Service-oriented architectures become popular by promoting the use of web services for systems integration, but do not address the issue of exporting semantically meaningful database functionality. Existing solutions simply associate with each exported query a web service with typed input and output parameters. The Query Set Specification Language (QSSL) publishes web services, which expose a set of supported queries against a database, as well as the schema they are executed against, in a concise specification. QSSL describes large sets of parameterized tree pattern (subset of XPath) queries, without requiring exhaustive enumeration of them. QSSL enriches a WSDL specification to form a specialized type of web services.

QSSL is particularly useful in integration scenarios, where participating sources typically export limited query capabilities, either for business reasons, security constraints, or technology limitations. Moreover, QSSL makes the relationship between the input and output types explicit by exporting the query statements and the underlying schema, thus facilitating mediators that exploit the capabilities of the underlying sources to answer user queries.