Concluding Thoughts

All in all, major initiatives are currently being taken to enhance interoperability among the various metadata schemas. Interoperability is a major issue, especially among digital collections, since metadata tends to be stored for use only by the institution that creates and maintains it. Thus, the driving force behind the development of metadata standards in the future will most likely be a desire for uniform access methodology across collections (Smiraglia, 2005). Union catalogs, cross-system searches, crosswalks, and metadata registries each attempt to address and overcome the prevalent barriers to semantic and/or syntactic interoperability. Nevertheless, it is important to acknowledge that some degree of inconsistency or discrepancy shall continue to exist due to the very nature of different institutions creating and using different schemas. As for now, there is still no “one size fits all” universal bibliographic control (Younger, 1997).

References:

Smiraglia, R.P. (Ed.). (2005). Metadata: A cataloger’s primer. New York: The Haworth Information Press.
Younger, J. A. (1997). Resources description in the digital age. Library Trends, 45(3), 462-488. Retrieved July 3, 2008, from InfoTrac OneFile database.

Metadata Registries

Metadata registries have also facilitated interoperability among schemas in that they record authoritative information about metadata elements from multiple sources. A metadata registry is a “…database used to organize, store, manage, and share metadata schemas. [They] provide information about metadata schemas, elements, profiles, definitions, and relationships, using a standard structure” (Taylor, 2004, p.153).

Thus, metadata registries facilitate interoperability since they provide a record of names, definitions, and properties of metadata elements. Metadata creators can consult a registry to clarify meaning and usage as well as exchange information. Additionally, metadata registries can help prevent duplication of effort (Taylor, 2004).

The Dublic Core Metadata Registry Lite is one example of a metadata registry, available at http://wip.dublincore.org/dcregistrylt/

References:

Taylor, A.G. (2004). The organization of information (2nd ed.). Westport, CN: Libraries Unlimited.

Crosswalks

Interoperability, particularly semantic interoperability, can also be facilitated through the use of crosswalks, which are authoritative mappings of metadata elements from one schema to another (Caplan, 2003). By analyzing the metadata elements in separate schemas and correlating the similar fields, metadata creators can “map” the equivalent relationships between the schemas. Thus, crosswalks are the “maps” that show these relationships (Woodley, 2000). Crosswalks are most useful when the schemas are relatively simple, are for similar communities or types of materials, and have overlapping concepts. Mapping becomes much more difficult when it involves cross-domains, schemas of different complexities, and schemas with great semantic differences (Taylor, 2004).

Crosswalks are primarily used as a basis for specifications of the physical conversions of records from one metadata schema to another with regards to record exchange. However, since crosswalks only provide lateral or one-way mapping from one schema to another, separate crosswalks are required to map from schema A to schema B and then from schema B to schema A. As a result, some information can become distorted or lost among pairs of crosswalks. This means that the information retrieved after a reversion may not be identical to the original (Taylor, 2004).

The Library of Congress provides a good example of the MARC to Dublin Core Crosswalk, which is available at http://www.loc.gov/marc/marc2dc.html.


References:

Caplan, P. (2003). Metadata fundamentals for all libraries. Chicago: American Library Association.
Taylor, A.G. (2004). The organization of information (2nd ed.). Westport, CN: Libraries Unlimited.
Woodley, M.S. (2000). Crosswalks: The path to universal access? In Introduction to metadata: Pathways to digital information. Retrieved July 1, 2008 from http://www.getty.edu/

Cross-system Searches

Another approach to reduce the barriers to interoperability is through the use of cross-system searches. Unlike a union catalog where a union database is maintained and a central search is used to retrieve data, the cross-system search stores metadata records in multiple databases, which are retrieved using the search facilities associated with each individual database system. ANSI/NISO Z39.50 is an example of an international standard protocol that allows one client system to request a search to be performed within another target system (Caplan, 2003). Here, the client receives the results back in a format that it can display. This cross-system search requires that the search be expressed in a common syntax so that every system only needs to comprehend its own search language and that of the international standard protocol.

References:

Caplan, P. (2003). Metadata fundamentals for all libraries. Chicago: American Library Association.

Union Catalogs

Although interoperability among diverse sets of metadata records can be problematic, there are several current approaches to address these issues. One approach is through the use of a union catalog, a centralized database of metadata from multiple sources. One such union catalog used among libraries, for example, would include the MARC-based library catalog. Union catalogs can exist at any level, from a local institutional level to an international level. In libraries, OCLC’s WorldCat is one example of an international union catalog (Caplan, 2003).

There are several methods of implementing union catalogs. One method is that participating institutions submit copies of their own cataloging records to an organization that maintains the centralized search catalog. Another method is to create records directly into the union catalog database and then copied into the institution’s local system. In either of these two methods, records for the same resource contributed by different institutions can either be maintained as duplicate records or consolidated into a single master record presenting multiple holding locations. A third method includes the creation of a false union catalog via a union index over multiple catalog files, instead of maintaining a compiled database. This approach displays records from the source catalogs when entries from the index are selected.

In general, union catalogs work best when the participating institutions share a common data format and common set of cataloging rules. For example, libraries tend to use similar data formats and cataloging rules, which contributes to the effectiveness of OCLC’s WorldCat. When the records in the central database and local contributing catalogs are relatively homogenous, the familiarity of the search will facilitate retrievals. Although it is more complicated, it is possible to create union catalogs from non-homogenous metadata sources. Non-homogenous contributions usually result when a variety of institutions, as opposed to just one type of institution, participate in the union catalog. These institutions can include archives, libraries, historical societies, museums, and so on. Typically, the creation of a union catalog from non-homogenous sources would require a conversion of the various metadata schemas submitted into a common format for storage and indexing before loading the records into the union catalog (Caplan, 2003).

References

Caplan, P. (2003). Metadata fundamentals for all libraries. Chicago: American Library Association.