Protege DL query; This reasoner only supports named classes

I have an OWL ontologyin Protege 5. When trying to ask some DL queries

DropOff exactly 1

This should return all classes that are related by means of exactly to-one cardinality by objectProperty DropOff.

Using Pellet reasoner, an exception raises "This reasoner doesn't support named classes". While when using Hermit reasoner, things are OK.

I know that a named class is a class with a referent URL. Here are my points:

• What is the semantic behind using unnamed classes?
• Why named classes are not supported in Pellet?
• can my query be expressed in such a way that is acceptable for Pellet?

Thanks.

The error in Pellet might be misreported. I have only managed to find the sentence "This reasoner only supports named classes" in the Pellet source code (in the IncrementalClassifier.java file). This exception is thrown if the incremental reasoning mode is used and queries like 'find all equivalent classes for this class ""' are run - e.g., DropOff exactly 1 is an anonymous class expression that Pellet incremental does not support.

I don't know if it's possible to not use the incremental feature in Pellet from Protege. If this behaviour is not configurable, then the only workaround would be to modify the Pellet plugin to not work incrementally. This would affect performances for other queries though.