XML schema with recursive SimpleType

Hello All,

 

I am trying to create a XML Schema which contains an element called as
"Pre-Condition" which defines a logical expression.

For this I need to define a type "LogicalExpressionType". This type will
look something like,

 

<xs:LogicalExpressionType>

                <union memberTypes="InfixExpressionType
PrefixExpressionType"/>

</ xs:LogicalExpressionType>

 

<xs: InfixExpressionType>

                A sequence of "LogicalExpressionType" "+|-|/|.."
"LogicalExpressionType"

<xs: InfixExpressionType>

 

Is there a way of defining such type, so as to ensure a valid pre-condition
value is specified in an XML. This is recursive simpleType, is it allowed?

Is there a better way of doing it?

 

-Sucheta.