Chapter 18 Working with XML

Sequence

XML-Schema elements can be constrained to appear in the same order as they are declared, this is called a sequence.

In PowerDesigner, depending on the type of sequence you need to design, you can use one of the following methods:

• If all the class attributes are defined in the sequence, you should create a class without stereotype and set the class extended attribute isSequence to true. In the following example, all attributes of class item_sequence are defined in the sequence:

<xsd:element name="item_sequence">
 <xsd:sequence>
  <xsd:element name="prodName" type="int"/>
  <xsd:element name="prodID" type="int"/>
  <xsd:element name="prodPrice" type="int"/>
 </xsd:sequence>
</xsd:element>

• If some of the class attributes do not belong to the sequence, you have to design the following construct: create a class containing the attributes belonging to the sequence and assign the <<sequence>> stereotype to this class. Create another class containing the other attributes. Select the Inner link tool in the palette and draw a link from the second class to the <<sequence>> class:
  
  
  The resulting code is the following:

<xsd:element name="PurchaseOrder">
 <xsd:sequence>
  <xsd:element name="shipTo" type="int"/>
  <xsd:element name="billTo" type="int"/>
 </xsd:sequence>
 <xsd:element name="prodID" type="int"/>
</xsd:element>

By default, inner classes are generated before attributes in a class (as defined in the Class\Template\body entry in the object language definition file). However, you can modify generation order among class attributes using the attribute migration feature. To do so, you should create an association from the parent class to the <<sequence>> class, right-click the association and select Migrate → Migrate Navigable Roles. The migrated attribute can then be moved in the list of class attributes in order to have the desired generation order.

<xsd:element name="PurchaseOrder">
 <xsd:element name="prodID" type="int"/>
 <xsd:sequence>
  <xsd:element name="shipTo" type="int"/>
  <xsd:element name="billTo" type="int"/>
 </xsd:sequence>
</xsd:element>

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