Valid Value Elements Additional Attribute

Valid Value elements (VVALUE) owned by a DDAT can have a Valid Rule set stored in the attribute VALRULE. VALRULE is an expression attribute that can store an expression that evaluates to a logical true or false value. If the expression does not evaluate to a logical result, or if there are errors in the evaluation of the expression, then the VALRULE will return FALSE when queried. The VVALUE element owns a Valid Value attribute (VALIDV) that is an expression returning a real, logical, text or reference value which supports the owning DDAT element. If the VALRULE is true, or if it is a null expression, then this VALIDV will be available to the DDAT.

VALRULEs are used by the system to control the choice of a Valid Value when property queries are made on the owning DDAT.

For example a DDAT element might own four VVALUE elements with VALIDV and VALRULE attributes as follows:

The current set of VALIDValues available for the owning DDAT are the set whose VALRULEs either are unset, or evaluate to TRUE. Those that are not available are those whose VALRULEs either evaluate to FALSE, or whose evaluation generate errors.