

![0_image_0.png](0_image_0.png)

International Journal of Web & Semantic Technology (IJWest) Vol.1, Num.4, October 2010 one class in σ **then Algorithm 1 reports mismatch when the corresponding class is not found in the** server ontology. When the length of σ **is greater than 1, Algorithm 1 continues to check whether**
ciis a subclass of ci+1 where 1 < i < k. A mismatch is reported by Algorithm 1 whenever ci**is a**
subclass of ci+1 for 1 < i < k**. Hence if there exists any mismatch in any specialization sequence,**
the algorithm reports it.

Type-2 Mismatch: Consider a query q made by the client and the set of variables is Vc in q**. The**
set of classes is denoted by Sc(q). We argue that, if there exists a Type-2 **mismatch for query** q, Algorithm 1 reports it. For Type-2 **mismatches Algorithm 1 first checks the presence of the equivalent classes** c s i in the server ontology and computes the union Vs **of the attributes corresponding**
to every c s i
. If there is any variable/s in Vc that are not present in Vs**, a conflict is reported by**
Algorithm 1. Hence if there exists a Type-2 **mismatch for a query, Algorithm 1 reports it.** ⊓⊔

## 5 Ontology With Back-End Database

In this section we describe the two level representation for describing ontologies - using OWL to describe the classification and using database to store the instances. This type of representation is helpful for describing domains with large number of instances. From **the point of view of the instances**
of classes, the classes in an ontology can be categorized as follows.

a. Classes of Abstract Type - these classes are used for purely the purpose of describing a domain in hierarchically. These classes does not have any instances. They act only as the super class of other classes.

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