via URL/Search/Retrieve Web service), which drop the Z39.50 communications protocol (replacing it with HTTP) while still attempting to preserve the benefits of the query syntax. SRU is REST-based, and enables queries to be expressed in URL query strings; SRW uses SOAP. Both expect search results to be returned as XML. These projects have a much lower barrier to entry for developers than the original Z39.50 protocol, allowing the relatively small market for library software to benefit from the web service tools developed for much larger markets. Alternatives include the following. Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH) SPARQL Firewall information The registered internet IP port for Z39.50 is 210. Although the majority of servers use this port, there are dozens of other port numbers used worldwide by Z39.50 (e.g. 2100, 2200, 2210, 2213, 3520, or in one case, ports 2101 and higher for different databases). See also Wide area information server (WAIS) Dynix Koha OpenURL OpenSearch References External links Z39.50 Maintenance Agency Z39.50 Standard Document (pdf) Application layer protocols Library automation Library of Congress Domain-specific knowledge representation languages