Subject Headings and Subject Classification

Historically, materials have been arranged by subject in libraries for centuries, but subject arrangement is not a complete answer to the problem of locating materials by the topic they cover. Library materials can only be shelved in one place in the library, usually by a classification system such as the Dewey Decimal System, organizing materials on the library shelves by their topic. This type of system can be rather limiting when used as a way to provide subject access to the collection. An item that deals with more than one aspect of a topic, or two related topics, can only be placed in one spot. The question then arises of how to provide access to the additional information an item contains, information that may be of interest to a library patron. 

For example, a library item that contains information about agriculture in a specific country may be shelved with other information about that country, but someone interested in agriculture may want to be able to find that item by the topic of agriculture.

Another subject access concern in libraries deals with non-book materials. These are often shelved by title or by an accession number assigned to the item when it is added to the collection. Browsing a non-book can be very tedious if this is the type of organization being used. Having access to the subject of a non-book item in the library catalog enables patrons to see a list of the possible titles, and to find the materials more easily.

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