Information Technology Reference
In-Depth Information
Web. A resource is generally understood as a piece of information that can be
identified by a dereferenceable URI.
Request messages in HTTP consist of a method invocation, some header
lines and an optional message body. The basic method of requesting a resource
from an HTTP server is HTTP GET. For instance, when you type the URI
http://www.wsmo.org
in your browser, it will initiate a GET request message
of the form
request method
GET
path to resource
/
HTTP version
HTTP/1.1
Host: www.wsmo.org
Thesecondline(
Host: ...
) is the header information for the GET request.
GET requests always have an empty message body. Apart from GET, some
other important request methods are:
•
HEAD: returns only the headers of what GET would return (useful for
testing);
•
PUT: to replace or create a resource;
•
DELETE: to remove a resource;
•
POST: to submit data to a resource for processing, or to manipulate an-
other resource.
An HTTP response in turn contains again the HTTP version, a status code
and, analogously to the request, headers and a message body which, in the
case of a website request, would be the respective HTML document, e.g.
HTTP/1.1 200 OK
Date: Fri, 10 Feb 2006 16:05:38 GMT
Content-Length: 1000
Content-Type: text/html
Connection: close
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN">
<html><head>
.
For further details on the two most commonly used versions of HTTP, we
refer to the respective latest RFCs 1945 (HTTP 1.0) and 2616 (HTTP 1.1).
The differences between these versions include, among other things, cache
control or keeping the socket connection alive for reuse after a response.
2.2.3 Hypertext for the Masses - HTML
In his quest for an easy-to-use layout language for the Web, Tim Berners-
Lee decided to base it on an application of Standard Generalized Markup
Language (SGML). SGML allows the definition of markup languages using a
format of text structured using tags dlimited by
<>
, of the following form:
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