Metadata and data
- A relation is a collection of tuples which may be regarded as elements of a Cartesian product of certain data domains.
- To each data domain one associates an attribute. An attribute usually has a name and defines the type of data.
- The set of attributes forms metadata.
- A table is an instance of a relation. Attributes correspond to columns in the table and tuples (records) form the rows. Rows and columns can not be interchanged.
- Two tables are considered equivalent if there is a one-to-one mapping between the corresponding metadata.