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. The system is fed by one or more data feeds, and produces a plurality of processed feeds for respective applications. The data items in the input data feeds are processed by the software components or applications which form a data feed processing graph, with each application having a processing path (or egress-rooted tree) which results in the processed feed for that application. Managing such systems is complex. This complexity is tackled by having each component processing a data feed item add 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). At an egress of the processing system, this history can be compared (186) with an application-specific specification. Arranging the management of a data feed processing system in this way simplifies the management of such systems, and hence improves the efficiency of resource utilisation of such systems.