A wide range of web service choreography constraints on the content and sequentiality of messages can be translated into Linear Temporal Logic (LTL). Although they can be statically on abstractions of actual services, it is desirable that violations of these specifications be also detected at runtime. In this paper, we show that, given a suitable translation of LTL formulæ into XQuery expressions, such runtime monitoring of choreography constraints is possible by feeding the trace of messages to a streaming XQuery processor. The forward-only fragment of LTL is introduced; it represents the fragment of LTL supported by available streaming engines. Categories and Subject Descriptors D.2.5 [Software Engineering]: Testing and Debugging— monitors; F.4.1 [Mathematical Logic and Formal Languages]: Mathematical Logic—temporal logic; H.3.5 [Information Storage and Retrieval]: Online Information Services—web-based services; I.7.2 [Document and Text Processing]: Document Preparation—XM...