# Package org.eclipse.viatra.query.runtime.extensibility

- Interface Summary
  Interface | Description
  --- | ---
  IQueryGroupProvider | Provider interface for `IQueryGroup` instances with added method for requesting the set of FQNs for the query specifications in the group.
  IQuerySpecificationProvider | Provider interface for `IQuerySpecification` instances with added method for requesting the FQN for the query specification.

- Class Summary
  Class | Description
  --- | ---
  PQueryExtensionFactory | An extension factory to access PQuery instances from Query Specifications.
  QuerySpecificationRegistry | Deprecated Use `QuerySpecificationRegistry.getInstance()` and read notes on deprecated methods for usage.
  SingletonExtensionFactory | Factory to register a static singleton instance in an extension point.
  SingletonQueryGroupProvider | Provider implementation for storing an existing query group instance.
  SingletonQuerySpecificationProvider | Provider implementation for storing an existing query specification instance.
  ViatraQueryRuntimeConstants | Utility class for Viatra Query runtime constants, such as extension point identifiers.