[rdfweb-dev] FOAF User Stories

[Russell Cloran]

Hi,

On Sat, 2005-04-09 at 23:11 +0700, Hendy Irawan wrote:
> BTW: What's the difference between IFP and (forward?)FP?

In mathematical terms a function is a one-to-one or many-to-one mapping,
never a one-to-many mapping.

A functional property, therefore, is a property for a resource which
always has one unique output for each input (one unique object for each
distinct subject). An example may be the foaf:dnaChecksum property (I
see it is not marked as such), or the foaf:sha1 property (also not
marked as such). Each person has a dnaChecksum, and only one
dnaChecksum. Each document has a sha1, and only one sha1. It is possible
for two documents to have the same sha1, and if the "checksum" part of
the dnaChecksum property has collisions, then two people could have the
same dnaChecksum.

An inverse functional property is a property for which the subject is a
function of the object. So, for each object, there is one distinct
subject. The classic example is the foaf:mbox. This is not a functional
property, because a person can have more than one mbox. It is an inverse
functional property because each mbox belongs to only one person - there
is a many-to-one relation for the mbox to person mapping.

You could also have tried to read the OWL specs:
 - http://www.w3.org/TR/owl-ref/#FunctionalProperty-def
 - http://www.w3.org/TR/owl-ref/#InverseFunctionalProperty-def

HTH

Russell
-- 
echo http://russell.rucus.net/spam/ |sed 's,t/.*,t,;P;s,.*//,,;s,\.,@,;'