These two classifications coincide rather often, as a matter of fact, and what is found as an independently folding unit of a polypeptide chain also carries specific function.

CDD defines conserved domains as recurring units in molecular evolution, the extents of which can be determined by sequence and structure analysis.

Manually curated models are organized hierarchically if they describe domain families that are clearly related by common descent.

To provide a non-redundant view of the data, CDD clusters similar domain models from various sources into superfamilies.

United States National Center for Biotechnology Information., that allows the computation and download of annotation for large sets of protein queries.