[DFDL-WG] proposal: assert message property as DFDL Expression or String - Fwd: proposal: add fn:error function ....
Steve Hanson
smh at uk.ibm.com
Wed Jul 24 07:34:09 EDT 2013
What happens if evaluating the message expression causes a schema
definition error?
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: Mike Beckerle <mbeckerle.dfdl at gmail.com>
To: dfdl-wg at ogf.org,
Date: 23/07/2013 16:44
Subject: [DFDL-WG] proposal: assert message property as DFDL
Expression or String - Fwd: proposal: add fn:error function ....
Sent by: dfdl-wg-bounces at ogf.org
Proposed:
Make the message property on dfdl:assert (and dfdl:discriminator) be
either a string or a DFDL Expression that returns a string. (Note: this is
not a DFDL String Literal, it is just a string.)
Example:
<dfdl:assert message="{ fn:concat('unknown whatever ', ../foobar) }">
{ if (...pred...) then ...expr1...
else if (...pred2...) then ...expr2...
else fn:false()
}</dfdl:assert>
If a processing error occurs while evaluating the test predicate, then
that processing error occurs. The assert is not considered to have passed
or failed because the assert predicate did not return ether true or false.
If a processing error occurs while evaluating the message expression, then
the assert causes an error of appropriate failureType: recoverableError or
processingError, but an implementation-dependent message is provided.
---------- Forwarded message ----------
From: Steve Hanson <smh at uk.ibm.com>
Date: Fri, Jul 12, 2013 at 4:25 AM
Subject: Re: [DFDL-WG] proposal: add fn:error function and dfdl:hex
function to DFDL
To: Mike Beckerle <mbeckerle.dfdl at gmail.com>
Cc: dfdl-wg at ogf.org, dfdl-wg-bounces at ogf.org
I agree that is simpler and making the message string an expression is an
easy change to make.
But in the your example if expr1 or expr2 evaluated to false, then in form
#1 no message would be issued, but in form #2 it would be issued. Is that
what you intended?
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: Mike Beckerle <mbeckerle.dfdl at gmail.com>
To: dfdl-wg at ogf.org,
Date: 11/07/2013 18:47
Subject: Re: [DFDL-WG] proposal: add fn:error function and dfdl:hex
function to DFDL
Sent by: dfdl-wg-bounces at ogf.org
Ignoring the dfdl:hexBinary thing.
I want to suggest a different idea than fn:error function for DFDL:
Suppose dfdl:assert (and dfdl:discriminator) message property could be an
expression that evaluates to a string.
Then instead of writing
<dfdl:assert>{
if (...pred...) then ...expr1...
else if (...pred2...) then ...expr2...
else fn:error(sym, fn:concat("unknown whatever ", ../foobar))
}</dfdl:assert>
You could write:
<dfdl:assert message="{ fn:concat('unknown whatever ', ../foobar) }">
{ if (...pred...) then ...expr1...
else if (...pred2...) then ...expr2...
else fn:false()
}</dfdl:assert>
This is almost equivalent. But the message would respect the failureType
of the assert.
This has advantages.
On Wed, Jul 10, 2013 at 3:14 PM, Garriss Jr., James P. <jgarriss at mitre.org
> wrote:
> You need a different mechanism, which is a fatalError type for the
dfdl:assert annotation.
Sounds like we are in agreement. Thanks for clarifying.
> But the CDS community uses validation to indicate an immediate need to
stop. I.e., invalid == "dangerous".
In some cases this is true, though in other cases it is not true. That’s
why it seems to me that it would be good if DFDL can handle either
mindset. For the work I’ve been doing with DFDL and email, the
“invalid=dangerous” mindset was a starting assumption.
From: Mike Beckerle [mailto:mbeckerle.dfdl at gmail.com]
Sent: Wednesday, July 10, 2013 1:57 PM
To: Garriss Jr., James P.
Cc: dfdl-wg at ogf.org
Subject: Re: [DFDL-WG] proposal: add fn:error function and dfdl:hex
function to DFDL
Actually, fn:error was added in order to allow a DFDL Expression to create
a normal processing error.
You need a different mechanism, which is a fatalError type for the
dfdl:assert annotation.
I have noticed that the use of 'validation' in DFDL is the opposite of the
way other people use 'validation'. In the DFDL spec, validation generally
just creates warnings and continues parsing. It can't even affect the
parse unless you call checkConstrants(....) from an assert. But the CDS
community uses validation to indicate an immediate need to stop. I.e.,
invalid == "dangerous".
...mikeb
On Wed, Jul 10, 2013 at 1:37 PM, Garriss Jr., James P. <jgarriss at mitre.org
> wrote:
> fn:error, if called from inside an assert or discriminator, causes the
assert or discriminator to fail (as with any processing error that occurs
during evaluation of the assert or discriminator expression).
Is this intended to address the issue I raised? If so, I think this is
not sufficient. I need to have the option to cause a validation error,
not a processing error. If not, please ignore this interruption. :-)
From: dfdl-wg-bounces at ogf.org [mailto:dfdl-wg-bounces at ogf.org] On Behalf
Of Mike Beckerle
Sent: Tuesday, July 09, 2013 11:29 AM
To: dfdl-wg at ogf.org
Subject: Re: [DFDL-WG] proposal: add fn:error function and dfdl:hex
function to DFDL
Proposal revised for dfdl:hex, and clarification added on fn:error when
used inside assert.
Revised language below:
Proposed: add fn:error function and add dfdl:hexBinary function.
DFDL only needs one of the several variations of fn:error.
fn:error($error as xs:QName?, $description as xs:string) as none
The behavior of fn:error in DFDL expressions is the same as described in
XPath 2.0, an example is given below.
dfdl:hexBinary($arg as xs:anyAtomicType?) as xs:hexBinary?
This function provides an extension to the behavior of the xs:hexBinary
constructor. The argument can be a string, in which case the behavior is
as the xs:hexBinary constructor. The argument can also be a long,
unsignedLong, or any subtype thereof, and in that case a string containing
hexadecimal digits is produced. The hexadecimal digits produced that are
letters are always uppercase. The number of hex digits in the resulting
string is a function of the input type. If byte or unsigned byte, exactly
2 hex digits are produced, for short and unsignedShort, 4 hex digits, and
so on. The hex digits correspond to a big-endian representation of a
twos-complement binary representation of the argument value. So:
dfdl:short(xs:concat('x', dfdl:hexBinary(xs:short(208)))) eq xs:short(208)
is true, and a corresponding tautology holds for all the other DFDL
functions that construct integers from hexadecimal, if you replace the 208
above with a value in range for the corresponding numeric type.
If the argument is a numeric literal, then the smallest signed integer
type (long, int, short, byte) is selected that can contain the value, and
the number of hexadecimal digits produced corresponds to that type. So:
dfdl:hexBinary(208) eq 'D0'
dfdl:hexBinary(-2084) eq 'F7FF'
Example of fn:error and dfdl:hexBinary:
This expression allows a meaningful error message that includes the
offending parts of data.
fn:error(ex:magic_number, fn:concat("The magic number: 0x",
dfdl:hexBinary(.), " was not 0xA1B2C3D4 (for bigEndian) or 0xD4C3B2A1 (for
littleEndian)."))
The $error argument (of type QName) is used in an implementation-dependent
manner to provide the context of the error. So for example, if namespace
prefix 'ex' is bound to 'http://example.com' then the above call might
produce:
"Error: {http://example.com}magic_number - The magic number: 0xFEFF0000
was not 0xA1B2C3D4 (for bigEndian) or 0xD4C3B2A1 (for littleEndian)."
Only the part of the above string after the hyphen is standardized. The
hyphen and part before the hyphen is implementation dependent.
fn:error, if called from inside an assert or discriminator, causes the
assert or discriminator to fail (as with any processing error that occurs
during evaluation of the assert or discriminator expression). If the
assert or discriminator has a message property, then it is implementation
dependent how that message string is combined with the description string
argument provided to the fn:error function.
On Thu, Jun 20, 2013 at 1:09 PM, Mike Beckerle <mbeckerle.dfdl at gmail.com>
wrote:
Proposed: add fn:error function and add dfdl:hex function.
DFDL only needs one of the several variations of fn:error
fn:error($error as xs:QName?, $description as xs:string) as none
dfdl:hex($num as xs:integer) as string
The dfdl:hex function inverts the behavior of the dfdl:byte, and related
functions (currently also proposed) which take a string specification of a
hex value. The argument to dfdl:hex can be a long, unsignedLong, or any
subtype thereof. The number of hex digits in the resulting string is a
function of the input type. If byte or unsigned byte, exactly 2 hex digits
are produced, for short and unsignedShort, 4 hex digits, and so on. The
resulting value contains a prefix 'x' character as its first character.
So:
dfdl:short(dfdl:hex(xs:short(208))) eq xs:short(208)
is true, and a corresponding tautology holds for all the other DFDL
functions that construct integers from hexadecimal, if you replace the 208
above with a value in range for the corresponding numeric type.
Example:
This allows a meaningful error message that includes the offending parts
of data.
fn:error(ex:magic_number, fn:concat("The magic number: 0", dfdl:hex(.), "
was not 0xA1B2C3D4 (for bigEndian) or 0xD4C3B2A1 (for littleEndian)."))
The $error argument (of type QName) is used in an implementation-dependent
manner to provide the context of the error. So for example, if namespace
prefix 'ex' is bound to 'http://example.com' then the above call might
produce:
"Error: {http://example.com}magic_number - The magic number: 0xFEFF0000
was not 0xA1B2C3D4 (for bigEndian) or 0xD4C3B2A1 (for littleEndian)."
Only the part of the above string after the hyphen is standardized. The
hyphen and part before the hyphen is implementation dependent.
--
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology |
www.tresys.com
--
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology |
www.tresys.com
--
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
--
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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
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