Defines document titles </Hn> Defines headers (n is an integer) Figure 28.6 HTML title and header tags. <CENTER> </CENTER> Centered </BR> Line break Figure 28.7 HTML dataflow tags. </OL> Ordered list </UL> Unordered list </LI> An item in a list Figure 28.8 HTML list tags. Image <IMG> </IMG> Defines an image Hyperlink Defines an address (hyperlink) Executable contents <APPLET> </APPLET> Document is an applet Figure 28.9 HTML image, hyperlink, and Applet tags. 2. Programming for dynamic documents Consider a dynamic document example that involves collection of the time stamp on the server to map logs obtained in the client to the time it was send from the server. Here the information is dynamic and changes from moment to moment. In this scenario, the client can request the server to run the sys- tem command that generates the data and sends the results to the client. The dynamic documents can be handled by the common gateway interface (CGI) technology that contains a set of rules and terms that allows the pro- grammer to define how the dynamic document should be written, how input Web Communication data should be supplied to the program, and how the output result should be used. The term common in CGI indicates that the set of rules are common to any language like C, C++, Unix Shell, or Perl. The term gateway in CGI indicates that a CGI program is a gateway used to access other resources like databases and graphic packages. The term interface in CGI indicates that there exists a set of predefined terms like variables and cells that can be used in any CGI program. Codes that are written in one of the languages that support CGI are known as a CGI program. A programmer can write a simple CGI program by encoding a sequence of thoughts in a program using the syntax of any of the languages specified above. 3. Programming for active documents The active documents are compressed at the server site SO that when the client requests the active document, the server sends a document copy in the form of a byte code. Thus the docu