Doubt on schema extension for String

[Rr Kumaran]

Hi All,

I am trying to represent java.util.HashMap as a schema definition assuming it can contain only java.lang.String as key and java.lang.String as value. Can anyone please tell me the difference between below 2 types of code specifically what does <extension base="xsd:string"> mean really ?

<element name="hash-map">
<complexType>
<sequence>
<element minOccurs="0" maxOccurs="unbounded" name="entry">
<complexType>
<attribute name="key" type="xsd:string"/>
</complexType>
</element>
</sequence>
<attribute name="size" type="xsd:int"/>
</complexType>
</element>

<element name="hash-map">
<complexType>
<sequence>
<element minOccurs="0" maxOccurs="unbounded" name="entry">
<complexType>
<simpleContent>
<extension base="xsd:string">
<attribute name="key" type="xsd:string"/>
</extension>
</simpleContent>
</complexType>
</element>
</sequence>
<attribute name="size" type="xsd:int"/>
</complexType>
</element>

Thanks & Regards,