Declaring ServiceData
ServiceData is a lot like xsd:element
ServiceData is a restriction of xsd:element
annotation;
name; type; minOccurs; maxOccurs; nillable; and anyAttribute
ServiceData is an extension of xsd:element
open content
modifiable
can this SDE be changed by requestor
mutability
how can requestor reason about how the SDE values change
static, constant, extendable, mutable