In this work we model the interaction signature concepts in a consistent and compact manner as well as their related type checking rules. First, we begin by literally analyzing those concepts in order to bring unambiguous definitions out of them. Following this analysis we shall formalize those concepts by mapping them into UML language constructs. Secondly, we specify constraints imposed on computational interfaces interaction signatures related to the computational language typing and subtyping rules. We shall show how we can we literally redefine those rules in order to steadily formalize them. After rewriting those rules in a compact way, we make use of OCL 2.0 which provides the means to exploit those new definitions. Then we introduce the concept of Functional computational interface and a set of related concepts which unify signal and operation interfaces notions. Based on the new additional concepts introduced, we introduce two new important concepts, namely; QoS-definable interactions and QoS-capable interfaces. We then provide a UML metamodel of interfaces and interaction signatures. The final metamodel being a first step towards a QoS-capable computational metamodel. Finally, as an application of our modeling choices we define ODP QoScapable computational interfaces type checking rules and then specify them using OCL 2.0