Controlled Vocabulary

In both IST 604 (Cataloging of Information Resources) and IST 616 (Information Resources: Organization & Access) we have been covering the concepts of subject headings in bibliographic records

What are they? Well, to the chagrin of my professors, none of my textbooks had a satisfactory, easy to understand definition. This one is from Wikipedia’s entry about Index term:

“...is a term that captures the essence of the topic of a document. Index terms make up a controlled vocabulary for use in bibliographic records. They are an integral part of bibliographic control, which is the function by which libraries collect, organize and disseminate documents. They are used as keywords to retrieve documents in an information system, for instance, a catalog or a search engine. A popular form of keywords on the web are tags which are directly visible and can be assigned by non-experts also. Index terms can consist of a word, phrase, or alphanumerical term. They are created by analyzing the document either manually with subject indexing or automatically with automatic indexing or more sophisticated methods of keyword extraction. Index terms can either come from a controlled vocabulary or be freely assigned.”

To be clear, subject headings are not the title, author, publication information, or any such data you might find in a catalog record (or, bibliographic record, if you prefer). They describe the content of the item itself. Most folks know this type of description from tags. You know them and use them all the time - here’s an example of some of my tags on a flickr photo of mine:



Pretty straightforward, right? Well, take a look at the image these tags describe and think about how you would tag it.



Let’s say, for example, you picked “overcast” as one of your tags. That’s a pretty subjective term - it has meaning for you, but someone else might say “cloudy” or “gloomy.” So what happens to this image if someone is searching for images that are “cloudy” on flickr? My image won’t appear in their search. And this is one of the problems with socially-based tagging (and cataloging): words have different meanings to different people.

This same concept is applicable for any item in a library’s catalog. Say you are searching for Shakespeare’s Romeo and Juliet and for some reason, all you can remember is that it’s about “love,” so you search the subjects in the catalog for that term. If the items in the catalog are sourced solely on the tagging system I mentioned above, then you might or might not find the play you were searching for, because the assigned tag might be “suicide” or “passion” for Romeo and Juliet.

I think you’ll agree with me in saying that this is a problem for library users. There needs to be one agree upon term for certain words for subject headings. Well, rest easy reader, as there is a concept called controlled vocabulary that will help you out of this information quandary. One of my textbooks has a reasonably good definition of this:

Controlled vocabulary: A list or database of terms in which all terms or phrases representing a concept are brought together. Often a preferred term or phrase is designated for use in surrogate records in a retrieval tool; the not to be used have references from them to the chosen term or phrase, and relationships (e.g., broader terms, narrower terms, related terms, etc.) among used terms are identified. There may also be scope notes to explain the terms and there may be hierarchical listings.
(Taylor, Joudrey; The Organization of Information, p. 450)

So in a controlled vocabulary environment, there is a single agreed upon term for many concepts, organizations, and even people - so that we are all talking about “the same thing” when describing an item. What does this look like in a catalog record? Well, these headings are in the 650 and 651 fields in this MARC record:



You see how they are linked (blue text) and are not editable? That means they are linked to a controlled vocabulary, which is in this case the Library of Congress’ Authorities, which is the most commonly used set of controlled vocabulary in the US.

Let’s take the first one “Camping” and talk about that for a moment. I know your sharp eyes already picked out how that heading is not just the word “Camping,” but that it is subdivided into more specific categories. This is always done in subject description - more specificity is preferable. So then. The “camping” heading tells us that this is a catalog from an exhibition of pictures about camping. All books like this would be described in the same way.

But what if someone doesn’t search by the specific keywords in the controlled vocabulary? Well, that’s not a problem, as the files for each word have synonyms that refer to the heading (the agreed-upon term) so that you can search with a different word and still find what you are looking for.

Pretty neat, right? I thought so too!

There is one problem with this system though. The Library of Congress’ Authorities are, as you can imagine, mind-bogglingly massive, and so is slow to change. Perhaps some sort of combination of social sourcing and controlled vocabulary would be in the best interest to the user? I have no broad plans for this or suggestions, just an idea.

If you want to know more, let me hear from you in the comments!