Many databases will have ‘subject terms’ that represent some components of your question. Controlled vocabulary is a necessary building block for knowledge syntheses, and subject terms that are identified generally have to be searched both as subject terms and as synonyms (keywords).

To use controlled vocabulary, access a database and find the database’s thesaurus (also called its index, descriptors, subject terms, subject headings, or MeSH) and search within that thesaurus to find terms that represent your concept.  

For example, a search for controlled vocabulary in Medline for 'stroke' shows us this (simplified):

• Cerebrovascular Disorders
  • Intracranial Hemorrhages
    • Cerebral Hemorrhage
    • Intracranial Hemorrhage, Hypertensive
    • Intracranial Hemorrhage, Traumatic
    • Subarachnoid Hemorrhage
  • Stroke
    • Brain Infarction
    • Hemorrhagic Stroke
    • Ischemic Stroke

This demonstrates the hierarchy of terms and shows us that Stroke is a narrower term of the broad category Cerebrovascular Disorders and contains other more specific terms such as Ischemic Stroke. 

The term you choose to include will depend on the topic you are researching. In this case, the researcher will need to decide if the broader topic of Cerebrovascular Disorders is appropriate or if their research requires a more specific term such as Ischemic Stroke. 

Each database will have its own controlled vocabulary and each will have its own system of identifying and selecting terms for search inclusion. As many of the databases at UNBC are housed on the EBSCO platform, we will utilize EBSCO's CINAHL database as an example in this guide. 

From the main CINAHL search page, ensure the "Suggest Subject Terms" box is checked. This will ensure your search term maps to a subject heading. Use the first search box to enter a search term and select "Search."

This will direct you to a list of terms that CINAHL thinks may be relevant to your topic. If you don’t find a relevant subject heading with your first search, try a few more synonyms, but be aware that there might just not be anything to find so don’t get too stuck on this step.  There may also be more than one subject term for your topic – for example, there are many different types of rehabilitation and they will often each have separate subject terms. Clicking directly on a term will take you to the "thesaurus tree" where you will see how these terms are nested within the subject heading structure. 

There are several important options on this page that you will need to be aware of for your structured search. 

• Explode - When you Explode a term, you create a search query that includes all of the narrow subject headings listed under the selected subject heading. The headings are exploded to retrieve all references indexed to that term as well as all references indexed to any narrower subject terms. This can be very useful for reviews, the exception is when the narrower terms are clearly not relevant to the search you want to perform. 
• Major concept - When you select Major Concept for a term, you create a search query that finds only records for which the subject heading has been designated a major point of the article. Systematic searches should not be limited to major concept as it is too restrictive. 
• Scope Note - Provides a definition of the subject heading. Sometimes the scope note will also provide other suggested subject headings, this are represented in CAPITAL LETTERS. 

Select your subject heading by clicking the check box to the left of the term, the will produce this additional box that offers the option of narrowing further by subheading. Don’t use these. Just ignore them entirely. Decide whether or not to explode. Decide whether or not to choose major concept. Then add your term to your search by clicking ‘search database.’