Parts of a Uniform Resource Locator
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The Uniform Resource Locator (URL) is a complete description of the location of a resource that is available over the net. It is composed of several parts that may be accessed by an application. These parts are illustrated in the following figure:
The first portion (not technically part of the URL) identifies the protocol (http). This portion can specify other protocols such as https (secure http), ftp, and so on.
The Host portion identifies the machine that runs the Web server and Web server application. Although it is not shown in the preceding picture, this portion can override the port that receives messages. Usually, there is no need to specify a port, because the port number is implied by the protocol.
The ScriptName portion specifies the name of the Web server application. This is the application to which the Web server passes messages.
Following the script name is the pathinfo. This identifies the destination of the message within the Web server application. Path info values may refer to directories on the host machine, the names of components that respond to specific messages, or any other mechanism the Web server application uses to divide the processing of incoming messages.
The Query portion contains a set a named values. These values and their names are defined by the Web server application.
URI vs. URL
The URL is a subset of the Uniform Resource Identifier (URI) defined in the HTTP standard, RFC1945. Web server applications frequently produce content from many sources where the final result does not reside in a particular location, but is created as necessary. URIs can describe resources that are not location-specific.