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  <title>Whiteboard notes for Chain of Responsibility
  Package</title>
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    <h1>Whiteboard notes for <em>Chain of Responsibility</em>
    Package</h1>
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  <h3>Agility</h3>

  <p>Agility is a working project name for a business applications
  framework based on the Commons Chain package.</p>

  <p>The core idea behind Agility that is as much work as possible
  should be pushed up to the business layer. Input and output is
  encapsulated with a Context object that is passed to and from
  Agility using a ProtocolAdaptor. Depending on its implementation,
  a ProtocolAdaptor may collect input and deliver output directly
  from the native platform or from a presentation framework.</p>

  <p>Agility is a Request/Response framework: for each request
  there is a response. The request is encapsulated in a Context
  object, which includes a Command identifier. Each request must
  correspond to a Command, which may also be a Chain of Commands.
  Commands may nest or chain other Commands as needed. The request
  Command is referred to as the "Action".</p>

  <p>When a request comes in from the presentation layer (or a
  presentation framework), it is received by a ProtocolAdaptor. The
  ProtocolAdaptor extracts the Action Command name from the native
  request and consults with a ContextFactory to generate a Context
  for the request. The request Context is then passed to the
  RequestProcessor for the given protocol.</p>

  <p>The RequestProcessor is a Command Chain which includes (at a
  minimum) an Action Command. Each protocol can have its own
  RequestProcessor, which may be a combination of protocol-specific
  and generic commands. The Action Command (or Chain) is the core
  unit of work for the request.</p>

  <p>The Action Command may consult business rules and the
  persistence layer to complete the unit of work. Any output or
  messages generated by the Action may be added to the Context
  under predetermined keys. If the Action completes normally, an
  attribute is added to the Context to signify the outcome of the
  Action. The value of the outcome attribute is arbitrary and
  defined by application implementing the framework ("success",
  "failure", "xylophone").</p>

  <p>When the RequestProcessor Chain completes, the Context is
  returned to the ProtocolAdaptor. Agility defines the
  ProtocolAdaptor interface but does not provide an implementation.
  If the ProtocolAdaptor is a simple Servlet, it may forward to a
  server page by munging the outcome value. If the ProtocolAdaptor
  is a presentation layer framework, it may pass the value to an
  internal mechanism that selects or assembles a server page, or
  generates a dynamic response. A ProtocolAdaptor might even
  utilitize its own "ResponseProcessor" to execute a series of
  Commands to assemble an approriate response.</p>
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