Datalog Rules and Queries
A datalog rule has the following form:
head :- atom1, atom2,
PerformingComp(name) :- Company(name,sp,c), sp > $50
Product(prod,pr,cat,mak), Company(mak, sp,USA)
All the variables in the head must appear in the body.
A single rule can express exactly select-from-where queries.