manual/new/docs/en/mapping-relations.txt

@@ -174,7 +174,7 @@ class Group extends Doctrine_Record
     }
 }
 
-class GroupUser extends Doctrine_Record 
+class GroupUser extends Doctrine_Record
 {
     public function setTableDefinition() 
     {
@@ -300,6 +300,31 @@ class Group extends Entity
 
 +++ One table, one class
 
+One-table-one-class inheritance is the only inheritance type that allows additional fields for inherited classes. As shown in the example above adding additional columns is very easy:
+
+<code type="php">
+class TextItem extends Doctrine_Record
+{
+    public function setTableDefinition() 
+    {
+        $this->hasColumn('topic', 'string', 100);
+    }
+}
+
+class Comment extends TextItem
+{
+    public function setTableDefinition() 
+    {
+        parent::setTableDefinition();    
+
+        $this->hasColumn('content', 'string', 300);
+    }
+}
+</code>
+
+
+In one-table-one-class inheritance you don't necessarily have to define additional columns, but in order to make Doctrine create separate tables for each class you'll have to make iterative setTableDefinition() calls. 
+
 In the following example we have three database tables called {{entity}}, {{user}} and {{group}}. Users and groups are both entities. The only thing we have to do is write 3 classes ({{Entity}}, {{Group}} and {{User}}) and make iterative {{setTableDefinition}} method calls.
 
 <code type="php">