A search query may return too many or too few hits because certain search terms are too general or too specific. It is advisable to find generic and subordinate terms and repeat the search with these.

For example, one possible generic term for flies is diptera; another is insects. Subordinate to flies are fruit flies.

Synonyms, different words with the same meaning, can also be used. In this case, synonyms can be linked with the Boolean operator OR.

Synonyms for fruit fly include fruit fly, fruit fly, etc. And of course the Latin name Drosophilidae.

Upper and lower terms as well as synonyms can be researched in the common keyword database of the Library Service Centre Baden-Württemberg. The entries are standardised keywords with a controlled vocabulary; new keywords and subject terms cannot be added by anyone. Instead, the existing ones must be used. Non-controlled vocabulary can be found, for example, at https://www.openthesaurus.de/.

It is more difficult with homonyms; terms that sound or are spelt identically but have different meanings in different contexts. The garment flies is a good match for the insect flies. Or the bank for sitting and withdrawing money.

Refining the search

Some databases allow you to refine a search or narrow down search results without performing a new search.

It may be better to start with a more general search and then restrict the search

• to certain additional specialist terms,
• or to subsequently adjust the search period or
• target authors.

If it is not possible to refine the current search result and a new search is started instead, Boolean operators can be used from the start

• , (see technical search tips)
  • to specifically exclude topics (NOT operator) or
  • to combine keywords (OR operator)
• phrase searches can be used, to make the search terms more specific

Expand search

If (unrealistically) too few hits are found, the search should be expanded or the search terms reconsidered. the search terms should be reconsidered.

• The consideration of synonyms by the OR operator makes it possible to combine different terms for the same question.
• Thesauri and controlled vocabularies help with the selection of possible synonyms and correct search terms
• The spelling may not be correct. Especially when searching in English, errors can quickly occur because supposedly correct terms are used
  • organic and inorganic chemistry vs Organic and Ainorganic chemistry
  • Translation tools and dictionaries provide the correct spelling

Boolean operators:

Use Boolean operators (AND; OR; NOT)

When stringing together search terms, these are usually linked with AND. The results must contain both search terms.

The search for

• fruit fly AND fruit fly

corresponds

• fruit fly fruit fly

and not

• "fruit fly fruit fly".

Synonyms are ideally combined with OR. It is sufficient if one of the two terms appears.

For

• fruit fly OR fruit fly

the hits contain either fruit fly or fruit fly and both terms.

With

• fruit fly NOT fruit fly

, texts only contain fruit fly, but not the term fruit fly.

Phrase search:

"Fruit fly fruit fly" corresponds to a phrase search. This only displays results in which "fruit fly fruit fly" is found exactly.

Masking and truncation :

If you want to search for terms that have different spellings or if you want to search for a word stem. If you want to search for a word stem, placeholders for masking and truncation are available.

• Both optimisation and optimisation are found with optimi?ation . The question mark represents AN arbitrary letter (masking).
• Placeholder for multiple characters is the asterisk *. Both microbiology and microbial are found by microb* . Here, both terms are traced back to a common word stem (truncation).

Many databases have special syntax for searching, the use of Boolean operators and also introduce their own operators. These are stored in the documentation of the respective database. For Scopus, for example, the search tips are available here and the advanced search is available here.