A subject search involves searching the subject headings of records in a database. Most databases have subject headings (or descriptors) for each item that is indexed. These headings are in the subject or descriptor field.
People who work as indexers assign subject headings to each book or article from a list of terms used specifically for that database. This list, called a database thesaurus, ensures that all items about the same topic have consistent subject headings. Users can then retrieve all the items on a topic using one term, even when there may be several good ways to state a concept.
For example, you may want to research the topic death penalty:
Possible ways to state this topic:In CLIDA the subject heading for death penalty is capital punishment, but the same term may not be used in all databases.
In the following example, the subject heading for heart attacks is listed differently in different databases. Some use heart attack, some use heart arrest, some use cardiac arrest, and others use myocardial infarction.
The thesaurus for CLIDA is called Library of Congress Subject Headings. These red books are kept in the Ready Reference area.
If you are unsure whether a database has a thesaurus, ask a librarian.
A keyword (also called word or free text) search retrieves words or phrases from several important fields of the records in a database. In most databases a keyword search finds words in fields that have descriptive content, such as title, subject/descriptor, and abstract . In some databases, additional fields may be included in the keyword search.
A keyword search usually retrieves more items than a subject search, but they may not all be relevant. In a keyword search you can retrieve a number of irrelevant items because the computer is looking for the exact word you typed, not for the meaning or context of the word.
For example, a search on AIDS will retrieve items onWhen searching by keyword, use only significant words, not common words, such as the, of, an, and that. Such words may be stop words, words that occur too frequently to search.
What would the significant words in the following topic be?| Subject Searching | Keyword Searching |
| Searches subject or descriptor field only Controlled terminology (from Thesaurus) High degree of relevancy High precision Low recall |
Searches subject, title, and abstract fields May search for any significant terms May retrieve irrelevant items Low precision High recall |