[dfdl-wg] Telecon minutes 2006-04-12

[Steve Hanson]

If my understanding is correct, you are proposing to replace the single
calendarPattern property within a calendarScheme by set of pattern
properties, one for each of the built-in XML Schema date/time logical
types. I'm ok with that.  So we would have the following pattern
properties, and the property to use for a given element is governed by the
schema type.

calendarDateTimePattern
calendarDatePattern
calendarTimePattern
calendarYearMonthPattern
calendarYearPattern
calendarMonthPattern
calendarMonthDayPattern
calendarDayPattern

I like the proposal for separatorEncoding too.

Regards, Steve

Steve Hanson
WebSphere Message Brokers,
IBM United Kingdom Ltd, Hursley, UK
Internet: smh at uk.ibm.com
Phone (+44)/(0) 1962-815848


                                                                           
             Mike Beckerle                                                 
             <beckerle at us.ibm.                                             
             com>                                                       To 
             Sent by:                  dfdl-wg at ggf.org                     
             owner-dfdl-wg at ggf                                          cc 
             .org                                                          
                                                                   Subject 
                                       [dfdl-wg] Telecon minutes           
             12/04/2006 17:52          2006-04-12                          
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           





DFDL WG call 2006-04-12

Bob McGrath
Geoff Judd
Mike Beckerle

Agenda
- arrays discussion
- issue of defaults
- outstanding property document discussion (deferred until a call with more
participants, particularly S. Hanson)

Arrays

We considered the 'string-with-all-lengths-first' example sent by MikeB. It
uses a @dfdl:index extension to our Xpath expression language. Email
traffic to the list asked for clarifications of why this is not just the
Xpath position() function. MikeB to post clarification.

We considered whether the @dfdl:index provides enough/too-much expressive
power. We agreed to create a 2d example. The parse/read direction seems
likely to work fine. The write/output direction seems less clear, but we'll
create a parse/read example first and then consider how/where to hang the
"inverse index calculations" on it.

Defaults

This is discussion of this issue raised by S. Hanson when he posted the
'properties' document on 3/23:

    - The issue of defaults poses some questions. We have agreed that
    hard-wired model defaults are not desirable as it means the absence of
a
    property implies a behaviour. If we wish to change this behaviour then
we
    are stuck because existing DFDL Schema then behave differently. So the
    proposal in the scoping document is that all properties that are used
    during a parse/serialise must have an explicit value defined somewhere
in
    the DFDL Schema, typically in a dfdl:defineFormat annotation. However,
    there are properties where we don't want a one-value-fits-all value,
but at
    the same time do not want to specify a value on every element. Example:

    justification, where typically all strings are left justfied, and all
    numbers are right justified.  Example: calendarPattern, where the
patterns
    for a date, dateTime, time, monthDay, etc are different. One approach
is to
    duplicate the properties - so we would have textStringJustification,
    textNumberJustification, and so on. You will see that this is what I
have
    done in the document for justification.  An alternative approach is to
have
    one property, but to add an additional enum 'schema', which means
derive
    the default from the logical type. You will see that this is what I
have
    done for calendarPattern. So calendarPatternKind set to 'schema' for
    xsd:date would yield "yyyy-MM-dd" and for xsd:time would yield
    "hh:mm:ss.sss". Of course, 'schema' can be considered a form of
    hard-wiring, so maybe we also need some properties that define what
these
    defaults are (they'd only ever be set at dfdl:defineFormat level)?  We
need
    to decide which of these approaches is preferred, whether they both
make
    sense, or if there is a better way.

We propose that the general approach here should be to split the
properties. That is, the textNumberJustification and
textStringJustification solution be used wherever this problem exists.

We couldn't see why the calendar stuff is sufficiently different. It seems
that there should be a datePattern, timePattern, dateTimePattern, and so
forth and these should be independent properties.

Another issue was identified which is exemplified by the separatorEncoding
property. It is possible for a separator to have a distinct character set
(obscure, but possible). However, in most cases it does not, and one would
like separatorEncoding to get its value from the regular encoding property.
However, if separatorEncoding was to have no binding at all in the entire
scope then this makes things quite confusing. Adding a binding for
separatorEncoding at an outer scope would affect lots of enclosed separator
behavior in unexpected ways.

Proposed solution: when properties are linked like this don't allow things
to be 'unbound', but rather require a binding which specifically states the
linkage between the properties. For example: in one of the include files at
top level there would be a defineFormat where separatorEncoding is bound to
a distinguished value which means "take the value for this property from
the encoding property". Scoping would then find this distinguished value
for separatorEncoding, and then start over from the scope of the separator
construct searching the scope/context for the encoding property. This can
be clarified in the next scoping draft and should solve the problem. The
syntactic device for specifying the value of one property to come from
another property is TBD.