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From jdo-comm...@db.apache.org
Subject [Apache JDO Wiki] Updated: MetadataMappings
Date Thu, 03 Feb 2005 16:53:04 GMT
   Date: 2005-02-03T08:53:04
   Editor: MichelleCaisse
   Wiki: Apache JDO Wiki
   Page: MetadataMappings
   URL: http://wiki.apache.org/jdo/MetadataMappings

   no comment

Change Log:

------------------------------------------------------------------------------
@@ -4,7 +4,7 @@
 
 There are three inheritance patterns possible:
  *One Table - All rows in the inheritance hierarchy are stored in one table that has a superset
of the required columns plus a discriminator column to specify the class of that row.
- *Joined Tables - Each class, including the parent class, maps to its own table. The tables
are joined by their primary keys.
+ *Joined Tables (aka Vertical Inheritance) - Each class, including the parent class, maps
to its own table. The tables are joined by their primary keys.
  *Subclass Tables - each subclass maps to a table that contains columns for both the subclass
and its parent class.
 
 The inheritance strategies are mapped by use of the metadata elements <inheritance>
and <discriminator>. The following metadata cases must be tested:
@@ -20,6 +20,8 @@
 ||Nested under <inheritance>||Nested under subclass <class> element||
 || <discriminator value="value-map" column="column_name">|| <discriminator value="pick_a_value">||
 || <discriminator value="class-name" column="column_name">||n/a||
+
+When the inheritance pattern is Joined Tables, a <discriminator> element is optional.
It may be used to increase efficiency in some cases.
 
 '''Question:''' What about index element or indexed attribute of <discriminator>? These
are in the dtd, but not mentioned in Chapter18TestCoverageNotes.
 

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