can i use element tag of xmlbeans in xsd file with out nested of sequence tag?

for example:
<xs:schema
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlnso="http://openuri.org/easypo"
targetNamespace="http://openuri.org/easypo"
elementFormDefault="qualified">
<xs:element name="purchase-order">
<xs:complexType>
<xs:element name="customer" type="po:customer"/>
<xs:element name="date" type="xs:dateTime"/>
</xs:complexType>
</xs:element>
</xs:schema>


in above example i use element tag without sequence tag.
is it possible ?
if yes than plz provide me the way.
and what is exact use of sequence tag.