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From froehl...@apache.org
Subject cvs commit: jakarta-avalon-phoenix/src/xdocs example-configuration.xml
Date Fri, 16 Nov 2001 10:43:21 GMT
froehlich    01/11/16 02:43:21

  Added:       src/xdocs example-configuration.xml
  add doc example configuration
  Revision  Changes    Path
  1.1                  jakarta-avalon-phoenix/src/xdocs/example-configuration.xml
  Index: example-configuration.xml
  <?xml version="1.0"?>
  <!DOCTYPE document SYSTEM "dtd/document-v10.dtd">
      <title>Example Configuration</title>
        <person name="Stephen McConnell" email="mcconnell@osm.net"/>
        <person name="Gerhard Froehlich" email="g-froehlich@gmx.de"/>
      <s1 title="Introduction">
        <p>This page contains a real production example of a block
        assembly and block .xinfo description based an extract from
        a B2B Enterprise Integration and Collaboration Platform developed by 
        <a href="http://www.osm.net">OSM</a></p>.  
        <p>This example was originally a Mailing List response to a 
        some user questions!</p>
        <p>The orginal post was written by Stephen McConnell from OSM.</p>
      <s1 title="The example">
        <p>First we start with a manifest file in a jar the contains 
        a block.  The manifest contains the declaration of the path 
        to the block implementation.  This path is also used to 
        resolve the .xinfo file.  In this case the <code>.xinfo</code> 
        description will be located under 
  Manifest-Version: 1.0
  Created-By: ACME Corporation
  Name: org/apache/acme/hub/gateway/pki/PKIProcessServer.class
  Avalon-Block: true
        <p>The <code>.xinfo</code> file contains a description of a
        reasonably simple block that serves as a factory for business
        processes that handle PKI certification requests:</p>
  <?xml version="1.0"?>
        This block could be declaring several services that it supports.
        Unlike a Java interface, the service includes a version tag. So
        it's possible for a block to have several services with possibly
        different versions. If there are multiple services then just
        declare them with multiple service entries here. Phoenix will make
        sure that the class with the same name as the .xinfo file
        implements these interfaces (if it doesn't then Phoenix will
        <service name="org.apache.acme.hub.gateway.FactoryService" version="1.0" />
    So far, we have the definition of a class that supports possibly
    multiple version interfaces. But things get much more interesting, when
    we think about the services that this block requires in order to function
    properly. That's partly handled by the dependencies element and partly by
    the assembly.xml file (which I'll explain later). In the following
    dependency example there are seven "service" dependencies (i.e. 7 versioned
    interface dependencies that must be fulfilled for this block to function.
        Each dependency contains a declaration of a role name and a service 
        interface and a version that can fulfil that role. The dependency 
        does not say anything about where that service implementation should
        come from (that's the job the assembly.xml file). The role element 
        is simply the label used in the implementation of your block configure 
        method that distinguishes a particular instance of the service.
            <service name="org.apache.acme.hub.gateway.GatewayContext" version="1.0"/>
        This dependency declaration simply states that in order to function,
        this block requires a <service/> (in this case a wrapper to a CORBA
        ORB version 2.4) and that the block implementation will lookup this
        service using the "ORB" keyword.
            <service name="org.apache.acme.hub.gateway.ORBService" version="2.4"/>
        This dependency declares a requirement for a PSS (Persistent State
        Service) Storage Home.
            <service name="org.apache.acme.hub.gateway.ProcessorStorageHomeService" version="1.0"/>
        This dependency enables the block to establish a call-back to the
        block supplying the service. This block uses the Registry interface
        to publish a business process description to a higher level manager.
            <service name="org.apache.acme.hub.gateway.Registry" version="1.0"/>
        <!-- etc. -->
            <service name="org.apache.acme.hub.gateway.DomainService" version="1.0"/>
            <service name="org.apache.acme.hub.gateway.RandomService" version="1.0"/>
            <service name="org.apache.acme.service.time.TimeService" version="1.0"/>
        <p>Next is the block declaration (an extract from an <code>assembly.xml</code>
        file). This enables the declaration of WHERE the services are coming from. 
        I.e. you may have a system with many blocks and even the potential for matching
        services available from more that one block. The class attribute provides the 
        link to the <code>.xinfo</code> file and the implementation class. The
        is used a key within the <code>assembly.xml</code> file when wiring things
        E.g. the provide element references a block by its name - and declares that the 
        named block will serve as the provider of the service. The role attribute matches

        the role element in the <code>.xinfo</code> dependency declaration.</p>
        The name attribute also serves a the key to lookup a configuration element in 
        the application configuration.xml file.
  <?xml version="1.0"?>
    <!-- other assembly information here -->
    <!-- Certification Request Processor Factory -->
    <block class="org.apache.acme.pki.process.CertificationRequestServer" name="certification"
      <provide name="gateway" role="GATEWAY"/>
      <provide name="gateway" role="ORB"/>
      <provide name="gateway" role="PSS"/>
      <provide name="gateway" role="DOMAIN"/>
      <provide name="gateway" role="RANDOM"/>
      <provide name="pki" role="REGISTRY"/>
      <provide name="time" role="CLOCK"/>
    <!-- more assembly information here -->
      <s1 title="Why this seperation?"/>
        <li>It forces structure and separation</li>
        <li>It provides a way of managing possibly multiple versions of the 
            same interface in a single environment</li>
        <li>It enables explicit declaration of the source of service provision</li>
      <p>For example you can have multiple blocks providing a TimeService. 
      One of those blocks uses an external time reference while the others 
      use a local time reference. The local time block
      declare dependencies on the external source time block and is periodically
      synchronised. In this example all of the TimeService services are exposing
      the same interface, same version (i.e. same service), but the decision as to
      which service is the provider to another can  be explicitly controlled.
      While the time example is perhaps trivial, there are significant policy
      security implications related to service provider selection.</p>
        Copyright (c) @year@ The Jakarta Apache Project All rights reserved.
        $Revision: 1.4 $ $Date: 2001/11/10 21:03:57 $

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