public class Employee : GenericBaseEntity, INotifyPropertyChanged
    {
        #region Fields

        private int depNum;
        private string name;
        private long nif;
        private string email;
        private BaseCompany company;
        private FamilyType famType = new FamilyType();
        private DateTime enterDate;
        private DateTime? exitDate;
        private State eState = State.ACTIVO;
       
        #endregion

        #region Properties

        public virtual int DepNum
        {
            get { return depNum; }
            set { depNum = value; }
        }

        public virtual string Name
        {
            get { return name; }
            set { name = value; }
        }

        public virtual long Nif
        {
            get { return nif; }
            set { nif = value; }
        }

        public virtual FamilyType FamType
        {
            get { return famType; }
            set { famType = value; }
        }

        public virtual DateTime EnterDate
        {
            get { return enterDate; }
            set
            {
                enterDate = value;
                NotifyPropertyChanged("EnterDate");
            }
        }

        public virtual DateTime? ExitDate
        {
            get { return exitDate; }
            set
            {
                exitDate = value;
                NotifyPropertyChanged("ExitDate");
            }
        }

        public virtual string Email
        {
            get { return email; }
            set { email = value; }
        }

        public virtual State EState
        {
            get { return eState; }
            set { eState = value; }
        }

        public virtual BaseCompany Company
        {
            get { return company; }
            set { company = value; }
        }

        #endregion

        #region Ctors

        public Employee(){}

        public Employee(string name, long nif, DateTime ed, DateTime exd, State state)
        {
            Name = name;
            Nif = nif;
            EnterDate = ed;
            ExitDate = exd;
            EState = state;
        }

        public Employee(int depNum, string name, long nif, DateTime ed, DateTime exd, State state, FamilyType ft, string email)
            :this(name, nif, ed, exd, state)
        {
            DepNum = depNum;
            famType = ft;
            Email = email;
        }

        public Employee(int depNum, string name, long nif, FamilyType ft, DateTime ed, DateTime exd, string email, State state, BaseCompany bc)
            :this(depNum, name, nif, ed, exd, state, ft,email)
        {
            Company = bc;
        }

        #endregion

        #region INotifyPropertyChanged Members

        public event PropertyChangedEventHandler PropertyChanged;

        public virtual void NotifyPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this,
                new PropertyChangedEventArgs(propertyName));
            }

        }

        #endregion
    }

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
 
  <class name="Save.Domain.Employee, Save" table="Employees" lazy="false">
    <id name="Id" unsaved-value="-1">
      <generator class="native"/>
    </id>

    <property name="DepNum" not-null="true" />

    <property name="Name" not-null="true" />

    <property name="Nif" not-null="true" unique="true" type="long"/>

    <property name="EnterDate" not-null="true" />

    <property name="ExitDate" not-null="false"/>

    <property name="Email" not-null="false" />

    <property name="EState" not-null="true" type="Save.Domain.State, Save" lazy="false"/>
   
    <many-to-one name="FamType" not-null="true" class="Save.Domain.FamilyType, Save" column="Id_FamType" lazy="false"/>

    <many-to-one name="Company" class="Save.Domain.BaseCompany, Save" lazy="false" not-null="false" column="Id_Company" />
   
  </class>
</hibernate-mapping>

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
 
  <class name="Save.Domain.BaseCompany, Save" table="Companies" lazy="false" >
    <id name="Id" column="Id_Company" unsaved-value="-1" >
      <generator class="native" />
    </id>

    <discriminator column="COMPANY_TYPE" type="string" />
   
    <property name="Name" not-null="true" unique="true" column="CmpName"/>

    <property name="ShortName" not-null="true" column="ShName"/>

    <property name="NIPC" not-null="true" unique="true" column="NIPC"/>

    <property name="State" not-null="true" type="Save.Domain.State, Save" />
   
    <many-to-one name="Business" class="Save.Domain.BusinessField, Save" not-null="true" column="Id_BusinessField" lazy="false"/>

    <bag name="Employees">
      <key column="Id" not-null="false" />
      <one-to-many class="Save.Domain.Employee, Save" />
    </bag>
   
    <subclass name="Save.Domain.GroupCompany, Save" discriminator-value="GROUP">
     
      <bag name="ChildCompanies" cascade="none" inverse="true" lazy="false">
        <key column="Id_Parent_Company"/>
        <one-to-many class="Save.Domain.Company, Save"/>
      </bag>
     
    </subclass>
   
    <subclass name="Save.Domain.Company, Save" discriminator-value="COMPANY">
     
      <many-to-one name="ParentCompany" class="Save.Domain.GroupCompany, Save" column="Id_Parent_Company" lazy="false"/>
     
      <bag name="ChildCompanies">
        <key column="Id_Parent_Company"/>
        <one-to-many class="Save.Domain.RCCompany, Save"/>
      </bag>
     
    </subclass>

    <subclass name="Save.Domain.RCCompany, Save" discriminator-value="RC">

      <many-to-one name="ParentCompany" class="Save.Domain.Company, Save" column="Id_Parent_Company" lazy="false"/>

    </subclass>

  </class>
</hibernate-mapping>

INSERT INTO Companies(COMPANY_TYPE, CmpName, ShName, NIPC,State, Id_BusinessField, Id_Parent_Company) VALUES('Company','Empresa 01', 'EM 01', 123123123, 1, 3, NULL);