Re: Question on FHIR references - relative and absolute URIs

Hi Vassil,

Technically a relative reference and an absolute reference are distinct
things.  Relative reference says if the data moves to a new server, the
reference movies to.  An absolute reference says if the data moves to a new
server, the reference points to the original server.  So I'm not sure that
we *want* them to resolve to the same thing from a canonicalization
perspective.  That said, it's an option to explore


Lloyd

*Lloyd McKenzie*, P.Eng.
Senior Consultant, Information Technology Services
Gevity Consulting Inc.

 E: lmckenzie@gevityinc.com
M: +1 587-334-1110 <1-587-334-1110>
W: gevityinc.com


*GEVITY**Informatics for a healthier world *

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On Wed, Apr 27, 2016 at 1:24 PM, Vassil Peytchev <vassil@epic.com> wrote:

> Would adding “FHIR Canonicalization” help in this case? I.e., you apply
> canonicalization of the serialized format (format-dependent, XML canonical
> form as an example), then replace relative URL with absolute URLs (one of,
> and so far the only form of FHIR canonicalization), and then sign, you will
> have the same digital signature every time….
>
>
>
> *From:* owner-its@lists.hl7.org [mailto:owner-its@lists.hl7.org] *On
> Behalf Of *Lloyd McKenzie
> *Sent:* Wednesday, April 27, 2016 12:11 PM
> *To:* tlukasik@exnihilum.com
> *Cc:* David Booth <david@dbooth.org>; Robert Hausam <rrhausam@gmail.com>;
> Grahame Grieve <grahame@healthintersections.com.au>; its@lists.hl7.org;
> w3c semweb HCLS <public-semweb-lifesci@w3.org>
> *Subject:* Re: Question on FHIR references - relative and absolute URIs
>
>
>
> Hi Thomas,
>
>
>
> Same digital signature means that - after cannonicalization - there are
> the same bytes.  That's key.  Indenting the XML changes the raw bytes, but
> doesn't change the bytes of the canonicalized form.  On the other hand,
> changing relative URLs to full URLs does change the bytes of the
> cannonicalized form).  It also changes server-portability of instances.
>
>
>
>
>
> Lloyd
>
>
> *Lloyd McKenzie*, P.Eng.
> Senior Consultant, Information Technology Services
> Gevity Consulting Inc.
>
>  E: lmckenzie@gevityinc.com
> M: +1 587-334-1110 <1-587-334-1110>
> W: gevityinc.com
>
>
> *GEVITY **Informatics for a healthier world *
>
> CONFIDENTIALITY – This communication is confidential and for the exclusive
> use of its intended recipients. If you have received this communication by
> error, please notify the sender and delete the message without copying or
> disclosing it*.*
>
> NOTE: Unless explicitly stated otherwise, the opinions and positions
> expressed in this e-mail do not necessarily reflect those of my employer,
> my clients nor the organizations with whom I hold governance positions
>
>
>
> On Wed, Apr 27, 2016 at 12:28 PM, <tlukasik@exnihilum.com> wrote:
>
> >> "*One is "having the same bytes".  That's a strict interpretation.
> Another is "having the same digital signature". That's looser*"
>
>
>
> I'd disagree with that statement, David.
>
>
>
> To have the same digital signature it would have to have * the same bytes*,
> and in fact if even a single bit is different then it won't produce the
> same digital signature.
>
>
>
> So I don't agree that those are different "definitions" of "the same
> thing", or that the digital signature interpretation is "looser".
>
>
>
> TJL
>
>
>
> ---------------------------- Original Message ----------------------------
> Subject: Re: Question on FHIR references - relative and absolute URIs
> From: "David Booth" <david@dbooth.org>
>
> Date: Wed, April 27, 2016 9:48 am
> To: tlukasik@exnihilum.com
> "Robert Hausam" <rrhausam@gmail.com>
> Cc: "Lloyd McKenzie" <lloyd@lmckenzie.com>
> "Grahame Grieve" <grahame@healthintersections.com.au>
> "its@lists.hl7.org" <its@lists.hl7.org>
> "w3c semweb HCLS" <public-semweb-lifesci@w3.org>
> --------------------------------------------------------------------------
>
> > On 04/27/2016 01:33 AM, tlukasik@exnihilum.com wrote:
> >> >> "We always had stated that we must be able to get back "the same
> >> thing"."
> >> That's true, Rob.. we've always included round-tripability in our
> >> conversations, but (and again, please correct me if I seem to be missing
> >> or misunderstanding something), "the same thing" does not always mean
> >> the same thing.
> >> It might mean "equality" or it might mean "equivalence". That's the
> >> reason that we have both an "==" and an "===" operator in many
> >> programmimg languages.
> >> So getting back to the original question that David asked and Lloyd
> >> offered some insight into, it sounds to me like the answer is that
> >> messing with the URI's might be OK if we're only required to make sure
> >> that they're "the same thing" in the sense that they're equivalent
> >> (meaning that "they point to the same thing"), but it wouldn't be OK if
> >> they have to be "the same thing" in the stricter sense of not altering
> >> the digital signature.
> >
> > Right now we essentially have two well-defined interpretations of what
> > "the same thing" might mean. One is "having the same bytes". That's a
> > strict interpretation. Another is "having the same digital signature".
> > That's looser, but it is still a clear definition that we do not need
> > to invent. If we were to invent a third interpretation that is even
> > looser then we would have to clearly define it and describe the problem
> > that it is intended to solve. Such a definition could have some utility
> > but I am doubtful that it would be enough to justify the work and the
> > confusion that would be added by having one more notion of equivalence.
> >
> > David Booth
> >
> >> TJL
> >>
> >> ---------------------------- Original Message
> ----------------------------
> >> Subject: Re: Question on FHIR references - relative and absolute URIs
> >>
> From: "Robert Hausam" <rrhausam@gmail.com>
> >> Date: Tue, April 26, 2016 11:54 pm
> >> To: tlukasik@exnihilum.com
> >> Cc: "David Booth" <david@dbooth.org>
> >> "Lloyd McKenzie" <lloyd@lmckenzie.com>
> >> "Grahame Grieve" <grahame@healthintersections.com.au>
> >> "its@lists.hl7.org" <its@lists.hl7.org>
> >> "w3c semweb HCLS" <public-semweb-lifesci@w3.org>
> >>
> --------------------------------------------------------------------------
> >>
> >> > Right. We always had stated that we must be able to get back "the same
> >> > thing". And signature is a means to verify that.
> >> >
> >> > Rob
> >> >
> >> > On Tue, Apr 26, 2016 at 6:05 PM, <tlukasik@exnihilum.com> wrote:
> >> >
> >> >> >> "It has been mentioned before, as a way to clarify what qualifies
> as
> >> >> successful round tripping."
> >> >>
> >> >> David..
> >> >>
> >> >> I wasn't doubting that it was ever mentioned. My concern was that we
> may
> >> >> not be keeping the additional challenge that signing introduces in
> mind
> >> >> when evaluating and testing the round tripping of our prototype RDF
> >> >> instances.
> >> >>
> >> >> I think that if we *were* doing that, we would have been aware of
> what
> >> >> Lloyd pointed out, and have been able to answer our own question RE
> the
> >> >> preservation of absolute and relative URIs.
> >> >>
> >> >> TJL
> >> >>
> >> >> ---------------------------- Original Message
> >> ----------------------------
> >> >>
> >> >> Subject: Re: Question on FHIR references - relative and absolute URIs
> >> >>
> >>
> From: "David Booth" <david@dbooth.org>
> >> >> Date: Tue, April 26, 2016 4:05 pm
> >> >> To: tlukasik@exnihilum.com
> >> >> Cc: "Lloyd McKenzie" <lloyd@lmckenzie.com>
> >> >> "Grahame Grieve" <grahame@healthintersections.com.au>
> >> >>
> >> >> "its@lists.hl7.org" <its@lists.hl7.org>
> >> >> "w3c semweb HCLS" <public-semweb-lifesci@w3.org>
> >> >>
> >>
> --------------------------------------------------------------------------
> >> >>
> >> >> > On 04/26/2016 03:44 PM, tlukasik@exnihilum.com wrote:
> >> >> >> >> "If we want the RDF to be an equal sibling to xml and JSON then
> >> >> >> round tripping needs to be signature safe."
> >> >> >> David..
> >> >> >> Lloyd's comment points out the need for a significant and
> non-trivial
> >> >> >> "uptick" in the level of care that will have to be taken when
> >> generating
> >> >> >> RDF.
> >> >> >> I certainly haven't been to every single FHIR RDF meeting (so
> please
> >> >> >> correct me if I'm wrong), but I don't recall "signature safety"
> being
> >> >> >> discussed much (if at all) when we've discussed aspects of round
> >> >> tripping.
> >> >> >
> >> >> > It has been mentioned before, as a way to clarify what qualifies as
> >> >> > successful round tripping. Successful round tripping means getting
> >> back
> >> >> > "the same thing" if you convert from one FHIR serialization to
> another
> >> >> > and back again. But in deciding what we mean by "the same thing"
> one
> >> >> > might not expect something like whitespace differences to count as
> >> >> > consequential differences, whereas other changes definitely should
> be
> >> >> > considered important. The digital signature criteria provide a way
> to
> >> >> > arbitrate between important and unimportant differences.
> >> >> >
> >> >> > David
> >> >> >
> >> >> >> TJL
> >> >> >>
> >> >> >> ---------------------------- Original Message
> >> >> ----------------------------
> >> >> >> Subject: Re: Question on FHIR references - relative and absolute
> URIs
> >> >> >>
> >> >>
> >>
> From: "Lloyd McKenzie" <lloyd@lmckenzie.com>
> >> >> >> Date: Tue, April 26, 2016 3:00 pm
> >> >> >> To: "Grahame Grieve" <grahame@healthintersections.com.au>
> >> >> >> Cc: "David Booth" <david@dbooth.org>
> >> >> >> "its@lists.hl7.org" <its@lists.hl7.org>
> >> >> >> "w3c semweb HCLS" <public-semweb-lifesci@w3.org>
> >> >> >>
> >> >>
> >>
> --------------------------------------------------------------------------
> >> >> >>
> >> >> >> > If we want the RDF to be an equal sibling to xml and JSON then
> >> round
> >> >> >> > tripping needs to be signature safe. At the moment, that means
> >> >> retaining
> >> >> >> > absolute vs. relative references.
> >> >> >> >
> >> >> >> > On Tuesday, April 26, 2016, Grahame Grieve <
> >> >> >> > grahame@healthintersections.com.au> wrote:
> >> >> >> >
> >> >> >> >> well, this is tricky. technically, it's not strictly required,
> but
> >> >> >> it's a
> >> >> >> >> lossy transform (lossy in both ways, in fact). One of the
> >> >> attractions of
> >> >> >> >> fhir;reference for me is that you can have an absolute
> >> reference for
> >> >> RDF
> >> >> >> >> and preserve the original fhir url
> >> >> >> >>
> >> >> >> >> Grahame
> >> >> >> >>
> >> >> >> >>
> >> >> >> >> On Wed, Apr 27, 2016 at 3:01 AM, David Booth <david@dbooth.org
> >> >> >> >> <javascript:_e(%7B%7D,'cvml','david@dbooth.org');>> wrote:
> >> >> >> >>
> >> >> >> >>> Grahame and/or Lloyd,
> >> >> >> >>>
> >> >> >> >>> In today's FHIR RDF teleconference, a question came up about
> >> >> >> relative and
> >> >> >> >>> absolute URIs in FHIR references.
> >> >> >> >>>
> >> >> >> >>> Must absolute and relative references be round tripped as is?
> >> I.e.,
> >> >> do
> >> >> >> >>> we need to maintain the distinction between relative and
> absolute
> >> >> >> >>> references when round tripping, or can relative URIs be
> >> turned into
> >> >> >> >>> absolute URIs and vice versa?
> >> >> >> >>>
> >> >> >> >>> I did not see any mention of normalizing references in the
> >> >> >> discussion of
> >> >> >> >>> Canonical JSON:
> >> >> >> >>> https://hl7-fhir.github.io/json.html
> >> >> >> >>>
> >> >> >> >>> Thanks,
> >> >> >> >>> David Booth
> >> >> >> >>>
> >> >> >> >>>
> >> >> >> >>
> >> >> >> >>
> >> >> >> >> --
> >> >> >> >> -----
> >> >> >> >> http://www.healthintersections.com.au /
> >> >> >> grahame@healthintersections.com.au
> >> >> >> >>
> >> <javascript:_e(%7B%7D,'cvml','grahame@healthintersections.com.au');>
> >> >> /
> >> >> >> >> +61 411 867 065
> >> >> >> >>
> >> >> >> >>
> >> >> >> >>
> >> >> >>
> >> >>
> >>
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> >> >> >> >
> >> >> >> >
> >> >> >> > --
> >> >> >> >
> >> >> >> > *Lloyd McKenzie*, P.Eng.
> >> >> >> > Senior Consultant, Information Technology Services
> >> >> >> > Gevity Consulting Inc.
> >> >> >> >
> >> >> >> > E: lmckenzie@gevityinc.com
> >> >> >> > M: +1 587-334-1110 <1-587-334-1110>
> >> >> >> > W: gevityinc.com
> >> >> >> >
> >> >> >> >
> >> >> >> > *GEVITY**Informatics for a healthier world *
> >> >> >> >
> >> >> >> > CONFIDENTIALITY – This communication is confidential and for the
> >> >> >> exclusive
> >> >> >> > use of its intended recipients. If you have received this
> >> >> >> communication by
> >> >> >> > error, please notify the sender and delete the message without
> >> >> copying or
> >> >> >> > disclosing it*.*
> >> >> >> >
> >> >> >> > NOTE: Unless explicitly stated otherwise, the opinions and
> >> positions
> >> >> >> > expressed in this e-mail do not necessarily reflect those of my
> >> >> employer,
> >> >> >> > my clients nor the organizations with whom I hold governance
> >> positions
> >> >> >> >
> >> >> >> >
> >> >> >>
> >> >>
> >>
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> >> >
> >> >
> >> > --
> >> > Robert Hausam, MD
> >> > +1 (801) 949-1556
> >> > rrhausam@gmail.com
> >> >
> >> >
> >>
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