DBMS
Finding All Candidate Keys of a Relation
A reliable method for finding every candidate key: classify attributes by where they appear in the dependencies, build a compulsory core, then extend...
#Database Keys
Super, candidate, primary, alternate, composite and foreign keys.
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DBMS
Attribute Closure, Step by Step
The closure of an attribute set is everything it determines. Computing it is a short mechanical loop, and it is the single tool used to find keys, tes...
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
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
Strong and Weak Entities
A weak entity has no key of its own and can only be identified through an owner entity. It is drawn with a double rectangle, joined by an identifying...
DBMS
Keys in the ER Model
A key attribute distinguishes one entity from another. Understanding super keys, candidate keys, primary keys and partial keys at design time prevents...