We address the question, "In the brave new world of Web services and service-oriented architectures (SOA), how does data fit in?" We bring data modeling concepts to bear on the world of services, yielding an approach in which enterprise data access is handled by a collection of interrelated data services. We show how the approach can be realized on a foundation of XML standards, namely XML Schema, Web services, and XQuery. We show that this approach provides a uniform and declarative framework for integrating enterprise data assets that are drawn from disparate underlying sources, including both queryable and non-queryable data sources as well as data that is encapsulated by Web services. We also show that the approach yields data services that are easily and efficiently reusable.