关于osworkflow的caller和owner问题

我现在要用osworkflow作一个待办任务列表，可是我现在无法理解流程中caller和owner的意思。。。doAction()后数据库中的caller和owner让我摸不着头脑。。能说下怎么和业务整合最好了。。。感激不尽
下面是我的例子：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE workflow PUBLIC "-//OpenSymphony Group//DTD OSWorkflow 2.6//EN"
"http://www.opensymphony.com/osworkflow/workflow_2_8.dtd">
<workflow>
     <initial-actions>
         <action name="开始工作流" id="0">
             <restrict-to>
                 <conditions type="AND">
                     <condition type="beanshell">
                         <arg name="script">true</arg>
                     </condition>
                     <condition type="class">
                         <arg name="class.name">com.opensymphony.workflow.util.OSUserGroupCondition</arg>
                         <arg name="group">UserGroup</arg>
                     </condition>
                 </conditions>
             </restrict-to>
             <pre-functions>
                 <function type="class">
                     <arg name="class.name">com.opensymphony.workflow.util.Caller</arg>
                 </function>
             </pre-functions>
             <results>
                 <unconditional-result old-status="Finished" status="Underway" step="1" owner="${caller}"/>
             </results>
         </action>
     </initial-actions>
     <steps>
         <step name="填写请假信息" id="1">
             <external-permissions>
                 <permission name="permA">
                     <restrict-to>
                         <conditions type="AND">
                             <condition type="class">
                                 <arg name="class.name">com.opensymphony.workflow.util.OSUserGroupCondition</arg>
                                 <arg name="group">UserGroup</arg>
                             </condition>
                             <condition type="class">
                                 <arg name="class.name">com.opensymphony.workflow.util.StatusCondition</arg>
                                 <arg name="status">Underway</arg>
                             </condition>
                             <condition type="class">
                                 <arg name="class.name"> com.opensymphony.workflow.util.AllowOwnerOnlyCondition</arg>
                             </condition>
                         </conditions>
                     </restrict-to>
                 </permission>
             </external-permissions>
             <actions>
                 <action name="申请" id="1">
                     <pre-functions>
                         <function type="class">
                             <arg name="class.name">com.ideamoment.function.MyApplyFunction</arg>
                         </function>
                     </pre-functions>
                     <results>
                         <unconditional-result old-status="Finished" status="Underway" step="2" owner="${caller}"/>
                     </results>
                 </action>
             </actions>
         </step>
         <step name="经理审批" id="2">
             <external-permissions>
                 <permission name="permA">
                     <restrict-to>
                         <conditions type="AND">
                             <condition type="class">
                                 <arg name="class.name">com.opensymphony.workflow.util.OSUserGroupCondition</arg>
                                 <arg name="group">ManagerGroup</arg>
                             </condition>
                             <condition type="class">
                                 <arg name="class.name">com.opensymphony.workflow.util.StatusCondition</arg>
                                 <arg name="status">Underway</arg>
                             </condition>
                         </conditions>
                     </restrict-to>
                 </permission>
             </external-permissions>
             <actions>
                 <action name="同意" id="2">
                     <pre-functions>
                         <function type="class">
                             <arg name="class.name">
                                 com.opensymphony.workflow.util.Caller
                             </arg>
                         </function>
                     </pre-functions>
                     <results>
                         <result old-status="Finished" status="Finished" step="3" owner="${caller}">
                             <conditions>
                                 <condition type="beanshell">
                                     <arg name="script">
                                         propertySet.getInt("daycount")>5
                                     </arg>
                                 </condition>
                             </conditions>
                         </result>
                         <unconditional-result old-status="Finished" status="Underway" step="4" owner="${caller}"/>
                     </results>
                 </action>
                 <action name="不同意" id="3">
                     <pre-functions>
                         <function type="class">
                             <arg name="class.name">
                                 com.opensymphony.workflow.util.Caller
                             </arg>
                         </function>
                     </pre-functions>
                     <results>
                         <unconditional-result old-status="Finished" status="Finished" step="4" owner="${caller}"/>
                     </results>
                 </action>
             </actions>
         </step>
         <step name="领导审批" id="3">
             <external-permissions>
                 <permission name="permA">
                     <restrict-to>
                         <conditions type="AND">
                             <condition type="class">
                                 <arg name="class.name">com.opensymphony.workflow.util.OSUserGroupCondition</arg>
                                 <arg name="group">LeaderGroup</arg>
                             </condition>
                             <condition type="class">
                                 <arg name="class.name">com.opensymphony.workflow.util.StatusCondition</arg>
                                 <arg name="status">Underway</arg>
                             </condition>
                         </conditions>
                     </restrict-to>
                 </permission>
             </external-permissions>
             <actions>
                 <action name="同意" id="4">
                     <pre-functions>
                         <function type="class">
                             <arg name="class.name">
                                 com.opensymphony.workflow.util.Caller
                             </arg>
                         </function>
                     </pre-functions>
                     <results>
                         <unconditional-result old-status="Finished" status="Underway" step="4" owner="${caller}"/>
                     </results>
                 </action>
                 <action name="不同意" id="5">
                     <pre-functions>
                         <function type="class">
                             <arg name="class.name">
                                 com.opensymphony.workflow.util.Caller
                             </arg>
                         </function>
                     </pre-functions>
                     <results>
                         <unconditional-result old-status="Finished" status="Underway" step="4" owner="${caller}"/>
                     </results>
                 </action>
             </actions>
         </step>
         <step name="审批完成" id="4"></step>
     </steps>
</workflow>

caller只是记录当前调用者，重要的是owner，指定下一个step的执行者。