World Wide Web (WWW) A Distributed Document-Based System

transcript

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 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