1. A system for processing triggering rules in Session Initiation Protocol (SIP) event notification filters, the system comprising: an XPath processor configured to collect a set of XPath expressions from at least one trigger of at least one SIP event notification filter of at least one subscriber in a set of subscribers who are subscribed to state information of a resource, and create a merged finite state automaton having a plurality of nodes and transitions that collectively represent the combination of said XPath expressions; and a processor for executing a streaming parser configured to parse previously-published state information of said resource and newly-published state information of said resource, and stream parsing events of said parsed information to said XPath processor, wherein said XPath processor is configured to employ said automaton to perform a streaming evaluation of said XPath expressions in parallel to determine which nodes of said parsed information satisfies any of said XPath expressions represented by said automaton; wherein any of said published state information is published in an Extensible Markup Language (XML) document; and wherein said XPath processor is configured to derive a value from either of said previously-published state information and said newly-published state information, said value being associated with said any of said XPath expressions.