalents in other languages and classification systems all point back to the same definition, so translation and cross referencing become something a system can do automatically instead of something a person has to reconcile by hand.

How bSDD actually works

Every term or definition published in bSDD gets a Global Unique Identifier, a language independent code that stays constant for the life of that definition. A definition moves through a lifecycle status, from Preview to Active to Inactive, but its identifier and its published URI never change, so anything that references it once can keep referencing it reliably. That stability is what makes bSDD usable as infrastructure rather than just a glossary, other standards and software tools can build on it and trust that a reference made today will still resolve correctly years later.

bSDD versus IDS

It is easy to mix up bSDD with IDS, since both showed up in the same conversation about openBIM standards, but they do different jobs. IDS, Information Delivery Specification, which we covered in our previous explainer, defines what information a specific project requires and lets you check a model against those requirements automatically. bSDD does not define requirements at all. It is a database of definitions and terms that IDS, or any other tool, can point to when it needs to reference exactly what a term means.

Put simply, bSDD defines what a term means. IDS defines what a project needs. A project's IDS file can reference a definition from bSDD to make sure "fire rating" or "glass type" means exactly the same thing to everyone checking the model, but bSDD itself has no opinion on what any particular project should require.

How bSDD fits with IFC

IFC, the open data format behind openBIM, is itself included in bSDD as one of its dictionaries, specifically the semantic definitions behind IFC's objects and properties. bSDD's coverage here is deliberately scoped to tangible objects such as a pipe or a wall, rather than abstract concepts, which keeps its definitions concrete and directly usable. The result is that IFC provides the structure a model is built from, while bSDD provides the shared meaning behind the terms that structure uses, two different, complementary layers of the same openBIM foundation covered in our IFC explainer.

Why this matters for your BIM data

None of this requires you to browse a dictionary by hand. What it means in practice is that when your BIM software, your classification system, or your project's IDS checks reference a term, there is a reasonable chance that reference is more reliable and more portable across languages and tools than it would otherwise be, because over 30 software tools already integrate bSDD, including Revit plugins and open source tools like BlenderBIM. For anyone working across international teams or multiple classification systems, that quiet consistency is exactly what keeps data usable instead of just present.

Frequently asked questions