Internal Structure of Relationship: Notation
Vertical: set of groups of data, each group is defined by a unique value of a key
- a relation is a set of data; each group is defined by a unique value of a key
- number of elements is its cardinal
- example: customer file, each group is a record
Horizontal: set of fields; some are the key; others make up attributes of the key
- a relation is a set of fields; some fields, considered together, make up the key; other are attributes of the key
- number of attributes is the dimension