So the fn:error() XPath function takes a problematic argument.

All the arguments are optional, so fn:error() is legal.

The first argument is of type xs:qQName, and we don't have that type in DFDL. So the best we could do is to accept a string that is in the "form" of a QName, e.g.,
"foo:bar".

The second argument is a description string, third and subsequent args are objects. The manner by which this string and objects are provided to the execution environment is implementation dependent according to the XQuery and XPath spec, and this is fine for DFDL implementations also.

The lack of the QName type for the first argument suggests we're going to need to create dfdl:error(string, string, item()*), where the first argument is a string in the form of a QName, and the other arguments are as per fn:error.


Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com
Please note: Contributions to the DFDL Workgroup's email discussions are subject to the OGF Intellectual Property Policy


On Tue, Jul 5, 2016 at 11:49 AM, Steve Hanson <smh@uk.ibm.com> wrote:
WG agreed that an error function is needed, action 288 raised.
No
Action
288
Decide on error function specification (Mike)
5/7: An error function is useful for expressions when unparsing. Mike to evaluate XPath fn:error().


Regards
 
Steve Hanson
IBM Integration Bus, Hursley, UK
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
smh@uk.ibm.com
tel:+44-1962-815848
mob:+44-7717-378890



From:        Mike Beckerle <mbeckerle.dfdl@gmail.com>
To:        "dfdl-wg@ogf.org" <dfdl-wg@ogf.org>
Date:        14/06/2016 17:10
Subject:        Re: [DFDL-WG] still no need for fn:error
Sent by:        "dfdl-wg" <dfdl-wg-bounces@ogf.org>




I want to re-open the discussion of fn:error.
Previously we said it was not needed because an assert could be used.
However, we've now run into where we want to cause an error, during unparsing, during outputValueCalc.

 <xs:element name="Protocol" type="pcap:bit" dfdl:length="8"
           dfdl:outputValueCalc="{
           if (fn:exists(../../pcap:ICMPv4)) then 1
           else if (fn:exists(../../pcap:TransportLayer/pcap:TCP )) then 6
           else if (fn:exists(../../pcap:TransportLayer/pcap:UDP )) then 17
           else -1 }"/>
That -1 at the end. That's an error case. We really want fn:error("Unrecognized protocol.")

We can't change to a dfdl:assert, because assertions aren't evaluated when unparsing.

Comments?

Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com
Please note: Contributions to the DFDL Workgroup's email discussions are subject to the OGF Intellectual Property Policy


On Thu, Jul 25, 2013 at 9:16 AM, Mike Beckerle <mbeckerle.dfdl@gmail.com> wrote:
Respin of this example:

Here's the example as suggested by Jonathan of how to issue an error that I previously was suggesting needed fn:error. I'm convinced this is sufficient and we can avoid the need for fn:error now.

<xs:element name="magic_number" type="ex:uint32" dfdl:byteOrder="bigEndian">
 <xs:annotation>
   <xs:appinfo source="http://www.ogf.org/dfdl/">
     <dfdl:assert
       test="{ (xs:unsignedInt(.) eq dfdl:unsignedInt('xa1b2c3d4')) |
               (xs:unsignedInt(.) eq dfdl:unsignedInt('xd4c3b2a1')) }" 
       message="{ fn:concat(
                     'Magic number ',
                     dfdl:hexBinary(dfdl:unsignedInt(.)),
                     ' was not 0xA1B2C3D4 (for bigEndian) or 0xD4C3B2A1 (for littleEndian).' }" />
   <dfdl:setVariable ref="ex:bOrd">{ xs:unsignedInt(.) }<dfdl:setVariable>
   </xs:appinfo>
 </xs:annotation>
</xs:element>
On Wed, Jul 24, 2013 at 11:58 AM, Steve Hanson <smh@uk.ibm.com> wrote:
Mike,  I think you meant:

       test="{ (xs:unsignedInt(.) eq dfdl:unsignedInt('xa1b2c3d4')) |
               (xs:unsignedInt(.) eq dfdl:unsignedInt('xd4c3b2a1')) }"


Regards

Steve Hanson
Architect, IBM Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848



From:        Mike Beckerle <mbeckerle.dfdl@gmail.com>
To:        dfdl-wg@ogf.org,
Date:        24/07/2013 16:46
Subject:        [DFDL-WG] still no need for fn:error
Sent by:        dfdl-wg-bounces@ogf.org



Here's the example as suggested by Jonathan of how to issue an error that I previously was suggesting needed fn:error. I'm convinced this is sufficient and we can avoid the need for fn:error now.

<xs:element name="magic_number" type="ex:uint32" dfdl:byteOrder="bigEndian">
 <xs:annotation>
   <xs:appinfo source="http://www.ogf.org/dfdl/">
     <dfdl:assert
       test="{ (xs:unsignedInt(.) eq dfdl:unsignedInt('xa1b2c3d4')) |
               (xs:unsignedInt(.) eq dfdl:unsignedInt('xd4c3b2a1')) }" 
       message="{ fn:concat(
                     'Magic number ',
                     dfdl:hexBinary(dfdl:unsignedInt(.)),
                     ' was not 0xA1B2C3D4 (for bigEndian) or 0xD4C3B2A1 (for littleEndian).' }" />
   <dfdl:setVariable ref="ex:bOrd">{ xs:unsignedInt(.) }<dfdl:setVariable>
   </xs:appinfo>
 </xs:annotation>
</xs:element>


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Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com
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--
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | www.tresys.com
--
 dfdl-wg mailing list
 dfdl-wg@ogf.org
 https://www.ogf.org/mailman/listinfo/dfdl-wg


Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU