Ambiguity Regarding UBL Calculation Model

To UBL-DEV and UBL-comment

I've been looking at prototyping some test assertions (TAs) to represent
the UBL Calculation Model (for possible conformance testing in future)
- albeit what is implied by the semantic definitions in the UBL 2.0
schema set. I'm using the OASIS Test Assertions TC TA model,
guidelines and markup. I anticipate needing to feedback to UBL TC any
ambiguities and/or corner cases in the definitions that this process turns
up. One which has just turned up is the LineExtensionAmount which
seems to be ambiguous in that it would appear (from the invoice example
in the 2.0 package) to be at document level the total of all
LineExtensionAmounts at line level. The ambiguity is that the definition
doesn't very well support this apprently safe interpretation in that it could
be read to mean that the document level total LineExtensionAmount
also includes allowances and charges. These would normally be
not in the LineExtensionAmount but in the TaxExclusiveAmount, as shown
in the UBL invoice example.

Here is a provisional prototype of my TA Set - no liability if it's wrong, etc

<?xml version="1.0" encoding="UTF-8"?>
<testAssertionSet xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:noNamespaceSchemaLocation="../../../TestAssertionMarkup-0-4/testAssertion-0-4.xsd"
 id="documentengineeringservices:sdg:ubl:2:ta:prototype:0-0-2">
   <header>
       <var name="ubl-invoice-2-0-schema"
lg="xpath20">doc("http://docs.oasis-open.org/ubl/os-UBL-2.0/xsd/common/UBL-CommonAggregateComponents-2.0.xsd")</var>
       <var name="ubl-invoice-sum-line-extensions"
lg="xpath20">sum(/Invoice/cac:InvoiceLine/cbc:LineExtensionAmount)</var>
       <tag name="invoice"/>
   </header>
   <testAssertion id="INVTOT001">
       <normativeSource>
           <refSourceItem
lg="xpath20">$ubl-invoice-2-0-schema/xsd:schema/xsd:complexType[@name='MonetaryTotalType']/xsd:sequence[1]/xsd:element[@ref='cbc:LineExtensionAmount']/xsd:annotation[1]/xsd:documentation[1]/ccts:Component[1]/ccts:Definition[1]</refSourceItem>
       </normativeSource>
       <target
lg="xpath20">number(/Invoice/cac:LegalMonetaryTotal[1]/cbc:LineExtensionAmount[1])</target>
       <prerequisite
lg="xpath20">exists(/Invoice/cac:InvoiceLine[1]/cbc:LineExtensionAmount[1])</prerequisite>
       <predicate
lg="xpath20">number(/Invoice/cac:LegalMonetaryTotal[1]/cbc:LineExtensionAmount[1])
eq (sum(/Invoice/cac:InvoiceLine/cbc:LineExtensionAmount) +
sum(/Invoice/cac:AllowanceCharge/cbc:Amount))</predicate>
       <prescriptionLevel>preferred</prescriptionLevel>
       <tag name="invoice:total"/>
   </testAssertion>
   <testAssertion id="INVTAX001">
       <normativeSource><comment>general practice but no known
normative source</comment></normativeSource>
       <target
lg="xpath20">count(distinct-values(/Invoice/cac:InvoiceLine/cac:TaxTotal/cac:TaxSubtotal/cbc:TaxAmount/@currencyID))</target>
       <prerequisite lg="ta">is-tax-invoice-001 = 'pass'</prerequisite>
       <predicate>count(distinct-values(/Invoice/cac:InvoiceLine/cac:TaxTotal/cac:TaxSubtotal/cbc:TaxAmount/@currencyID))
gt 0</predicate>
       <prescriptionLevel>preferred</prescriptionLevel>
       <tag name="invoice:tax"/>
   </testAssertion>
   <testAssertion id="INVTAX002">
       <normativeSource><comment>general practice but no known
normative source</comment></normativeSource>
       <target
lg="xpath20">count(distinct-values(/Invoice/cac:InvoiceLine/cac:TaxTotal/cac:TaxSubtotal/cbc:TaxAmount/@currencyID))</target>
       <prerequisite lg="ta">is-tax-invoice-001 = 'pass' and
INVTAX001 = "pass"</prerequisite>
       <predicate
lg="xpath20">count(distinct-values(/Invoice/cac:InvoiceLine/cac:TaxTotal/cac:TaxSubtotal/cbc:TaxAmount/@currencyID))
lt 2</predicate>
       <prescriptionLevel>preferred</prescriptionLevel>
       <tag name="invoice:tax"/>
   </testAssertion>
   <testAssertion id="INVTAX003">
       <normativeSource>
           <refSourceItem>$ubl-invoice-2-0-schema/xsd:schema/xsd:complexType[@name='TaxTotalType']/xsd:sequence[1]/xsd:element[@ref='cbc:TaxAmount']/xsd:annotation[1]/xsd:documentation[1]/ccts:Component[1]/ccts:Definition[1]</refSourceItem>
           <refSourceItem>$ubl-invoice-2-0-schema/xsd:schema/xsd:complexType[@name='TaxSubtotalType']/xsd:sequence[1]/xsd:element[@ref='cbc:TaxAmount']/xsd:annotation[1]/xsd:documentation[1]/ccts:Component[1]/ccts:Definition[1]</refSourceItem>
       </normativeSource>
       <target
lg="xpath20">sum(/Invoice/cac:TaxTotal/cbc:TaxAmount[1])</target>
       <prerequisite lg="ta">is-tax-invoice-001 = 'pass' and
INVTAX001 = 'pass'</prerequisite>
       <predicate
lg="xpath20">sum(/Invoice/cac:TaxTotal/cbc:TaxAmount[1]) eq
sum(/Invoice/cac:TaxTotal/cac:TaxSubtotal/cbc:TaxAmount[1])</predicate>
       <prescriptionLevel>preferred</prescriptionLevel>
       <tag name="invoice:tax"/>
   </testAssertion>
   <testAssertionSet id="is-tax-invoice-001" definesNormativeProperty="true">
       <header>
           <normativePropertyTag>TaxInvoice</normativePropertyTag>
       </header>
       <testAssertion id="TAXINV001">
           <normativeSource><comment>general practice but no known
normative source</comment></normativeSource>
           <predicate
lg="xpath20">exists(ubl-invoice-2-0-instance//cbc:TaxAmount)</predicate>
           <prescriptionLevel>mandatory</prescriptionLevel>
           <tag name="invoice:tax"/>
       </testAssertion>
       <testAssertion id="TAXINV002" lg="en-us">
           <normativeSource><comment>is a tax invoice according to
most relevant tax rules</comment></normativeSource>
           <predicate lg="en-us">is a tax invoice</predicate>
           <prescriptionLevel>mandatory</prescriptionLevel>
           <tag name="invoice:tax"/>
       </testAssertion>
   </testAssertionSet>
</testAssertionSet>

Stephen D Green