Encapsulation, Inheritance, Polymorphism In XML Schema

I found this fantastic article on this topic. The url is here -

http://www.ibm.com/developerworks/library/x-flexschema/

BPEL does not support elements defined as xsi:type="someAbstractElement" where someAbstractElement is defined as -

<xsd:complexType name="someAbstractElement" abstract="true">

This type of xml elements also cannot be validated using validate activity of BPEL. The workaround for this is mentioned in this forum post -

https://forums.oracle.com/forums/thread.jspa?threadID=463434

As per this post -

<MessageBusinessPayload xsi:type="MessagePayload.BusinessAcknowledgementType">

Needs to be:
<MessageBusinessPayload xsi:type="ns1:MessagePayload.BusinessAcknowledgementType">

Where ns1 has been defined in the xml to the correct schema!