XSD problem

[Ratters1]

I have to elements that can appear in a XML file i recieve.

This would be valid

<a>data</a>
<b>data</a>

So would this be valid

<a/>
<b/>

This would not be valid

<a/>
<b>data</b>

Also it should be valid for both not to appear at all in the XML file who can I achieve this ??

THA

 

[tsuji]

It is not easy... What have you tried sofar? Let's say show us the more elementary stuff in place like how do you validate empty element and nonempty element?