Update Research Note Form
Research Note Topic:
Research Note Description:
The first version-
"No update opertaions must be ever allowed to leave any relvar in a state that violates its own predicate"
It applies to all the relvars,derived as well as base.Relvar stands for relational variable.There are two predicates -internal(formal) which is understood by both user and the system,and external(informal) which is understood by the user but not by the system.
The Golden Rule (extended) is-
"No update operation must ever be allowed to leave any relvar in a state that violates its own predicate.Likewise,no update transaction must ever be allowed to leave the database in a state that violates it own predicate."
Each relvar has an associated predicate ,so does every database-the database predicate,which is defined as the logical AND of all database and relvar constraints that apply to the database in question.
The rule is not widely supported though in principle it is quite straightforward.
Reference-C.J.Date,"An Introduction to Database Systems".
Prof. Ashay Dharwadker