URL location bar showing an URL with the query string title=Main_page&action=raw]]
When a Web Page is requested via the HyperText Transfer Protocol , the server locates a file in its File System based on the requested URL . This file may be a regular file or a program. In the second case, the server may (depending on its configuration) run the program, sending its output as the required page. The query string is a part of the URL which is passed to the program. This way, the URL can encode some data that is accessible to the program generating the web page.
The URLs of documents to be generated by programs may contain a query string that is passed to the program. A typical such URL is as follows:
:http://server/path/program?query_string
When a server receives a request for such a page, it runs a program (if configured to do so) passing the query_string unchanged to the program in some way. The question mark is used as a separator and is not part of the query string. The query string is passed as is to the program.
A link in a Web page may have a URL that contains a query string. However, query strings have been introduced to the aim of passing the content of a Web Form to a program. In particular, when a form containing the fields field1, field2, field3 is submitted, the content of the fields are encoded as a query string as follows:
:field1=value1&field2=value2&field3=value3...
- The query string is composed of a series of field=value pairs
- The field-value pairs are each separated by an Equal Sign
- The series of pairs is separated by the Ampersand , '&' (also by ';' in the newer W3C recommendations {Link without Title} )
For each Field of the form, the query string contains a pair field=value. Web forms may include fields that are not visible to the user, and these fields are included in the query string when the form is submitted.
Technically, the form content is encoded as a query string when the form submission method is GET. The same encoding is used by default when the submission method is POST, but the result is not sent as a query string, that is, is not added to the action URL of the form. Rather, the string is sent as the body of the request.
Some characters cannot be part of a URL (for example, the space) and some other characters have a special meaning in a URL: for example, the character # is used to locate a point within a page; the character = is used to separate a name from a value. A query string may need to be converted to satisfy these constraints. This can be done using a schema known as URL Encoding .
- '(),", and reserved characters used for their reserved purposes may be used unencoded within a URL”. All characters in a query string can be replaced by their hexadecimal value precedeed by the symbol
%. For example, the equal sign can be replaced by %3D. All characters can be replaced this way; for the characters that are forbidden in a query string, this is not only possible but necessary.
The space character can be also represented by +.
As defined in RFC 1738, an URL of scheme http can contain a ''searchpart'' following the rest of the URL and separated from it by a ? character. RFC 3986 specifies that the ''query component'' of an URI is the part between the ? and the end of the URI or the character #. The term ''query string'' is of common usage for referring to this part for the case of HTTP URLs.
If a form embedded in an HTML page as follows:
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