Say in a UML Sequence diagram, I am showing a call to the database using ADO.NET. Do I need to include the SqlConnection, SqlCommand, SqlDataReader object in the diagram? Is it just preference determined by the level of depth/detail?
In the end, UML is a Universal Modelling Language. Languages are intended for communication. Who is the target audience for your diagram? Would they find it useful to know about the framework classes?
Therein lies your answer. If it's useful, put it in; if it's not, leave it out.
It really depends. Are you trying to create an outline with this UML diagram or a detailed map? If it's only an outline, you need only include the name of the class if it holds some important significance on how the program works. Even then I would argue that it's better simply to leave it off for simplicity's sake.