QoS-Aware Service Composition: A Retrospective

We provide a retrospective on our article “QoS-Aware Middleware for Web Service Composition” published in the May 2004 issue of IEEE Transactions on Software Engineering. We start by defining the concept of Web service composition, and reviewing key paradigms emerging from early research on this topic. We then explain how the 2004 QoS article laid down a conceptual foundation that spawned a prolific line of research into the estimation and optimization of Quality of Service (QoS) properties of composite Web services. We close with a reflection on how the challenges tackled by the 2004 QoS article and other research on service composition are reemerging in the field of Large Language Model (LLM) agents. We argue that the design of LLM agents raises challenges similar to those that the 2004 QoS article tackled, while bringing in new challenges due to the non-deterministic nature of LLMs and the fact that they consume and produce unstructured data.