content model question

[Ashish Jain]

This question from IBM XML sample test.
Which one of the following XML content models is NOT allowed?
1. <!element Customer (Name, Ship-to-address?, Bill-to-address?)>
2. <!element Customer ((Name, Ship-to-address) | (Name, Bill-to-address))>
3. <!element Customer (Name, (Ship-to-address | Bill-to-address)?)>
4. <!element Customer (Name, (Ship-to-address, Bill-to-address)?)>
Can anybody answer me with good reason?
Thanks
Ashish Jain

[Mapraputa Is]

Check this link: http://www.javaranch.com/ubb/Forum31/HTML/000710.html

[Ashish Jain]

Thanks Mapraputa