1. A method comprising: receiving, by a computer system, a runtime policy set for a web service endpoint, the runtime policy set identifying a list of all web service policies whose attachment metadata indicates attachment to the web service endpoint; receiving, by the computer systems, a constraint expression for each web service policy in the runtime policy set, each constraint expression specifying one or more runtime values; aggregating, by the computer system, the web service policies included in the runtime policy set into a set of groups based on each web service policy's corresponding constraint expression, each group in the set of groups grouping web service policies by constraint expression; identifying, by the computer system, one or more groups in the set of groups whose constraint expressions indicate grouped web service policies are simultaneously attached to the web service endpoint at runtime; applying, by the computer system, one or more validation rules to the web service policies in the one or more groups; evaluating the one or more runtime values at runtime, wherein the evaluating determines whether the attachment metadata of a corresponding web service policy in a group validated by the one or more validation rules is enforced attaching the corresponding web service policy to the web service endpoint; and controlling execution behavior of the web service endpoint based on the one or more runtime values and the corresponding web service policy, wherein the execution behavior includes at least one of authentication, authorization, message encryption, or message logging.