Idenitifying a need for an alternative way to include XPathexpressions in UBL documents

[Stephen D Green <stephengreenubl@gmail.com>]

[I submit this comment now because it does not so much concern the

additional features added to UBL in in-progress version 2.1 so much

as existing features of UBL 2.0 so it seemed less appropriate to wait

for the UBL 2.1 second public review.]

 

In UBL 2.x there is an XPath BBIE which allows an XPath expression
to be included in a UBL document. It is used in the DocumentReference.

Currently it has one deficiency which might introduce unexpected errors:
It does not include any supplementary components to allow the version of
XPath to be declared. Users of documents which include DocumentReference
would need to make clear which version of XPath is used and possibly
would need to make this clear for future understanding of those documents.
The use of XPath without version information may result in different
results for the same expression and the same target document with the
same XPath evaluation tools depending on which XPath version is assumed.

There is also to some extent a deficiency in that bindings of namespaces
to prefixes in the XPath expression must be determined before the XPath
expression can be evaluated but if XPath 2.0 is assumed then there may
be built-in assumptions made in the way tools evaluate a default namespace
without a prefix. The absence of clear guidance on how tools must determine
these bindings can leave room for unexpected results and lack of assurance
of correct results in future interpretation of the document.

I suggest that improvements would be possible to some extent if a new
ABIE were introduced to allow implementers to replace the use of this
XPath BBIE with the use of rather more rigorous XQuery expressions which
are able to include XPath 2.0(+) expressions (a subset of XQuery 1.0+)
but are less ambiguous with regard to namespace bindings and versions.

Here is a suggestion for inclusion of such an ABIE, although of course
(defined here using suggested additions to the schema modules, but of
course this would be more properly defined using the model). It does
not require the addition of any new qualified datatypes (but one of two
alternatives suggested is to add a new codelist).

<!-- ------------------------------- -->
<!-- UBL-CommonAggregateComponents-2 -->
<!-- ------------------------------- -->

<!-- ... -->
<!-- addition -->
    <xsd:element name="XmlExpression" type="XmlExpressionType"/>

<!-- ... -->
<!-- extension -->
    <xsd:complexType name="DocumentReferenceType">
        <xsd:sequence>
            <xsd:element maxOccurs="1" minOccurs="1" ref="cbc:ID"/>
            <xsd:element maxOccurs="1" minOccurs="0" ref="cbc:CopyIndicator"/>
            <xsd:element maxOccurs="1" minOccurs="0" ref="cbc:UUID"/>
            <xsd:element maxOccurs="1" minOccurs="0" ref="cbc:IssueDate"/>
            <xsd:element maxOccurs="1" minOccurs="0" ref="cbc:IssueTime"/>
            <xsd:element maxOccurs="1" minOccurs="0" ref="cbc:DocumentTypeCode"/>
            <xsd:element maxOccurs="1" minOccurs="0" ref="cbc:DocumentType"/>
            <xsd:element maxOccurs="unbounded" minOccurs="0" ref="cbc:XPath"/>
            <xsd:element maxOccurs="1" minOccurs="0" ref="cbc:LanguageID"/>
            <xsd:element maxOccurs="1" minOccurs="0" ref="cbc:LocaleCode"/>
            <xsd:element maxOccurs="1" minOccurs="0" ref="cbc:VersionID"/>
            <xsd:element maxOccurs="1" minOccurs="0" ref="cbc:DocumentStatusCode"/>
            <xsd:element maxOccurs="unbounded" minOccurs="0" ref="cbc:DocumentDescription"/>
            <xsd:element maxOccurs="1" minOccurs="0" ref="cac:Attachment"/>
            <xsd:element maxOccurs="1" minOccurs="0" ref="cac:ValidityPeriod"/>
            <xsd:element maxOccurs="1" minOccurs="0" ref="cac:IssuerParty"/>
            <xsd:element maxOccurs="1" minOccurs="0" ref="cac:ResultOfVerification"/>
<!-- addition -->
            <xsd:element maxOccurs="1" minOccurs="0" ref="cac:XmlExpression"/>
        </xsd:sequence>
    </xsd:complexType>

<!-- ... -->

<!-- addition -->
    <xsd:complexType name="XmlExpressionType">
        <xsd:sequence>
            <xsd:element maxOccurs="1" minOccurs="1" ref="cbc:XmlExpressionLanguageID"/>
            <xsd:element maxOccurs="1" minOccurs="0" ref="cbc:XmlExpressionLanguageVersionID"/>
            <xsd:element maxOccurs="unbounded" minOccurs="1" ref="cbc:XmlExpressionString"/>
        </xsd:sequence>
    </xsd:complexType>

<!-- alternative addition -->
    <xsd:complexType name="XmlExpressionType">
        <xsd:sequence>
            <xsd:element maxOccurs="1" minOccurs="1" ref="cbc:XmlExpressionLanguageCode"/>
            <xsd:element maxOccurs="unbounded" minOccurs="1" ref="cbc:XmlExpressionString"/>
        </xsd:sequence>
    </xsd:complexType>

<!-- ... -->

<!-- --------------------------- -->
<!-- UBL-CommonBasicComponents-2 -->
<!-- --------------------------- -->

<!-- ... -->

<!-- additions -->
<!-- needs specification of how to use spec URIs and version IDs for XQuery, etc here -->

    <xsd:element name="XmlExpressionLanguageID" type="LanguageIDType"/>
    <xsd:element name="XmlExpressionLanguageVersionID" type="VersionIDType"/>

<!-- alternative additions -->
<!-- needs a codelist, e.g. XPath2XPath1CompatibilityMode, XQuery1, XPath2, XQuery2, XPath3 ... -->

    <xsd:element name="XmlExpressionLanguageCode" type="XmlExpressionLanguageCodeType"/>
<!-- ... -->
    <xsd:complexType name="XmlExpressionLanguageCodeType">
        <xsd:simpleContent>
            <xsd:extension base="udt:CodeType"/>
        </xsd:simpleContent>
    </xsd:complexType>
   
<!-- ... -->

<!-- addition -->
    <xsd:element name="XmlExpressionString" type="XmlExpressionStringType"/>

<!-- ... -->

<!-- addition -->
    <xsd:complexType name="XmlExpressionStringType">
        <xsd:simpleContent>
            <xsd:extension base="udt:TextType"/>
        </xsd:simpleContent>
    </xsd:complexType>

<!-- ... -->

This would give a way to include an adequately declared XPath 2.0
expression in a UBL document:
 
<cac:XmlExpression>
<cbc:XmlExpressionLanguageID>http://www.w3.org/TR/xquery/</cbc:XmlExpressionLanguageID>
<cbc:XmlExpressionLanguageVersionID>1.0</cbc:XmlExpressionLanguageVersionID>
<cbc:XmlExpressionString>declare default element namespace "urn:oasis:names:specification:ubl:schema:xsd:Invoice-

2"; declare namespace cbc = "urn:oasis:names:specification:ubl:schema:xsd:CommonBasicComponents-2";

(/Invoice/cbc:ID)[1]</cbc:XmlExpressionString>
</cac:XmlExpression>

Since XQuery itself allows the version information to be declared in the expression itself, the

XmlExpressionLanguageVersionID could be optional and that version information included in the XQuery expession:

 
<cac:XmlExpression>
<cbc:XmlExpressionLanguageID>http://www.w3.org/TR/xquery/</cbc:XmlExpressionLanguageID>
<cbc:XmlExpressionString>xquery version "1.0"; declare default element namespace

"urn:oasis:names:specification:ubl:schema:xsd:Invoice-2"; declare namespace cbc =

"urn:oasis:names:specification:ubl:schema:xsd:CommonBasicComponents-2"; (/Invoice/cbc:ID)[1]

</cbc:XmlExpressionString>
</cac:XmlExpression>

Best regards

 

----

Stephen D Green