23、Camunda DMN决策初探

Camunda DMN 决策

Camunda 中使用DMN决策

Camunda 支持DMN1.3版本，在BPMN业务活动流程中，可通过业务规则任务调用DMN决策。DMN决策目的是想把业务代码和决策进行解耦，使决策分析人员只需关心决策即可。

Camunda DMN案例

通过幼儿园学生年龄age和身高height分配不同的班级，决策表可随时修改。校长审核时向流程中传递决策表所需要的流程变量age、height。流程径流决策表后自动提交到相关班级老师审批。

创建学生分配班级审核流程

<bpmn:process id="Process_DMN2" name="幼儿园班级选择-决策表" isExecutable="true"> <bpmn:startEvent id="StartEvent_1"> <bpmn:outgoing>Flow_1kmfo50</bpmn:outgoing> </bpmn:startEvent> <bpmn:sequenceFlow id="Flow_1kmfo50" sourceRef="StartEvent_1" targetRef="Activity_09yea1p" /> <bpmn:userTask id="Activity_09yea1p" name="校长审核" camunda:assignee="admin"> <bpmn:incoming>Flow_1kmfo50</bpmn:incoming> <bpmn:outgoing>Flow_1ohj7ez</bpmn:outgoing> </bpmn:userTask> <bpmn:sequenceFlow id="Flow_1ohj7ez" sourceRef="Activity_09yea1p" targetRef="Activity_0lqrqvr" /> <bpmn:businessRuleTask id="Activity_0lqrqvr" name="调用决策表,判断哪个班" camunda:resultVariable="dmnResult" camunda:decisionRef="MyDMN02" camunda:mapDecisionResult="singleEntry"> <bpmn:incoming>Flow_1ohj7ez</bpmn:incoming> <bpmn:outgoing>Flow_0jaf2y3</bpmn:outgoing> </bpmn:businessRuleTask> <bpmn:exclusiveGateway id="Gateway_0c6380i"> <bpmn:incoming>Flow_0jaf2y3</bpmn:incoming> <bpmn:outgoing>Flow_0x76o56</bpmn:outgoing> <bpmn:outgoing>Flow_03o01yz</bpmn:outgoing> <bpmn:outgoing>Flow_16wz3jj</bpmn:outgoing> </bpmn:exclusiveGateway> <bpmn:sequenceFlow id="Flow_0jaf2y3" sourceRef="Activity_0lqrqvr" targetRef="Gateway_0c6380i" /> <bpmn:sequenceFlow id="Flow_0x76o56" sourceRef="Gateway_0c6380i" targetRef="Activity_1rh5001"> <bpmn:conditionExpression xsi:type="bpmn:tFormalExpression">${dmnResult==2}</bpmn:conditionExpression> </bpmn:sequenceFlow> <bpmn:sequenceFlow id="Flow_03o01yz" sourceRef="Gateway_0c6380i" targetRef="Activity_1c2dxw0"> <bpmn:conditionExpression xsi:type="bpmn:tFormalExpression">${dmnResult==3}</bpmn:conditionExpression> </bpmn:sequenceFlow> <bpmn:sequenceFlow id="Flow_16wz3jj" sourceRef="Gateway_0c6380i" targetRef="Activity_0ol6tq7"> <bpmn:conditionExpression xsi:type="bpmn:tFormalExpression">${dmnResult==1}</bpmn:conditionExpression> </bpmn:sequenceFlow> <bpmn:userTask id="Activity_0ol6tq7" name="幼儿园小班" camunda:assignee="admin"> <bpmn:incoming>Flow_16wz3jj</bpmn:incoming> <bpmn:outgoing>Flow_13fe5iy</bpmn:outgoing> </bpmn:userTask> <bpmn:userTask id="Activity_1rh5001" name="幼儿园中班" camunda:assignee="admin"> <bpmn:incoming>Flow_0x76o56</bpmn:incoming> <bpmn:outgoing>Flow_0pero7b</bpmn:outgoing> </bpmn:userTask> <bpmn:userTask id="Activity_1c2dxw0" name="幼儿园大班" camunda:assignee="admin"> <bpmn:incoming>Flow_03o01yz</bpmn:incoming> <bpmn:outgoing>Flow_1k33ruz</bpmn:outgoing> </bpmn:userTask> <bpmn:endEvent id="Event_09q2lsr"> <bpmn:incoming>Flow_13fe5iy</bpmn:incoming> </bpmn:endEvent> <bpmn:sequenceFlow id="Flow_13fe5iy" sourceRef="Activity_0ol6tq7" targetRef="Event_09q2lsr" /> <bpmn:endEvent id="Event_0r6p8f2"> <bpmn:incoming>Flow_0pero7b</bpmn:incoming> </bpmn:endEvent> <bpmn:sequenceFlow id="Flow_0pero7b" sourceRef="Activity_1rh5001" targetRef="Event_0r6p8f2" /> <bpmn:endEvent id="Event_1icnobe"> <bpmn:incoming>Flow_1k33ruz</bpmn:incoming> </bpmn:endEvent> <bpmn:sequenceFlow id="Flow_1k33ruz" sourceRef="Activity_1c2dxw0" targetRef="Event_1icnobe" /> </bpmn:process> 

创建决策

<decision id="MyDMN02" name="幼儿园班级判断"> <decisionTable id="DecisionTable_1hc3c2q" hitPolicy="COLLECT" aggregation="MAX"> <input id="InputClause_1vbdtew" label="年龄" biodi:width="192" camunda:inputVariable="age"> <inputExpression id="LiteralExpression_1hfef7m" typeRef="integer" /> </input> <input id="InputClause_13b3rh9" label="身高" camunda:inputVariable="height"> <inputExpression id="LiteralExpression_1hr6wum" typeRef="double"> <text></text> </inputExpression> </input> <output id="OutputClause_1poncf1" label="选择班级" name="clsName" typeRef="integer" /> <rule id="DecisionRule_1029rws"> <description>大于3岁并且身高高于70cm，可上幼儿园小班</description> <inputEntry id="UnaryTests_1e4z08i"> <text>&gt;3</text> </inputEntry> <inputEntry id="UnaryTests_0t3xek6"> <text>&gt;70</text> </inputEntry> <outputEntry id="LiteralExpression_0l1lpg2"> <text>1</text> </outputEntry> </rule> <rule id="DecisionRule_023jo7u"> <description>大于等于5岁并且身高高于95cm，可上幼儿园中班</description> <inputEntry id="UnaryTests_0jeku2j"> <text>&gt;=5</text> </inputEntry> <inputEntry id="UnaryTests_1w0xn25"> <text>&gt;=96</text> </inputEntry> <outputEntry id="LiteralExpression_0qkdpew"> <text>2</text> </outputEntry> </rule> <rule id="DecisionRule_09zimc1"> <description>大于7岁并且身高高于120cm，可上幼儿园大班</description> <inputEntry id="UnaryTests_1852h8n"> <text>&gt;7</text> </inputEntry> <inputEntry id="UnaryTests_1e7igfg"> <text>&gt;120</text> </inputEntry> <outputEntry id="LiteralExpression_1o3xlmi"> <text>3</text> </outputEntry> </rule> </decisionTable> </decision> 

开启流程，校长审核时，指定决策表中所需要的变量

通过决策表后，当前学生到幼儿园中班老师审批

注意

1. 决策表中的决策逻辑完全可由流程变量+流程网关实现，用决策可把流程业务活动和业务决策信息解耦，业务决策人员只需关系决策即可；决策信息可随时进行调整，不需发布流程和代码；
2. BPMN 业务流程活动可通过 “业务规则任务” (Business Rule Task) 调用DMN决策表逻辑；调用的DMN决策表策略结果可输出到流程变量中，流程中通过此变量进行流程流转；
3. 决策DMN文件中只有决策表、文本表达式参与到决策引擎运算，其它输入源、知识源和知识模型等符号会被camunda DMN引擎忽略；
4. 决策DMN文件中可有多个决策表、其他符号组成决策需求图(DRG)。决策需求图(DRG)为决策领域建模，展示相关的最重要的元素和它们的依赖关系。建模的元素是决策（decisions）,输入数据（input data）,和知识源（knowledge sources）这些只是告诉决策人员，当前决策表需要的输入条件信息，不与DMN引擎计算。
5. 决策表里面可以有多个输入源，输入源可以选择表达式或计算流程变量，作为输入值，条件对这个表达式进行判断，满足条件时，当前决策符合。
6. 

参考资料