acomputer programming language used to retrieve information from a database.
The uses of databases are manifold. They provide a means of
retrieving records or parts of records and performing various calculations
before displaying the results. The interface by which such manipulations are
specified is called the query language. Whereas early query languages were
originally so complex that interacting with electronic databases could be done
only by specially trained individuals, modern interfaces are more
user-friendly, allowing casual users to access database information.
The main types of popular query modes are the menu, the
“fill-in-the-blank” technique, and the structured query. Particularly suited
for novices, the menu requires a person to choose from several alternatives
displayed on a monitor. The fill-in-the-blank technique is one in which the
user is prompted to enter key words as search statements. The structured query
approach is effective with relational databases. It has a formal, powerful
syntax that is in fact a programming language, and it is able to accommodate
logical operators. One implementation of this approach, the Structured Query
Language (SQL), has the form
select [field Fa, Fb, . . . , Fn]
from [database Da, Db, . . . , Dn]
where [field Fa = abc] and [field Fb = def].
Structured query languages support database searching and other
operations by using commands such as “find,” “delete,” “print,” “sum,” and so
forth. The sentencelike structure of a SQL query resembles natural language
except that its syntax is limited and fixed. Instead of using a SQL statement,
it is possible to represent queries in tabular form. The technique, referred to
as query-by-example (or QBE), displays an empty tabular form and expects the searcher
to enter the search specifications into appropriate columns. The program then
constructs a SQL-type query from the table and executes it.
The most flexible query language is of course natural language. The
use of natural-language sentences in a constrained form to search databases is
allowed by some commercial database management software. These programs parse
the syntax of the query; recognize its action words and their synonyms;
identify the names of files, records, and fields; and perform the logical
operations required. Experimental systems that accept such natural-language
queries in spoken voice have been developed; however, the ability to employ
unrestricted natural language to query unstructured information will require
further advances in machine understanding of natural language, particularly in
techniques of representing the semantic and pragmatic context of ideas.
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