DBMS
Relations, Tuples, Attributes and Domains
The relational model has exactly four structural terms. A relation is a set of tuples, a tuple is one fact, an attribute is a named column and a domai...
Relational Model
Relations, tuples, attributes, domains, schema and instance, every key type, and entity, referential and domain integrity.
6 notes
Notes
DBMS
Relation Schema and Relation Instance
A relation schema is the fixed definition of a relation; a relation instance is the set of tuples in it right now. A relational database schema is the...
DBMS
Keys in the Relational Model
Super key, candidate key, primary key, alternate key, composite key, foreign key and surrogate key, defined formally with a worked method for finding...
DBMS
Entity, Referential and Domain Integrity
The three integrity rules of the relational model: a primary key may not be null, a foreign key must match an existing primary key or be null, and eve...
DBMS
Foreign Keys and Referential Actions
What happens to child rows when a referenced parent row is deleted or updated. Cascade, restrict, set null, set default and no action, with the rule f...
DBMS
Null Values and Three Valued Logic
Null means the absence of a value, not zero and not empty. Comparisons with null produce unknown, which turns two valued logic into three and changes...