HOPEX UML : HOPEX XML Schemas : More UML Features : Other Features Related to Inheritance : Overloading Attributes
   
Overloading Attributes
The concept of overloading is common in object-oriented programming, but it usually only applies to operation methods. It is a mechanism for defining additional properties on an inherited attribute.
To overload an attribute in the schema editor:
1. Select the attribute in the navigator.
2. In its properties dialog box, select the Complements tab.
3. Select Overloaded Attribute parameter and click the Connect button.
The Query dialog box appears:
4. Select List of attributes to be overloaded.
5. In the results list, select the attribute and click Connect.
UML modeling
To overload an attribute in a diagram:
1. Open the properties dialog box for the inherited class.
2. In the Attribute tab, select the attribute to be overloaded, then click the Properties button.
3. Proceed as described above.
When a class inherits another class, it is possible to modify the inherited attributes.
This overloading (modifying the inherited attributes) is used to define the specific characteristics of the attribute in the child class.
All properties of the attribute that are not redefined in the child class remain identical to those of the parent class.
Result
In the diagram below, the "Web address" attribute is overloaded in the "Web Author" class.
 
Diagram
Diagram
 
*Restriction: The overloaded attribute must be an attribute inherited from an ancestor class.
*The type of the overloading attribute is not defined, as the type is considered to be that of the overloaded attribute (STRING).
Example
The "Author" class has a "Web Address" attribute. This attribute is overloaded in the "Web Author" class. The difference between the original version and the overloaded version of the attribute is its multiplicity: in the first case the attribute is optional, and in the second case it is required.
XSD
<xsd:ComplexType name="Author">
<xsd:attribute name="lastname" type='xsd:string' use="required"/>
<xsd:attribute name="firstname" type='xsd:string' use="required"/>
<xsd:attribute name="webaddress" type="xsd:string" />
</xsd:complexType>
<xsd:complexType name="WebAuthor">
<xsd:simpleContent>
<xsd:restriction base="Author">
<xsd:attribute name="lastname" type='xsd:string' use="required"/>
<xsd:attribute name="firstname" type='xsd:string' use="required"/>
<xsd:attribute name="webaddress" type="xsd:string" use='required' />
</xsd:restriction>
</xsd:simpleContent>
</xsd:complexType>