Decomposition annotation example: A value mapped to a single table that yields a single row

Mapping a value from an XML document to a single table and column pair is a simple form of mapping in annotated XML schema decomposition. This example shows the simpler case of a one to one relationship between values in a rowSet.

The result of this mapping depends on the relationship between items mapped to the same rowSet. If the values that are mapped together in a single rowSet have a one to one relationship, as determined by the value of the maxOccurs attribute of the element or the containing model group declaration, a single row will be formed for each instance of the mapped item in the XML document. If the values in a single rowSet have a one to many relationship, where one value appears only once in the document for multiple instances of another item, as indicated by the value of the maxOccurs attribute, then multiple rows will result when the XML document is decomposed.

<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>
</publications>

If you wanted the values of the <isbn> and <publicationDate> elements, as well as the title attribute, to be decomposed into the TEXTBOOKS table as follows, you need to add annotations to the declarations for these elements and attributes in the corresponding XML schema document. The annotations would specify the table and column names that each item is mapped to.

Depending on the annotation, an annotation can be specified in the schema document as an attribute or an element. Some annotations can be specified as either. Refer to the documentation for each specific annotation to determine how a particular annotation can be specified.

For the case of mapping a value to single table and column pair, you need to specify the table and column on the value being mapped. This is done using either db2-xdb:rowSet and db2-xdb:column as attributes of <xs:element> or <xs:attribute> or the <db2-xdb:rowSet> and <db2-xdb:column> children elements of <db2-xdb:rowSetMapping>. Specifying these mappings as elements or attributes are equivalent.

The following example shows how to map elements and attributes from the <textbook> element to the TEXTBOOKS table by specifying annotations as attributes.

<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="TEXTBOOKS" db2-xdb:column="ISBN"/>
            <xs:element name="author" type="xs:string" maxOccurs="unbounded"/>
            <xs:element name="publicationDate" type="xs:gYear"
                        db2-xdb:rowSet="TEXTBOOKS" db2-xdb:column="DATE"/>
            <xs:element name="university" type="xs:string" maxOccurs="unbounded"/>
          </xs:sequence>
         <xs:attribute name="title" type="xs:string" use="required"
                       db2-xdb:rowSet="TEXTBOOKS" db2-xdb:column="TITLE"/>
        </xs:complexType>
      </xs:element>
    </xs:sequence>
  </xs:complexType>
</xs:element>

The maxOccurs XML Schema attribute has a default value of 1, and so each of the items mapped to the TEXTBOOKS rowSet has a one to one relationship with each other. Because of this one to one relationship, a single row is formed for each instance of the <textbook> element.