Questions about querying on the description logic knowledge base?

hi,

Given an DL knowledge base O which includes TBox, RBox and ABox, I have two
questions about querying on the description logic knowledge base:

Firstly, what's the standard query language? SPARQL, Conjunctive queries, or
some else. What's relationships between them? Can they be transformed into
each other? Do they have been realized in some software such as Pellet,
Jena, etc.?

Secondly and more important, when executing some queries on O, such as a
conjunctive query: (x) <--- C(x)P(x,y)D(y), what's the implementation in the
reasoning level, I means which reasoning tasks are the query transform
into?  For instance, the following is a simplest implementation for (x) <---
C(x)P(x,y)D(y):

for a in all individuals of O
for b in all individuals of O
     check if O \entail C(a)P(a,b)D(b)

Obviously, in practice, so "stupid" implementation will not be used. So what
are these optimizing techniques? Would you please give me some indications
or references.

Thanks very much!


-- 
Best Regards!

Jun Fang