What does discriminator used for? - nhibernate

Question

Forgive me I am a newbie in NHibernate, I found some example in hbm.xml like below.
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="test" >
<class name="test.FieldSetMapping" table="fieldsetmapping" discriminator-value="2352" lazy="false">
<id name="Id" column="fieldsetmapping_id" type="Int64">
<generator class="test.NHibernate.IdGenerator, test">
<param name="table">nextinstanceid</param>
<param name="column">next</param>
<param name="max_lo">9</param>
</generator>
</id>
<discriminator column="mapping_type" type="Int32" />
<version name="LastUpdateNumber" column="last_update_number" type="Int32" unsaved-value="-1"/>
<property name="OwnerName" column= "owner_name" type="String"/>
<component name="FieldSetDefinitionId" class="test.ObjectId">
<property name="InstanceId" column= "fieldsetdefinition_id" type="Int64"/>
</component>
<property name="OwnerTypeClassId" column= "owner_type" />
<bag name="FieldMappings" cascade="all-delete-orphan" generic="true" lazy="false">
<key column="fieldsetmapping_id" not-null="true" />
<one-to-many class="test.FieldSet.FieldMapping, test" />
</bag>
<property name="MappingHandlerClass" column="handler_class" />
</class>
<subclass name="test.EntityFieldSetMapping, test" discriminator-value="2353" extends="test.FieldSetMapping, test" lazy="false" >
<property name="TargetEntityType" type="test.Internal.NHibernate.ClassIdType, test" not-null="false">
<column name="target_entity_type"/>
</property>
</subclass>
<class ...>
...
</class>
<class ...>
...
</class>
</hibernate-mapping>
But I don't know what does discriminator mean . I check the Nhibernate Doc 5.1.6.
The <discriminator> element is required for polymorphic persistence
using the table-per-class-hierarchy mapping strategy and declares a discriminator
column of the table. The discriminator column contains marker values that tell
the persistence layer what subclass to instantiate for a particular row.A restricted
set of types may be used: String, Char, Int32, Byte, Short, Boolean, YesNo, TrueFalse.
Does it mean if the mapping_type > 2352 the NH will initialize the subclass test.EntityFieldSetMapping for the row of the table fieldsetmapping? thanks.

Answer 1

NHibernate will use the discriminator to detect which class needs to instantiate on a polymorphic scenario.
If mapping_type = 2352, it will create an instance of test.FieldSetMapping
if mapping_type = 2353, it will create an instance of test.EntityFieldSetMapping
Any other value should generate an exception.