Vocabulary Harmonization

Problem: Complexity of vocabularies and interoperability

A controlled vocabulary can be defined as a set of restricted words used by an information community when describing resources or discovering data. Controlled vocabularies exist in different representation systems (e.g. thesaurus, ontologies, plain list) and in different formats ( XML Schemas, Relational Database records, Microsoft Excel files, text files with comma-separated values, and so on.). These complexities make it difficult to reconcile differences among vocabularies (e.g. saying that term A from one vocabulary is the same as term B from another vocabulary). The resulting integrated vocabularies can be used as the basis of many data services to provide interoperability among distributed systems. One first step is to represent all the vocabularies in a common system and format. For this purpose MMI is using ontologies and the Web Ontology Language as the mechanism to represent marine vocabularies.

Vocabularies Harmonization

Two or more vocabularies are said to be harmonized if they are represented in a unique similar system allowing to create relations among them which are inherent of the system/model used (See Figure 1). For example if two vocabularies are harmonized in a tree-type model the only relations allowed among them are parent and child. A relational database schema can be another harmonization mechanism, allowing the terms to be expressed following a unique schema and store in records in a table. Relations among the terms depends on the design on the schema. For example a table could have an attribute parent, which points to another record in the table where the parent term resides. Ontologies are another example of a harmonization model. In particular the Web Ontology language (OWL), allows the creation of classes (that could be seen as categories) and individuals (members of categories). Individuals are related to each other via properties. We can create a property "hasParent" and relate terms using this property.

Figure 1. Harmonization using OWL

At MMI we provide guidance of how to construct ontologies in OWL format to have marine vocabularies harmonized.