Details
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Type:
Code Smell Detection
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Status: Active
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Resolution: Unresolved
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Message:Remove this "restriction", and consider "extension" instead.
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Highlighting:
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Default Severity:Major
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Impact:Low
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Likelihood:High
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Default Quality Profiles:Sonar way
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Targeted languages:XML
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Irrelevant for Languages:ABAP, C#, C, C++, Cobol, CSS, Flex, HTML, Java, JavaScript, Objective-C, PHP, PL/I, PL/SQL, Python, RPG, Swift, VB.Net, VB6
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Remediation Function:Constant/Issue
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Constant Cost:15min
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Analysis Scope:Main Sources, Test Sources
Description
Complex types can be restricted by means of an xs:restriction element. But restriction is anti-inheritance: the derived type has less information than the base type. Further, restriction causes the redefinition of the complex types elements and attributes, which leads to fragility in your XML schema; any change to a super type will require corresponding changes in all restricting subtypes, even those in other schemas. For example, if the base type defines a mandatory "color" element of type xs:int, the restricting type must also define a "color" element whose type cannot be, say, xs:string.
xs:extension, on the other hand, allows the extending element to inherit the base class' elements and add new ones.
Noncompliant Code Example
<xs:complexType name="Fruit>
<xs:sequence>
<xs:element name="name" type="xs:string"/>
<xs:element name="color" type="xs:string" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="UncoloredFruit">
<xs:complexContent>
<xs:restriction base="Fruit"> <!-- Noncompliant -->
<xs:sequence>
<xs:element name="name" type="xs:string"/>
</xs:sequence>
</xs:restriction>
</xs:complexContent>
</xs:complexType>
Compliant Solution
<xs:complexType name="FruitBase>
<xs:sequence>
<xs:element name="name" type="xs:string"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="ColoredFruit>
<xs:sequence>
<!-- Bottom-up design, using aggregation -->
<xs:element name="base" type="FruitBase"/>
<xs:element name="color" type="xs:string" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
