RDF and logic

Hello RDF community,

I read in John F. Sowa's book on Knowledge Representation the following thing: existential
conjunctive logic is used to represent all the information stored in databases (relational, OO,
...). Existential logic is logic making use of the 'AND' operator and the 'there exists' operator.

If I write in RDF:

Mike --- language --> English

then I imply that there exists a Mike and there exists an English language and language(Mike,
English).

This means that EC logic is also implicitly available in RDF. I would like to boost up this EC logic
to full FOL (first order logic; adding OR, forall, NOT and implies).

I know there has been some work around this (SILRI, DATALOG) but I wonder, do we need a separate
logic layer on top of RDF or can we use RDF to define a logical layer? I tried the latter by
introducing operator resources. This looks good in schema form, but writing software to support
these constructs looks quite difficult. Simple example: if I introduce an AND node, do I AND
adjacent nodes or the complete trees that originate from these adjacent nodes? So ad hoc rules need
to support the schema on how to interpret the AND.

Has anyone got some experience with this kind of modelling? Do I have to leave the RDF framework in
order to introduce a logic layer or does anyone have a schema for logics that is easily supportable
in software?

Greetings,

Tom.