While there is not much discussion on the importance of formally describing and analysing quantitative requirements in the process of software construction; in the paradigm of API-based software systems it could be vital. Quantitative attributes can be thought as attributes determining the \emph{Quality of Service} – QoS provided by a software component published as a service. In this sense, they play a determinant role in classifying software artifacts according to specific needs stated as requirements.

In this work we present a research program consisting of the development of formal languages and tools to characterize and analyze Quality of Service attributes of software components in the context of distributed systems.