[DFDL-WG] Fw: What are the consequences of a failed assert?
Steve Hanson
smh at uk.ibm.com
Thu Jul 11 10:30:59 EDT 2013
Let me give a bit more context.
As assert can complete in exactly one of three ways:
1) evaulate to true
2) evaluate to false -> failureType says what kind of error to throw -
recoverable, processing, or fatal (proposed)
3) fail to evaluate -> processing error
There's only ever one error. There's no concept of multiple errors.
Let me phrase my question another way. I have an assert which has
failureType 'fatalError'. If the assert evaluates to false then the parser
will stop. But if the assert fails to evaluate the parser will throw a
processing error and backtrack. The latter includes use of fn:error(), as
that is classed as a failure to evaluate.
Regards
Steve Hanson
Architect, IBM Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848
From: "Garriss Jr., James P." <jgarriss at mitre.org>
To: "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>,
Date: 11/07/2013 15:03
Subject: Re: [DFDL-WG] Fw: What are the consequences of a failed
assert?
Sent by: dfdl-wg-bounces at ogf.org
Is there a reason why the processor can’t throw both errors?
If one of the errors is fatal, it should stop. IOW, respond the “worse”
error first.
From: dfdl-wg-bounces at ogf.org [mailto:dfdl-wg-bounces at ogf.org] On Behalf
Of Steve Hanson
Sent: Thursday, July 11, 2013 5:07 AM
To: dfdl-wg at ogf.org
Subject: [DFDL-WG] Fw: What are the consequences of a failed assert?
Let's say I have an assert with 'fatalError'. What happens if the assert
has a processing error when it is being evaluated. Is this still a
processing error, or does it get converted into a fatal error? I include
the use of fn:error() here as well.
Regards
Steve Hanson
Architect, IBM Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848
----- Forwarded by Steve Hanson/UK/IBM on 11/07/2013 09:59 -----
From: "Garriss Jr., James P." <jgarriss at mitre.org>
To: Steve Hanson/UK/IBM at IBMGB, Tim Kimber/UK/IBM at IBMGB,
Cc: "Cranford, Jonathan W." <jcranford at mitre.org>, "dfdl-wg at ogf.org
" <dfdl-wg at ogf.org>
Date: 10/07/2013 18:06
Subject: RE: [DFDL-WG] What are the consequences of a failed
assert?
> What is being asked for here sounds like the ability to throw an error
and stop the parser regardless of what points of uncertainty are in scope
Exactly!
> James, would this 'fatal error' give you the capability you are looking
for?
Yes, I think it would. I would like to encourage the WG to add this
feature if at all possible.
From: Steve Hanson [mailto:smh at uk.ibm.com]
Sent: Monday, July 08, 2013 6:11 AM
To: Tim Kimber
Cc: Cranford, Jonathan W.; dfdl-wg at ogf.org; Garriss Jr., James P.
Subject: RE: [DFDL-WG] What are the consequences of a failed assert?
Errata 3.4 added the failureType attribute to dfdl:assert so that an
assert could report the equivalent of a validation error and carry on
('recoverable error') instead of throwing a 'processing error'. What is
being asked for here sounds like the ability to throw an error and stop
the parser regardless of what points of uncertainty are in scope. That
does sound like a genuinely useful thing to be able to do, and gives
dfdl:assert the full range of failure actions. We'd have to create a new
error type, say 'fatal error'. It would have the same effect as a 'schema
definition error'.
James, would this 'fatal error' give you the capability you are looking
for?
Regards
Steve Hanson
Architect, IBM Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848
From: Tim Kimber/UK/IBM
To: "Cranford, Jonathan W." <jcranford at mitre.org>,
Cc: "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>, "dfdl-wg-bounces at ogf.org"
<dfdl-wg-bounces at ogf.org>, "Garriss Jr., James P." <jgarriss at mitre.org>,
Steve Hanson/UK/IBM at IBMGB
Date: 08/07/2013 09:29
Subject: RE: [DFDL-WG] What are the consequences of a failed
assert?
It depends on whether there was exactly one point of uncertainty active
when the discriminator expression evaluated to 'true'. Points of
uncertainty can be nested within one another. A POU can be resolved ( or
made 'inactive' as I was trying to hint at ) by a discriminator that
evaluates to 'true'. When a processing error occurs, it is caught by the
nearest ( most deeply nested ) *active* POU. If there is no active POU
then the parser halts and reports the error.
regards,
Tim Kimber, DFDL Team,
Hursley, UK
Internet: kimbert at uk.ibm.com
Tel. 01962-816742
Internal tel. 37246742
From: "Cranford, Jonathan W." <jcranford at mitre.org>
To: "Garriss Jr., James P." <jgarriss at mitre.org>, Steve
Hanson/UK/IBM at IBMGB, Tim Kimber/UK/IBM at IBMGB,
Cc: "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>, "dfdl-wg-bounces at ogf.org"
<dfdl-wg-bounces at ogf.org>
Date: 05/07/2013 20:31
Subject: RE: [DFDL-WG] What are the consequences of a failed
assert?
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] On Behalf
Of Steve Hanson
Sent: Thursday, July 04, 2013 4:26 AM
To: 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?
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
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848
From: Tim Kimber/UK/IBM at IBMGB
To: 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
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
Tel. 01962-816742
Internal tel. 37246742
From: "Garriss Jr., James P." <jgarriss at mitre.org>
To: "dfdl-wg at ogf.org" <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
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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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
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
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