buildingSMART Data Dictionary (bSDD)
The buildingSMART Data Dictionary (bSDD) is a library of classes, properties, relations and units. It is a service provides by buildingSMART International to help users find the right classifications, properties and allowed values.
The bSDD is an "API-first" service. End-users can access the bSDD through software tools that have implemented the bSDD API. Info about the bSDD API can be accessed at Swaggerhub.
Developers that want to connect to the API can find code examples on GitHub.
Read more about the bSDD on https://www.buildingsmart.org/users/services/buildingsmart-data-dictionary/