Querying and Splicing of XML Workflows

In both industry and the research community, it is now common to represent workflow schemas and enactments using XML. This is a natural evolution from the explosion in the usage of XML for interoperability with more conventional forms of data. As a matter of fact, more and more commercial systems (e.g., Excelon, Microsoft, HP) are using XML to represent workflows within or across enterprise boundaries. In this paper we explore the ability of the recently proposed XML query languages (specifically, the W3C XML Algebra underlying the forthcoming XML Query) to query and manipulate workflow schemas and enactments represented as XML data. The paper focuses on a simple, yet expressive, model called Workflow Query Model (WQM). This model abstracts from commercial WFMSs, and offers four primary constructs, namely sequence, choice, parallel, and loop. Three classes of queries are considered: simple (e.g., to check the status of enactments), traversal (e.g., to check the relationship between tasks, or check the expected running time of a schema), and schema construction (e.g., to create new workflow schemas from a library of workflow components). This querying functionality is quite useful for specifying, enacting and supervising e-services in various e-commerce application contexts. Modern XML query languages, such as the XML Algebra, are seen to be sufficiently expressive for specifying the above workflow queries.