Page 53 - DCAP512_WAP_AND_WML

Unit 4: Introduction to WML

Notes
Figure 4.3
Content CGI Scripts
Web Server

Request as URL
Response
+

Content

Web Browser

 Standard Naming Model: All servers and content on the WWW are named with an Internet-
standard Uniform Resource Locator (URL).
 Content Typing: All content on the WWW is given a specific type thereby permitting web
browsers to correctly process the content based on its type.
 Standard Content Formats: All web browsers support a set of standard content formats.
These include the Hypertext Markup Language (HTML), the JavaScript scripting language,
and a large number of other formats.
 Standard Protocols: Standard networking protocols permit any web browser to interact
with any web server. The most commonly used protocol on the WWW is the Hypertext
Transport Protocol (HTTP).

This infrastructure permits user to easily reach a enormous of third party applications services.
It also permit developers to simplify create applications and content services for a large community
of clients.

The WWW protocols define three classes of servers:
 Origin Server: The server on which a given resource (content) resides or is to be created.
 Proxy: An intermediary program that acts as both a server and a client for the purpose of
making requests on behalf of other clients. The proxy typically resides between clients
and servers that have no means of direct communication, e.g., across a firewall. Requests
are either serviced by the proxy program or passed on, with possible translation, to other
servers. A proxy must implement both the client and server requirements of the WWW
specifications.
 Gateway: A server, which behaves as an intermediary for some other server. Unlike a
proxy, a gateway receives requests as if it were the origin server for the server resource.
The requesting client may not be aware that it is communicating with a gateway.

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