DBStructDef :: IsA - Is structure of passed type
The function returns, whether the complex data type has exactly the type passed in sTypeName. The function returns true, when types are identical.
When calling the function with an invalid type definition or when the type definition does not refer to a complex data type, the function throws an exception.
Return value: Return value ( logical )
The function returns YES when the question was answered positively. Otherwise it returns NO.