Listing 1. Share: OCL rules.

context Share::attach(s:Service)   pre: services->excludes(s)   post: services->includes(s) context Share::detach(s:Service)   pre: services->includes(s)   post: services->excludes(s) context Share::discovery(s:String):Set(Service)   post: result = Set(services->select(name.matches(s))) context Share   inv: services->asSet()