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An Introduction to the Search/Retrieve URL Service (SRU)

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Another nifty feature of SRW/U is the use of 'extra data parameters'. These parameters, always prefixed with x- in an SRU URL, allow implementers to add additional functionality to their applications. The author has used this option to create an x-suggest feature. By turning 'x-suggest' on (x-suggest=1), the system will examine the number of hits returned from a query and attempt to suggest additional searches ready for execution. For example, if the number of hits returned from a search is zero (0), then the ap- plication will create alternative searches analogous to Google's popular Did You Mean? service by look- ing up the user's search terms in a dictionary. If the number of hits is greater than twenty-five (25), then the application will help users limit their search by suggesting alternative searches such as title searches or phrase searches.

The next steps for Journal Locator are ambiguous. One one hand the integrated library system may be able to support this functionality some time soon, but the solution will be expensive and quite likely not exactly what we desire. On the other hand, a locally written solution will cost less in terms of cash out- lays, but ongoing support may be an issue. In any event, Journal Locator provided a suitable venue for SRU exploration.


SRW/U and OAI-PMH are complementary protocols. They have similar goals, namely, the retrieval of metadata from remote hosts, but each provides functionality that the other does not. Both protocols have similar 'about' functions. SRW/U's explain operation and OAI-PMH's identify verb both return charac- teristics describing the properties of the remote service.

Both protocols have a sort of "browse" functionality. SRW/U has its scan function and OAI-PMH has ListSets. Scan is like browsing a book's back-of-the-book index. ListSets is similar to reading a book's table of contents.

SRW/U and OAI differ the most when it comes to retrieval. SRW/U provides a much more granular ap- proach (precision) at the expense of constructing complex CQL queries. OAI-PMH is stronger on recall allowing a person to harvest the sum total of data a repository has to offer using a combination of the ListRecords and GetRecords verbs. This is implemented at the expense of gathering unwanted informa- tion.

If a set of data were exposed via SRW/U as well as OAI-PMH, then SRW/U would be the tool to use if a person wanted to extract only data crossing predefined sets. OAI-PMH would be more apropos if the person wanted to get everything or predefined subsets of the data.


There is a plan to use SRU as a means to implement an alerting service in a sponsored NSF grant called OCKHAM [6]. The OCKHAM Project is lead by Martin Halbert (Emory University), Ed Fox (Virginia Tech), Jeremey Frumkin (Oregon State), and the author. The goals of OCKHAM are three-fold:


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