XML and Scripting Languages

By Parand Tony Darugar
2005-05-18

Acting on the rules

Each stock quote is contained within a stock_quote tag. By the time the end tag for stock_quote is reached, all of the necessary information has been stored (the stock symbol, price, and volume). Thus we can act on the rules in the stock_quote_ function:



 sub stock_quote_ {

   my $symbol = $::state::storage{'symbol'};

 

   # Grab the rules for the given stock from the rules table

   my $sth = $::state::dbh->prepare("select * from rules where symbol='$symbol'");

   $sth->execute();

 

   while (my $ref = $sth->fetchrow_hashref()) {

     my $field   = $ref->{'field'};

     my $value   = $ref->{'value'};

     

     if ($::state::storage{$field} > $::state::storage{$value}) {

       # This rule applies

       print "Rule \"$field > $value\" applies for $symbol\n";

       take_action($symbol, $ref->{'action'});

     }

   }

   $sth->finish();

 }

The applicable rules for the given stock symbol are retrieved, and the comparison is performed. If the rule applies, the take_action function is called, which in this case is simply a stub.

The complete program is available as a separate listing, as well as the schema for creating the rules table. Running the program with the original XML file produces the following output:



 Rule "price > 120.0" applies for IBM

 Taking action "buy" on stock "IBM" .

 Rule "volume > 65000000" applies for MSFT

 Taking action "sell" on stock "MSFT" .

Tutorial Pages:
» Converting XML to HTML
» Simple substitution
» Function-based substitution
» Tree-based processing
» Active XML documents
» Storing tag contents
» Retrieving the rules
» Acting on the rules
» Next steps
» Resources

First published by IBM DeveloperWorks

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