When speaking of interoperability and metadata, it is possible to distinguish among three different levels. The first level normally refers to semantic interoperability, or agreement about content description standards¹. The Dublin Core, the description standard adopted by the Clearing-House Mechanism, is an example of a semantic interoperability standard. Because of its importance to the Clearing-House Mechanism, and because it was adopted as the descriptive standard for the Convention web site and the Biosafety Clearing-House, it is described in detail in the next section.

The second level deals with structural interoperability where models, such as the Resource Description Framework (RDF), offer a means for specifying semantic schemas so as they can be shared. The Pilot Phase of the BCH, RDF is used as the semantic schema.

The third level, syntactic interoperability, is of significant importance to the Clearing-House Mechanism because it specifies how to tag and mark data to facilitate the exchange and sharing of the data. The Clearing-House Mechanism has adopted eXtensible Markup Language (XML) as the syntactic interoperability standard.

By using semantic, structural and syntactic levels of interoperability, users will be able to:

· Describe a document, item or web page;
· Facilitate the searching, locating and retrieving of information;
· Facilitate the creation of distributed interoperable information systems.

In summary, metadata offers the Clearing-House Mechanism the means to:

· Improve remote searching of contents found on the Convention site;
· Improve the ability of remote users to locate needed information;
· Allow users to more easily ascertain the value of information on the site;
· Offer better interoperability through the use of semantic structural and syntactic interoperability standards;
· Foster the use of controlled vocabulary.

¹Weibel, Stuart L. (1998). The Metadata Landscape: Conventions for Semantics, Syntax and Structure in the Internet Commons. In Metadiversity: The Grand Challenge for Biodiversity Information Management through Metadata, proceedings of the Symposium, Natural Bridge Virginia, 9-12 November 1998 (p. 26).