Mapping-Based Merging of Schemas - Schema Matching and Mapping - page 226

5 Ontology Merging

An ontology specifies a domain-specific vocabulary of objects and a set of rela-
tionships between the objects in the vocabulary [ Fikes 1996 ] (see also Chap. 2).
In general, an ontology can be viewed as a graph of hierarchical objects that have
specific attributes and constraints on those attributes and objects. The hierarchies
in an ontology can be more than simple is-a generalizations and specializations -
ontologies can also have notions of “containment” or “type of” or “part of.” For the
purposes of this paper, the different kinds of relationships do not matter; the fact
that there are different kinds of relationships is the only part that is relevant. The
objects in an ontology may have various structures; for the purpose of this paper, we
can think of them as either being classes with various attributes or instances. While
constraints may exist on attributes, classes, or instances, in general these constraints
are not treated in the ontology merging literature.
Two sample ontologies are shown in Fig. 8.2 . The classes are shown as ovals. The
attributes are represented by text. A solid line represents inheritance. A dashed line
indicates that an attribute is a member of that class. An example constraint might
state that “SAT score” is at most 1,600.

5.1 SMART and Prompt

One representative work on merging ontologies began with an algorithm called
SMART [ Noy and Musen 1999a , b ] and was later renamed Prompt [ Noy and Musen
2000 ].
SMART tackles the problems of both merging and aligning ontologies. Align-
ment is the problem of taking two related ontologies and establishing links between
them to indicate where they match (much as in the database literature). Merging is

Ontology A Ontology B

Student Student

Name Name

Ugrad Grad Undergrad Grad

SAT score Office SAT score Location

Fig. 8.2 Two sample ontologies. The classes are shown as ovals . The attributes are represented by
text .A solid line represents inheritance. A dashed line represents that an attribute is a member of
that class