Defining Search Terms

One of the most important first steps in locating relevant information is to identify unique ideas or concepts associated with your research topic.  In the sciences, these concepts commonly fall into one of these categories: subject; taxonomic; geographic; time; habitat; life stage, population or age group; organ system; chemical substance; genetic sequence; disease; or methodology, technique or test. 

Each concept usually can be described using several specific keywords. These keywords can be developed in several ways - your personal knowledge of the topic, suggestions of others, or background reading that you do in secondary sources.  When you search by keyword, all instances of that word will be brought up in your search results.  You may get some irrelevant search results.  By also searching using synonyms and related terms, you'll be more likely to retrieve more information out there on a given topic.  Searching by the correct subject heading, as we'll talk more about below, will enable you to search an entire collection more efficiently.

Each discipline has its own distinctive approach to its body of research literature.   Becoming familar with the unique terminology can also be of help to you in constructing successful searches.  Below are some of the common terms used in each discipline. 



Man with a floppy disk held up and he is looking through center of disk


 Software Products, Algorithms,

 Programming Languages,

 Security Issues...



Biologist with Squid

 Biology  Taxa, Scientific/Common Names, Chemicals,

 Diseases, Structure, Equipment...



 Chemistry  Substances, Reactions, Physical Constants,

 Structures, Compound Names, Registry



Physics Lecture


 Instrumentation, Nuclear Cross Section,

 Fundamental Constants, Fundamental Forces,

 Treatment (applied,  theoretical, experimental)...


Big Bang Expansion


 Star Positions, Object Identifiers, Stellar 

 Classifications, Observational Wavelengths...




 Proofs, Equations, Solutions...




 Epochs, Strata, Seismic Events, Minerals, 

 Composition, Geography...

What is a Controlled Keyword or Controlled Vocabulary?

"Controlled" keywords bring together similar ideas under one standardized word or phrase.  In a database record they may be called "descriptors" or  "subject headings."

Libraries organize and catalog information using the Library of Congress Subject Headings.  These subject headings are agreed upon terms that do not vary from library to library.  This is why they are called a controlled vocabulary. Sometimes information is a bit more challenging to locate because the item has been organized and categorized by subject heading.  If you do not know what "controlled" keywords to use, conduct an initial search using the
keyword(s) you have. In reviewing the search results look for "controlled" keywords, often called descriptors or subject headings, which commonly appear as part of each citation.  In the example below you can see that when we did a keyword search for "mollusks", we found a book, Pacific Coast Nudibranchs,  that lists three subject headings:

Example of subject headings for the keyword search 'mollusks'.

Re-enter your search adding these "controlled" keywords to your existing keywords.

                                           Revised list of keywords
                                           nudibranchia identification
                                           mollusks identification
                                           mollusks North American Pacific Coast Identification

Once you know the correct subject heading, your search will be made easier allowing you to find all items in a collection with a specific subject heading.  To provide another example, if you are looking for books on the death penalty, it is important to know that the correct subject heading is "capital punishment."  If you are looking for books on American Indians, the correct subject heading is "Indians of North America."   

Napa Valley College librarians use the same subject headings to catalog a book as would UC Davis librarians, or New York University librarians.  If you were given an assignment by your instructor to locate all the books in the library on the chemical compounds and elements found in the Periodic Table of Elements, it would be best to search by subject heading using the correct controlled vocabulary term below:

Initial search term                                           The correct controlled vocabulary term

chemical compounds                                          chemical elements
Periodic Table of the Elements                           chemical elements

In Napa Valley College's online catalog, Solano, Napa and Partners (SNAPweb), we can see a subject heading search for the search term "chemical elements":

SNAP subject search for chemical elements 

Our search results have returned 25 + 30 (a total of 55) items with the subject heading "Chemical elements." There are of course other types of materials on chemical elements such as handbooks, manuals, pictorial works, popular works, juvenile literature, and history etc. 

 SNAP results for search of chemical elements


  • Hierarchical Relationships

    In developing keyword lists consider possible hierarchical relationships within a particular concept. For example, with a taxonomic concept are you only interested in locating research on a particular species or is a broader taxonomic classification also of interest?

    marine biology

    marine flora

    marine algae

    red algae (Rhodophyta)

    coralline algae (Coralinales)


    Sporolithon ptychoides
  • Word Truncation

    Examine each keyword to see if it can be beneficially truncated to retrieve variant forms of the word. This is especially true for single and plural variants of a word. You can use wildcard symbols (e.g., *, #, ?, +) available in a database to truncate words back to a base root. To find the correct wild card symbols to use in a database check its help section. Examples:

    sediment* retrieves sediment, sediments, sedimentation
    silt* retrieves silt, silts, silting, silted, siltation

  • Scientific Nomencalature

    For taxonomic concepts use both common and scientific names of organisms. Using both will normally increase the number of citations retrieved.

    salmon or oncorhynchus


    Scientific Information Literacy Modules

    Unit 1:  What is Science?
    Unit 2:  Scientific Information
    History Information Literacy Modules
    copyright 2011 Napa Valley College

    updated June 14, 2011, by Nancy McEnery, Reference Librarian-Instructor