Understanding Web Internals--URLs and Resources

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Uniform resource locators(URLs) are the standardized names for the Internet's resources.URLs point to pieces of electronic information,telling you where they are located and how to interact with them.

URL syntax

URLs provide a means of locating any resource on the Internet,but these resources can be accessed by different schemes,and URL syntax varies from scheme to scheme.

Most URL schemes base theri URL syntax on this nine-part general format:

<scheme>://<user>:<password>@<host>:<port>/<path>;<params>?/<query>#<frag>

Almost no URLs contain all these components.The three most important parts of a URL are the scheme,the host,and the path.

General URL components

Component    Description                                                                              Default value

scheme         Which protocol to use when accessing a server to get                    None

                   a resource

user             The username some schemes require to access a resource               anonymous

password      The password that may be included after the username,                   <Email address>

                   separated by a colon(:).          

host             the hostname or dotted IP address of the server hosting                      None

                   the resource

port              The port number on which the server hosting the resource                   Scheme-specific

                    is listening.Many schemes have default port numbers.

path              The local name for the resource on the server,separated                       None

                    from the previous URL components by a slash(/).The syntax

                    of the path component is server- and scheme-specific.

params          Used by some schemes to speicfy input parameters.                            None

                    Params are name/value pairs.A URL can contain multiple

                    multiple params filelds,separated from themselves and the

                    rest of the path by semicolons(;).

query             Used by some schemes to pass parameters to active applications          None

                     (such as databases,bulletin boards,search engines,and other

                      Internet gateways.)There is no common format for the contents

                     of the query component.It is separated from the rest of the URL

                     by the "?" character.

frag                A name for a piece or part of the resource.The frag field is not              None

                     passed to the server when referencing the object;it is used

                     internally by the client.It is separated from the rest of the URL

                     by the "#" character.

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