Keyword searching improved significantly in the first decade of the 21st century and is now the default search mode for most databases and search engines. Keyword searching works by matching the words you type in the search box to words found in the full-text article or the article information (title, author, abstract, etc.)
Still, there are some weaknesses in keyword searching, due to the inherent ambiguity of the English language.
- one keyword can mean multiple things to different people or in different contexts
- there can be multiple keywords used to describe one thing
A controlled vocabulary is a system designed to overcome that ambiguity of the English language. In a controlled vocabulary, there is only one word (subject term) for a concept, and only one concept per word. For example, if there are articles that mention cars and automobiles, indexers might select automobiles as the subject term (a.k.a. subject heading or descriptor.) If you look up the subject term automobiles, you will get all the articles in the database that are about that topic, regardless of what terminology the author used.
- Detailed article information (what you get when you click on the article title in the search results) often includes a list of subject terms that describe the topic of the article. These subject terms are usually links. If you click one of them, the database will pull up all the articles categorized under that subject term. This is a great way to get more articles on the same topic.
- The Advanced Search feature of most databases has a pull-down menu next to the search box. You can use it to select subject or descriptor from the options and then type in a subject term to search.
- A database’s thesaurus is a list of all the subject terms used in that database. You can look up a keyword in the thesaurus and it will tell you which subject term to use instead. Some databases have a dynamic thesaurus where you can browse for subject terms and click them to add them to your search.
* This kind of thesaurus is difference from the kind of thesaurus that is a reference resource for looking up synonyms!
Every database handles subject terms and thesauri differently, but the basic functionality is the same.