The system will report an error if you attempt to use an implementation of a query library that has a different INTERFACE from the one specified in the LIBRARY function.

There is one particularly notable restriction on the ECL that can be included within a library: they cannot include workflow services such as INDEPENDENT, PERSIST, SUCCESS, and especially, STORED. STORED attributes don't make sense inside a query library because a query library should be independent of both the queries that use it, and other query libraries. Instead of using STORED attributes (like SOAP-enabled Roxie queries use) to pass parameters to the library queries, the parameters must be explicitly passed into the query library--either as an individual parameter, or as part of an INTERFACE definition that provides the arguments. The query that uses the query library can use stored variables, and then map those stored variables to the parameters expected by the query libraries.

Query libraries can currently only EXPORT datasets, datarows, and single-valued expressions. In particular they cannot EXPORT actions (like OUTPUT), TRANSFORM structures, or other MODULE structures.