Classification Systems
The general role of classification systems today
The classification systems that most people are familiar with are the biological classification systems and library classification systems. While we could classify all of the DEMML™ content using only the names of things - as is done in biology - it would be hard to use that in a computer and translation into different languages would be problematic. Since both DEMCS™ and library systems use code numbers, we will use these for our discussion.
The primary goal of library systems is to classify books and other physical materials. These physical materials are then shelved in a linear fashion. One book follows another down the line. There is only one first book and only one last book in a collection. Another major characteristic of all this material is that it usually covers many different but related topics in one volume. These often dictate or limit the design of these library classification systems but it is still important to understand them in order to see how DEMCS™ is - and must be - different.
Enumerative Classification Systems
An enumerative classification system is one where the entire body of knowledge is broken down into distinct major groups. Each of those groups is broken down into distinct sub-groups, and so on as far down as is necessary. This produces a hierarchical tree where each item has a unique place on the tree. If any items are about multiple subjects, then a single, most-important subject is chosen and the item is placed at that location within the tree.
In libraries, this means that a book about Algebra and Calculus must be located in the section which holds other books about Math in general instead of the section about Algebra or the section about Calculus. This may mean that the book is placed next to another book about Trigonometry and Game Theory even though neither of those books cover the exact same thing. (Note: these are admittedly poor examples but are, hopefully, examples that everyone can understand.)
Well known examples of enumerative classification systems are the Library of Congress Classification System (LCC) and the Dewey Decimal System (DDS).
Faceted Classification Systems
Faceted classification systems place much greater emphasis on the fact that most books cover multiple topics. These systems define multiple facets, or ways that a book could be classified, and assign a code to each of those facets. For instance, a book about the history of wheat in Kansas has a chronological facet, a general topic facet, and a location facet, each of which has a code. Books about birds in Kansas would have the same code for the location but different codes for chronology and general subject. An example of a faceted classification system is the Colon Notation System invented by Shiyali Ramamrita Ranganathan in India and used in many libraries there.
With faceted classification systems, libraries can choose which facet they consider most important. One library may choose to sort first on the location facet then sort on the chronological facet. A history department library may choose to sort first on the chronological facet. A library may even choose to sort some books based on one facet and sort others based on a different facet. This means that a book may be located on a different shelf in different libraries depending on what the local librarians felt was most important. While it seems random, it does allow librarians to sort books in such a way that books will be grouped in the way that is most convenient for their customers. People who are interested in their state would find it convenient to have all the books about their state in one place. Many advocates of faceted classification systems point out that enumerative classification systems like LCC often end up with related books spread out throughout a library and customers have to do a lot of work to find what they need. Whereas customers in libraries that use faceted classification systems can often find everything they need on one shelf. But only if the librarians have adequately predicted the needs of the customers.
