Transcript Algorithms 444

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Web Design
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Objectives
• Internet History and Protocols
• Domain Name System
• Client and Server
• Web server
• Document root
• Uniform Resource Locator
• Hypertext Transfer Protocol
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Internet History
•Origins
–ARPAnet - late 1960s and early 1970s
• Network reliability
• For ARPA-funded research organizations
•BITnet, CSnet - late 1970s & early 1980s
• email and file transfer for other institutions
–NSFnet - 1986
• Originally for non-DOD funded places
• Initially connected five supercomputer centers
• By 1990, it had replaced ARPAnet for non-military uses
• Soon became the network for all (by the early 1990s)
- NSFnet eventually became known as the Internet
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•What the Internet is:
• A world-wide network of computer networks
• At the lowest level, since 1982, all connections use TCP/IP
• TCP/IP hides the differences among devices connected to
the Internet
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Internet Protocols
• Internet Protocol (IP) Addresses
– Every node has a unique numeric address
– Form: 32-bit binary number
– New standard, IPv6, has 128 bits (1998)
• Organizations are assigned groups of IPs for their
computers
• By the mid-1980s, several different protocols had
been invented and were being used on the Internet,
all with different user interfaces (Telnet, FTP, Usenet,
mailto
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Internet Protocols
• What Is a 'Domain Name System '?
• Domain Name System, or “DNS”, is the recognized system
for assigning addresses to Internet web servers.
 The domain names keep the real technical IP address invisible
to most viewers. Example: Internet domain names
http://www.w3schools.com/
 Domain names are organized right to left, with general
descriptors to the right, and specific descriptors to the left.
“These descriptors are called "domains”
 The "top level domains" (TLD, or parent domain ) is to the far
right of a domain name. Mid level domains (children and
grandchildren) are in the middle. The machine name, often
"www", is to the far left. Levels of domains are separated by
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periods ("dots").
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Domain name conversion
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Client and Server
• Clients and Servers are programs that
communicate with each other over the
Internet
• A Server runs continuously, waiting to be
contacted by a Client
– Each Server provides certain services
– Services include providing web pages
• A Client will send a message to a Server
requesting the service provided by that server
– The client will usually provide some information,
parameters, with the request
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The World-Wide Web
Web or Internet?
 The Web uses one of the protocols, http, that runs on the
Internet. The internet is a collection of computers……….etc
Web Browsers:
Browsers are clients - always initiate, servers react (although
sometimes servers require responses). Most requests are for
existing documents, using HyperText Transfer Protocol (HTTP)
Web Servers:
 Provide responses to browser requests, either existing
documents or dynamically built documents. Browser-server
connection is now maintained through more than one requestresponse cycle. All communications between browsers and
servers use Hypertext Transfer Protocol
(HTTP)
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Web Server Operation Details
• Web servers have two main directories:
1. Document root (servable documents)
2.Server root (server system software)
• Document root “is accessed indirectly by clients”, “localHost”
– The document root is the folder where the website
files for a domain name are stored. Example:
“C:\wamp\www” Browsers : http://localhost/mylocalsite
– Virtual document root “VirtualHost” run
independent websites on the same machine
multiple
– Instead of typing http://localhost/mylocalsite every time to
view our site. just type http://mylocalsite and it works
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•
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Proxy servers
Web servers now support other Internet protocols as ftp…etc
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Web Server
• Web Server Operation : Apache (open source, fast,
reliable)
• Web Server Operation : IIS
• Operation is maintained through a program with a GUI
interface
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URL
• General form: scheme:object-address
 The scheme is the communication protocol.
 These protocols include - http, ftp, telnet, mailto.
 Different schemes use different object addresses.
 HTTP uses an object address of the following form:
//fully-qualified-domain-name/path-to-document
//www.pnu.edu.sa/ar/Pages/Home.aspx
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URLs
• Host name may include a port number, as in :80 (80 is
the default)
• URLs cannot include spaces or any of a collection of
other special characters (semicolons, colons, ...)
• The doc path may be abbreviated as a partial path
– The rest is furnished by the server configuration
• If the doc path ends with a slash, it means it is a
directory
• Example: URL path  http://www.google.com.sa/
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Multipurpose Internet Mail
Extensions (MIME) read only
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Client
Server
 The client will initiate the communication by:
- sending a request (HTTP Request) and
- the HTTP Server (or Web Server) will respond back by sending a response
(HTTP Response).
 Every time a client needs to send the request, it first establishes a TCP reliable
connection with the Web Server and then transfer the request via this connection.
 The same happens in case a Web Server needs to send back an HTTP Response to
a client.
 Any of the two parties - the client or the server can prematurely stop the transfer
by terminating the TCP connection.
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- Cookies are key/value pairs used by
websites to store state information
on the browser
- client-side cookies are often used
to remember data that is not
relevant to the server
- UI stuff; which check boxes
have been checked; past login
info; etc.
The Hypertext Transfer Protocol
 The protocol used by ALL Web communications
 Request Phase
 Form:
HTTP method domain part of URL HTTP ver.
Header fields
blank line
Message body
 An example of the first line of a request:
GET /degrees.html HTTP/1.1
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The Hypertext Transfer Protocol:
Methods
 GET - Fetch a document
 HEAD - Fetch just the header of the document
 POST - Execute the document, using the data in body
 PUT - Store a new document on the server
 DELETE - Remove a document from the server
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HTTP Request Methods
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HTTP Headers
HTTP header fields are components of the header section of request and
response messages in the Hypertext Transfer Protocol (HTTP). They define
the operating parameters of an HTTP transaction “both sender and recipient
refer to either the client or the server, depending on who sends and who
receives the entity”
The Accept request-header field can be used to specify certain media types
which are acceptable for the response
Accept: text/plain
Accept: text/*
If no Accept header field is present, then it is assumed that the client accepts
all media types
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Media types
 The asterisk "*" character is used to group media types
into ranges, with "*/*" indicating all media types and
"type/*" indicating all subtypes of that type.
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HTTP Response is in the form of- status line:
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Web Security
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XHTML
To describe the general form and layout of documents
An XHTML document is a mix of content and controls
 Controls are tags and their attributes
Tags often delimit content and specify something
about how the content should be arranged in the
document
Attributes provide additional information about the
content of a tag
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Creating XHTML documents
 XHTML editors - make document creation easier
 Shortcuts to typing tag names, spell-checker,
 WYSIWYG XHTML editors
 What you see is what you get (MS FrontPage)
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Plug-ins and Filters
Plug-ins
 Integrated into tools like word processors, effectively
converting them to WYSIWYG XHTML editors.
Filters
 Convert documents from X formats to XHTML
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CSS
 To control the style and layout of multiple Web pages
all at once.
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Plug-ins and Filters: Advantages and
Disadvantages
 Advantages of both filters and plug-ins:
 Existing documents produced with other tools can be converted to
XHTML documents.
 Use a tool you already know to produce XHTML
 Disadvantages of both filters and plug-ins:
 XHTML output of both is not perfect - must be fine tuned
 XHTML may be non-standard
 You have two versions of the document, which are difficult to synchronize
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JavaScript
 A client-side HTML-embedded scripting language
 Only related to Java through syntax
 Dynamically typed and not object-oriented
 Provides a way to access elements of HTML
documents and dynamically change them
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XML
 A meta-markup language
 Used to create a new markup language for a particular
purpose or area.
 Because the tags are designed for a specific area, they can
be meaningful.
 No presentation details.
 A simple and universal way of representing data of any
textual kind.
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PHP
A server-side scripting language
An alternative to CGI
Similar to JavaScript
Great for form processing and database access
through the Web
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Java
General purpose object-oriented programming
language
Based on C++, but simpler and safer
Focuses on applets, servlets, and JSP
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ASP.NET
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Perl, Ruby, Rails and Ajax no need
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