Once the literature databases and other research sources have been selected, search terms are defined. For this purpose, the research topic/questions is/are divided into blocks of terms of equal ranking. This approach is called the block-building method (Guba 2008, p. 63). The so-called document-term matrix, which lists topic blocks and search terms according to a scheme, is helpful in this regard. The aim is to identify as many different synonyms as possible for the partial terms. A precisely formulated research question facilitates the identification of relevant search terms. In addition, keywords from particularly relevant articles support the formulation of search terms.
A document-term matrix for the topic “The influence of management style on the performance of project teams” is shown in the image to the right.
Identification of headwords and keywords
When setting search terms, a distinction must be made between subject headings and keywords, both of which are described below:
- appear in the title, abstract and/or text
- sometimes specified by the author, but in most cases automatically generated
- different spellings and forms (singular/plural) must be searched separately
- describe the content
- are generated by an editorial team
- are listed in a standardized list (thesaurus)
- may comprise various keywords
- include different spellings
Subject headings are a standardized list of words that are generated by the specialists in charge of some databases. This so-called index of subject headings (thesaurus) helps searchers find relevant articles, since the headwords indicate the content of a publication. By contrast, an ordinary keyword search does not necessarily result in a content-related fit, since the database also displays articles in which, for example, a word appears once in the abstract, even though the article’s content does not cover the topic.
Nevertheless, searches using both headwords and keywords should be conducted, since some articles may not yet have been assigned headwords, or errors may have occurred during the assignment of headwords.
To add headwords to your search in the Business Source Complete database, please select the Thesaurus  tab at the top. Here you can find headwords in a new search field and integrate them into your search query. In the search history, headwords are marked with the addition DE (descriptor).
The EconBiz database of the German National Library of Economics (ZBW – Leibniz Information Centre for Economics), which also contains German-language literature, has created its own index of subject headings with the STW Thesaurus for Economics . Headwords are integrated into the search by being used in the search query.
Since the indexes of subject headings divide terms into synonyms, generic terms and sub-aspects, they facilitate the creation of a document-term matrix. For this purpose it is advisable to specify in the document-term matrix the origin of the search terms (STW Thesaurus for Economics, Business Source Complete, etc.).
Searching in literature databases
Once the document-term matrix has been defined, the search in literature databases begins. It is recommended to enter each word of the document-term matrix individually into the database in order to obtain a good overview of the number of hits per word. Finally, all the words contained in a block of terms are linked with the Boolean operator OR and thereby a union of all the words is formed. The latter are then linked with each other using the Boolean operator AND. In doing so, each block should be added individually in order to see to what degree the number of hits decreases.
Since the search query must be set up separately for each database, tools such as LitSonar have been developed to enable a systematic search across different databases. LitSonar was created by Professor Dr. Ali Sunyaev  (Institute of Applied Informatics and Formal Description Methods – AIFB) at the Karlsruhe Institute of Technology.
Additional searches in sources other than literature databases
In addition to literature databases, other sources should also be searched. Fink (2014, p. 27) lists the following reasons for this:
the topic is new and not yet included in indexes of subject headings;
search terms are not used congruently in articles because uniform definitions do not exist;
some studies are still in the process of being published, or have been completed, but not published.
Therefore, further search strategies are manual search, bibliographic analysis, personal contacts and academic networks (Briner & Denyer, p. 349). Manual search means that you go through the source information of relevant articles and supplement your hit list accordingly. In addition, you should conduct a targeted search for so-called gray literature, that is, literature not distributed via the book trade, such as working papers from specialist areas and conference reports. By including different types of publications, the so-called publication bias (DBWM video “Understanding publication bias” ) – that is, distortions due to exclusive use of articles from peer-reviewed journals – should be kept to a minimum.
Proceed to step 4. Merging hits from different databases