[DFDL-WG] What are the consequences of a failed assert?

Fri Jul 5 15:31:11 EDT 2013

Wouldn’t the use of a discriminator suppress the backtracking behavior in the face of a processing error?

That is, if a discriminator is used to confirm that the Content-Type header branch is the correct one, wouldn’t a subsequent assert that causes a processing error force the parser to halt with an error?

-Jonathan Cranford

From: dfdl-wg-bounces at ogf.org [mailto:dfdl-wg-bounces at ogf.org] On Behalf Of Garriss Jr., James P.
Sent: Friday, July 05, 2013 12:09 PM
To: Steve Hanson; Tim Kimber
Cc: dfdl-wg at ogf.org; dfdl-wg-bounces at ogf.org
Subject: Re: [DFDL-WG] What are the consequences of a failed assert?

Very helpful, guys, as always.  Thank you.

Question:  Is it possible to force the failure of an assert to be a validation error instead of a processing error?

Here’s why:  All the email headers are modeled as an unordered list.  The last item on the list is a catch-all, designed to scoop up all the unexpected headers and hide them from the infoset (via hiddenGroupRef).

So if I have an Content-Type header that is obviously invalid:

Content-Type: bogus/data

The assert fails as expected.  But since there is always another choice, the catch-all, the Content-Type header quietly disappears.  What I really want is for there to be a validation error for “bogus/data,” so that processing stops!

Is that possible?  Is that reasonable?

From: dfdl-wg-bounces at ogf.org<mailto:dfdl-wg-bounces at ogf.org> [mailto:dfdl-wg-bounces at ogf.org] On Behalf Of Steve Hanson
Sent: Thursday, July 04, 2013 4:26 AM
To: Tim Kimber
Cc: dfdl-wg at ogf.org<mailto:dfdl-wg at ogf.org>; dfdl-wg-bounces at ogf.org<mailto:dfdl-wg-bounces at ogf.org>
Subject: Re: [DFDL-WG] What are the consequences of a failed assert?

Almost.  A Recoverable Error does not cause backtracking. It was added to enable an assert to perform validation that checked the data stream rather than just the infoset. For example, checking the max physical length of a non-string value. So it has the same effect on the parse as a Validation Error. I've corrected your summary.

The definition and description of the different errors is covered in the spec by section 2. There have been some errata in this section to clarify the behaviour. Some of the wording has been around since early drafts of the spec, so any suggestions for improvement are welcome.

Regards

Steve Hanson
Architect, IBM Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group<http://www.ogf.org/dfdl/>
IBM SWG, Hursley, UK
smh at uk.ibm.com<mailto:smh at uk.ibm.com>
tel:+44-1962-815848

From:        Tim Kimber/UK/IBM at IBMGB
To:        dfdl-wg at ogf.org<mailto:dfdl-wg at ogf.org>,
Date:        03/07/2013 21:51
Subject:        Re: [DFDL-WG] What are the consequences of a failed assert?
Sent by:        dfdl-wg-bounces at ogf.org<mailto:dfdl-wg-bounces at ogf.org>
________________________________

There are four types of error in DFDL:
- a Schema Definition Error : The schema itself is not valid. ( at least three kinds: xsd not valid, xsd not in the DFLD subset, DFDL annotations not following the rules )
- A Processing Error : The data cannot be parsed. Or if unparsing, the info set cannot be unparsed.
- A Recoverable Error : ( see the Errata ). This is effectively a user-defined form of Validation Error, raised while executing a DFDL assert,
- A Validation Error : The info set does not conform to the XSD

A Schema Definition Error is immediately fatal. Most of these can be detected by the processor before parsing/unparsing begins.
A Processing Error or a Recoverable Error will cause the parser to suppress the error and backtrack to the nearest point of uncertainty. So it will only stop the parse if there are no points of uncertainty currently active.
A Recoverable Error does not cause backtracking - the parser continues to parse after reporting the error.
A Validation Error is only reported if validation is enabled in the DFDL processor. It does not cause backtracking - the parser continues to parse after reporting the error.

That's the gist of it. Further details from other WG members may follow shortly, depending on how accurate I have managed to be.

regards,

Tim Kimber, DFDL Team,
Hursley, UK
Internet:  kimbert at uk.ibm.com<mailto:kimbert at uk.ibm.com>
Tel. 01962-816742
Internal tel. 37246742

From:        "Garriss Jr., James P." <jgarriss at mitre.org<mailto:jgarriss at mitre.org>>
To:        "dfdl-wg at ogf.org<mailto:dfdl-wg at ogf.org>" <dfdl-wg at ogf.org<mailto:dfdl-wg at ogf.org>>,
Date:        03/07/2013 19:06
Subject:        [DFDL-WG] What are the consequences of a failed assert?
Sent by:        dfdl-wg-bounces at ogf.org<mailto:dfdl-wg-bounces at ogf.org>
________________________________

I have an element with an assert,

          <xsd:element name="Type" dfdl:inputValueCalc="{ fn:lower-case(../MixedCaseType) }">
              <xsd:annotation>
                  <xsd:appinfo source="http://www.ogf.org/dfdl/dfdl-1.0/">
                      <dfdl:assert test="{ dfdl:checkConstraints(.) }" message="The type must match one of the values on the enumerated list."/>
                  </xsd:appinfo>
              </xsd:annotation>
              <xsd:simpleType>
                  <xsd:restriction base="xsd:string">
                      <xsd:enumeration value="application"/>
                      <xsd:enumeration value="multipart"/>
                      <xsd:enumeration value="message"/>
                      <xsd:enumeration value="text"/>
                  </xsd:restriction>
              </xsd:simpleType>
          </xsd:element>

and the assert is failing (as it should in this case!).

Parse Error: Assertion failed. The type must match one of the values on the enumerated list.

What are the consequences of a failed assert?  I have an old version of the spec—is there a place to a get a current, complete copy?—but it says “An unsuccessful dfdl:assert causes a processing error.”

1.     What does “processing error” mean in English?
2.     Does it mean the input is invalid?
3.     Does it mean the processor should stop here and go no further?
4.     Does it mean the process should simply ignore the problem and move on to the next item in the schema?

TIA
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