[tdwg-guid] LSID metadata persistence (or lack thereof)[Scanned]

P. Bryan Heidorn pheidorn at uiuc.edu
Sat Jul 14 00:17:29 CEST 2007

Hmmm, we are in trouble. It seems that placing the "record" in the  
LSID metadata is gaming the system. An observation record of a bird,  
is on some real sense data. We can say it is metadata about the bird  
but this is not data about data under that use, it is data about an  
object, that instance of a bird at that point in time. I would prefer  
not to treat the record as abstract. We can not put the observation  
record into the metadata because metadata has the nice property of  
allowing us to change the form. The LSID metadata should tell us the  
semantics of the data. If we use the metadata to save the record we  
need meta-metadata to save the semantics.

 From page 10 of the spec:
"bytes getData (LSID lsid)
This method is used to return data associated with the given lsid. If  
a copy of the data represented by an LSID cannot be
returned for any reason, an exception should be raised.
If the given lsid represents an abstract entity (a concept), this  
method returns an empty array of bytes.
Note that the semantics of the returned bytes is not defined by this  
specification. It is either known from an external
documentation, or (preferably) it is available by reading the  
metadata for this particular lsid. "<----

As Dave points out. The bit identity constraint is a problem when XML  
is a payload. Current TDWG standards do not enforce a particular  
canonical form for the XML documents. They could when being carried  
by data in LSID. That additional constraint or specification would  
need to be carried in the metadata.

-- Bryan

PS: Someone should send a medic to Chuck's office. Chuck is likely  
under his desk pulling out his hair muttering something about never  
"doing" anything.


On Jul 13, 2007, at 4:19 PM, Richard Pyle wrote:

>> LSID data does not change meaning it always has the same bit
>> pattern for a given LSID.
>> Since XML allows different bit level expressions for
>> equivalent records there is a mismatch with the LSID
>> mechanism.
> There is only a mismatch if you try to return XML as LSID "data".   
> I don't
> see any reason to do this, unless the XML file *is* the object to  
> which the
> LSID is applied (as opposed to the object that the XML content  
> attempts to
> describe, such as a specimen or a taxon name). If, for some reason,  
> someone
> would want to encapsulate an XML file as the LSID-identified  
> "data", then
> you would have to do it in a way that "locked in" the bytestream of  
> the XML
> in a way that is bit-level persistent.
>> The community can live with this as long as there
>> are additional constraints put on the generation of XML-based
>> records. For the sake of simplicity keep the fixed bitlevel
>> exppression. The existing metadat mechanism handles the
>> semantics of interpretation of the data (sorry to use the
>> word "semantics" but it is nothing really special, just a
>> definition of the "meaning" of the data)
> No problem on the use of "sematics", because it's clear which  
> meaning you
> intended from the context of how you used it (i.e., the semantics  
> of the
> word semantics was not opaque... :-) )
> Aloha,
> Rich
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