[DFDL-WG] Action 186: Re: DFDL Statement Evaluation Timing (Assert, Discriminator, SetVariable, NewVariableInstance)
Steve Hanson
smh at uk.ibm.com
Tue Nov 20 06:49:55 EST 2012
Hi Mike
I have incorporated all this into Errata v011. A couple of comments:
- You use 'parse error' in a few places where correct term is 'processing
error'
- I think your new section 7.10 should be in section 9, as it is talking
about order of execution and consequences of failure which are introduced
in section 9.
- Regarding "It is also a processing error to read any variables defined
by any dfdl:newVariableInstance statement evaluations that failed, or to
read any variables set by any dfdl:setVariable statements that failed. ",
can you give a scenario where the processor can get into this situation?
Regards
Steve Hanson
Architect, 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: Steve Hanson/UK/IBM at IBMGB,
Cc: dfdl-wg at ogf.org
Date: 19/11/2012 20:15
Subject: Re: [DFDL-WG] Action 186: Re: DFDL Statement Evaluation
Timing (Assert, Discriminator, SetVariable, NewVariableInstance)
Ok, third time's the charm.... I did look for minutes mentioning whether
we decided to move when these were evaluated....
On Mon, Nov 19, 2012 at 2:57 PM, Steve Hanson <smh at uk.ibm.com> wrote:
Mike, discriminators and asserts with testKind 'expression' are always
evaluated after the component's format annotation, the timing does not
depend on the component kind. See your original write up.
Regards
Steve Hanson
Architect, 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: Steve Hanson/UK/IBM at IBMGB,
Cc: dfdl-wg at ogf.org
Date: 19/11/2012 17:43
Subject: Re: [DFDL-WG] Action 186: Re: DFDL Statement Evaluation
Timing (Assert, Discriminator, SetVariable, NewVariableInstance)
Easily fixed. Global replace done.
On Mon, Nov 19, 2012 at 12:36 PM, Steve Hanson <smh at uk.ibm.com> wrote:
Mike, I think we agreed on 'resolved set of annotations' instead of
'combined annotations' ?
I had the action to create the final errata wording for this item (Action
186).
Last action issue was to change wording to insure it was all dealing with
combined annotations uniformly, and change "annotated construct" to
"schema component".
I've done that, but also reorganized this as errata on specific sections
of the spec consistent with the rest of our errata, and turned the
'ordering' section into numbered lists for clarity.
-------------------------------------------------------
Errata section 6.2. Clarification: At any single annotation point of the
schema, there can be only one format annotation (dfdl:format,
dfdl:element, dfdl:sequence, dfdl:choice, dfdl:group, dfdl:simpleType).
Errata section 3. Glossary entries
Glossary: Annotation point: A location within a DFDL schema where DFDL
annotation elements are allowed to appear.
Note that annotation point is defined in section 6.2, but it belongs also
in the glossary.
Glossary: DFDL Statement annotations, or just DFDL Statements, are the
annotation elements dfdl:assert, dfdl:discriminator, dfdl:setVariable, and
dfdl:newVariableInstance.
Glossary: DFDL Defining Annotations are the annotation elements
dfdl:defineFormat, dfdl:defineVariable, and dfdl:defineEscapeScheme
Glossary: DFDL Format Annotations are the annotation elements dfdl:format,
dfdl:element, dfdl:simpleType, dfdl:group, dfdl:sequence, and dfdl:choice.
Glossary: Remove existing definition for "Format Annotations"
Glossary: Physical layer - revised to: "Physical Layer - A DFDL Schema
adds DFDL annotations onto an XSDL language schema. The annotations
describe the physical representation or physical layer of the data."
Glossary: Resolved set of annotations: When DFDL annotations appear on a
group reference and the sequence or choice of the referenced global group,
or appear among an element reference, an element declaration, and its type
definition, then they are combined together and the resulting set of
annotations is referred to as the resolved set of annotations for the
schema component.
Errata Section 7.3.1:
Remove "DFDL asserts can be placed on components within a DFDL model." as
this is made more specifically subsequently.
Replace "More than one dfdl:assert may be used at an annotation point. The
dfdl:asserts will be evaluated in the order defined in the schema." with
"If the resolved set of annotations for a schema component contain
multiple dfdl:assert statements, then those with testKind='pattern' are
executed before those with testKind='expression' (the default). However,
within each group the order of execution among them is not specified.
Schema authors can insert sequences to control the timing of evaluation of
statements more precisely. See Section REF: Evaluation Order for Statement
Annotations."
Property testPattern: Add this to the description:
Note that the pattern is used to match against the entire representation
of the component; hence, the framing (including initiators) is visible to
the pattern.
It is a schema definition error if dfdl:alignment is not 1 .
It is a schema definition error if dfdl:leadingSkip is not 0.
It is a schema definition error if dfdl:encoding is not defined.
Errata Section 7.3.1, and 7.4.1: Assert and Discriminator Placement
Correct description to be consistent with: dfdl:assert and
dfdl:discriminator can be placed as annotations on sequence, choice, group
references, local and global element declarations, element references, and
simple type definitions.
Errata Section 7.4.1:
Replace: "Any one annotation point can contain only a single
dfd:discriminator or one or more dfdl:asserts,
but not both. It is a schema definition error otherwise." with:
"The resolved set of annotations for a schema component can contain only a
single dfd:discriminator or one or more dfdl:asserts, but not both. It is
a schema definition error otherwise."
Property testPattern: Add this to the description:
Note that the pattern is used to match against the entire representation
of the component; hence, the framing (including initiators) is visible to
the pattern.
It is a schema definition error if dfdl:alignment is not 1 .
It is a schema definition error if dfdl:leadingSkip is not 0.
It is a schema definition error if dfdl:encoding is not defined.
Errata Section 7.8 newVariableInstance
dfdl:newVariableInstance can be placed as an annotation on sequence,
choice, and group references.
Replace: "It is a schema definition error to have more than one
newVariableInstances for the same variable at any given point in the
document." with "The resolved set of annotations for any schema component
can contain multiple dfdl:newVariableInstance annotations, but they must
each refer to a different variable. It is a schema definition error
otherwise."
Errata Section 7.9: setVariable
Correct language to be consistent with: "dfdl:setVariable may be placed as
an annotation on sequence, choice, group references, local and global
element declarations for elements of simple type, element references to
elements of simple type, and simple type definitions. "
Replace "It is a schema definition error to have more than one
dfdl:setVariable for the same variable at any given point in the
document." with "The resolved set of annotations for any schema component
can contain multiple dfdl:setVariable annotations, but they must each
refer to a different variable. It is a schema definition error otherwise."
Errata: New Section 7.10: Evaluation Order for Statement Annotations
Of the resolved set of annotations for a schema component, some are
statement annotations and the order of their evaluation relative to the
actual processing of the schema component itself (parsing or unparsing per
its format annotations) is as given in the ordered lists below.
Implementations are free to optimize by recognizing and executing
discriminators or assertions with testKind='expression' earlier so long as
the resulting behavior is consistent with what results from the this
description:
For elements:
1. dfdl:discriminator with testKind='pattern' (parsing only)
2. dfdl:assert(s) with testKind='pattern' (parsing only)
3. Processing of the element schema component itself (as per format
annotations)
4. dfdl:setVariable(s) - See note below.
5. dfdl:discriminator with testKind='expression' (parsing only) -
Evaluated even on failure of steps 3, or 4. See note below.
6. dfdl:assert(s) with testKind='expression' (parsing only)
For sequences and choices:
1. dfdl:discriminator with testKind='pattern' (parsing only)
2. dfdl:assert(s) with testKind='pattern' (parsing only)
3. dfdl:newVariableInstance(s)
4. dfdl:setVariable(s)
5. Processing of the sequence/choice component itself (as per
format annotations)
6. dfdl:discriminator with testKind='expression' (parsing only) -
Evaluated even on failure of steps 3, 4, or 5. See note below.
7. dfdl:assert(s) with testKind='expression' (parsing only)
Note on Discriminators with testKind='expression'
When parsing, an attempt to evaluate a discriminator must be made even if
preceding statements or the parse of the schema component ended in a parse
error.
This is because a discriminator's expression could evaluate to true
thereby resolving a point of uncertainty even if the complete parsing of
the construct ultimately caused a parse error.
Such discriminator evaluation has access to the DFDL Infoset of the
attempted parse as it existed immediately before detecting the parse
failure. Attempts to reference parts of the DFDL Infoset that do not exist
are parse errors.
It is also a parse error to read any variables defined by any
dfdl:newVariableInstance statement evaluations that failed, or to read any
variables set by any dfdl:setVariable statements that failed.
Note on the dfdl:setVariable Statement for Elements
Of the resolved set of annotations, the dfdl:setVariable statements for an
element schema component (combined from an element reference, element
declaration, and base and derived simpleType definitions) are executed
after the parsing of the element. This is incontrast to the evaluation
order for dfdl:setVariable statements on the resolved annotations of a
sequence/choice, which are executed before the parsing of the
sequence/choice.
For elements, this implies that these variables are set after the
evaluation of expressions corresponding to any computed DFDL format
properties for that element, and so the variables may not be referenced
from expressions that compute these DFDL properties.
That is, if an expression is used to provide the value of a format
property (such as dfdl:terminator, or dfdl:byteOrder), the evaluation of
that format property expression occurs before any dfdl:setVariable
annotation from the resolved set of annotations for that element are
executed; hence, the expression providing the value of the format property
may not reference the variable. Schema authors can insert sequences to
provide more precise control over when variables are set.
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