DEV01 - Using XML Services for Web Application Development

Christian Langanke for netlabs.org

Overview

• XML Basics and Features
• Using XML within applications
• Benefits of XML within applications
• Access Web Services with SOAP
• Sample XML service
• Sample Web Application Layout
• Local Result Cacheing

Solution Demo

XML Basics and Features

• Data Language for tranferring data between computer systems
• Meta Language for creation of application specific languages
  • Human readable data interface
  • Mixup of several XML languages possible by using distinct namespaces
• Automated syntax and data validation available by DTD or XML Schema
• Easy XHTML Generation out of XML data with XSL Schema templates

Using XML within applications

• Create own XML language for your application
  • is not visible outside your application
  • can be modified or extended at any time later for new requirements
• Create XML data with XMLWriter PHP class
• Pass either XML object or XML data string between application modules
• Generate XHTML output by XSLTProcessor PHP class
  • Use XSL templates to form XHTML output per use case
  • Use shared templates for covering similar parts of different use cases

Benefits of XML within applications

• Generic data interface between application modules
• Well-defined, human-readable data interface, very useful in debugging
• No validation required, as data does not leave the application
• Own XML language easy to maintain and extend
  • XML data can be dumped to web page for debug purposes
  • Backend changes are made to code generating the XML data
  • Frontend changes are made to the XSL template

Solution Demo

Access Web Services with SOAP

• Simple Framework to invoke object methods
• SOAP XML Language defines data envelopes
• Machine readable data interface definition for
  • Service location
  • Parameter and return value type
• No direct XML programming required with PHP
  • Language native interface available, returns PHP object tree

Sample XML service

• openligadb.de provides arbitrary league data
• Service provider supplies
  • A database
  • The XML Service interface
  • A website with web forms to maintain league data
• Registered users can create any desired league or tournament data and maintain matchday and match data
• Everybody can request any league data in the system
• Most of interest: matchdata of 1. Fußball Bundesliga
  • Match results usually available 10-20 mins after end of match
• Service access is not charged, service provider asks for sponsoring

Solution Demo

Sample Web Application Layout

• PHP class OpenLigaDB
  • Calls methods of the OpenligaDB Service (1-1 method implementation, where applicable)
  • Returns PHP object trees, returned by SOAP interface
  • Performs all SOAP handling
  • Implements local cacheing for performance/availability reasons
• PHP class LeagueData
  • Calls methods of OpenLigaDB class, passes XSL Template filename
  • Returns XHTML string
  • Includes all required result calculation
    • Matchday overview, tip player ranking, league season table
    • Creation of PDF documents (calls additional Print Framework Class)

Sample Web Application Layout

Local Result Cacheing

• implement cacheing for
  • increasing performance
  • providing at least access to cached data when service is not available
• unfortunately no cache synchronization method implemented in
  SOAP protocol (like e.g. in HTTP)
• in service access class implement internal/private cache methods, like e.g. readcache() and writecache()
• needs own way of determination if a certain piece of result data is outdated or not per access method

Ways of determining cache expiration

• guess expiration date according to the expected data modification scheme
  • The team data for a season will not change after start of session
• determine expiration date according to data from the database
  • The matchday data will not change before start of the next match
• expiration date is part of the data of each service method
  • not implemented in OpenLigaDB
• determine expiration date from additinal service method
  • OpenLigaDB provides new methods
    • GetLastChangeDateByLeagueSaison
    • GetLastChangeDateByGroupLeagueSaison

Writing the Local Cache - Tasks

• serialize PHP object tree to a string
• write sring and timestamp to cache

Writing the Local Cache - Sample

private function _writecache( $expiredate, $name,
                              $parm1, $parm2, $parm3,
                              $result)
{
$cachefilename =
  $this->_getcachefilename( $name, $parm1,
                            $parm2, $parm3);
$fh = fopen( $cachefilename, 'w');
if (!$fh) return false;

fputs( $fh, $expiredate);
fputs( $fh, "\n");
fputs( $fh, serialize( $result));
fclose( $fh);

return true;
}

Reading the Local Cache - Tasks

• read cached content and timestamp
• unserialize the content to a PHP object tree
• if cache is outdated, return nothing
  (allows caller to call the service instead)
• if cache is not outdated, return the cached object tree

Reading the Local Cache - Sample

private function _readcache( $name, $parm1, 
                             $parm2, $parm3)
{
$cachefilename =
  $this->_getcachefilename( $name, $parm1,
                            $parm2, $parm3);
$fh = fopen( $cachefilename, 'r');
if (!$fh) return false;
$expiredate = trim( fgets( $fh));
$result = unserialize( trim (fgets( $fh)));
fclose( $fh);

$expiretime  = strtotime( $expiredate);
if (time() > $expiretime)
  return false;
return $result;
}

Using the Local Cache

• readcache()

  before calling the external service, to determine if there is valid cache data available

• writecache()

  after having received new result data from the external service

Using the Local Cache

public function GetNextMatch()
{
$response = $this->_readcache( "GetNextMatch",
                               false, false, false);
if (!$response)
  {
  $params = new stdClass;
  $params->leagueShortcut = $this->LEAGUESHORTCUT;
  $response = $this->SOAPclient->GetNextMatch( $params);

  $dateexpire =
     $response->GetNextMatchResult->matchDateTime;
  $this->_writecache( $dateexpire, "GetNextMatch",
                      false, false, false, $response);
  }
return $result;
}

Solution Demo

Session Close

The End

Thank you very much for your your attention!