PRO-2016-0353
Discussion on XSD open issues
Group Name: PRO WG
Source: Qualcomm Inc., Wolfgang Granzow
Meeting Date: PRO#24.2, 2016-08-17
Agenda Item: TS-0004 / XSD
Background
• Contribution PRO-2016-0263 suggested a number of changes required to
handle <flexContainer> specializations, which may use namespace prefixes
other than “m2m:”:
– as children of <CSEBase>, <remoteCSE>, <AE> and <container> resources
– when included into primitiveContent
• At PRO#24, required corrections to TS-0004 have been agreed
• However, the decision was postponed how to update the XSD to reflect
the TS-0004 changes, simply due to lack of discussion time
• There are essentially two XML concepts suitable to address the problem:
1) use of substitution groups
2) use of wildcard elements
• This contribution reviews both concepts and proposes a solution how to
change the XSD
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Use of substitution groups
• A substitution group is a feature of XML schema that allows to
specify global elements which can replace another global
element in an XML representation
• The replaceable element is called head element of the
substitution group
• Each element of a substitution group must be derived from
the same datatype as the head element
• The inheritance model used for grouping of common and
universal attributes lends itself to the creation of substitution
groups
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Definition of substitution groups
•
The following XSD global element declarations define suitable head elements which
can be used as placeholders for a corresponding resource type
–
prefix “sg_” is used here to emphasize that each element defines a head element of a substitution
group (the name “resource” cannot be reused because it is already defined for another purpose)
<xs:element name="sg_resource" type="m2m:resource" abstract="true" />
<xs:element name="sg_regularResource" type="m2m:regularResource" abstract="true" />
<xs:element name="sg_announcedResource" type="m2m:announcedResource" abstract="true" />
<xs:element name="sg_announceableResource" type="m2m:announceableResource" abstract="true"/>
<xs:element name="sg_subordinateResource" type="m2m:subordinateResource" abstract="true" />
<xs:element name="sg_announceableSubordinateResource" type="m2m:announceableSubordinateResource" abstract="true" />
<xs:element name="sg_announcedSubordinateResource" type="m2m:announcedSubordinateResource" abstract="true" />
<xs:element name="sg_mgmtResource" type="m2m:mgmtResource" abstract="true" />
<xs:element name="sg_announcedMgmtResoure" type="m2m:announcedMgmtResource" abstract="true" />
<xs:element name="sg_flexContainerResource" type="m2m:flexContainerResource" abstract="true" />
<xs:element name="sg_announcedFlexContainerResource" type="m2m:announcedFlexContainerResource" abstract="true" />
•
Global elements defined in each resourceType-specific XSD file, need to be assigned to a
substitution group (i.e. both normal and announced resource type names:
<xs:element name="container" substitutionGroup="m2m:sg_announceableResource">
<xs:complexType>
<xs:complexContent>
<xs:extension base="m2m:announceableResource">
<xs:sequence>
…
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
</xs:element>
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Use of substitution groups
• Allows more compact representation of datatypes which
otherwise consist of long lists of references to resource types
– Example: datatype m2m:resourceWrapper
• Present definition:
<xs:complexType name="resourceWrapper">
<xs:sequence>
<xs:choice minOccurs="1" maxOccurs="1">
<xs:element ref="m2m:accessControlPolicy" />
<xs:element ref="m2m:activeCmdhPolicy" />
<xs:element ref="m2m:AE" />
…
<xs:element ref="m2m:software" />
<xs:element ref="m2m:statsCollect" />
<xs:element ref="m2m:statsConfig" />
<xs:element ref="m2m:subscription" />
</xs:choice>
<xs:element name="URI" type="xs:anyURI" />
</xs:sequence>
</xs:complexType>
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Use of substitution groups
• Redefinition of m2m:resourceWrapper based on substitution groups:
<xs:complexType name="resourceWrapper">
<xs:sequence>
<xs:choice minOccurs="1" maxOccurs="1">
<xs:element ref="m2m:sg_resource" />
<xs:element ref="m2m:sg_regularResource" />
<xs:element ref="m2m:sg_announceableResource" />
<xs:element ref="m2m:sg_announcedResource" />
<xs:element ref="m2m:sg_subordinateResource" />
<xs:element ref="m2m:sg_announcedSubordinateResource" />
<xs:element ref="m2m:sg_announceableSubordinateResource" />
<xs:element ref="m2m:sg_mgmtResource" />
<xs:element ref="m2m:sg_announcedMgmtResoure" />
<xs:element ref="m2m:sg_flexContainerResource" />
<xs:element ref="m2m:sg_announcedFlexContainerResource" />
</xs:choice>
<xs:element name="URI" type="xs:anyURI" />
</xs:sequence>
</xs:complexType>
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Use of substitution groups
• When substituting a head element in an XML
representation by some other global element, the
XSD of that global element must be known to the
schema validation tool
– There is no way to skip schema validation for undefined
elements
• Elements not found cause schema validation errors
– This means the schema of all applicable global elements
still must be made available to the XML processor for
schema validation
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Use of wildcard elements
• Wildcard elements is a feature of XML schema that allows to
include global elements with yet unspecified XSD
• The current definition of datatype m2m:primitiveContent uses
such wildcard element:
<xs:complexType name="primitiveContent">
<xs:sequence>
<xs:any namespace="http://www.onem2m.org/xml/protocols" processContents="lax" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
• processContents attribute set to “lax” means that the XML
processor will validate elements and attributes for which it can
obtain schema information, but it will not signal errors for those
it cannot obtain any schema information
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Use of wildcard elements
• The present definition of m2m:primitiveContent does not allow to
include elements with a namespace prefix other than “m2m:”
• This can be fixed as follows:
<xs:complexType name="primitiveContent">
<xs:choice minOccurs="0" maxOccurs="unbounded">
<xs:any namespace="http://www.onem2m.org/xml/protocols" processContents="lax" />
<xs:any namespace="##other" processContents="lax" />
</xs:choice>
</xs:complexType>
• In a future XSD version, the wildcard used for elements with m2m:
prefix should be replaced by explicit references to the permitted
global elements as defined in Tables 7.5.2-1 and 7.5.2-2 of TS0004.
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Proposal (1)
• Define substitution groups in CDT-commonTypes as shown on
slide 4
• Apply substitution groups
– to redefine m2m:resourceWrapper in CDT-primitiveContent as shown on
slide 6
– to include flexContainer specializations in
• CDT-CSEBase, CDT-remoteCSE, CDT-AE and CDT-container
• by adding child resource references
<xs:element ref="m2m:sg_flexContainerResource" />
(for both normal and announced types)
<xs:element ref="m2m:sg_announcedFlexContainerResource" /> (for announced types)
• In each XSD file which defines a resource type, add the
assignment of the substitution group to each global element
declaration, e.g. in CDT-container:
<xs:element name="container" substitutionGroup="m2m:sg_announceableResource">
<xs:element name="containerAnnc“ substitutionGroup="m2m:sg_announcedResource">
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Proposal (2)
• NOTE: Addition of substitutionGroup attribute needs to be
done also for resource types associated with TS-0023 (Home
Appliances)
• Redefine m2m:primitiveContent in CDT-commonTypes as
shown on slide 9 by adding wildcard choice enabling
elements with prefix other than “m2m:”
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