Z39.50 search protocol

As you have just seen, the kind of search server you install or create depends on the search protocol (or technical language) that you use. As with all languages, technical or not, different protocols have different demands, advantages and disadvantages.

The GeoConnections Discovery Portal mainly supports the Z39.50 search protocol that supports searching and retrieval of information, full-text documents, bibliographic data, images and multimedia in a distributed network environment. While HTTP is an Internet protocol for hypertext transfer based on URL-encoded requests for information, Z39.50 is an Internet protocol for metadata retrieval based on a set of detailed search specifications in the request.

Some search protocols have several profiles. A profile identifies a set of base standards, together with appropriate options and parameters necessary to accomplish identified functions for purposes including: (a) interoperability, and (b) methodology for referencing the various uses of the base standards by both users and suppliers.

Z39.50 is ratified by ANSI, a US national standards body, and it is widely used in many application areas around the world. The FGDC has developed a Z39.50 application profile for geospatial metadata, called GEO, which provides a specification on how to implement the Content Standard for Digital Geospatial Metadata (CSDGM) metadata elements within a Z39.50 service.

The Z39.50 GEO profile states that a Z39.50 GEO Profile server must:

• Use "Init", "Request", "Present", 3 of the 10 services and operations available;
• Understand 340 attributes defined by the profile. The server must support 17 of those attributes for use in a client search request. Each attribute also has a recommended data type defined for implementation (e.g. string, integer); and
• Understand 18 relations (e.g. equal, near) that must be supported in a client search request.