World Wide Web (WWW) A Distributed Document-Based System
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World Wide Web (WWW) World Wide Web (WWW) A Distributed A Distributed Document-Based System Document-Based System Group E Ricky Tong (D-A0-1611) Eddy Leong (D-A0-1623) Dick Lei (D-A0-1658)
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World Wide Web (WWW) A Distributed Document-Based System. Group E Ricky Tong (D-A0-1611) Eddy Leong (D-A0-1623) Dick Lei (D-A0-1658). Schedule of Presentation. Overview of World Wide Web Document Model HTML DOM XML Document Type MIME Architectural Overview Discussion Time. - PowerPoint PPT Presentation
Transcript of World Wide Web (WWW) A Distributed Document-Based System
World Wide Web (WWW)World Wide Web (WWW)A Distributed Document-Based A Distributed Document-Based
SystemSystem
Group E
Ricky Tong (D-A0-1611)
Eddy Leong (D-A0-1623)
Dick Lei (D-A0-1658)
Schedule of PresentationSchedule of Presentation Overview of World Wide Web Document Model HTML DOM XML Document Type MIME Architectural Overview Discussion Time
The World Wild WebThe World Wild Web
The www is a document-based systemIt can be view as a huge distributed system
consisting of millions of clients and servers for accessing linked documents
Sever maintain collections of documents, while clients provide users an easy-to-use interface for presenting and accessing those documents
Overview of Overview of World Wide Web World Wide Web
Documents are stored as files in the servers.Servers receive request and files are sent to
the clients.The client usually interacts with the web
server through a browser.
The overall organization of the The overall organization of the WebWeb
Document ModelDocument Model
Some documents are represents are ASCII text files.
Some are expressed as a collection of script that will run on the browser automatically
Some contains references to other document such as: hyperlink.
The new document may replace the current one or open in a new browser
HTMLHTML
Most web document are expressed in HTML.
An HTML file contains small markup tags telling the Web browser how to display the page.
An HTML file must has .htm or .html extension.
Create the HTML file by simple text editor
Example of HTMLExample of HTML
<html><head><title>Title of page</title></head><body>This is my first homepage. <b>This text is bold</b></body></html>
Document Object ModelDocument Object Model
DOM provides a standard programming interface to parsed web documents.
The interface is specified in CORBA IDL.The interface is used by the scripts
embedded in a document.Scripts can be used to inspect and modify
the document that they are part of.
XML XML (Extensible Markup (Extensible Markup
Language)Language)XML is a meta-markup language providing
a format for describing structured data This facilitates more precise declarations of
content and more meaningful search results across multiple platforms.
XML ExampleXML Example
<?xml version="1.0" ?><?xml-stylesheet href="greeting.xsl" type="text/xsl"?
><message> <greeting>Hi</greeting> <target>you all</target></message>
Other Document TypesOther Document Types
There are many types of documents besides HTML and XML:
Audio: .mp3Others: .pdf, etcImage : .gif and .jpeg
MIME (Multipurpose Internet MIME (Multipurpose Internet Mail Extensions)Mail Extensions)
It was originally developed to provide information on the content of a message body that was sent as part of E-mail.
It is a specification for enhancing the capabilities of standard Internet E-mail.
It offers a simple standardized way to represent and encode a wide variety of media types for transmission via Internet mail.
The 7 Content-types defined The 7 Content-types defined in MIMEin MIME
Text - represent textual information Image - transmit still images Audio - transmit audio or voice data Video - transmit video data or moving image data Message - encapsulate an entire RFC 822 format
messages Multipart - combine several body parts of possibly
different types & subtypes Application - transmit application or binary data
CGICGI(Common Gateway Interface)(Common Gateway Interface)
It is a standard for interfacing external applications with information servers. Such as HTTP or Web severs
It is executed real time and give dynamic information.
The principle of using server-The principle of using server-side CGI programs side CGI programs
Server-side scriptServer-side script
It is executed by the server when the document has been fetched locally.
Client-side using JavaScript
<script language="JavaScript">
<!--
script code here
--!>
</script>
Server-Side Using ASP
<%
'
'script code here
'
%>
Client-side scriptClient-side script
Client-side script is just software designed to be run by the browser
AppletApplet
It is another method to pass precompiled programs to a client
Applet is a Small Java program embedded in an HTML page.
For security reasons applets cannot read or write data on client computer.
The applet can only be executed if your browser supports Java.
ServletServlet
Servlet is a precompiled program that is executed in the address space of the server.
Servlet is Java technology's answer to CGI programming.
The Web page is based on data submitted by the user.
The data change frequently.
Architectural details of a client Architectural details of a client and server in the Weband server in the Web
HTTP ConnectionsHTTP Connections
HTTP is a client-server protocol by which two machines can communicate over a TCP/IP connection.
HTTP is the protocol used for document exchange in the World-Wide-Web.
Everything that happens on the web happens over HTTP transactions.
HTTP Headers HTTP Headers
General Header Field (Use in both request and response messages)
Request Header Fields (Use in request messages only)
Response Header Fields (Used in response message only)
Entity Header Fields (Use in both request and response messages, containing the information about the entity-body of the message)
Request Header Example Request Header Example
GET /articles/news/today.asp HTTP/1.1Accept: */*Accept-Language: en-usConnection: Keep-AliveHost: localhostReferer: http://localhost/links.aspUser-Agent: Mozilla/4.0 (compatible; MSIE 5.5; Wi
ndows NT 5.0)Accept-Encoding: gzip, deflate
Response Header ExampleResponse Header Example
HTTP/1.1 200 OKServer: Microsoft-IIS/5.0Date: Thu, 13 Jul 2000 05:46:53 GMTContent-Length: 2291Content-Type: text/htmlSet-Cookie:
ASPSESSIONIDQQGGGNCG=LKLDFFKCINFLDMFHCBCBMFLJ; path=/
Cache-control: private
Web ServerWeb Server
A Web server uses the client/server model and the WWW Hypertext Transfer Protocol
Every computer on the Internet that contains a Web site must have a Web server program.
Two leading Web servers are Apache the most widely-installed Web server, and Microsoft's Internet Information Server (IIS).
Apache Server Apache Server
Processing HTTP Requests in Processing HTTP Requests in Apache ServerApache Server
1. Resolving the document reference to a local file name.
2. Client authentication. 3. Client access control. 4. Request access control. 5. MIME type determination of the response. 6. General phase for handling leftovers. 7. Transmission of the response. 8. Logging data on the processing of the request.
Server ClusterServer Cluster
The principle of TCP handoff The principle of TCP handoff
Scalable content-aware Scalable content-aware cluster of web servers cluster of web servers
Uniform Resource Identifiers Uniform Resource Identifiers (URI) (URI)
A URI (Uniform Resource Identifier) is the way to identify the points of content.
The most common form of URI is the Web page address.
A URI typically describes: The mechanism used to access the resource
The specific computer that the resource is housed in
The specific name of the resource (a file name) on the computer
Uniform Resource Locator Uniform Resource Locator (URL) (URL)
A URL contains information on how and where to access a document.
Uniform Resource Name Uniform Resource Name (URN) (URN)
A URN is an Internet resource with a name that has persistent significance.
A URN looks something like a Web page address or URL
Example: urn:def://blue_laser Both URN and URL are types of a concept called
the URI. The URN is still being developed by members of
the Internet Engineering Task Force (IETF).
Web Distributed Authoring and Versioning (WebDAV)
An extension to HTTP is called WebDAVWebDAV provides a simple means to lock a
shared document, and to create, delete, copy, and move documents from remote Web servers.
WebDAV supports a simple locking mechanism.
There are two types of write locks, the exclusive write lock, and the shared write lock.
Web Proxy Caching Web Proxy Caching
Simply caching facility of BrowserWeb-proxy cachingcache cover region or even country
hierarchical caching.
Neighbor Proxy CachingNeighbor Proxy Caching
Server Replication Server Replication
Fault tolerance in the Web is mainly achieved through client-side caching and server replication.
High availability in the Web is achieved through redundancy that makes use of generally available techniques in crucial services such as DNS.
Security Security
Most of the security issues in the Web deal with setting up a secure channel between a client and server.
The predominant approach for setting up a secure channel in the Web is to use the Secure Socket Layer (SSL)
Transport Layer Security (TLS) an update of SSL.
The position of TLS in the The position of TLS in the Internet protocol stack Internet protocol stack
TLS with mutual TLS with mutual authenticationauthentication
The EndThe End
