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define view *- construct a virtual class
define view view_name
( [ dom_name_1 =] expression_1
{, [dom_name_i =] expression_i} )
[ from from_list ]
[ where qual ]
"Define view" will define a view of a class. This view is not physically materialized; instead the rule system is used to support view processing as in [STON90]. Specifically, a query rewrite retrieve rule is automatically generated to support retrieve operations on views. Then, the user can add as many update rules as he wishes to specify the processing of update operations to views. See [STON90] for a detailed discussion of this point.
/* define a view consisting of toy department employees */ define view toyemp (e.name) from e in emp where e.dept = "toy" /* Specify deletion semantics for toyemp */ define rewrite rule example1 is on delete to toyemp then do instead delete emp where emp.OID = current.OID
postquel(commands), create(commands), define rule(commands).