Dintinguish among ontology, metadata repositories and data dictionary

Dear netter,

I'm working on a briefing for our company high level managers to present
the applications of ontoloy (especially in e-commerce context). However,
most of them have software engineering experience and got confused with
ontology, metadata repositories and data dictionary. 
Please help me to distinguish them in a clear way.

Thank you in advance!

Ketty Gann, Ph.D.
Booz.Allen & Hamilton Inc.
Annapolis Junction, MD