A system for managing compositions of software components or applications is disclosed. In particular, systems in which the software components or applications communicate with one another using message-oriented middleware are considered. Each component processing a data feed item adds an annotation to the data feed item, so that the cumulative annotation which is seen in the processed feed for an application provides a history of the processing carried out on the input data feed(s). Each software component or application in the processing system is arranged to store a log of each message it inputs, the process(es) it carries out on that message, and the output message generated. The software component or application further includes a reference to a log interface (e.g. a Uniform Resource Locator) in the entry it makes to the message annotation. A downstream node is then able to use that interface reference to extract (192) the more detailed information to be found in the log. Because the more detailed information is only sent when the downstream node determines that such information is of use, the burden placed by the management function on the communication resources of the distributed system is reduced.