XML Integration into an SQL-based CEP Engine

In order to address the lack of XML support in Complex Event Processing (CEP) systems, we propose an approach for XML integration into a CEP engine we call EQL/XA (XML-aware event query language). As event query languages are generally SQL-based, our approach is based on the independent part of the SQL standard – XML-related Specifications (SQL/XML). EQL/XA consists of several concepts that together offer significant XML support. We introduce a data type for representing XML, an XQuery function that is able to query and construct XML data, an aggregate function that concatenates a group of XML values into a single value and last but not least, we have proposed two stream-to-stream operators that together are capable of flattening XML events into events containing only atomic EQL data types. Thus, we have significantly enhanced the expressiveness of pure EQL.