Views Defined Using Other Views One view may be used in the expression defining another view A view relation v is said to depend directly on a view relation v2 if v2 is used in the expression defining vi A view relation v is said to depend on view relation v2 if either v depends directly to v2 or there is a path of dependencies from vi to v2 A view relation vis said to be recursive if it depends on itself. Database System Concepts-6th Edition 4.17 @Silberschatz,Korth and Sudarshan
Database System Concepts - 6 4.17 ©Silberschatz, Korth and Sudarshan th Edition Views Defined Using Other Views One view may be used in the expression defining another view A view relation v1 is said to depend directly on a view relation v2 if v2 is used in the expression defining v1 A view relation v1 is said to depend on view relation v2 if either v1 depends directly to v2 or there is a path of dependencies from v1 to v2 A view relation v is said to be recursive if it depends on itself
View Expansion A way to define the meaning of views defined in terms of other views. Let view vi be defined by an expression e1 that may itself contain uses of view relations. View expansion of an expression repeats the following replacement step: repeat Find any view relation vi in e1 Replace the view relation v;by the expression defining vi until no more view relations are present in e1 As long as the view definitions are not recursive,this loop will terminate Database System Concepts-6th Edition 4.18 @Silberschatz,Korth and Sudarshan
Database System Concepts - 6 4.18 ©Silberschatz, Korth and Sudarshan th Edition View Expansion A way to define the meaning of views defined in terms of other views. Let view v1 be defined by an expression e1 that may itself contain uses of view relations. View expansion of an expression repeats the following replacement step: repeat Find any view relation vi in e1 Replace the view relation vi by the expression defining vi until no more view relations are present in e1 As long as the view definitions are not recursive, this loop will terminate