Electronic Searching Techniques
	Vocabulary for Searching

Controlled Vocabulary: Key to Successful Searching

What's that stuff that plants grow in? Is it soil, dirt, earth, the ground?

How might your little sister feel if you gave her an ice cream cone? Would she be happy, delighted, pleased, thrilled, glad, joyful?

What color is the water at a tropical beach on a sunny afternoon? Is it blue-green, bluish-green, greenish-blue, aqua, aquamarine, turquoise?

Professional indexers add controlled vocabulary terms from a standard list to records as they are entered into the database, so that all the records on the same topic can be retrieved using the same search term. The controlled vocabulary terms are entered into a special field in each record. In library catalogs, including ours, controlled vocabulary terms are in the subject headings field. In other databases, they are often in fields labeled descriptors or subjects.

TIP: When you find a record that you like in a database, look at its descriptor or subject field to find what controlled vocabulary terms were used to index that record. If any of the terms are appropriate to your topic, use them to expand your search.

Another way to find controlled vocabulary terms is to search or browse the same standard list that professional indexers use. This list is called a thesaurus.

A database thesaurus is similar to a language thesaurus; it lists synonyms and indicates relationships among terms. It has additional features that help with searching:

• It often includes definitions, or scope notes, for the chosen terms, explaining their meaning in the database.
• It also lists synonyms that are not used in the database and directs the user from those to the chosen terms.
• Under a chosen term, it lists other chosen terms that are more specific or more general.
• It may also list equally specific terms that are used for another facet of the chosen term.

Here is an entry from the thesaurus of the ERIC database, which indexes articles about education. "self-concept" is the term.

Many electronic indexes have online versions of their thesauri that you can use to construct your search. We also have print thesauri for many of our indexes and databases. For help with thesauri, please see a librarian.

The Library of Congress Subject Headings (LCSH) is the thesaurus for many library catalogs, including ours, and several general periodical indexes. LCSH information is in the HSU Library Catalog, and we have a print copy, too. Library of Congress Subject Headings, has information and suggestions for using the LCSH both online and in print.

Free Text: When Controlled Vocabulary Isn't Enough

Controlled vocabulary is a big help in retrieving relevant records in your search, but it doesn't solve all the problems with language. For example:

• It takes time to create a controlled vocabulary, and new terms are always coming into use, so the controlled vocabulary for a database may always be a little out of date.
• Some terms go in and out of use very quickly and are never added to the controlled vocabulary.
• Sometimes no terms in the controlled vocabulary are a good match for the concepts you are searching for. (If there are no terms even close to your topic, this may be an indication that you should use a different database.)

To help solve these problems, database producers include searchable fields for free text terms in database records. Free text is "uncontrolled vocabulary." Concepts are expressed in free text fields without reference to the database thesaurus. The usual free text fields are title and abstract (if there are abstracts in your database). In some fulltext databases, the entire text of the article is a free text field. Authors of the articles, rather than indexers, are usually the ones who decide on the terms in free text fields.

Keywords: The Best of Both Worlds

Most databases allow you to search by keyword. This type of search retrieves terms from both controlled vocabulary and free text fields. A keyword search usually retrieves more items than a controlled vocabulary search, but, because of ambiguity, there is more chance that not all of the results will be relevant.

For example, a search on AIDS may retrieve items on:

• aids for the hearing impaired
• school aids
• AIDS (disease)

When searching by keyword, use only significant words. Don't include articles or prepositions, such as the, an, at, with, for, etc. These are stop words, which the computer is programmed to ignore. Also, leave out words that indicate relationships among the concepts you are researching. Nearly always, records that include terms for all your concepts will be relating them to one another.

TRY IT!

Choose the significant words in the following topics:

Searching by Keyword is best when:

• there is no descriptor or subject heading for your topic
• the descriptors or subject headings are too general or too specific
• you are searching for a new trend or concept
• the database you are searching does not have controlled vocabulary

TIP: Keyword searching can be a good way to begin your search. Find some relevant records in your results, then look at the descriptors or subject headings assigned to those records, and modify your search to include any of those terms that are relevant to your topic.