abstract Salesperson {}

Employee extends Salesperson {
// retreived from LDAP
}

Contractor extends Salesperson {
// stored in database
}

public class Item {
   Salesperson thisSalesperson;

}

public class abstract Employee {
   private int id;
   private string name;
   private string employeeName;

   public get.../set...
}

public class Programmer extends Employee {
}

public class SalesPerson extends Employee {
   private BigDecimal commission;

   public BigDecimal getCommission();
   public void setCommission(BigDecimal comm) { ... }
}

  <class name="Employee" table="employees"  discriminator-value="employee" >

    <id name="id" column="id">
        <generator class="{your choice here}"/>
    </id>

    <!-- descriminator (must precede properties) -->
    <discriminator column="employee_type" type="string" />

    <property name="name" column="employee_name" type="string" length="32" not-null="true" access="field"/>
    <property name="employeeNumber" column="employee_number" type="string" length="32" not-null="true" access="field"/>


    <!-- programmer -->
    <subclass name="Programmer"
        discriminator-value="programmer">
    </subclass>

    <!-- Sales person -->
    <subclass name="SalesPerson"
        discriminator-value="sales">
        <property name="commission" column="commission" type="big_decimal" access="field" />
    </subclass>

   ...

<meta attribute="scope-class">public abstract</meta>