In both industry and the research community it is now common to represent workflow schemas and enactments using XML. As a matter of fact, more and more enterprise application integration platforms (e.g., Excelon, Bea, iPlanet, etc.) are using XML to represent workflows within or across enterprise boundaries. In this paper we explore the ability of modern XML query languages (specifically, the W3C XML Algebra underlying the forthcoming XQuery) 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) offering four primary constructs: sequence, choice, parallel, and loop. Then three classes of queries are considered against WQM workflows: 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 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 and it can be easily specified using the W3C XML Query Algebra.