Hi, neill
You are right. Both "minOccurs" and "use" are occurence constraints. But "minOccurs" (along with "maxOccurs") is used for element definition while "use" for attribute.
The value of the minOccurs attribute is 0 means the element is optional. An element is required to appear when the value of minOccurs is 1 or more. Also value 1 is the default.
Attributes can be declared with a use attribute to indicate whether the attribute is required or optioal or even prohibited (something like DTD). "Optional" is its default value.
Please refer to
W3C's Schema Primer for detail. Have fun with XML Schema.
Doug.