 Welcome back to the authority control class. We are starting week two and we are going to be talking about the concept of controlled vocabularies this week. This first session we're going to talk about basically what a controlled vocabulary is. Here's a formal definition from a book called Metadata for Digital Collections and according to this author, a controlled vocabulary is a standardized list of terms that have been selected for consistent use in describing or indexing information resources. So basically you'll see this is basically the same definition as the authority file concept we talked about last week and we will continue to talk about concepts like this but basically it's making sure that everybody is using the same terms for particular concepts when you do authority control whether it's for subjects or name authorities for authors or things like that. Next we're going to talk about four different features of controlled vocabularies and why they work for our purposes for authority control. One feature of controlled vocabularies is that they provide ambiguity control. This refers to the fact that the same word can mean more than one thing and if you have items about both of these things in your collection you're going to want to be able to distinguish between the different uses of the word. For example, mercury could be referring to the planet, it could be referring to the metal or it could be referring to the Roman god and so a controlled vocabulary should have a way of dealing with the different concepts. For example, the Library of Congress subject headings which we'll talk a little bit more about in the second video this week, they use parenthetical qualifiers to describe a little bit more thoroughly what they're talking about. A good controlled vocabulary should also provide synonym control and this deals with the fact that more than one word can represent the same concept. Some people when they're referring to things that drive down the street they call them cars, some people call them automobiles, the controlled vocabulary needs to decide which term is used and direct a cataloger to use the correct term when they might try and look up the incorrect term. So if the established term is automobiles then you will be told to use this term for cars and also to use this term instead of autos for example. A controlled vocabulary also has hierarchical relationships. This means that there is a use of broader and narrower terms so if you look up a term you will sometimes see a broader term that it's included in in case you want to re-evaluate and see if your subject is really a broader term and also has narrower terms. So for example again our term automobiles has a broader term in motor vehicles and for example among many I'm sure narrower terms of antique and classic cars as well as sports cars. And lastly a controlled vocabulary usually has some kind of associates to your relationships. This is the use of terms that are related in ways other than broader or narrower. So they're not necessarily saying you have to use this instead of a particular term like what we saw with the use for terms but they're saying if you're looking at something on votes and voting you might also be interested in using the heading sailing and shifts. So cross-references are provided in that way. So those are a few characteristics of controlled vocabularies.