See the Javadocs in <EPM_ORACLE_HOME>/common/docs/ReportingAnalysis/SDK/javadoc.
Your program obtains this interface using the Repository interface when the program wants to search EPM Workspace for data artifact sets that match filter specifications. The Query interface defines methods that enable you to obtain lists of groups and users. It also provides other more generic methods that enable searching by artifact name, by keywords, or by a list of other artifact attributes, such as creation and access dates, artifact type, or artifact ownership.