[DFDL-WG] Proposed feature: lookup tables via simple type unions
Steve Hanson
smh at uk.ibm.com
Wed Sep 12 11:56:13 EDT 2018
Hi Mike
I have taken a look at your revised proposal at
https://cwiki.apache.org/confluence/display/DAFFODIL/Proposal%3A+Features+to+Support+Table-Lookup
.
Can you augment the example with use of the simple type by an element? I
think this might highlight a problem. Today we allow the DFDL
representation properties for a simple element to be split across the
element declaration and the (hierarchy) of simple types. Your proposal is
allowing the rep type of an element to be other than the allowed set for
the simple type of the element. This prevents the combination of rep
properties across the element and the simple type. In fact, it means that
all type dependent rep properties would have to be carried by the rep
type. That's not going to work because of scoping rules - you can't just
switch off property applicability.
Regards
Steve Hanson
IBM Hybrid Integration, Hursley, UK
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
smh at uk.ibm.com
tel:+44-1962-815848
mob:+44-7717-378890
Note: I work Tuesday to Friday
From: Steve Hanson/UK/IBM
To: Mike Beckerle <mbeckerle.dfdl at gmail.com>
Cc: "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>
Date: 04/04/2017 13:42
Subject: Re: [DFDL-WG] Proposed feature: lookup tables via simple
type unions
Although signed-up to Confluence I couldn't see a way to comment on the
proposal there.
I'm not comfortable with the proposal.
1) It relies upon validation being enabled, which is an optional feature.
There is a long-held principle that switching on validation does not
change the behaviour of a parse, but this will do exactly that.
[unionMemberSchema] String. For simple element information items, this
member contains an SCD reference to the member of the union that matched
the value of the element. Empty if validation is not enabled. Empty if the
element's type is not a union.
2) DFDL does not allow the concept of an annotation on a simple type that
is a union member. We would be allowing that, but with a completely
disjoint property set.
Unions; the memberTypes must be derived from the same simple type. DFDL
annotations are not permitted on union members
3) The proposal does not help the case where I am not using unions but
still would like enums translated into meaningful strings, a far more
common situation.
I think this processing is best left to either an independent post-parse
step or a parser extension via a set of non-DFDL annotations.
Regards
Steve Hanson
IBM Hybrid Integration, Hursley, UK
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
smh at uk.ibm.com
tel:+44-1962-815848
mob:+44-7717-378890
From: Mike Beckerle <mbeckerle.dfdl at gmail.com>
To: "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>
Date: 22/02/2017 17:38
Subject: [DFDL-WG] Proposed feature: lookup tables via simple type
unions
Sent by: "dfdl-wg" <dfdl-wg-bounces at ogf.org>
A write up of the proposal, which we are prototyping in Daffodil, is here:
https://opensource.ncsa.illinois.edu/confluence/display/DFDL/Enumerations+and+Range+Tables+via+Simple+Type+Unions
This is needed by a number of data formats we are working with where there
are large enumerations having as many as 2000 members. Often these
enumerations are a mixture where single values correspond to some
enumerated strings, and ranges of values correspond to others.
Using expressions to translate representation integers into strings is
infeasible, as no constant-time case-statement-like construct is available
in DFDL.
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology |
www.tresys.com
Please note: Contributions to the DFDL Workgroup's email discussions are
subject to the OGF Intellectual Property Policy
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Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
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