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Filter procedures evaluate binary algebraic functions given to them, and respond with a boolean True or False. When called, this function will be told which filter it is evaluating along with the name of the attribute and the data to be compared against. If some command calls the finished OSA with a filter command that is not implemented, or calls a filter with an attribute that will not accept that filter being worked on it (as defined in the ADT) it will receive an error message. Valid filter functions are: EQ, GE, LE, Subset, Superset, Intersect and Present.
If the class being designed is going to enable operation requests to be filtered, then the OSA will need to define a filter execution procedure. For each valid filter operation the filter execution procedure will have to determine if a given attribute satisfies that filter. Like the per object, per attribute and action execution procedures described previously, filter also receives the same data structure all the other execution procedures do.
In the passed data structure, only these parameters are important to filter procedures: