Hi Rich, the question I posed about getData() has nothing to do with the actual data being referenced - that is, and should be opaque to the LSID service itself (apart from the metadata describing the data, but that is not part of the service). Heck, it could be data about the number of coconuts consumed last year for all that matters. The question was about the functionality of the protocol and services that implement it. If an LSID is assigned to some data, then right now it is required that the data retrieved by getData() is always exactly the same byte sequence. That's fine. No more discussion required. Leave it be.
The issue that does concern me though is that requiring the exact same byte stream for data identified by an LSID can raise unexpected implementation issues that seem to be overly restrictive without improving functionality. My impression of LSIDs and their utility has always been as pointers to data which must always be consistent regardless of how or when the data is retrieved. This is not necessarily the same thing as saying the byte stream used to represent the data is always the same, and many examples of this can be provided. There are however, simple ways around this limitation (such as creating a new method as I outlined elsewhere) and perhaps there should be a little further discussion on this specific aspect of the LSID specification.
Dave V.
On Jul 16, 2007, at 06:22, Richard Pyle wrote:
I'm not sure I understand this fixation with the getData() call. Why is it so important to use that call to retrieve bytestream information relating to objects that are not themselevs inherently digital? Much of what we are intereseted in within the biodiversity informatics community, in terms of what we want to establish identifiers for, are not inherently digital objects and therefore should NOT have any bytes returned for getData (). Some of our objects *are* inherently digital (PDFs, image files of various formats, video clips, audio files, possibly Genbank sequences in a specified format and encoding, etc.) To me, the distinction is very simple: is the object that the LSID identifies a binary data file? If yes, then the binary data become the data of the LSID. If no, then the LSID has no binary "data" (sensu LSID Spec), and returns only metadata through getMetadata (). The LSID spec refers to such LSIDs as "Abstract" (or sometimes "Conceptual") LSIDs.
It's really not that complicated -- unless, as I suggested previously, I am missing something fundamentally important.
I don't understand the advantage we gain by "force-fitting" some digitized rendering of an otherwise non-digital object. Taxon Names (for example) have no inherent digital manifestation. We create an artificial digital representation of them by stringing ASCII or Unicode characters together in a way that resembles (in principle) the characters otherwise represented by ink on paper. But if we want to embed such a character string as "data" for an LSID, then the LSID is teally an identifier for the *character string* itself, NOT the "notion" or "idea" or "concept" of the taxon name. As a taxonomist and biodiversity informatics manager, I have very little use for LSIDs that identify specific charcter strings. I want an LSID that itentifies the shared understanding of a taxon name -- not an artificial/substitute rendering of the taxon name. I see no advantage to creating one LSID for a text string that encodes a taxon name as UTF-8, and another LSID for the same name encoded as UTF-16,and so on, and so on. These variants are purely artificial from the perspective of what I want an LSID for (i.e., the idea/notion/concept of a taxon name).
I do acknowledge that the idea of an "Abstract" LSID was really meant to serve as an "umbrella" of sorts to tie together multiple data- bearing LSIDs. The classic example is an image that can be represented as a RAW, a TIFF, or a JPEG file format. Assuming all three image files derive from the same shutter-release event of a camera, then the intended function of an "Abstract" LSID is to serve to gather together the LSIDs established for each of the three file formats of the "same" image. The images are the "same" only in the conceptual -- i.e., that they all derive from the shutter-release event. But the point is, the purpose of the "Abstract" LSID is really intended to be a mechanism of organizing data-bearing LSIDs that refer to different digital renderings of the "same thing". From the "LSID Best Practices" website (http://www-128.ibm.com/developerworks/opensource/library/os- lsidbp/), under the heading "Abstract LSIDs":
"The abstract LSID provides the anchor point for software and users to explore the metadata and obtain further pointers to all the concrete LSID references that contain data, along with the data's exact relationship to the abstract concept."
This implies that "Abstract" LSIDs should exist primarily to aggregate data-bearing LSIDs.
For the most part, I don't think this is what we are really trying to do when we want to assign LSIDs to non-digital objects like taxon names, specimens, etc. So, in a sense, what I am advocating deviates a bit from the intention of an "Abstract" LSID. But at least I'm not outright violating the fundamental tenents of the LSID spec, like trying to apply a single LSID to more than one bytestream returnable via getData().
So, again, I return to my original confusion: why all the fixation with the getData() call?
The only reasons I can think of are:
- Semantics (of the human communcation kind): We're uncomfortable
thinking of things like refering to the text string C-e-n-t-r-o-p-y-g-e (minus the dashes) as being mere "metadata" for the angelfish genus described by Kaup in 1860 -- when it just feels like the "actual" name to us (and hence should be thought of as "data").
- Persistence: We want to embed information as "data" for the LSID
because we want to make sure the "same information" is always there, and the LSID spec emphasizes the permanent relationship between an LSID and its data. The only trouble is, we want to define the word "same" in this context in a way that is utterly incomprehensible (without all manner of comparison algorithms) to a computer. *We* know that "Chaetodon" is the "same" as "Chætodon", so we want a single LSID to refer to the genus name for butterflyfishes described by Linnaeus in 1758. And we don't like being required to always choose one rendering or the other to embed as the bit-identical "data" for the LSID.
- Performance(?): This is where I may be missing something
fundamental. Are there characteristics of the getData() call that are far superior to getMetadata()?
As for number 1: all I can say is "get over it". Our unfortunate reality in biodiversity informatics is a proponderence of homonymy -- not just in taxon names, but in our human-mitigated communication lexicon as well.
As for number 2: We can deal with persistence through layers of standards and convention within our community. Almost everything we talk about involves an assumption of adherence to standards and conventions. If we want persistent metadata, then we need to formalize a document detailing which metadata elements should be mandatory and/or persistent and/ or have other properties that we as a community feel are important. This document would also outline when metadata may be modified for a given LSID, vs. when a new LSID should be generated, allowing certain metadata elements for each to remain unchanged (e.g., perhaps one LSID for "Chaetodon" and another for "Chætodon", for the object type "Digital Taxon Name Rendering"). The document would also outline how multiple LSIDs should be cross- referenced to each other (e.g., the two "DTNR" objects identified by two different LSIDs in the previous example would both refer to the same Abstract LSID established for the butterflyfish genus name described by Linnaeus in 1758).
As for number 3: I just hope someone can explain to me where I missed the boat.
One final note: I do see a way that we can preserve the spirit of intent for the "Abstract LSID" in our domain for things like Taxon Names. Rather than explain it here, I follow up with another email describing it.
Aloha, Rich
Richard L. Pyle, PhD Database Coordinator for Natural Sciences and Associate Zoologist in Ichthyology Department of Natural Sciences, Bishop Museum 1525 Bernice St., Honolulu, HI 96817 Ph: (808)848-4115, Fax: (808)847-8252 email: deepreef@bishopmuseum.org http://hbs.bishopmuseum.org/staff/pylerichard.html
From: tdwg-guid-bounces@lists.tdwg.org [mailto:tdwg-guid-bounces@lists.tdwg.org] On Behalf Of Chuck Miller Sent: Saturday, July 14, 2007 2:29 PM To: Ricardo Pereira Cc: tdwg-guid@lists.tdwg.org Subject: RE: [tdwg-guid] LSID metadata persistence (or lack thereof)
Ricardo, I disagree on your assertion of consensus on a couple of points.
On 2) there is no consensus/decision on whether XML can be returned from a getData call. I asked this question and it has not been answered. We could disallow XML as an allowed format for getData and allow it only for getMetadata. We do not have consensus and actually have disagreement on "We shouldn't for example return the bare scientific name of a species in the getData() call just because that can be immutable" because "the name itself is in the metadata" I for one believe that we cannot avoid returning a scientific name byte stream in the getData for an LSID for a scientific name. That requirement is fundamental to what we need for biodiversity data. Pragmatically and empirically, names and specimens/observations are THE most fundamental data objects existing today in the databases published by GBIF. So if we can't put LSIDs on names, we have failed to enable one of the most fundamental needs of this community. If the definition of LSIDs needs to be amended to enable that, then so be it.
Chuck
From: tdwg-guid-bounces@lists.tdwg.org on behalf of Ricardo Pereira Sent: Fri 7/13/2007 8:12 PM Cc: tdwg-guid@lists.tdwg.org Subject: Re: [tdwg-guid] LSID metadata persistence (or lack thereof)
Folks, Thanks much to all of you who replied to my post. All the postswere really relevant to our discussion.
Before we go ahead, however, let us stop for a minute to try andsummarize the points we agree upon and the points in which there is still significant controversy.
I believe that we reached consensus in the following issues:
- We do agree that *LSID metadata is not required to be persistent*
(i.e. clients cannot assume it is immutable). See note [1].
- We should not force XML representations of data to be byte
identical just to return that in the LSID getData() call. We must find another way to fulfill this requirement.
- We should not try to return something in the LSID getData() call
just for the sake of it. We shouldn't for example return the bare scientific name of a species in the getData() call just because that can be immutable and thus fulfill the requirement from the LSID spec. This is counterproductive because the name itself is in the metadata already and no client would gain anything from calling getData() in this case.
We have also raised new issues that may be worth discussing (intheir own separate thread if possible):
- We "may" bend the immutability rule of LSID getData() to our
benefit and accept data that is not byte stream identical, but only "semantically" identical (depending on content type maybe). If we do this, we may use the LSID getData() call more effectively to identify real datasets such as matrices, identification keys, etc.
- As Brian pointed out, we may need to revisit what we call data
and metadata. We have been using the LSID getMetadata() call to return what some people may call data (taxon names, specimens, collections). And we forgot completely that there may be other kinds of data out there that may be returned in the getData() call and that those still need metadata to describe them. I think this may be worth discussing in a separate thread.
Did I leave anything out? If so, please let us know by replyingto my post and adding a short entry to either list above.
Cheers,Ricardo
Notes:
[1] Matt may disagree with me here, but my point is that we can't force all authorities (i.e. data providers) to keep perfect archives of all versions of their databases given a heterogeneous and distributed environment we operate in. While some may want to provide this feature, other providers may not want or be able to.
Richard Pyle wrote:
It seems to me that there is a third method to resolving the
problem:
When we want to identify an object that is itself digital in
nature (e.g., a
database record, or a binary data file such as a PDF, JPG, ASCII,
Unicode,
or whatever), we resolve said binary object via getData(). If,
for some
reason, we change the exact bit-sequence of that digital/binary
object
(e.g., color-correct an image, change a text string from ASII to
Unicode, or
whatever...), we assign a new LSID to it (whether that "new" LSID
differs
from the "old" LSID only via the optional "Revision" part of the
LSID, or
via a new Object Identification part, is a topic for another
debate).
When we want to identify an object that does not itself have a
digital
manifestation -- like a physical object (e.g., specimen or a
particular
printed copy of a publication) or an abstract/conceptual object
(e.g., a
taxon name, a taxon concept, a geographica place, or a cited
publication) --
then we return *nothing* in response to getData(), and we treat
all the
attributes of said physical/abstract/conceptual object of interest
to us as
metadata.
If there are cases where certain metadata elements of an object
without an
inherent digital existence need to persists (and there are), yet
we also
want to allow modifications to metadata elements without the need
to
generate new identifiers for the underlying object (and we do) --
then we
deal with those within our own community via adopted standards and
best
practices.
I would disagree strongly with bending the existing LSID standard,
and would
just as strongly favor working within its existing framework
(which, I
think, we can). I would also disagree with the practice of
embedding XML
documents as "data" for an LSID, unless the LSID is intended to
represent
the XML document itself (in which case there might be a different
LSID to
represent the database record that was used to generate the XML
document;
and yet another LSID to represent the abstract concept that the
database
record was created to represent -- like a taxon name, for
example).
If we want to use LSIDs to pass around XML packages (that are not
rendered
as RDF) about abstract objects (e.g., taxon names), why doesn't
our
community define within our semantic vocabulary something along
the lines of
"TCS_XML", which can be established as a standard metadata
component for
LSIDs assigned to taxon concepts (i.e., abstract objects,
identified by
"data-less" LSIDs). The exact bytestream of the content of that
metadata
element can change, without changing its canonical rendering.
I'm beginning to suspect (strongly) that I am completely missing
some
fundamental point here -- and perhaps is is the same point that
underlies
the apparent antagonism towards LSIDs in general (which I do not
yet share).
But I am fairly certain we are dealing with some level of
miscommunication
here.
Aloha, Rich
-----Original Message----- From: tdwg-guid-bounces@lists.tdwg.org [mailto:tdwg-guid-bounces@lists.tdwg.org] On Behalf Of P. Bryan Heidorn Sent: Friday, July 13, 2007 12:48 PM To: Dave Vieglais Cc: tdwg-guid@lists.tdwg.org Subject: Re: [tdwg-guid] LSID metadata persistence (or lack thereof)[Scanned]
There seems to be two methods to resolving this problem.
One is to change the LSID definitions to allow semantic equivalence in the data and not require exact bit stream
equivalence.
The other option is to change the data representation so that it is "easily" reduced to a repeatable canonical form. For example, it is almost as easy as saying where XML ordering does not specify order of elements, elements will be ordered alphabetically. Seems stupid but it almost works.. except where you have repeating elements with the same element name where it does not work.
It seems a little odd to bend the standards for the data being delivered to fit the requirement of the LSID spec. In theory, the other standard developers who set the data being delivered did not fix order because it did not matter.
This is different from Chuck's observation that the semantics of the element within some of the standards are insufficiently specified. So, what we mean is a darwin mode species name is just a string and nothing more now.
--Bryan
On Jul 13, 2007, at 5:18 PM, Dave Vieglais wrote:
I think we are all in agreement that the data and metadata
referenced
by an LSID remains unchanged (in the case of the metadata,
semantic
equivalence is a requirement for reasons such as outlined
by Matt).
My question is to do purely with the data that an LSID
references
through the getData() operation. The form of that data could be anything really - an encrypted byte stream, digital image,
Open Office
document, spreadsheet, xml document...
We all know that the same data can be represented many ways
that are
logically, semantically and functionally equivalent yet form a different set of bytes when serialized. Data expressed in
XML is one
example (is <a/> = <a /> = <a></a> ?). A pallet based image is another - the order of colors in the palette may be
changed, and the
pixel values adjusted to match the new palette order, but
the image is
still the same. There are many more simple examples that can be constructed that violate the unchanged bytes rule but for all practical and functional purposes the data are unchanged.
As mentioned previously, enforcing and implementing the
unchanged
bytes rule is not challenging. It is however quite different
from
stating that the data are returned unchanged. It is this
that I, and
I'm sure a lot of other implementors would appreciate consensus
on.
Dave V.
On Jul 14, 2007, at 09:20, Matthew Jones wrote:
In terms of the metadata returned from an LSID, or any
other digital
identifier, there are definite cases where metadata must be semantically persistent in order to preserve the utility
of data and
accuracy of scientific results.
As a trivial example, given a set of observations
collected at time
t, one can represent the data for those observations in
dataset D and
the metadata for the dataset, including the time value t, in a metadata document M. In a later event, it is discovered
that t was
entered incorrectly, and needs to be adjusted, creating
metadata
document M'. That M and M' are not congruent is critical
knowledge
when analyzing data from D with data from another dataset D2.
In
other words, because there is no true distinction between data
and
metadata (any given piece of information can be stored in
either
location), a proper archive must be able to distinguish
any changes
in the data and any changes in the metadata.
That said, there are some metadata that could change with
little or
no impact on data interpretation (e.g., the spelling of
the street on
which Technician Tom gets his snailmail). But at the current
time
its impossible to distinguish this kind of metadata from the important kind in the general case of the existing
metadata standards
in use (e.g., FGDC BDP, ISO 19115, EML, GML, etc).
Our process in the KNB/SEEK/NCEAS and other ecological
data archives
is to give persistent identifiers to both data objects and
metadata
objects, and provide new identifiers when either changes.
Matt
Dave Vieglais wrote:
Hi Bob, Just because a standard is published does not mean that it is practical. Requiring that a set of bytes referenced by
an LSID are
unchanged has a lot of implications with respect to the implementation of data services. For example, if it is agreed
to
abide by the rule that the blob referenced by an LSID remains forever unchanged, then that implies that the data
provider stores
the data as a blob, rather than risking the process of reconstructing on the fly from some database, especially for
the
example of data expressed in XML where functionally identical objects (constructed using different DOM libraries for
example) are
not identical blobs. Asserting that two instances of an object with the same LSID
are
semantically equivalent is a vastly more complicated
processes than
asserting that the canonical representation of those
instances are
identical. Generally there can be defined a simple set of guidelines for constructing the canonical form of an
object (eg. for
xml http:www.w3.org/TR/xml-c14n ) whereas asserting semantic equivalence is an ongoing topic of research. Requiring identical blobs is certainly possible, but
people need to
be aware of the implications of such a requirement in the
early
stages of designing a system to support such a specification.
My
preference for the canonical form relaxes the implementation requirements considerably whilst still maintaining the
integrity of
the data and the intent of the LSID. regards, Dave V. On Jul 14, 2007, at 08:08, Bob Morris wrote:
> This entire discussion confuses me. The LSID standard is >
published.
> Why is there a discussion of what an LSID should be? The >
standard
> requires that the data, as defined by the return of >
getData, to be
> identical for all resolutions of the LSID. From page 9 >
of the LSID
> spec: > > " bytes getData (LSID lsid) > bytes getDataByRange (LSID lsid, integer start, integer
length)
> Metadata_response getMetadata (LSID lsid, string[] > accepted_formats) > Metadata_response getMetadataSubset (LSID lsid, string[] > accepted_formats, string selector) The data retrieval >
services may
> implement all of the methods, or only methods for >
retrieving data,
> or only methods for retrieving associated metadata. > The same LSID named data object must be resolved always >
to the same
> set of bytes. Therefore, all of the data retrieval >
services return
> the same results for the same LSID. The user has, however,
the
> choice of which one of these to utilize depending on its >
location,
> known quality of service and other attributes. With >
metadata, the
> situation is different. Each data retrieval service can
provide
> different metadata for the same LSID." > > This doesn't seem very ambiguous to me, and doesn't have >
anything
> to do with imperfect storage of data or anything else about
the
> physical or electronic world. If two calls to getData() with
the
> same argument on two occasions to possibly two different >
resolution
> services do not yield the same set of bytes, then one or >
the other
> or both of those is not executing a compliant service
response.
> Unless this discussion is really "Shall we call something
other
> than the return of getData by the term 'data associated with
the
> LSID?' there seems to be nothing to discuss. > > Bob > > > > > On 7/13/07, Paul Kirk p.kirk@cabi.org wrote: > >> >> In an imperfect world there is no such thing as an
'identical-
>> byte-stream' >> because the technology we use is imperfect ... the disk >> controllers which manage our bytes and the disk we use to
store
>> our bytes have recognized error rates. Perhaps I'm >>
being a pedant
>> in the above analysis but I was almost persuaded that >>
except for
>> digital objects (images, >> sounds) which can >> be data all other 'things' (names, specimen accession >>
numbers) had
>> to be metadata. This to me makes no sense in the real but >> imperfect world we live in. An LSID assigned to a name >>
(e.g. Homo
>> sapiens) is assigned to the name as data, not metadata. What
is
>> 'identical' here it that if the spelling has to change for
any
>> reason the new spelling gets a new LSID and the now
incorrect
>> spelling gets deprecated (but is still resolvable) with >>
a pointer
>> to the correct spelling/LSID in the metadata. >> >> OK? >> >> Paul >> >> ________________________________ >> From: tdwg-guid-bounces@lists.tdwg.org on behalf of >>
Chuck Miller
>> Sent: Fri 13/07/2007 19:03 >> To: Dave Vieglais >> Cc: tdwg-guid@lists.tdwg.org >> Subject: RE: [tdwg-guid] LSID metadata persistence (or lack >> thereof)[Scanned] >> >> >> >> >> Dave, >> What you say is true. But, I think we already have too many >> variations, subtleties, and reinterpretations which are >>
endlessly
>> debated. >> >> The LSID standard would be simple, clear and consistent >>
if we used
>> the identical-byte-stream definition. The LSID would >>
uniquely tag
>> a persistent byte stream. A persistent byte stream is >>
always the
>> same thing without any further explanation or clarification. >> >> The provider of an LSID byte-stream would need to commit to >> keeping that byte-stream persistent and not represent it in >> multiple ways, even though technically they could. If >>
they can't
>> commit to that, then it can't be an LSID byte-stream. >> >> And in the name of simplicity and clarity, if they had >>
to provide
>> different byte-stream representations then they would have
to
>> assign a different LSID to each and use "SameAs" metadata. >> >> Chuck >> >> -----Original Message----- >> From: Dave Vieglais [mailto:vieglais@ku.edu] >> Sent: Friday, July 13, 2007 12:42 PM >> To: Chuck Miller >> Cc: Ricardo Pereira; tdwg-guid@lists.tdwg.org >> Subject: Re: [tdwg-guid] LSID metadata persistence (or lack >> thereof) >> >> Hi Ricardo, Chuck, >> Asserting that the byte stream returned as data >>
associated with an
>> LSID should never change is perhaps a bit confusing from a >> programmatic view. There are for example many ways to >>
represent
>> data in xml that are identical from an information >>
content point
>> of view, but the byte streams could be very different. >> >> Perhaps it might be better to state something like "the >>
canonical
>> representation of the data associated with an LSID must not >> change", or something to that effect? >> >> Dave V. >> >> On Jul 14, 2007, at 05:29, Chuck Miller wrote: >> >> >>> Ricardo, >>> >>> Looking at this definition: "Persistence of LSID >>>
Data: The data
>>> associated with an LSID (i.e, the byte stream returned by
the
>>> >> LSID >> >>> getData call) must never change" >>> >>> >>> >>> Perhaps this is a more straightforward way to conceive >>> >> LSIDs. The >> >>> LSID goes with a byte stream. It's that byte stream that >>> >> must stay >> >>> the same. So, if there is a byte stream associated with a >>> collection that needs to stay the same, then whatever >>>
that byte
>>> stream happens to be is the data that gets an LSID assigned >>> >> to it. >> >>> That sure seems a clearer definition of what is data >>>
and what is
>>> metadata, rather than the issue of primary object and >>>
all that.
>>> >>> So we can create a new definition in the context of LSIDs: >>> >> Data is >> >>> a byte stream that is persistent, never changes and >>>
can have an
>>> LSID. Metadata is a byte stream is non-persistent, >>>
might change
>>> and is only associated with an LSID. >>> >>> >>> >>> The institution who assigns an LSID can make their >>>
own decision
>>> about whether the byte stream being provided is persistent
or
>>> >> non- >> >>> persistent. By assigning an LSID to any byte stream, >>> >> whatever it >> >>> is, the institution is declaring it to be data and
persistent.
>>> >>> >>> >>> So, in the example given of an observation record with a >>> determination that needs to remain fixed and unchanged, by >>> assigning an LSID to that observation+determination >>>
it would be
>>> "declared to be data" and unchangeable. A different >>> >> determination >> >>> would then be different data with a different LSID. >>>
That would
>>> provide a solution for those who want to employ it. Others >>> >> could >> >>> choose not to use it. >>> >>> >>> >>> Chuck >>> >>> >>> >>> From: tdwg-guid-bounces@lists.tdwg.org [mailto:tdwg-guid- >>> bounces@lists.tdwg.org] On Behalf Of Ricardo Pereira >>> Sent: Friday, July 13, 2007 9:47 AM >>> To: tdwg-guid@lists.tdwg.org >>> Subject: [tdwg-guid] LSID metadata persistence (or >>>
lack thereof)
>>> >>> Hi there folks, >>> >>> As Chuck mentioned a few weeks ago, we do have a few >>> outstanding issues to address regarding LSIDs. I >>>
would like to
>>> discuss those one by one, in an orderly manner, and reach >>> >> consensus >> >>> as much as we can. Then we can sum them up in a TDWG >>>
standard,
>>> possibly by or shortly after the Bratislava conference. >>> >>> The first issue I would like to discuss is LSID
metadata
>>> persistence. First, let me remind you of a corollary >>> >> established by >> >>> the LSID specification: >>> >>> Corollary 1: LSIDs are not guaranteed to be >>> >> resolvable >> >>> indefinitely. >>> >>> In other words, there is no guarantee that one will >>> >> always be >> >>> able to retrieve the data associated with an LSID as the >>> >> authority >> >>> may choose (or be forced) not to resolve an LSID anymore. >>> >>> Second, let me distinguish this kind of persistence I'm >>> >> talking >> >>> about from other two related concepts (which we'll not >>> >> discuss in >> >>> this thread): >>> >>> 1) Persistence of Assignment: Once assigned to an >>> >> object, >> >>> an LSID is indefinitely associated with it. The same LSID >>> >> cannot be >> >>> assigned to another object. Ever! The LSID may not be >>>
resolvable
>>> anymore, but it cannot be assigned to another object. This
is
>>> established by the LSID specification. >>> >>> 2) Persistence of LSID Data: The data >>>
associated with an
>>> LSID (i.e, the byte stream returned by the LSID getData
call)
>>> >> must >> >>> never change. Although the LSID may not be resolvable
anymore
>>> (according to corollary 1), the data associated with an
LSID
>>> >> must >> >>> never ever change. That's defined by the LSID spec, too. >>> >>> What I want to discuss here is the persistence of LSID >>> >> metadata >> >>> (what is returned by the getMetadata call) or the >>>
lack thereof.
>>> A use case associated with metadata persistence is when >>> >> someone >> >>> collects observation records (and implicitly, their >>> >> determinations) >> >>> and runs an experiment (a model or simulation) with it.
This
>>> >> person >> >>> may want to record the identifiers of the points used so
that
>>> someone using the results of that experiment may refer back >>> >> to the >> >>> primary data, to validate or repeat it the experiment. >>> >>> The bad news is that LSID identification scheme (or any >>> >> other >> >>> GUID that I know of) was not designed to guarantee metadata >>> persistence, and thus it cannot implement the use >>>
case above by
>>> itself. To implement that use case, the specification would >>> >> have to >> >>> guarantee that the metadata (which we are using here >>>
as data) is
>>> immutable. But it doesn't. >>> >>> Most of us wish that metadata was persistent, but >>>
it isn't.
>>> Many things can change in the metadata: a new >>>
determination, a
>>> mispeling that is corrected, many things. We just cannot >>> >> guarantee >> >>> that the metadata will look like it was sometime ago. >>> >>> We then reach the following conclusion. >>> >>> Corollary 2: LSIDs metadata is not immutable
nor
>>> persistent. >>> >>> The consequence of this corollary is that, if you need
to
>>> >> refer >> >>> back to a piece of information (metadata) associated with
an
>>> >> LSID, >> >>> exactly as it was when you got it, you must make a copy of >>> >> it, or >> >>> arrange that someone else make that copy for you. >>> >>> In other words, a client cannot assume that the
metadata
>>> associated with an LSID today will be the same >>>
tomorrow. If the
>>> client does assume that, it may be relying on a false >>>
assumption
>>> and its output may be flawed. >>> >>> If we are not happy with that conclusion, we may >>>
develop an
>>> additional component in our architecture, an archive of
some
>>> >> sort, >> >>> to handle (meta)data persistence. That is exactly what the >>> >> STD-DOI >> >>> project (http://www.std-doi.de/) and SEEK (http://
>>> seek.ecoinformatics.org) have done to some extent. >>> >>> While we cannot guarantee that LSID metadata is >>> >> persistent nor >> >>> immutable, we can definitely document how the metadata have >>> >> changed >> >>> through metadata versioning. That's the topic of the next >>> >> thread. >> >>> We will move on to discuss metadata versioning as >>>
soon as we are
>>> done with metadata persistence. >>> >>> Cheers, >>> >>> Ricardo >>> >>> _______________________________________________ >>> tdwg-guid mailing list >>> tdwg-guid@lists.tdwg.org >>> http://lists.tdwg.org/mailman/listinfo/tdwg-guid >>> >> _______________________________________________ >> tdwg-guid mailing list >> tdwg-guid@lists.tdwg.org >> http://lists.tdwg.org/mailman/listinfo/tdwg-guid >> >> >> P Think Green - don't print this email unless you really
need to
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>> ******** >> _______________________________________________ >> tdwg-guid mailing list >> tdwg-guid@lists.tdwg.org >> http://lists.tdwg.org/mailman/listinfo/tdwg-guid >> >> >> > --Robert A. Morris > Professor of Computer Science > UMASS-Boston > ram@cs.umb.edu > http://bdei.cs.umb.edu/ > http://www.cs.umb.edu/~ram > http://www.cs.umb.edu/~ram/calendar.html > phone (+1)617 287 6466 > _______________________________________________ tdwg-guid mailing list tdwg-guid@lists.tdwg.org http://lists.tdwg.org/mailman/listinfo/tdwg-guid
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