docs(blog): new post about scripting with DMN

content/post/2018/07/dmn-scripting.md

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+title = "Scripting with DMN inside BPMN"
+description = ""
+date = "2018-07-13T09:00:00+01:00"
+author = "Philipp Ossler"
+categories = ["Community"]
+tags = ["DMN"]
++++
+
+In Camunda, you can use scripts at different places of a process. For example, inside a Script Task, as an execution/task listener, as a condition expression on a sequence flow or inside an input/output mapping. Usually, the scripts are written in JavaScript, Groovy or JUEL.
+
+Using the [FEEL extension](https://github.com/camunda/feel-scala), it is also possible to write scripts in FEEL (Friendly Enough Expression Language) which is a part of the DMN specification.
+
+<!--more-->
+
+# Why should I care about it?
+
+Some highlights of FEEL are:
+
+* date and time calculations
+* useful list operations (e.g. filter, projection, all/at-least-one-test)
+* a lot of built-in functions 
+* Camunda Spin integration
+
+If you already use DMN then you are more or less familiar with FEEL. So you can use this knowledge to write scripts also in BPMN. 
+
+In general, it can be nice to have only one expression language for both: BPMN and DMN. This makes it easier to understand and modify the process and the involved decisions.
+
+# Example
+
+Assuming that you have the following order process
+
+{{< figure src="order-process.png">}}
+
+
+and the data model
+
+```javascript
+class Order {
+  private String id;
+  private Date date;
+  private List<OrderItem> items = new ArrayList<OrderItem>();
+}
+
+class OrderItem {
+  private String id;
+  private double price;
+  private String status;
+  private boolean inStock;
+}
+```
+
+when you can implement the script task, the conditions and the multi-instance expression using the following FEEL expressions:
+
+* Check if all items are available:
+
+```javascript
+every item in order.items satisfies item.status = "available"
+```
+
+* Calculate the total price:
+
+```javascript
+sum(order.items.price) 
+```
+
+* Select the items to fetch (as input parameter):
+
+```javascript
+(order.items[not(isInStock)]).id
+```
+
+* Check if the processing took more than 3 days:
+
+```javascript
+now() - order.date > duration("P3D")
+```
+
+
+Note that the expressions works in both cases: if the variable `order` is a regular Java object (i.e. default serialization) and if it is a Camunda Spin JSON object. You don't need to transform the variable or use Spin in the expressions itself.
+
+# How to use it?
+
+**With the Camunda distribution**
+
+* download the JAR from [Github](https://github.com/camunda/feel-scala/releases/tag/1.5.0) (_feel-engine-plugin-1.5.0-complete.jar_) 
+* copy it to the _lib_ folder of the Tomcat server
+* add the plugin to the process engine configuration (_conf/bpm-platform.xml_)
+
+```xml
+<process-engine>
+    <plugins>
+        <!-- ... -->    
+        <plugin>
+            <class>org.camunda.feel.CamundaFeelEnginePlugin</class>
+        </plugin>
+    </plugins> 
+</process-engine>
+```
+
+**With an embedded Camunda engine**
+
+* add the extension as dependency to your project POM 
+
+```xml
+<dependency>
+  <groupId>org.camunda.bpm.extension.feel.scala</groupId>
+  <artifactId>feel-engine-plugin</artifactId>
+  <version>1.5.0</version>
+</dependency>
+```
+
+* register the plugin in your process engine configuration
+
+```xml
+<bean id="processEngineConfiguration" 
+ class="org.camunda.bpm.engine.impl.cfg.StandaloneProcessEngineConfiguration">
+    <property name="processEnginePlugins">
+        <list>
+           <!-- ... -->
+           <bean class="org.camunda.feel.CamundaFeelEnginePlugin" />
+        </list>
+    </property>
+</bean>
+```
+
+# Additional Information
+
+You can find more information about the FEEL engine, the integration in Camunda BPM and examples on [GitHub](https://github.com/camunda/feel-scala) and the [Wiki](https://github.com/camunda/feel-scala/wiki).