In this chapter we will look at the alternative ways in which information can be organized, and the role that language plays in ordering and retrieval. Many of the challenges associated with indexing and searching, the design of indexing tools, and the consequent effectiveness of retrieval arise in large part from the richness and diversity of language. This is true of all languages, but is particularly the case in English, which has a huge stock of words and many linguistic influences.

Systematic and alphabetic approaches to information

There are two fundamental approaches to the organization and retrieval of information for its subject content. First, the information may be arranged in a systematic way using some sort of scheme or map of knowledge that provides an overview of a subject area and shows the structure and relationships between topics. This is a very useful approach for users who are not very clear about what might be available, or not very precise in their search requirements. It allows users to scan material, to find items on the same topic together, and related topics nearby, and to discover more specific items within broad subject groups. This browsing behaviour is supported by schemes of classification or categorization for the physical arrangement of resources, such as those used in libraries and bookshops. Similar approaches are often found in digital libraries and subject gateways and portals, where a directory style arrangement offers users some basis for the initial search and encourages them to focus and refine search by drilling down into the various categories and sub-categories. The bringing together of topics is known technically as collocation.

Such systematic structures are essentially conceptual in nature; they work on the basis of abstract classes, categories, or ideas, and, in order to keep the systematic structure in place, codes (such as classmarks or URIs) may be used to represent the concept. Tools that assist this kind of search include conventional library classification schemes (such as the Dewey Decimal Classification and the Library of Congress Classification scheme), and user interest classifications common in many public libraries. For digital resources, taxonomies and concept maps work in a similar way.