Closing properties in OWL/DAML+OIL
Deborah L. McGuinness

State that there will be no new information added about some aspect of a knowledge base. Many applications find some use for knowing that there will be no added information added to some aspect of the knowledge base after a certain point. OWL and OWL/DAML+OIL are said to make the "open world assumption", thereby assuming that just because some piece of information is not known now, there is no guarantee that it will not be known later. This allows for example an OWL or DAML+OIL reasoner to assume that just because we know that Deborah has one cat, there is no reason to assume that she does not have other cats, and more generally, there is no reason to assume that she only has one cat.

Observation:
There is no direct OWL/DAML+OIL constructor for the notion of closing a role on an individual, closing off information about an individual, or reasoning using the closed world assumption.

Abstracted solution:
The problem is given a particular individual, I, and a particular property, P, state that there will be no more values added to the property P on the individual I. Use a three step process as the solution.

• Retrieve the values for P on I.
• Count the number of values.
• Assert a max cardinality restriction on P for I that is equal to the count of known values.

• Now, the property P is closed on I so that if a new valued for R is asserted, the max cardinality restriction will be violated and a conflict will arise. This allows future reasoning to count on the fact that no new values will be allowed.

Example:
Given the inviduals Deborah and Panda, the property hasPet, and the relationship that Deborah has a pet named Panda, close the hasPet property on Deborah. First retrieve the values for the hasPet property on Deborah. Count the set of elements that contains the single indivual named Panda. Assert a max cardinality restriction of 1 on the hasPet property for Deborah. The hasPet property is now closed on the individual Deborah and later if we add a relationship that Deborah also has a pet named Scarlet (given that Scarlet is distinct from Panda), an OWL or DAML+OIL reasoner will identify that a conflict has occured.

DAML+OIL code:

Other examples of modeling issues and solutions in a language similar to DAML+OIL are available in:
Ronald J. Brachman , Deborah L. McGuinness , Peter F. Patel-Schneider , Lori Alperin Resnick , and Alex Borgida. ``Living with CLASSIC: When and How to Use a KL-ONE-Like Language,'' in John Sowa, ed., Principles of Semantic Networks: Explorations in the representation of knowledge , Morgan-Kaufmann: San Mateo, California, 1991, pages 401--456.  http://www.ksl.stanford.edu/people/dlm/papers/living-with-classic-abstract.html

Acknowledgments:
The following people have contributed to this list of modeling issues and solutions:
Jeff Hefflin
Ian Horrocks
Deborah McGuinness

Last Update:   November 8, 2001