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Re: How to implement validation rules in an environment where

• From: "G. Ken Holman" <gkholman@CraneSoftwrights.com>
• To: XML-Dev Mailing list <xml-dev@lists.xml.org>
• Date: Mon, 20 Aug 2012 11:05:19 -0400

At 2012-08-20 13:19 +0000, you wrote:
>-----------
>Solution
>-----------
>Schematron schemas can be used for the category "enumeration list 
>changes." For example, in the XSD schema declare the <Publisher> 
>element of type xs:string" and then in the Schematron schema have 
>assertions that specify the list of today's valid publishers.
>
>-------------
>Questions
>-------------
>1. Rick Jelliffe says, "the assertions should be dynamically 
>loaded." What does that mean? How does one dynamically load Schematron?

Two passes.  See Figure D-2 after scrolling down from:

   http://docs.oasis-open.org/ubl/prd2-UBL-2.1/UBL-2.1.html#CODELISTS
   (the XSLT is created from Schematron, which is from CVA and genericode)

>2. How would "metadata changes" be implemented? For example, how 
>would we add to each <Book> element an indication of whether it is in-stock?

To me that isn't metadata.  To me metadata is "data about data" and 
isn't really very dynamic but needs to be flexible (the two concepts 
are different).  To me "in-stock" is simply data related to a 
book.  It isn't metadata regarding the book, just data regarding the 
book.  Metadata about the book would be a descriptor type (e.g. 
"ISBN") of the book number (e.g. "978-1-894049-24-5").  Without 
metadata you wouldn't know which scheme the book number was using to 
express its information, so the metadata tells you about the data point.

"In-stock" is simply information.  Now, an example of metadata about 
"in-stock" would be the unit of measure, distinguishing what the data 
"2" means in:

    <cbc:Quantity unitCode="T3">2</cbc:Quantity> <!--thousand piece-->
    <cbc:Quantity unitCode="DPC">2</cbc:Quantity> <!--dozen piece-->
    <cbc:Quantity unitCode="H87">2</cbc:Quantity> <!--single piece-->

... as found in:

http://docs.oasis-open.org/ubl/prd2-UBL-2.1/mod/summary/reports/UBL-AllDocuments-2.1.html#t-CommonLibrary-1754
    "The quantity that is currently on stock."

... in the instance as follows:

http://docs.oasis-open.org/ubl/prd2-UBL-2.1/mod/summary/reports/UBL-AllDocuments-2.1.html#Table_StockAvailabilityReport
    <StockAvailabilityReport>
      <cbc:ID>...</cbc:ID>
      <cbc:IssueDate>...</cbc:IssueDate>
      <cac:StockAvailabilityReportLine>
        <cbc:ID>...</cbc:ID>
        <cbc:Quantity>...</cbc:Quantity>
        <cac:Item>
          <cbc:Name>...</cbc:Name>

The units of measure are documented here for UBL 2.1:

  http://docs.oasis-open.org/ubl/prd2-UBL-2.1/cva/UBL-DefaultDTQ-2.1.html#d27e1

Sure Schematron could be used to, say, check limits of "In-stock" 
(throw an error, say, when the quantity is less than 100), but, 
again, that isn't metadata ... it is just data.

>3. I listed two "Categories of Data that Frequently Change." Are 
>there other categories? If yes, would you provide an example please?

I don't think the second pass necessarily applies simply to data that 
frequently change, rather, to data that need to be flexible between 
different users of the inflexible schemas.

In UBL the schemas are normative, the CVA/genericode files are 
not.  Users can change their value constraints all they want and 
still call their instances "UBL Conformant" because their instances 
validate against the XSD schemas.

In the above example, I could insist in my legal trading agreement 
with my trading partner that quantities for stocking levels always 
use "pieces" so that I can reject an instance using "thousand piece" 
or "dozen piece" as units of measure (because, say, my software 
doesn't comprehend other units of measure than "piece").  I back that 
up by creating a custom subset genericode file where "H87" is the 
only allowed unit of measure, and then in my CVA file I constrain the 
unitCode= attribute of <cbc:Quantity> when a child of 
<cac:StockAvailabilityReportLine> to use that custom one-line code 
list.  Then my second-pass XSLT validation can reject a document that 
violates that data point with invalid (per the trading agreement) 
information.  And we can exchange agreed-upon genericode and CVA 
files as declarative codexes of our trading agreement.

This is what Fraser was talking about regarding contextualizing the 
subset code lists.  I wouldn't want that same "piece" constraint on 
<cbc:Quantity> when used as a child of some other element.

Forgive me for always bringing up UBL examples in my posts, but we 
have been all over this stuff for a decade now, making mistakes along 
the way and arriving at a point where we think the issues are being 
successfully addressed for users.

I hope you still find the comments useful.

. . . . . . . . . .  Ken


--
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