This section is fairly short, but it is important to understand the term controlled vocabulary. When searching in a system (catalog, database, etc.), there are two types of search terms: keyword (or natural language), and controlled vocabulary. The term keyword can refer to several things, but in this case it is referring to the terms you select to search with, not the type of search you are performing. So for the sake of clarity, we will refer to the other description of natural language.
Natural language searching is the process where you search using the terms to describe your topic you have found. These terms may be ones you knew before the beginning of the research process, or they may be terms you encountered when looking for background information. This type of search can be productive, though at times not as concise as controlled vocabulary. Have you ever done any natural language searching? Almost certainly, as this is the type of searching employed by search engines (Google, Bing, etc.).
Controlled vocabulary searching involves using search terms that are designated in a search system (i.e. catalog, database) as the formal description of a subject. In other words, these terms are applied to all records on the topic so they can be cross-referenced. This function can be extremely helpful when searching. Most systems refer to this as subject searching. We will examine what that is in the next section.
Do all finding tools use the same controlled vocabulary? Unfortunately no. The terms may be close, but don’t always match up. Library catalogs use the Library of Congress Subject Headings for their controlled vocabulary. While some of the databases may use these subject headings, others do not. Some don’t employ any controlled vocabulary. In our catalog, the subject headings appear as seen in the image below:
Since not all finding tools use the same controlled vocabulary, why use it when searching? Within a search system, controlled vocabulary provides the ability to find all of the materials on that topic in that system. This can be extremely useful when retrieving a large amount of results in a search, and wanting to narrow the amount down to a manageable set. Now we will move on to the searching process.