07-02-2013, 04:13 PM
Incompleteness Errors in Ontology
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Abstract
Ontology evaluation is one of the most important
phases of Ontology Engineering. Researchers have
identified different types of errors that should be
catered in ontology evaluation process for fulfillment
of the Semantic Web vision and classified them in
error’s taxonomy. We have found that some important
errors are missing in the error’s taxonomy. We have
identified and defined two new incompleteness errors
i.e. Functional Property Omission (FPO) for single
valued property and Inverse-Functional Property
Omission (IFPO) for a unique valued property. We
have demonstrated the importance of such errors by
giving different scenarios where appropriate. We have
evaluated different ontologies and presented empirical
results.
Introduction
Ontology is regarded as the formal specification of
the knowledge of concepts and the relationships among
them [3]. They require formal syntax and semantics to
represent domain concepts. They have played a key
role for describing semantics of data in both traditional
knowledge engineering and the emerging Semantic
Web. Ontology has to go through a repetitive process
of refinement during its development lifecycle.
Ontology engineers have to pay much attention to
produce high quality bug free ontology. But there is a
possibility that the ontologists unintentionally make
some errors in ontology [5]. Ontology evaluation is
one of the most important phases of Ontology
Engineering because if ontology itself is error prone
then the applications dependent on the ontology have
to face some critical and catastrophic problems [6].
Extension in Error’s Taxonomy
In OWL, it is possible to specify property
characteristics that provide a powerful mechanism for
enhanced reasoning about a property [2,7]. OWL
functional and inverse-functional properties indicate
how many times a property can be used for a given
subject or object. Sometimes ontologists do not give
significance to these properties and do not declare
datatype or object properties as functional or inversefunctional.
This results machine not to reason about a
property effectively leading to serious complications.
Functional Property Omission (FPO) for
single valued property
A functional property is one that has just one value
for any particular subject. A formal definition of
functional property [17] is: If a property, P, is tagged
as functional then for all x, y, and z: P(x,y) and P(x,z)
implies y = z. Both object properties and datatype
properties can be declared as "functional". An example
of object property is the hasBirthday relation between
a person and his or her birthday. Everyone has just one
birthday, so for any given subject (person), there can
be just one object (birthday). Likewise datatype
properties can be declared as “functional” that can
have only one value y for each instance x, i.e. there
cannot be two distinct values y1 and y2 such that the
pairs (x,y1) and (x,y2) are both instances of this
property. An example is the Rank_No datatype
property that belongs to the student concept. Every
student has just one Rank_No in the department, so for
any given subject (student), there can be just one object
(Rank_No).
Conclusion
The main contribution of this paper is an extension
in error’s taxonomy. We have identified two new types
of incompleteness errors i.e. Functional Property
Omission (FPO) for single valued property and Inverse
Functional Property Omission (IFPO) for a unique
valued property. We have also described the
importance of detection of these errors by explaining
different scenarios. We evaluated different ontologies
and found that the FPO and IFPO errors are present in
them. In future work, we will give the detection
method to find these incompleteness errors to enable
the fulfillment of the Semantic Web vision and further
evaluate error’s taxonomy and try to find some other
type of errors that are usually encountered by
ontologist.