A catalog is a container for metadata objects that you can import.
A container is a collection of packages.
A package contains flat records. A package may also contain other packages.
A flat record represents the structure of the native metadata object that you can import. The flat record structure contains fields, relationships, index, and constraints.
A field is a data structure for a single piece of data in a data source.
A record relationship represents the relationship between flat records.
An index represents a native index that orders the flat records or uniquely identifies a flat record.
A constraint represents the unique key and primary key for a flat record.