BPML Coding Patterns

Body

Have you ever wondered how the basic programming paradigms work for ISBI's BPML dialect? In this short Introduction a few of the basic BPML coding patterns are explained:

• IF THEN
• IF THEN ELSE
• SWITCH
• FOR
• WHILE
• FOR EACH

IF THEN

Lets start with a simple IF THEN. In the ISBI Version of BPML there is a separation between the definition of the condition and the evaluation.

• In the rule the condition is defined
• In choice the rule is evaluated
• In the example below we want to check if value is set to true
• If this is the case then the action action will be executed.

<process name = "IfThen">
	<rule name="condition">
		<condition>value/text()='true'</condition>
	</rule>
	<sequence>
		<assign to="value">true</assign>
		<choice>
			<select>
				<case ref="condition" activity="IfAction" />            
			</select>         
			<sequence name="IfAction">
				<assign to="Result">IF Branch</assign>
			</sequence>
		</choice>
	</sequence>
</process>

IF THEN ELSE

The IF THEN ELSE is pretty much like the IF THEN pattern. The ELSE Branch of the code is addressed by using the negative="true" line in the select operation. It makes sure if the condition is negative another activity will be executed.

<process name = "IfThenElse">
	<rule name="condition">
		<condition>value/text()='true'</condition>
	</rule>
	<sequence>
		<assign to="value">false</assign>
		<choice>
			<select>
				<case ref="condition" activity="IfAction" />            
				<case ref="condition" negative="true" activity="ElseAction" />            
			</select>         
			<sequence name="IfAction">
				<assign to="Result">IF Branch</assign>
			</sequence>
			<sequence name="ElseAction">
				<assign to="Result">ELSE Branch</assign>
			</sequence>
		</choice>
	</sequence>
</process>

SWITCH

The switch Operation itself does not exist in the ISBI BPML Dialect. But due to the nature of the mechanics of the rule/condition choice/select you can have multiple case statements in the select operation.

• First you have to set the rule/conditiondefinitions. One for each case
• In the choice you will then use the select to pick the right activity

<process name = "SWITCH">
	<rule name="conditionOne">
		<condition>value/text()='ONE'</condition>
	</rule>
	<rule name="conditionTwo">
		<condition>value/text()='TWO'</condition>
	</rule>
	<rule name="conditionThree">
		<condition>value/text()='THREE'</condition>
	</rule>
	<sequence>
		<assign to="value">TWO</assign>
		<choice>
			<select>
				<case ref="conditionOne" activity="OneAction" />
				<case ref="conditionTwo" activity="TwoAction" />
				<case ref="conditionThree" activity="ThreeAction" />
			</select>         
			<sequence name="OneAction">
				<assign to="Result">One Piece</assign>
			</sequence>
			<sequence name="TwoAction">
				<assign to="Result">Two Pieces</assign>
			</sequence>
			<sequence name="ThreeAction">
				<assign to="Result">Three Pieces</assign>
			</sequence>
		</choice>
	</sequence>
</process>

WHILE

The WHILE coding pattern is implemented with a choice and a repeat operation. The Engine would call a certain operation over and over again until a certain condition is true

As an example we will concatenate a character to a string variable until a certain length is achieved

• First you define a condition. This example would be true as long as the length of value would be less than 10
• Next is the select/case that would execute a certain activity if the condition is true
• Inside this activity you will see the repeat step that will make sure that you jump back to the beginning of the Loop

<process name="while">
	<rule name="conditionToRun">
		<condition>string-length(value) < 10</condition>
	</rule>
	<sequence name="loopSequence">
		<assign to="value">X</assign>
		<choice name="loop">
			<select>
				<case ref="conditionToRun" activity="proceed" />
			</select>
			<sequence name="proceed">
				<assign to="currentValue" append="true" from="value/text()" />
				<assign to="value" from="concat(value,'X' )" />
				<repeat ref='loop' />
			</sequence>
		</choice> 
	</sequence>
</process>

FOR

The FOR in ISBI BPML is just a special case of the WHILE pattern. Think of it as a WHILE operation combined with a counter

In this example we do the classic

for(int i=0;i<10;i++){//Do something with i}

implementation

• The condition will be true as long as counter is less than 10
• In the sequence we start with initializing the counter to 0
• Then we start a loop that runs until the countver is 10

<process name="forLoop">
	<rule name="conditionToRun">
		<condition>counter<10</condition>
	</rule>
	<sequence name="loopSequence">
		<assign to="counter">0</assign>
		<choice name='loop'>
			<select>
				<case ref="conditionToRun" activity="proceed"/>
			</select>
			<sequence name="proceed">
				<assign to="counter" from="counter+1" />
				<assign to="currentValue" append="true" from="counter/text()" />
				<repeat ref='loop' />
			</sequence>
		</choice> 
	</sequence>
</process>

FOR EACH

The FOR EACH pattern is used to go through a list of objects and execute an operation on each of those objects.

• In our sample we first create a set of Elements with the same name as test data. This is the kind of data that you would usually get from certain Adapters that create lists
• In the next operation we calculate the number of elements that we received dynamically by using the count XPATH operation
• Here as well a counter is initialized with 0
• From there on it is a WHILE pattern that would loop until the counter would reach the number of Elements that was evaluated with the count operation

<process name="foreach">
	<rule name="conditionToRun">
		<condition>counter<numberOfMyElements</condition>
	</rule>
	<sequence name="loopSequence">
	    <!-- Test Data -->
		<assign to="input/value">one</assign>
		<assign to="input/value" append="true">two</assign>
		<assign to="input/value" append="true">three</assign>
		<assign to="input/value" append="true">four</assign>
		<assign to="input/value" append="true">five</assign>
		
		<!-- Calculate number of elements -->
		<assign to="numberOfMyElements" from="count(/ProcessData/input/value)" />
		<assign to="counter">0</assign>
		<!-- now loop over the elements -->
		<sequence name="loopSequence">
		<choice name='loop'>
			<select>
				<case ref="conditionToRun" activity="proceed"/>
			</select>
			<sequence name="proceed">
				<assign to="counter" from="counter+1" />
				<assign to="temp" from="concat('Element ' , counter)" />
				<assign to="temp" from="concat(temp, ' contains Value ')" />
				<assign to="temp" from="concat(temp, /ProcessData/input/value[number(/ProcessData/counter)])" />
				<assign to="currentValue" append="true" from="temp/text()" />
				<repeat ref='loop' />
			</sequence>
		</choice> 
	</sequence>
	</sequence>
</process>