The function of the Relativity catalog is similar to that of the "system catalog" in a relational database management system. It serves as a repository for information regarding the structure of relational tables as well as operational information required by runtime components of Relativity, such as the Query Optimizer.
Additionally, the Relativity catalog contains complete information regarding the physical COBOL data file structure (that is, the COBOL file definition, or FD information) and information produced by the database design process (Relativity Designer) that defines the association between COBOL data files and data elements, and the relational tables and their constituent columns. Together, all of this information allows Relativity to present the COBOL data files through the ODBC interface of an ODBC-enabled application as a Relativity database of well-normalized tables substantially independent of the original COBOL data file structure of the application. See also Relativity DBMS and relational table.