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https://issues.apache.org/jira/browse/DAFFODIL-2692?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17581540#comment-17581540
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Mike Beckerle commented on DAFFODIL-2692:
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Recent email discussion suggests this idea should evolve to be not just value
pattern, but the pattern should be expressed by way of the XSD facets on an
element.
See: [https://lists.apache.org/thread/3t3j72k9z6dcpyb4pqsh5mh5lg53mgt9]
The name 'valuePattern' may not be well-chosen given this different direction.
At the crux of this all is the realization that the value patterns must be
regex with longest-match for alternatives as the semantics. XSD pattern facet
matching has this behavior, the dfdl:lengthKind 'pattern' regex engine does
NOT. it has the left-to-right order behavior.
(Also: Apache Xerces has an XSD validator which contains a regex matcher for
pattern facets that implements this longest-match behavior, so there's at least
one source of an open-source acceptable license code-base for this regex
engine.)
> Add lengthKind 'valuePattern' which uses regex to match allowed data values
> ---------------------------------------------------------------------------
>
> Key: DAFFODIL-2692
> URL: https://issues.apache.org/jira/browse/DAFFODIL-2692
> Project: Daffodil
> Issue Type: New Feature
> Components: Back End, Front End
> Affects Versions: 3.3.0
> Reporter: Mike Beckerle
> Priority: Major
>
> Existing dfdl:lengthKind 'pattern' uses the pattern to determine the length.
> No match means length 0.
> People want to use regular expression (or regex) matches differently from
> this. They want to specify the allowed data patterns, with no match meaning
> parse error.
> This should be added as a dfdlx experimental feature to develop experience
> with it.
> A few design issues: we need to decide if this pattern includes nil values in
> its syntax, or if those get added as allowed value patterns automatically. It
> is simpler if we define this to require that the regex pattern specify all
> possible data patterns that are accepted, whether they become nilled
> elements, or elements with values. That, however, requires one to redundantly
> express the dfdl:nilValue information.
> There may also be an interaction with properties like
> dfdl:emptyValueDelimiterPolicy and the empty representation. I.e., does the
> pattern have to allow for a zero-length successful match in order for the
> data to be zero-length?
>
>
>
>
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