ID 352 An XML / PowerBuilder Messaging System

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ID 352An XML / PowerBuilder Messaging System

• Paul Donohue
• Technical Architect
• JP Morgan (London)
• techwave_at_pauldonohue.com

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Overview
Topics we will cover

• The AutoTrade System
• Overview of XML
• PowerBuilder and XML
• PowerBuilder and NT Services
• Summary
• Questions

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The AutoTrade System
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The AutoTrade System
Bond trading in England was old fashioned

• Deals were sent by phone or fax
• Systems did not communicate
• Data was entered many times
• Delays were common

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The AutoTrade System
Something had to be done

• A multi-bank working group investigated possible
  solutions and chose IssueLink from a vendor
  called CapitalNET.
• JP Morgan developed the AutoTrade suite of
  programs to interface with IssueLink.

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The AutoTrade System
IssueLink is a B2B bond trading system

• Browser based
• Automates workflow
• Interfaces with back office systems
• XML messaging

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The AutoTrade System
The participants
JP Morgan
Dealers
IssueLink
Clearing Systems
Other Banks
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The AutoTrade System
The technology
AutoTrade (PB)
Browser or In-house
HTTP or XML
XML
IssueLink (C)
HTTP or XML
CNTrade (C)
Browser or In-house
XML
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The AutoTrade System
There are four AutoTrade components

• All developed with PowerBuilder
• AutoTrade Server
• AutoTrade Console
• AutoTrade Administrator
• AutoTrade Support

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The AutoTrade System
What is AutoTrade Server?

• An NT Service
• Receives XML messages
• Parses XML messages
• Processes XML messages
• Sends XML messages

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The AutoTrade System
A success story

• 6 weeks development
• Runs 24 x 7
• Processed 20,000,000,000 USD in 9 months
• Quickest trade was 1 minute 8 seconds
• 25 of trades in less than 15 minutes

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Overview of XML
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Overview of XML
What is XML?

• XML Extensible Markup Language
• Uses tags like in HTML
• A format for describing structured data
• Describes data structure and content
• Separates data from its presentation

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Overview of XML
Why use XML?

• Industry standard
• Platform vendor independent
• Self describing
• Flexible
• Caters for nested repeating data

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Overview of XML
An example

• lt?xml version"1.0"?gt
• lt!--Example XML file--gt
• ltpresentation code"ID352"gt
• lttitlegtA PB / XML Messaging Systemlt/titlegt
• ltpresentergtPaul Donohuelt/presentergt
• ltaudiencegtPowerBuilder Developerslt/audiencegt
• lttimegt1330lt/timegt
• ltdategt2001-08-13lt/dategt
• lt/presentationgt

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Overview of XML
Parts of an XML document

• XML Declaration

lt?xml version"1.0"?gt lt!DOCTYPE presentation
SYSTEM DEMO.DTD"gt lt!--Example XML
file--gt ltpresentation code"ID352" gt lttitlegtA PB
/ XML Messaging Systemlt/titlegt ltpresentergtPaul
Donohuelt/presentergt ltaudiencegtPowerBuilder
Developerslt/audiencegt lttimegt1330lt/timegt ltdategt200
1-08-13lt/dategt lt/presentationgt

• Prolog

• Elements

• Attributes

• Comments

• Other Parts

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Overview of XML
Valid and well formed

• Document Type Definitions (DTDs) define rules
  about XML data
• DTDs are optional
• Well formed XML follows the basic rules of XML
• Valid XML follows the rules of the DTD
• Get your DTD correct before you code

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Overview of XML
SAX vs DOM

• Two XML interfaces
• DOM Document Object Model
• SAX Simple API for XML
• AutoTrade uses DOM

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Overview of XML
Demonstration
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PowerBuilder and XML
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PowerBuilder and XML
Why use PowerBuilder?

• Why not?
• PB can access OLE objects
• PB is good at data manipulation
• PB is good at database access

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PowerBuilder and XML
The Microsoft Redistributable XML Parser

• There are many XML parsers
• Internet Explorer includes a parser
• An OLE object
• Can be distributed royalty free
• Current version is 3
• Easy to use

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PowerBuilder and XML
How to parse an XML file

• Connect to the parser
• Load the XML file
• Walk the tree
• Process the results
• Disconnect

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PowerBuilder and XML
Parsing XML - Connecting

• Declare an OLE object variable
  oleobject iole_xml
• Connect to the XML parser
  iole_xml .ConnectToNewObject("Microsoft
  .XMLDOM")
• Set parser attributes
  iole_xml.async
  FALSE iole_xml.validateOnParse TRUE
  iole_xml.preserveWhiteSpace FALSE

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PowerBuilder and XML
Parsing XML - Loading

• Load the XML file
  iole_xml.load(filename)
• Any errors will be in the parseerror property
  iole_xml.parseerror
  .errorCode iole_xml.parseerror.reason
  iole_xml.parseerror.filepos iole_xml.parseerror.li
  ne iole_xml.parseerror.linepos iole_xml.parseerror
  .srcText

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PowerBuilder and XML
Parsing XML - Walking

• Find the root element
  lole_root iole_xml.documentElement
• Use a recursive function to walk the tree
• Arguments for the function are
• The node to process (start with the root)
• This nodes level (start with 1)
• A stack to hold node details

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PowerBuilder and XML
Parsing XML - Walking (in circles)

• Find the nodes name, type and value
  ls_node_name aole_node.nodename
  ls_node_type aole_node.nodetypestring
  ls_node_value String(aole_node.nodevalue)
• Add this nodes details to the stack
  ll_max_nodes UpperBound(ai_level) 1
  ai_xml_node_levelll_max_nodes ai_node_level
  as_xml_node_namell_max_nodes ls_node_name
  as_xml_node_typell_max_nodes ls_node_type
  as_xml_node_valuell_max_nodes ls_node_value

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PowerBuilder and XML
Parsing XML - Walking (in circles)

• Process this nodes attributes
  
• ll_max_nodes 0
• lole_node_list aole_node.attributes
• IF IsValid(lole_node_list) THEN
• ll_max_nodes lole_node_list.length
• END IF
• FOR ll_idx 0 TO ll_max_nodes 1
• lole_node lole_node_list.Item(ll_idx)
• of_process_node (ai_level 1, lole_node,
  stack)
• NEXT

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PowerBuilder and XML
Parsing XML - Walking (in circles)

• Repeat the recursion for the child elements
  lole_node_list
  aole_node.childNodes
• There is a hasChildNodes property
  lb_any_children aole_node.hasChildNodes
• But there is no hasAttributeNodes property

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PowerBuilder and XML
Parsing XML - Processing

• After parsing the XML data can be processed
• Examples
• Update the database
• Call a business rule object
• Write to a file
• Send an email

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PowerBuilder and XML
Parsing XML - Disconnecting

• Disconnect from the XML parser
  iole_xml.DisConnectObject()
• Destroy the OLE object variable
  DESTROY iole_xml

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PowerBuilder and XML
The XML DOM tree
Presentation
Code (ID352)
text (ID352)
comment (Example XML file)
Title (NULL)
text (A PB/XML Messaging System)
Presenter (NULL)
text (Paul Donohue)
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PowerBuilder and XML
Handy hints

• Record macros
• Generating XML files

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PowerBuilder and XML
Demonstration
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PowerBuilder and NT Services
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PowerBuilder and NT Services
Why use PowerBuilder?

• Why not?
• PB can generate an EXE
• PB is fairly reliable

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PowerBuilder and NT Services
How to write an NT service

• Create a timer object
• Use the NT event log
• Run the EXE as a service

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PowerBuilder and NT Services
Creating the timer object

• Standard class inherited from timing
• Add a function to initialise the service
• Add a function to finalise the service
• Add code to the timer event

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PowerBuilder and NT Services
The initialise function

• Open an invisible window
  Open (w_service)
  ll_app_handle Handle(xml_service)
  IF ll_app_handle 0 THEN
  w_service.Visible True
  END IF
• Record the start in the NT event log
• Start the timer running
  This.Start(5)

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PowerBuilder and NT Services
The finalise function

• Perform any housekeeping
  
• Record the stop in the NT event log

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PowerBuilder and NT Services
The timer event

• Stop the timer
  This.Stop()
• Perform one cycle of work
  This.of_process_a_cycle()
• Force garbage collection
  GarbageCollect()
• Restart the timer
  This.Start(5)

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PowerBuilder and NT Services
A cycle of work

• A discrete unit of work
• Should be stateless
• For an XML messaging service this might be
• Check for incoming XML files
• Parse the XML files
• Process the XML
• Generate any outgoing XML files

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PowerBuilder and NT Services
A cycle of work

• Services can not access network drives
• Services can not interact with the user
• Connect to database each cycle?
• Maintain connection between cycles?

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PowerBuilder and NT Services
The NT event log

• Use Win32 API calls to write to the event log
• RegisterEventSource() Retrieves a handle to the
  event log
• ReportEvent() Writes an entry to the event log
• DeregisterEventSource() Closes the event log
  handle

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PowerBuilder and NT Services
The nasty event log warning

• All messages are prefixed by a nasty warning
• This is because we dont have a message file

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PowerBuilder and NT Services
Message files

• The wording of events is stored in message files
• Each has a unique ID
• Messages can have placeholders
• Message files are compiled into DLLs
• PowerBuilder cant create message file DLLs
• Make a generic message file

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PowerBuilder and NT Services
Using the timer object

• Declare a global variable
  n_cst_service gnv_service
• Instantiate the object in Application Open event
  gnv_service CREATE n_cst_service
  gnv_service.of_initialise()
• Destroy the object in Application Close event
  gnv_service.of_finalise() DESTROY
  gnv_service

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PowerBuilder and NT Services
Running as a service

• Compile your application into an EXE.
• Windows NT4 Resource Kit utilities
• SRVANY run any EXE as an NT service
• SRVINSTW install an NT service

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PowerBuilder and NT Services
Using SRVINSTW Step 1

• An easy to follow wizard interface

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PowerBuilder and NT Services
Using SRVINSTW Step 2

• Select local machine

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PowerBuilder and NT Services
Using SRVINSTW Step 3

• Give your service a name

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PowerBuilder and NT Services
Using SRVINSTW Step 4

• The executable is SRVANY.EXE
• Not your Power Builder executable

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PowerBuilder and NT Services
Using SRVINSTW Step 5

• The service should be its own process

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PowerBuilder and NT Services
Using SRVINSTW Step 6

• The system account does not require a user id or
  password
• SRVANY needs to interact with the desktop

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PowerBuilder and NT Services
Using SRVINSTW Step 7

• Set the startup option to automatic
• NT will start the service when the machine boots
• With no need for a user to log on

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PowerBuilder and NT Services
Using SRVINSTW Step 8

• Press Finish to create the service

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PowerBuilder and NT Services
Configuring SRVANY

• SRVINSTW will create an registry entry for your
  service under the key
  HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services
• Add two new keys called Parameters and Enum
  under your service

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PowerBuilder and NT Services
Configuring SRVANY

• Add three string values under the Parameters
  key
• Application Your services path EXE
• AppDirectory Your services working directory
• AppParameters Any command line parameters
• Do not add any values under the Enum key
• These will be added when the service is first run

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PowerBuilder and NT Services
Controlling your service

• SRVANY uses TerminateProcess() to stop your EXE
• No application or window Close events
• Use a registry entry to request a shut down
• Check the registry each cycle
• Close the invisible window to stop your EXE

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PowerBuilder and NT Services
Handy hints

• Make your app bullet proof
• Test for memory leaks
• Reconnect lost database connections
• Write an administration utility

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PowerBuilder and NT Services
Demonstration
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Summary
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Summary
What have we learnt?

• A little about XML
• How XML can be used in a B2B system
• How to process XML with PowerBuilder
• How to write an NT Service with PowerBuilder

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Summary
Recommended reading
Title Professional XML Author Mark Birbeck et
al Publisher Wrox Press Inc ISBN 1861003110
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Summary
Recommended reading
Title Professional NT Services Author Kevin
Miller Publisher Wrox Press Inc ISBN 1861001304
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Summary
XML resources on the internet

• http//www.xml.com
• http//www.xml.org
• http//www.w3.org/xml
• http//msdn.microsoft.com/xml/default.asp

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Summary
Free downloads from Microsoft

• The Microsoft Parser other tools
  http//msdn.microsoft.com/downloads
  
• XML Notepad http//msdn.microsoft.com/xml/notepad/
  intro.asp
• Windows NT4 Resource Kit utilities
  ftp//ftp.microsoft.com /bussys/winnt/winnt-public
  /reskit/nt40/i386/

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Questions

• If you have any questions about this presentation
  or you would like a copy of the PB objects please
  email me or visit my web site.
• Email techwave_at_pauldonohue.com
• Web http//www.pauldonohue.com/techwave

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About The Author
Paul Donohue

• Paul has 15 years experience as a solution
  provider.
• He has worked with PowerBuilder since version 2
  and is a Certified PowerBuilder Developer.
• He now concentrates on XML, Java, EJB, JSP and
  other distributed technologies.