This requires a general knowledge of how queries should be formulated and specific knowledge for the implementation of the query language in many search engines. The differences between search engines are the differences between the indexes and the syntax used in the user interface to construct queries. Generally, queries are created by the selection of keywords to represent the researcher's information need. Queries can be made more specific by the use of Boolean operators, structured searches, searches for phrases, proximity searches, and similarity searches. Different engines implement some or all of these search operations with varying degrees of success.
Structured searches look only at specific parts of a document to see if it qualifies as a hit.
A search may look only at the URL, title, first paragraph, or some other part of the document. Searching for phrases requires that the whole phrase specified be present in the document. Proximity searches require that the different keywords in the search request are close to each other to result in a hit. Similarity searching may work in one of two ways. Or, similarity may mean that similar documents are found.