Selection of the implementation technique

Selection of the implementation technique A variety of implementation techniques were considered for the GDMS Internet interface before a final selection was made. This section documents the various alternatives that were considered, and then justifies the decision that was made. PHP: Hypertext Preprocessor There is some evidence that the name of PHP originally stood for Personal Home Page tools (Lerdorf 1995). PHP is an in-page scripting language which was originally developed by Rasmus Lerdorf (Lerdorf 1995). It is now maintained and extended by a on line team of developers lead by Rasmus Lerdorf (AIMS Group, 2002). Because PHP is an in-page scripting language, the actual code to generate the HTML page viewed by the user of the web browser is actually stored within the HTML page on the servers secondary storage. A trivial example is: <html> <head> <title>PHP Test</title> </head> <body> <?php echo "Hello World<p>"; ?> </body> </html> In this example, the tag starting with ?php is the script element. The output of this script is a simple HTML page saying Hello World. The main advantage of in-page scripting is that the source code of the application is very tightly tied to the HTML presentation of the application's user interface. This means that when a user is editing a page, it is apparent what the given code does at the time that the page is created. The main disadvantage of such as system is that it requires that the users who are editing the HTML appearance of an application must also understand the scripting language in which the application is implemented. This means that graphics designers and layout consultants require further training. The application is no longer a black box in which the HTML designer can simply be a user. A second drawback is that the inclusion of the scripting within the HTML pages is that it clutters the HTML representation of the user interface, making it much harder to read. This problem is compounded by poor in-page scripting support in many HTML editors, including Mozilla. These editors discard tags they don't comprehend at the time of editing the page, and this unfortunately includes tags such as PHP. Developing the GDMS Internet interface in PHP would necessitate the users of the application running web servers with PHP modules installed (PHP Documentation Group, 2002). This is a extra level of configuration for systems administrators for little additional benefit. Active Server Pages Active Server Pages (ASP) is Microsoft's equivalent of PHP. Discussion of this alternative is deliberately brief, because ASP effectively has all the advantages and disadvantages of PHP, with the additional constraint that it only operates of Microsoft web server products running on Microsoft Operating Systems. This is not an acceptable constraint for the main target user of the application — the University of Canberra Survey Laboratory, who are not heavy users of Microsoft products. C or C++ Common Gateway Interface Another implementation alternative considered was to implement the system in either C or C++ using the Common Gateway Interface (CGI) subsystem offered by most web servers. This implementation technique has the advantage of the code for the GDMS Internet interface being in the same language as the GDMS application itself. However it has the disadvantage that parsing the incoming URLs is less trivial, as there is limited language support without the inclusion of non-standard application libraries (Kahan 2002). C and C++ are not idiomatic methods of implementing CGI applications, and this would therefore increase the difficulty of maintaining the system for future students and administrators. Perl CGI Perl was originally developed by Larry Wall in 1987 (Perl Mongers, 1999) and is now developed by a team of Open Source developers. Perl is a shell script like scripting language, although it's syntax is much more powerful than that of shell script. Perl also has world class regular expression support as a standard, well integrated, feature. Perl has well integrated CGI support built into the language itself, and is optimized for the parsing of complex strings (such as the requests which are returned by a web browser to the GDMS Internet interface via the CGI apparatus). Perl's inbuilt handling of CGI web interfaces makes it much easier to develop web applications than it would be in C or C++. For example, the following is a simple hello world application in Perl: # Import some modules use strict; use CGI; # Declare variables because strict is enabled my($result); # Setup the CGI module, and output headers $result = new CGI(); print $result->header; print "Hello World"; It can be seen from this example that Perl makes CGI programming trivial. This same program in C or C++ would have taken many more lines, and would have needed to include the hard coding of the required headers. Perl is also extremely stable, well documented, and is already installed at most sites. Conclusion After consideration of all of the factors outlined above, Perl CGI was identified as the most suitable implementation language for the GDMS Internet interface.