[DFDL-WG] Fw: Agenda for OGF DFDL WG call 03 February 2010- 13:00 UK (8:00 ET)
Alan Powell
alan_powell at uk.ibm.com
Wed Feb 3 05:18:11 CST 2010
1. Action 077 Cobol and numberFormats
Review two options (attached)
2. Remaining 037 review issues
See below
3. Go through Actions
Current Actions:
No
Action
045
20/05 AP: Speculative Parsing
27/05: Psuedo code has been circulated. Review for next call
03/06: Comments received and will be incorporated
09/06: Progress but not discussed
17/06: Discussed briefly
24/06: No Progress
01/07: No Progress
15/07: No progress. MB not happy with the way the algorithm is documented,
need to find a better way.
29/07: No Progress
05/08: No Progress. Will document behaviour as a set of rules.
12/08: No Progress
...
16/09: no progress
30/09: AP distributed proposal and others commented. Brief discussion AP
to incorporate update and reissue
07/10: Updated proposal was discussed.Comments will be incorporated into
the next version.
14/10: Alan to update proposal to include array scenario where minOccurs >
0
21/10: Updated proposal reviewed
28/10: Updated proposal reviewed see minutes
04/11: Discussed semantics of disciminators on arrays. MB to produce
examples
11/11: Absorbing action 033 into 045. Maybe decorated discrminator kinds
are needed after all. MB and SF to continue with examples.
18/11: Went through WTX implementation of example. SF to gather more
documentation about WTX discriminator rules.
25/11: Further discussion. Will get more WTX documentation. Need to
confirm that no changes need to Resolving Uncertainty doc.
04/11: Further discussion about arrays.
09/12: Reviewed proposed discriminator semantic.
16/12: Reviewed discriminator examples and WTX semantic.
23/12: SF to provide better description of WTX behaviour and invite B
Connolley to next call
06/01:B Connolly not available. SF to provide more complete description.
13/01: Stephaine took us through a description of WTX identifiers. Mike
agreed to write up in DFDL terms.
20/01: Mike will write up
27/01: further discussion of discriminators
29/01: Alan had emailed bot proposals but not enough time to discuss
049
20/05 AP Built-in specification description and schemas
03/06: not discussed
24/06: No Progress
24/06: No Progress (hope to get these from test cases)
15/07: No progress. Once available, the examples in the spec should use
the dfdl:defineFormat annotations they provide.
...
14/10: no progress
21/10: Discussed the real need for this being in the specification. It
seemed that the main value is it define a schema location for downloading
'known' defaults from the web.
28/10: no progress
04/11: no progress
11/11: no update
18/11: no update
25/11: Agreed to try to produce for CSV and fixed formats
04/12: no update
09/12: no update
16/12: no update
23/12: no update
06/01: no progress. If there is no resource to complete this action it can
be deferred
13/01:no progress
20/01: no progress
27/01: no progress
29/01: No progress. The predefined formats do not need to be available
when the spec is published.
Suman said that he had been mapping COBOL structures to DFDL and it didn't
look as though the way text numbers are define is very usable. He will
document for next call
066
Investigate format for defining test cases
25/11:IBM to see if it is possible to publish its test case format.
04/12: no update
09/12: no update
16/12: reminded dent to project manager
23/12: SH will send another reminder.
06/01: Another reminder will be sent
13/01: no update
20/01: no update
27/01: no progress
29/01: no progress
077
SKK: mapping of COBOL numbers to textNumberFormats.
A few comments in-line below
On Wed, Jan 20, 2010 at 7:01 AM, Alan Powell <alan_powell at uk.ibm.com>
wrote:
I have answered most of the issues and comments raised by Steve and Mike
but some need further discussion.
Issues from Steve H
2. I agree with the existing comment that the RFC2119 key words should be
upper case.
16.2. I'm not sure that scannability in this constant encoding sense is
necessary for patterns. I can create a regular expression that extracts
all characters up to hex value xXX or all characters up to xYY, thereby
treating the content as an encoding in-sensitive black box.
If your byte pattern happens to be a legal part of a multi-byte character
sequence, then you'll get a false recognition, or you won't get what you
expect.
Example: You are searching for byte 0xAA, but that can legally appear as
byte 3 of a 3-byte UTF-8 encoded character. When you say you are looking
for hex AA in a string, DFDL is currently defined to mean you are looking
for the character reprsented by that raw byte. If the encoding is UTF-8,
that isn't a legal character encoding sequence even, so the decoder should
cause an error or something.
Even for a fixed length single byte character set, you have to have no
unused code that have no mapping to ISO 10646, because our infoset is
defined in terms of translations into that.
I think we need encoding="none" or encoding="bytes" or something if you
really want to scan bytes without encoding causing problems.
Issues from Mike B
· Tracker issue: codepoints outside BMP, as literals and in data.
· If I put in a value that requires use of a high/low surrogate
pair, is that an error, does it require me to put in two separate %#...;
thingys, one for each of the surrogates (in which case these are not
really code points in ISO10646). If I put in a codepoint for one of the
supplemental characters and the schema itself is written in UTF-16 then
that has to translate into literal surrogate pair. Ok, but I?m very
uncertain about all this stuff
The above item had two issues glomed together. There really are two
separate issues. The above is about these crazy codepoints that use
surrogate pairs. That's a minor corner case given the amount of use those
get.
The bigger issue is the one below, which is about things that either are
in strings and are broken character encodings, but we still need to be
able to process the data. There's also the matter of recovery from errors
in decoding, and what we put out when the infoset contains a character
code where there is no valid encoding, or just a character code which
isn't even in ISO 10646 (e.g., character code 0xFFFFFFFF, which is not a
valid character at all.
Tracker Issue: illegal character encodings for parsing and unparsing. TBD:
how do these make it into the infoset or are they replaced, and if so how
TBD: can one represent these in the infoset for output? Ideally not, but?
· Tracker Issue: Processing-time Schema Definition Errors
This section (2.3.1 in this draft), is problematic as we?re trying to
allow simple DFDL implementations to not do a bunch of static checking,
yet if implementations differ on when Schema Definition errors are
detected, then the second paragraph says they are converted to processing
errors. This lets different implementations do very different things in
terms of how the speculative parsing back-tracks around.
Grammar ambiguity is a very tricky case. Unless a DFDL implementation can
prove a grammar to be unambiguous, then it is very hard to say that any
particular combinatino of delimiters make up a legal DFDL schema
definition. If the parser simply fails because the grammar was ambiguous,
there?s no way to tell the difference between this and just broken data
without proving the grammar is unambiguous. In general it is formally
undecidable whether a grammar is ambiguous or unambiguous. (
http://books.google.com/books?id=lIuu53IcKWoC&pg=PT217&lpg=PT217&dq=proving+a+grammar+is+unambiguous&source=bl&ots=wie8TAt-MT&sig=ZSD7tIwnXZIT8Ic91BWMH2H2dKg&hl=en&ei=hAQ5S5vPOIri7APc37CKBg&sa=X&oi=book_result&ct=result&resnum=10&ved=0CDAQ6AEwCQ#v=onepage&q=proving%20a%20grammar%20is%20unambiguous&f=false
)
Since DFDL v1.0 doesn?t allow recursive declarations/definitions, it may
be possible to provide the ambiguity or unambiguity of a DFDL schema (or
rather, the data syntax grammar described by it ? if you want to bother to
distinguish the two), but recursion isn?t something we want to rule out
for the future, so
Type checking is decidable in DFDL?s expression language, so we could
always detect type safety before run time; however, if we allow a
simplistic DFDL implementation to just check types at run time then this
would, by the definition in this section (2.3.1), issue processing errors
when it detects these at run time, thereby allowing backtracking of the
speculative parser to be driven off of type-checks in the expression
language. It seems to me that we need to find a way to put this problem
back into the hands of the user, and say that a schema where this actually
matters (one where a type error causes a backtrack, which ultimately
causes a successful parse) are illegal but implementations are allowed to
not detect this particular illegality.
It seems to me we need to put this problem back into the hands of the
user.
· Tracker Issue: "round trip" for infoset. Should we omit the
whole point?
· Tracker Issue: [schema] is an absolute or relative SCD. Why
bother allowing absolute?
· Tracker Issue: Glossary as the place for centralized
definitions, or should they be repeated there, but also introduced at
point of first use, or should we put the definitions only at the places
where they are discussed, and xref from the glossary?
· TBD: Issue - semantics of expressions containing relative paths
that are inherited via ref to a dfdl:defineFormat. (also section 10.3)
· TBD: Issue - XPath term - we are not consistent about using the
term XPath, or "expression" when referring to our expression language. I
prefer to call it our expression language, and then in the section that
defines it state that it is a strict subset of XPath 2.0.
· TBD: Issue - fn:position is unclear given that we've just said
we don't support sequences in the expression language.
· TBD: Issue - order of sections. Scoping rules section should
come before variables section, which uses these concepts.
TBD: Issue: Case sensitivity of enum names - did we say whether this is
case sensitive or not? I believe it should be case sensitive.
· Issue: dfdl:representation - Strings in binary rep. I see no
reason why elements of type xs:string will examine dfdl:representation.
They shouldn?t' care what it is, they are always "text". I should be able
to specify a bunch of inter-mixed binary number and string elements
without having to specify dfdl:representation="text' just to avoid an
error on the string type elements. I believe xs:string type ignores
dfdl:representation (always behaves as if dfdl:representation is
'text').(If we change this then the property precedence section for
simpletypes changes slightly as representation="text" is implied if type
is string.)
That will make it impossible to introduce a binary representation of text
later
What is "a binary representation of text"? Is there a real issue here.
This is a primary convenience and clarity issue for me. I do not want to
have to change to representation="text" for every string inside a cobol
structure, which is ultimately a binary representation object. To me
type="string" is enough. I want to put in the file scope level of the
schema a representation="binary", and then decorate the elements with the
specifics of their types, but I do not expect to have to put
representation="text" on anything.
I do not understand what you are trying to achieve by requiring
representation="text" for things that are already textual based on the
type.
The rest of the issues below I think we need to discuss on calls.
textStringPadCharacter textNumberPadCharacter - did we agree that this
character must be a "minimum width" character if the char set encoding is
variable width? (i.e., the pad char must be 1 byte if the encoding is
UTF-8.
numberInfinityRep numberNanRep - Is this applicable only to xs:double and
xs:float? Also, what I've seen requires a distinction of sign. I.e., there
are positive and negative infinities often printing as -inf and +inf.
· TBD: Issue - \n in regular expressions - clarify relationship of
this to entities like NL entity. Also, if I include an entity like WSP* in
a regular expression (can I?) does it then match accordingly?
It appears that some of our multi-valued entities like WSP+ create
conditional "matching" behavior without having to use regular expressions,
e.g., when WSP+ is used as a separator. But can you use entities like WSP+
in a regular expression? It seems you should be able to use regular
"single valued" entities in a regular expression, its these multi-valued
ones that have tricky semantics.
Added Unicode values to /n, /t,/r. Disallow DFDL entities in regular
expressions.
14.1 Alignment - TBD: Issue - zero-based thinking here. But all the bits
stuff and everything else in DFDL uses 1-based reasoning. Need to revisit
to make this sensible for 1 based world.
Added implicit alignment table. TBD zero-based
finalTerminatorCanBeMissing - spec is not clear. Also is there a
finalSeparatorCanBeMissing
Chaned to finalDocumentTerminatorCanBeMissing and
finalDocumentSeparatorCanBeMissing. Not sure where
finalDocumentSeparatorCanBeMissing should be specified. Looks odd on
'distinguished root'. These properties operate differently from other
properties as they are defined on the 'distinguished root' but affect some
lower down element. Effectively they are put in scope by a different
mechanism
Regards
Alan Powell
Development - MQSeries, Message Broker, ESB
IBM Software Group, Application and Integration Middleware Software
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