With the combination of three operators AND, OR and NOT (sometimes correct: AND NOT) you can narrow your search by looking directly for documents which contain either some or all search items or exclude search items from the result list.
Most searching services have added the AND-function as a default in their easy search menu.
An "AND" function limits a search.
You should use the operator "AND" ...
... if you want to find all items in your list of catch words.
... if you are sure of the formulation and wording of your search item.
... to limit general search items.
The "OR" function extends a searching inquiry.
You should use the operator "OR" ...
... if you are not sure about the wording of an item
... if you would like to find documents in different languages, for example "strawberry OR fraise", "democracy OR démocratie"
... to find documents with synonyms, e.g., "EU OR European Union", "Sri Lanka OR Ceylon"
... to increase the number of results
The operator "NOT" or "AND NOT" can be very helpful in improving the quality of your results. With this function you can exclude phrases and items which might increase the number of your searching results needlessly.
The distance operators NEAR and ADJ (for adjacent = adjoining) offer you the possibility to fix the maximum distance between request items in a document. If, for instance, an "AND" linking incurs too many results and you can not find any additional search items in order to further limit the amount of results, it can be helpful to find documents in which the items you are searching for are in closer vicinity to one other.
The distance operator ADJ insures that the request items are found directly side by side.
Jokers, search strings and more
A wildcard or joker offers the possibility of searching for parts of a word or word endings. Thus you can search for a particular section of a catchword, and combine different searching inquiries into one. To mark the missing part of the word which must be contained in the result document, special characters are used. Use of the star "*" is very wide-spread; with some data banks utilizing the dollar sign "$", and other searching services using the question mark "?".
A phrase search uses fixed and compound items and is an excellent instrument in order to search more specifically as compared to utilizing several catchwords.
A phrase search helps if you are searching for documents with persons, companies or products, for example. You should also investigate with items such as "Federal Minister of Economics" or other specific names in this manner.
If you are not familiar with the terminology of a special theme, a thesaurus-search can be valuable. A thesaurus is a controlled, hierarchical list of terms.
Humanities and Social Science Electronic Thesaurus
Thesauri in the WWW
a list in German.
Tips and tricks
The inclusion operator "+" is very often mistaken with the boolean operator "AND". However, there is a very important difference: the inclusion operator ensures that the preceding search item is contained in the result list. Example: the search inquiry "party + labour" will find all documents which contain the item "party", while "labour" might be contained, but does NOT have to be. - Google search engines are interpreting "+" as "posted in Google Plus". Use quotation marks!
Some searching services permit the search for single web page elements. This can be an additional help in the case of very high result numbers. The following elements are searchable:
This is the best and most efficient way of summarizing possible search words into one searching inquiry with the help of brackets. Indeed, many "extended search options" offer this in their menu already, however, line oriented input with the help of brackets offers you more freedom for creating a precise inquiry.