Appendix B. An Introduction to the Search/Retrieve URL Service (SRU)
Note: This is a pre-edited version of an article appearing in Ariadne. It describes sibling Web Service protocols designed to define a standard form for Internet search queries as well as the structure of the re- sponses.
This article is an introduction to the "brother and sister" Web Service protocols named Search/Retrieve Web Service (SRW) and Search/Retrieve URL Service (SRU) with an emphasis on the later. More spe- cifically, the article outlines the problems SRW/U are intended to solve, the similarities and differences between SRW and SRU, the complimentary nature of the protocols with OAI-PMH, and how SRU is being employed in a sponsored NSF (National Science Foundation) grant called OCKHAM to facilitate an alerting service. The article is seasoned with a bit of XML and Perl code to illustrate the points. The canonical home page describing SRW/U  is also a useful starting point.
The Problems SRW and SRU are Intended to Solve
SRW and SRU are intended to define a standard form for Internet search queries as well as the structure of the responses. The shape of existing queries illustrates the problem. The following URLs are searches for 'dogs and cats' against three popular Internet search engines:
Even though the queries are the same, the syntax implementing the queries is different. What is worse is the structure of the responses. Each response not only contains search results but lots of formatting as well. SRW and SRU address these shortcomings by specifying the syntax for queries and results. Such specifications open up Internet-accessible search functions and allow for the creation of tools to explore the content of the 'hidden Web' more effectively. SRW/U allow people and HTTP user agents to query