Distinguish a data dictionary, a system catalog, and an information repository.

Answer

A data dictionary documents one database’s data elements (tables, columns, types, keys). A system catalog is the DBMS-maintained, always-current "active" data dictionary describing all database objects plus user access. An information repository is broader still, holding metadata about the organization’s data and all its data-processing resources, including the application portfolio and development tools.

Nesting: data dictionary ⊆ system catalog (auto-maintained, all objects + access) ≪ information repository (whole information-processing environment). The repository is essential for data warehousing.