element with attribute and string value

i would like to ask the syntax of xml schema for the following case:
<A>
<B D="abc"> b_value</B>
</A>

for B element, i use  complexType :
<complexType name="Btype">
<attribute name="D" type="string"/>
</complexType>
however, Element 'B' must have no character or element information item 
[children], because the types content type is empty.

How can I solve it? Please help. Thanks a lot.