John wrote:
>
> A major problem with OWL is the deliberate limitation to models that can be
> represented as trees. That restriction is key to their proof of decidability.
> But cycles are required in every branch of science and engineering. (01)
Not quite 'trees' -- classification lattices, with 'property links' that
produce more or less general semantic networks, including cycles. The problem
is that the expressiveness (intentionally) limits path navigation, and thus
limits the nature and scope of axiomatic constraints on paths through the
network. (02)
It is always possible to see a semantic network as a viewpoint lattice. Pick
one class to be a focal point -- the root -- and the part of the network that
is connected at all is a lattice emanating from that point, as long as you can
ignore any 'direction' on the arcs in the base network. (This is why
relational algebras are powerful.) The problem with languages like OWL is that
the stated network includes directed arcs, and thus the viewpoint lattice has
arcs that cannot be traversed 'downward' from the end of a navigable path from
the root. (03)
-Ed (04)
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