WWWP Exam:

Mid-term

1. [30%] A common WWW practice is for a user to click on an anchor in a page shown in a browser and, shortly later, a form appears. The user then types information (e. g., a search request) into the form and selects a submit button. After a few moments, a page of information (e. g., search results) is displayed, apparently in response to the data entered into the form.

   What , exactly, is going on here? Answer the question by addressing the following two points. Refer to Figure 1 in writing your answer.

   

   Figure 1:
   WWW Architecture

   
   
   
   1. Trace the flow of messages/data that occurs in this scenario.

   2. What protocols or communication conventions are used in those parts of Figure 1 that are labeled Internet and CGI ? Give brief, but plausible, examples of what a message at the highest level of protocol or convention would look like at those two points (e. g., not the IP level).

2. [30%] Write comments for each executable statement in the following Perl program; explain briefly, but comprehensively, what each statement is doing. (You may write on this page.)

   #!/usr/local/bin/perl
   #
   $qs = "name_var=%28+john+++smith%29&submitbutton=submit";
   
   #DEPLUS
   $qs =~ tr/\+/ /s;
   
   #TOKENIZE
   @av_strings = split(/&/, $qs);
   
   #SPLIT
   foreach $avs (@av_strings) {
   
   @av_pair = split(/=/, $avs);
   
   $attr_value{$av_pair[0]} = $av_pair[1];
   }
   
   #DECODE
   foreach $key (keys %attr_value) {
   
   $key =~ s/%(..)/pack("c",hex($1))/ge;
   
   $attr_value{$key} =~ s/%(..)/pack("c",hex($1))/ge;
   }
   

   
   
   
3. [40%] Explain briefly (3 - 4 sentences) the following concepts, within the context of Java. Illustrate each with a brief segment of syntactically-correct Java code.

   1. class

   2. method

   3. object

   4. inheritance

   5. method override

   6. event

   7. package

   8. Java.awt.Component

Signed: __________________________

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