Decomposition annotation example: Grouping multiple values mapped to a single table

In annotated XML schema decomposition, you can map multiple values from unrelated elements to the same table, while preserving the relationship between logically-related values. This is possible by declaring multiple rowSets, which are used to group related items to form a row, as shown in this example.

<publications>
  <textbook title="Programming with XML">
    <isbn>0-11-011111-0</isbn>
    <author>Mary Brown</author>
    <author>Alex Page</author>
    <publicationDate>2002</publicationDate>
    <university>University of London</university>
  </textbook>
  <childrensbook title="Children's Fables">
    <isbn>5-55-555555-5</isbn>
    <author>Bob Carter</author>
    <author>Melaine Snowe</author>
    <publicationDate>1999</publicationDate>
  </childrensbook>
</publications>

To generate the following table after decomposition, you need to ensure that values relating to a textbook are not grouped in the same row as values associated with a children's book. Use multiple rowSets to group related values and yield logically meaningful rows.

In a simple mapping scenario, where you are mapping a single value to a single table and column pair, you could just specify the table and column you want to map the value to.

This example shows a more complex case, however, where multiple values are mapped to the same table and must be logically grouped. If you were to simply map each ISBN and title to the PUBS_ISBN and PUBS_TITLE columns, without the use of rowSets, the decomposition process would not be able to determine which ISBN value belonged with which title value. By using rowSets, you can group logically related values to form a meaningful row.

The following XML schema document shows how two rowSets are defined to distinguish values of the <textbook> element from values of the <childrensbook> element.

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:db2-xdb="http://www.ibm.com/xmlns/prod/db2/xdb1"
           elementFormDefault="qualified" attributeFormDefault="unqualified">
  <xs:annotation>
    <xs:appinfo>
      <db2-xdb:table>
        <db2-xdb:name>ALLPUBLICATIONS</db2-xdb:name>
        <db2-xdb:rowSet>textbk_rowSet</db2-xdb:rowSet>
        <db2-xdb:rowSet>childrens_rowSet</db2-xdb:rowSet>
      </db2-xdb:table>
    </xs:appinfo>
  </xs:annotation>
  <xs:element name="publications">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="textbook" maxOccurs="unbounded">
          <xs:complexType>
            <xs:sequence>
              <xs:element name="isbn" type="xs:string"
                         db2-xdb:rowSet="textbk_rowSet" db2-xdb:column="PUBS_ISBN"/>
              <xs:element name="author" type="xs:string" maxOccurs="unbounded"/>
              <xs:element name="publicationDate" type="xs:gYear"/>
              <xs:element name="university" type="xs:string" maxOccurs="unbounded"/>
            </xs:sequence>
            <xs:attribute name="title" type="xs:string" use="required"
                        db2-xdb:rowSet="textbk_rowSet" db2-xdb:column="PUBS_TITLE"/>
          </xs:complexType>
        </xs:element>
        <xs:element name="childrensbook" maxOccurs="unbounded">
          <xs:complexType>
            <xs:sequence>
              <xs:element name="isbn" type="xs:string"
                     db2-xdb:rowSet="childrens_rowSet" db2-xdb:column="PUBS_ISBN"/>
              <xs:element name="author" type="xs:string" maxOccurs="unbounded"/>
              <xs:element name="publicationDate" type="xs:gYear"/>
            </xs:sequence>
            <xs:attribute name="title" type="xs:string" use="required"
                    db2-xdb:rowSet="childrens_rowSet" db2-xdb:column="PUBS_TITLE"/>
          </xs:complexType>
        </xs:element>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

Notice how the db2-xdb:rowSet mappings in each of the element and attribute declarations do not specify the name of a table, but rather the name of a rowSet. The rowSets are associated with the ALLPUBLICATIONS table in the <db2-xdb:table> annotation, which must be specified as a child of <xs:schema>.

By specifying multiple rowSets that map to the same table, you can ensure that logically related values form a row in the table.