A method for performing a monitoring function for an application that passes messages between two or more endpoints, comprising: receiving a message including transaction data, the transaction data including data relating to transport of the transaction data; storing the message and transaction data in respective message data and transaction data buffers in a data store; storing status and semantic information associated with the message in the data store; receiving a signal selecting one or more module instances to define the monitoring function, each module instance for independently performing a respective aspect of the monitoring function, each module instance having related module instance data stored in a respective module instance data buffer in the data store, each module instance having a respective service access point for accessing the data store, each service access point having related service access point data stored in a respective service access point data buffer in the data store, each module instance independently accessing one or more of the message, transaction, module instance, and service access point data buffers to process data contained therein to perform its aspect of the monitoring function; and, initiating operation of the one or more module instances in accordance with a schedule defined by one or more routing rules, the one or more routing rules for routing a pointer to the message, as stored in the message data buffer, between the one or more module instances to thereby perform the monitoring function.