11. At a computer system including one or more processors and system memory, a method for determining if a reference that is to be created or modified is a member of a set, the method comprising: an act of receiving a resource request corresponding to a specified resource; an act of accessing one or more membership conditions for the set, the one or more membership conditions having been previously translated from a set definition defining the set, matching at least one of the one or more membership conditions being an indication of membership in the set, each membership condition including one or more membership condition statements that are to be satisfied for a resource to match the membership condition, each membership condition statement including: a referent field, an attribute field, an operator field, and a value field that collectively represent the membership condition statement, each of the referent field, attribute field, operator field, and value field being defined within the membership condition grammar as: <Referent>::=<Referent Reference><Attribute>, <Attribute>::=a name of an attribute of a resource identified by an expression to its left, <Operator>::=<Relational Operator>|<Inverted Operator>, and <Value>::=<Literal Value>|<Function Value>|<De-referenced Value>, and further: the attribute field naming an attribute, the operator field indicating a relational operator, the value field representing a value, the referent field indicating a referent, the referent referring either directly to the resource currently being evaluated for membership in the set or to another resource that is related in some way to the resource that is currently being evaluated for membership in the set; for each of the one or more membership condition statements, an act of evaluating the named attribute of the specified resource against the value in the value field in view of the operator in the operator field to determine if the specified resource satisfies the membership condition statement; an act of determining that the specified resource satisfies membership condition statements for at least one of membership conditions based on the evaluations; an act of matching the specified resource to the condition statement as a result of the specified resource satisfying membership condition statements for the at least one of the membership conditions; and an act of including the specified resource as a member of the set in response to the specified resource matching the condition statement.
11. At a computer system including one or more processors and system memory, a method for determining if a reference that is to be created or modified is a member of a set, the method comprising: an act of receiving a resource request corresponding to a specified resource; an act of accessing one or more membership conditions for the set, the one or more membership conditions having been previously translated from a set definition defining the set, matching at least one of the one or more membership conditions being an indication of membership in the set, each membership condition including one or more membership condition statements that are to be satisfied for a resource to match the membership condition, each membership condition statement including: a referent field, an attribute field, an operator field, and a value field that collectively represent the membership condition statement, each of the referent field, attribute field, operator field, and value field being defined within the membership condition grammar as: <Referent>::=<Referent Reference><Attribute>, <Attribute>::=a name of an attribute of a resource identified by an expression to its left, <Operator>::=<Relational Operator>|<Inverted Operator>, and <Value>::=<Literal Value>|<Function Value>|<De-referenced Value>, and further: the attribute field naming an attribute, the operator field indicating a relational operator, the value field representing a value, the referent field indicating a referent, the referent referring either directly to the resource currently being evaluated for membership in the set or to another resource that is related in some way to the resource that is currently being evaluated for membership in the set; for each of the one or more membership condition statements, an act of evaluating the named attribute of the specified resource against the value in the value field in view of the operator in the operator field to determine if the specified resource satisfies the membership condition statement; an act of determining that the specified resource satisfies membership condition statements for at least one of membership conditions based on the evaluations; an act of matching the specified resource to the condition statement as a result of the specified resource satisfying membership condition statements for the at least one of the membership conditions; and an act of including the specified resource as a member of the set in response to the specified resource matching the condition statement. 15. The method as recited in claim 11 , wherein the operator field indicates a relational operator selected from among: <, >, <=, =>, ==, and !.