Tool Agents

A workflow process can specify that an activity requires the use of an external service, which can be invoked client-side as an APPLICATION or server-side as a PROCEDURE. The OBE server and worklist clients both use a Tool Agent to invoke such external logic.

Tool Agent Meta-data

Tool agent meta-data are used to register a tool agent in the factory. The basic tool agent factory implementation that comes with OBE reads and stores these data in the configuration file BasicToolAgentFactory.xml; entries have the following common format, with additional elements and attributes for specific tool agent types:

<!-- attributes and child elements common to all tool agents (denoted with ... below). -->
</entry>
    <tool-agent-type id="nmtoken" type="nmtoken"? threadsafe="boolean"?>
        <display-name .../>?
        <author .../>?
        <description .../>?
        <doc-url .../>?
        <formal-parameters>?
            <formal-parameter id="nmtoken" mode="IN|INOUT|OUT"?>
                <data-type>
                    <!-- One of the following types. -->
                    <basic-type type="STRING|FLOAT|INTEGER|REFERENCE|DATETIME|BOOLEAN|PERFORMER"/>?
                    <declared-type type="refid"/>?
                    <schema-type>xsd:any</schema-type>?
                    <external-reference location="document-uri" xref="fragment"? namespace="namespace-uri"? />?
                </data-type>
                <description .../>?
            </formal-parameter>
        </formal-parameters>
    </tool-agent-type>
</entry>

tool-agent-type: The tag for the particular tool agent type.
id: The unique tool agent ID, as referenced from <xpdl:Application Id="tool-agent-id"> and any embedded <xpdl:ExternalReference location="tool-agent-id">.
type: The unique ID of the tool agent which this one extends.
threadsafe: Whether the tool agent implementation is threadsafe. Default is true.
display-name: The name to be displayed in design tools.
author: The name of the author or organisation which created the entry.
description: Textual description of the entry.
doc-url: A URL to online documentation for the entry.
formal-parameters: XPDL-style formal parameter definition.
id: The formal parameter ID.
mode: The parameter mode, IN, INOUT or OUT.
data-type: The parameter's data type.
description: Standard XPDL-style parameter description.

Tool Agents

A tool agent provides a pluggable means for invoking custom procedures and external applications implemented using arbitrary technologies. When a tool is executed as a procedure, it is invoked locally by the workflow engine. When a tool is invoked as an application this is done by the worklist handler application, which can be a console application, Swing- or other GUI-, web-based or other application. Currently, tool agents support console, Swing and web-based invocation. When invoked from a web application tool agents typically either direct the browser to display content in a separate window using the browser's native content-handling capabilities or in a particular usage of the latter, use the Java Net Launch Protocol (JNLP) to launch a Java applet or application.

OBE comes with a variety of tool agents:

BSF Script: Executes a sub-program in an arbitrary BSF-supported scripting language.
Document Handler: Launches the appropriate content handler for a document.
Dummy: A dummy 'no-op' tool agent.
EJB Method: Invokes a method on an Enterprise JavaBean.
Java Application: Runs a Java application.
Java Method: Invokes a Java method.
Native Executable: Launches a native executable program.
Python Script: Executes in script in the Python programming language.
Update Process Attributes: Captures new values for process attributes from the worklist user.
Web Service: Invokes a web service.
XForm: Displays a W3C XForm.