Untyped messages and Business Rules Engine (part 2)

This is a follow up post to my previous post on this topic. The method described in that post doesn’t seem to work when the policy is called from an orchestration. For more background information see this blogpost.

I this post I will use the exact same sample as in the previous post. These are the schemas used:

<?xml version="1.0" encoding="utf-16"?>
<xs:schema xmlns:b="http://schemas.microsoft.com/BizTalk/2003"

xmlns="http://UntypedBRE.FirstSchema"
targetNamespace='http://UntypedBRE.FirstSchema'

xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="FirstSchema">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="FirstName" type="xs:string" />
        <xs:element name="LastName" type="xs:string" />
        <xs:element name="IsJohn" type="xs:string" />
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

<?xml version="1.0" encoding="utf-16"?>
<xs:schema xmlns:b="http://schemas.microsoft.com/BizTalk/2003"
xmlns="http://UntypedBRE.SecondSchema"
targetNamespace='http://UntypedBRE.SecondSchema'
xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="SecondSchema">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="FirstName" type="xs:string" />
        <xs:element name="LastName" type="xs:string" />
        <xs:element name="IsJohn" type="xs:string" />
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

<?xml version="1.0" encoding="utf-16"?>
<xs:schema xmlns:b="http://schemas.microsoft.com/BizTalk/2003"

xmlns="http://UntypedBRE.ThirdSchema"
targetNamespace='http://UntypedBRE.ThirdSchema'

xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="ThirdSchema">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="FirstName" type="xs:string" />
        <xs:element name="LastName" type="xs:string" />
        <xs:element name="IsJohn" type="xs:string" />
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

In my sample policy I want to check the ‘FirstName’ element. If the value is equal to ‘John’ I want to fill the ‘IsJohn’ element with value ‘yes’. The policy (and single rule) should work for all the above schemas.

The problem is that mentioned schemas belong to a different namespace and have a different rood node, hence in BizTalk terms have a different message type. Because XML schemas facts in the BRE are by default tightly coupled to a specific schema the consequence is that those facts can only operate on a single type of message.

In order to make this generic you have to do the following:

1. Add one of the schemas to the Facts Explorer in the BRE

2. Make the schema general

As you can see the Document Type resembles the type of the schema I added. To make this generic I change this value to ‘Microsoft.XLANGs.BaseTypes.Any’. This will make sure that if I use a fact from this schema in a rule it will not be typed to this schema but will be generic:

3. Create the rule

In this step I create the rule. The facts will be filled in later.

4. Modify the XML facts

In the rule I need to evaluate the ‘FirstName’ fact and optionally set the ‘IsJohn’ fact. Because I want this to work on all schemas I need to define the facts in a generic way. If I click on the ‘FirstName’ fact I can see the xpath statements that point to this fact in the property pane:

The ‘Xpath Field’ and ‘Xpath Selector’ properties are directly referring to ‘FirstSchema’ root node and namespace. I change the values to make them generic also:

Note that I’m using ‘self::node()’ here. I described this trick before here.

Now the XML fact is no longer pointing to a specific namespace or root node. It just points to a ‘FirstName’ node somewhere in Xml message.

There are of course other possible values for ‘Xpath selector’ and ‘Xpath Field’ to solve this. It all depends on the schemas. If for example the facts you need all have the same parent node you can make the ‘Xpath selector’ select the parent node and the ‘Xpath Field’ select the ‘FirstName’ element.

I do the same for the fact I want to update in the action of the rule:

5. Complete the rule by adding the facts

Finally I can drag the XML facts from the Facts Explorer to my rule to complete the condition and create a new action. Like this:

You can see that the both the condition and the action are not referring (anymore) to any specific schema  but instead to any schema that has ‘FirstName’  and ‘IsJohn’  elements.

Testing the rule with instances from two different schemas shows that this works:

One thing to note about this is that the way I changed the xpath statements for the Xml facts comes with a performance penalty. Using things like ‘//*…….’.  will make the engine go through the whole xml tree which is less efficient then using the original full xpath statement. So if performance is a strict requirement be careful using techniques like these.

Another thing is that I do not check for the existence of the nodes first. The policy will crash when an message is processed that does not contain on of the nodes used in the rule.