relying on developer's mutual agreement. In a distributed environment mutual agreement is hard to come by if not impossible. Thus it is crucial for the domain model and the vocabulary to be represented in such a way that enables programs to reuse them as they were originally intended with minimum human intervention during their execution. 

Semantic heterogeneities represent another major problem that must be carefully analyzed. Heterogeneity in many domains is inevitable because the concerned systems are often developed by autonomous participants. Semantically equivalent concepts: 
- **Different terms are used to refer the same concept by two** 
models. These terms are often called synonyms. However, synonyms in their common usage do not necessarily denote semantically equivalent concepts. 

- **Different properties are modelled by two systems** 
(heterogeneity). As an example, for the same product, one catalogue has included its colour but the other has not. 

- **Property-type mismatches. For example, the concept length may** 
be given in different units of measure. 

Semantically unrelated concepts here the conflicting term are a concept. The same term may be chosen by two systems to denote completely different concepts. 

Semantically related concepts are: 
- **Generalization and specification. As an example is that student** 
in one system refers to all students, but the other only to PhD students. 

- **Definable terms or abstraction - A term may be missing from one** 
ontology, but which can be defined in other terms in the ontology, 
- **Overlapping concepts.** - **Different conceptualisation. Example: one ontology classifies** 
person as male, female, and the other person as employed unemployed. 

Ontology can be seen as a way to resolve semantic heterogeneity by specifying explicitly the semantics of the terms used in information systems. Between multiple ontology definitions the two following seem to be useful for our intentions. Ontology is an explicit specification of a conceptualisation [Gru92]. Ontology is a logical theory accounting for the intended meaning of a formal vocabulary, i.e., its ontological commitment to a particular conceptualisation of the world [Gua98]. 