What Does Url Stand For - URL - UNIFORM  RESOURCE  LOCATOR

•   Uniform Resource Locator (URL), uniquely identify resources on the  Internet

•  URL provides information about its location on the Web

•   When a user enters URL, browser forms a request message and sends it to the Server.

•   Web server retrieves the requested URL=URL - UNIFORM  RESOURCE  LOCATOR

•   Web browser renders the response in HTML or appropriate format.

•  Format : http://www.domain_name/filename

• Example : http://www.cs.hello.org/index.html
•   The URL defines four parts - Method, Host computer, Port, and Path.

o   Method: The method is the protocol used to retrieve the Document from a server. For example, HTTP.

o   Host: The host is the computer where the information is stored, and the computer is given an alias name. Web pages are mainly stored in the computers and the computers are given an alias name that begins with the characters "www". This field is not mandatory.

o   Port: The URL can also contain the port number of the server, but it's an optional field. If the port number is included, then it must come between the host and path and it should be separated from the host by a colon.

o   Path: Path is the pathname of the file where the information is stored. The path itself contain slashes that separate the directories from the subdirectories and files.

URL- UNIFORM  RESOURCE  LOCATOR PATHS

•   The path of the document for a http protocol is same as that for a document or file or a directory in a client.

•   In Unix the path components are separated by forward slashes (/) and in windows backward slashes (\).

•   But an URL need not include all the directories in the path.

•   A path which includes all the directories is a complete path, else it is a partial path.

URI - Uniform Resource Identifiers

•   URI is a string that identifies resources such as document, image, service, etc.

•   It is of the form scheme:scheme-specific

•   Scheme identifies a resource type, such as mailto for mail address, file for file name, etc. and scheme-specific is a resource identifier.

•   Example is mailto: [email protected]

•   URI identifies a resource, whereas URL is used to locate a resource.

WEB DOCUMENTS OF URL

Static Documents

•   Static documents are fixed-content documents that are created and stored in a server.

•   The client can get a copy of the document only.

•   In other words, the contents of the file are determined when the file is created, not when it is used.

•   Of course, the contents in the server can be changed, but the user cannot change them.

•   When a client accesses the document, a copy of the document is sent.

•   The user can then use a browser to see the document.

•   Static documents are prepared using one of several languages:

1. HyperText Markup Language (HTML)

2. Extensible Markup Language (XML)

3. Extensible Style Language (XSL)

4. Extensible Hypertext Markup Language (XHTML).

Dynamic Documents

•   A dynamic document is created by a web server whenever a browser requests the document.

•   When a request arrives, the web server runs an application program or a script that creates the dynamic document.

•   The server returns the result of the program or script as a response to the browser that requested the document. 

•   Because a fresh document is created for each request, the contents of a dynamic document may vary from one request to another.

•   A very simple example of a dynamic document is the retrieval of the time and date from a server.

•   Time and date are kinds of information that are dynamic in that they change from moment to moment.

•   Dynamic documents  can be retrieved using one of several scripting languages:

1. Common Gateway Interface (CGI)

2. Java Server Pages (JSP)

3. Active Server Pages (ASP)

4. ColdFusion

Active Documents

•   For many applications, we need a program or a script to be run at the client site. These are called active documents.

•   For example, suppose we want to run a program that creates animated graphics on the screen or a program that interacts with the user.

•   The program definitely needs to be run at the client site where the animation or interaction takes place.

•   When a browser requests an active document, the server sends a copy of the document or a script.

•   The document is then run at the client (browser) site. 

•   Active documents can be created using one of several languages:

1. Java Applet – A program written in Java on the server. It is compiled                     and ready to be run. The document is in bytecode format.

2. Java Script - Download and run the script at the client site.