xreferplus is a giant online reference library that provides access to an aggregated and integrated collection of 100 reference books from 21 leading publishers, including Oxford University Press, Penguin, Grove, Houghton Mifflin, Columbia, and Macmillan. It offers general reference works—encyclopedias, dictionaries, thesauri, and books of quotations—and a range of subject-specific titles covering everything from art to accountancy and literature to law. There are over 1 million entries, the equivalent of 70,000 paper pages. The cross-referencing technology connects related information across all the works and has generated an additional network of over 5 million "xreferences."

The company claims that xrefer and xreferplus are different from other services because their technology brings an extra dimension to reference books. According to xrefer's Web site: "Our unique technology generates a network of cross-references that provide an easy-to-follow trail to related information contained anywhere within the library. Whereas normal reference books have cross-references that are restricted to that book, xrefer links cross-references in different books as well." The xreferences are generated mostly by a suite of algorithms that are continually being enhanced. In addition, the xreferences become stronger as more additional content goes into the system (as the system learns more about the properties of the entries).

New functionality added into xreferplus includes a flexible search system that allows users to search individual topics and titles, an advanced search facility, and a new browse interface that lets users drill down through content. The advanced search capabilities include Boolean operators; thematic searching; truncation and wild card searching; phrase searching; and customized search options, such as searching the full text or just headings. I loved the "spelt or sounds like" search. I deliberately misspelled the Greek mythological character Sisyphus as "sysifus" and still retrieved the appropriate results.

Search results are ranked by relevancy and include 200 characters from the entry around your keyword, which is highlighted. An entry page from a source will provide both cross-references within the same work as well as xreferences to other works. There's an option to view a printer-friendly version of the text. xreferplus is also free of commercial advertising.

Adam Hodgkin, managing director of xrefer, said of the launch: "The library market has been in need of a high-quality, integrated digital reference resource for some time. Through liaising and cooperating with the library community at all stages of development, we're confident that we have delivered a service that meets librarians' needs. This is the beginning of a new and exciting phase not only for xrefer, but for the whole reference community."

Austin McCarthy of the University of Northumbria in the U.K. has been testing the service. He said: "xreferplus is an extremely useful online research tool. Not only can the user search and browse 100 high-quality reference titles, but the additional links provided by the xreferencing technology give the user a set of signposts to related information. I expect it to be a well-used addition to any library's general reference collection."

xrefer is not just a site or a reference tool, it's also a technology company that provides services that leverage the Internet to add value to reference content. xrefer's proprietary patent-pending technology lies at the core of all areas of the business. The company adds value to reference content through its intelligent yet automated system of cross-referencing across a collection of books. xrefer's services for publishers include the digital production of texts, complex Web hosting, and the development of both content-syndication solutions and subscription-based Web platforms.

This first release of xreferplus contains 100 titles from 21 publishers, but the company has ambitious plans to add more publishers and titles. According to a company representative, the majority of these titles will only be available online through xreferplus. (Actually, at this time only 57 titles are available, with the others marked "coming soon." According to a company representative, titles are added each week and all 100 will be in the system by early next year.) While xrefer.com still offers access to titles for free, it unfortunately now provides fewer sources than before because some publishers only wanted certain titles made available on a subscription basis. So, for example, the Grove Dictionary of Music had been available on xrefer.com but is now only available through xreferplus. A recent count of the title list for xrefer.com yielded 43 sources.

xreferplus will also offer librarians the flexibility to cater to their patrons' needs. Specialty data subsets will be made available in the future to complement the core service. Each subset will provide in-depth specialist information on a particular subject, allowing libraries to offer specialist information within the xreferplus system. Libraries will be able to pick and mix options to suit their needs.

Subscription rates are determined by library size, and start at $1,500 per year. The service is aimed at public, academic, and corporate libraries. Individuals can use xreferplus through their public library's remote-access option. At this time, there are no plans to offer individual subscriber rates.

xrefer is currently talking with publishers of foreign-language reference works and is considering producing foreign-language reference engines in the future. The company is also looking to make xrefer accessible from a range of new-media platforms, including WAP and interactive TV.

xrefer was formed in September 1999 and is based in central London. Libraries are invited to participate in a free trial of the service. They can sign up at http://www.xreferplus.com/trial/signup.jsp.