ACE XML in the CORBA Component Model

1
ACE XML in the CORBA Component Model

• Krishnakumar B
• kitty_at_cs.wustl.edu
• Center for Distributed Object Computing
• Department Of Computer Science
• Washington University, St.Louis, MO

2
Overview
3
Software Composition Challenges

• Context
• Component composition is increasingly common
  software paradigm
• Meta-data is needed to decouple
• Components from Components
• Components from infrastructure
• Problems
• Flat representation of meta-data
• Increased task specific glue code
• Overwhelming configuration options
• Non-standard feature descriptions
• Lack of extensibility
• Limited reuse

Display
File
Print
Database
4
CCM Provides a Partial Solution

• CCM Specifies
• Component Descriptor
• Functional Capabilities
• Assembly Descriptor
• Specify collection of components
• Specify partitions
• Specify connections
• How to specify QoS ?
• XML for Meta-data

Your Motif
5
CIAO Provides an Extended Solution Real-Time QoS
ltcomponentassemblygt ... ltpartitioninggt
ltciaocreatethreadpool id"tp_a" priority"30"
number"10"/gt
ltciaocreatethreadpoolwithlane id"tp_l"gt
ltciaoprioritylevel lane"30" number"3"/gt
ltciaoprioritylevel lane"60" number"3"/gt
ltciaoprioritylevel lane"80" number"10"/gt
lt/ciaocreatethreadpoolgt

• XML in CIAO
• Specify attributes
• Specify QoS requirements
• Specify policies

lthomeplacement id"ProximityHome"gt
ltcomponentfileref idref"Proximity"/gt
ltcomponentinstantiation id"left"gt
ltcomponentpropertiesgt ltfileinarchive
name"left-switch.cpf"/gt
ltciaousethreadpool idref"tp_a"/gt
lt/componentpropertiesgt lt/componentinstantiat
iongt ltcomponentinstantiation id"right"gt
ltcomponentpropertiesgt
ltfileinarchive name"right-switch.cpf"/gt
ltciaousethreadpoolwithlane idref"tp_l"
lane"60"/gt
lt/componentpropertiesgt lt/componentinstantia
tiongt lt/homeplacementgt
6
CIAO Support for Packaging Deployment

• Context
• Packaging Deploying COTS middleware
• Problem
• Handling dependencies
• Initialization order of inter-dependent
  components
• CIAO uses XML to
• Specify dependencies
• Setup inter-connections

Software Package
Assembly Descriptor
Component Assembly
Component Descriptor
XML
Component
Component
Component Descriptor
7
Overview of ACE XML
Default Handler

• ACE XML library
• SAX v2.0
• Events-based API
• Low memory footprint
• Fully functional Parser
• Features
• XML Namespaces
• Locator
• Filters
• DTD Validator
• Extensible
• Plug-in Content Handlers

Client
2 create
1 extend
Content Handler
3 instantiate
4 register
ACEXML Parser
6 callback
5 read
lt?xml version"1.0"?gt ltdocgt ltparagtHello,
world!lt/paragt lt/docgt
XML File
8
ACE XML Service Configurator

• ACE Service Configurator
• A framework based on the Component Configurator
  pattern
• Assembles/configures services
• Lazy binding
• Run-time or installation-time
• New ACE XML Service Configurator
• XML DTD for svc.conf file
• Implemented as a SAX ContentHandler
• Dynamically loads Parser

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ACE XML Service Configurator Example

• Classic SVC Conf
• dynamic Test_Object_1 Service_Object
  Service_Config_DLL_make_Service_Config_DLL() "2
  3"
• dynamic Test_Object_4 Service_Object
  Service_Config_DLL_make_Service_Config_DLL() "5
  6"
• dynamic Final_Object Service_Object
  Service_Config_DLL_make_Service_Config_DLL()
  "FINAL"

• XML SVC Conf
• lt?xml version'1.0'?gt
• ltACE_Svc_Confgt
• ltdynamic id"Test_Object_1" type"Service_Object"gt
  
• ltinitializer init"_make_Service_Config_DLL"
  path"Service_Config_DLL" params"2 3"/gt
  lt/dynamicgt
• ltdynamic id"Test_Object_4" type"Service_Object"gt
  
• ltinitializer init"_make_Service_Config_DLL"
  path"Service_Config_DLL" params"5 6"/gt
  lt/dynamicgt
• ltdynamic id"Final_Object" type"Service_Object"gt
• ltinitializer init"_make_Service_Config_DLL"
  path"Service_Config_DLL" params"FINAL"/gt
  lt/dynamicgt
• lt/ACE_Svc_Confgt

10
Concluding Remarks

• Goal Separate meta-data from implementation
• CIAO
• Uses XML to describe meta-data
• Uses ACE XML for the XML infrastructure needed
• ACE XML available under ACE_ROOT/ACEXML
• Parser is complete as of ACE 1.2.3
• Validator will be available in the next beta
• XML as default for svc.conf in ACE/TAO soon
• define ACE_HAS_XML_SVC_CONF 1
• CIAO Deployment Packaging
• Will be available by the end of 2002