A stream processing unit for processing a stream of message data relating to a web service application, comprising: at least one input pipe (301, 302) for receiving a plurality of interrelated messages according to an order with which said messages are originated; a processor for processing an accumulation of said messages upon reaching a trigger point related to a grammar characterizing said messages, wherein the trigger point is a particular pattern of data included in the plurality of interrelated messages; wherein the processor is configured to: process information included in the plurality of interrelated messages for the particular pattern as the plurality of interrelated messages are streamed to the processor, and upon detecting the particular pattern in a currently received one of the interrelated messages, initiate processing of those previously received messages that were received prior to detecting the particular pattern; at least one output pipe wherein the at least one output pipe connects the stream processing unit to at least one subsequent stream processing unit over a packet switched network; and wherein the processor is configured to: generate a new message during the processing the accumulation of messages; and place the new message in a particular output pipe for transmission over the packet switched network to a subsequent stream processing unit, wherein the new message is sent thereto using the particular output pipe. at least one input pipe (301, 302) for receiving a plurality of interrelated messages according to an order with which said messages are originated; a processor for processing an accumulation of said messages upon reaching a trigger point related to a grammar characterizing said messages, wherein the trigger point is a particular pattern of data included in the plurality of interrelated messages; wherein the processor is configured to: process information included in the plurality of interrelated messages for the particular pattern as the plurality of interrelated messages are streamed to the processor, and upon detecting the particular pattern in a currently received one of the interrelated messages, initiate processing of those previously received messages that were received prior to detecting the particular pattern; process information included in the plurality of interrelated messages for the particular pattern as the plurality of interrelated messages are streamed to the processor, and upon detecting the particular pattern in a currently received one of the interrelated messages, initiate processing of those previously received messages that were received prior to detecting the particular pattern; at least one output pipe wherein the at least one output pipe connects the stream processing unit to at least one subsequent stream processing unit over a packet switched network; and wherein the processor is configured to: generate a new message during the processing the accumulation of messages; and place the new message in a particular output pipe for transmission over the packet switched network to a subsequent stream processing unit, wherein the new message is sent thereto using the particular output pipe. generate a new message during the processing the accumulation of messages; and place the new message in a particular output pipe for transmission over the packet switched network to a subsequent stream processing unit, wherein the new message is sent thereto using the particular output pipe.