One of our goals in creating taxonomies and thesauri is to express the concepts in natural language. Natural language means that you have written it the way somebody would say it. We don’t invert it.

All of you have probably used a card catalog in college. You know that the catalog records will refer to a topic rather awkwardly: Wars, Civil wars, Battle of Gettysburg 1863, something like that. When you are talking about it, you will talk about the Battle of Gettysburg. You will not include all of that other stuff, and you certainly are not going to invert it.

In library science, post-coordination is a phrase you will hear a lot as opposed to pre-coordination. Post-coordination is when you are going to let the searcher put the terms together at the time that they do a search. That was not possible in 1893, when Cutter and Dewey starting designing their Dewey Decimal Classification and Cutter Expansive Classification. When shelving a book or whatever, you could put it in only one place on a shelf, so the classification had to serve as a guide to the single physical location for each item.

To make things more awkward, searches for library items necessarily relied on alphabetical order, which meant that phrases had to be inverted (with commas thrown in to indicate the inversions) for the sake of findability. As for finding material within a book, there was usually a back-of-the-book index, with the same kind of inverted phraseology.

With a computer, we can put together those intersections at the time the search is made.  Since the 1960s, we’ve been able to do post-coordination. We still have a heavy legacy of pre-coordination around, though. We are frequently taking classification systems and moving them from a pre-coordinate fragment level to a post-coordinated, or single concept, approach.

The challenge that we face in developing taxonomies for post-coordination of terms is stating things effectively in natural language, so that the wording is really is the way somebody would talk about those topics.

Marjorie M.K. Hlava President, Access Innovations

This posting is one of a series based on a workshop, “Thesaurus Creation and Management,” that Marjorie Hlava presented in December of 2012.