OWL ontology database

we are looking forward to make an OWL ontology database as a mirror of a
relational database for an upcoming social network semantic website is it a
good decision to make?

actually we can go for three options:

1. complete owl database, no relational db
2. owl mirror of relational db
3. only relational

we are very much interested in the second option   is it wise to use mirror
of ontology database as a relation database? how can owL Ontology database
be efficient than a relational one considering that we will need to query a
lot of external databases like dbpedia,freebase etc?

for the second option,  ontological databases requires us to make a query
against hundreds of different schemata and classes properties which seems to
be a costly affair. And is it a wise decision to go for a complete
ontological database for a social networking website ? The project is
involves sharing of lot of small chunks of information across an array of
distributed users building a personalized model of the user.

ontotext, http://www.systap.com,http://www.opencalais.com/ provides a
solution for semantic repositories , its really difficult to determine which
is the best option for a STARTUP like us and we can't go in for these
expensive paid consultations. so what are the options and solutions
availaible for us?