Re: something startling I just noticed...

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I agree with Russ. A creation-sequence-number should be as information-free as possible. Same as an OID. Attributes like time-of-creation can be saved in some other form.


At 11:28 AM 11/12/2003, Russ Rew wrote:

>     My current idea is to add a "creation time" piece of metadata to each
> object as it is created in the file, and then the H5Giterate() call (or
> something resembling it) could choose whether to use creation times or the
> object names (or last modification times, etc.) as the method of indexing the
> objects to iterate over.  Fairly simple and straightfoward, I think...

Even simpler would be a "creation sequence number" piece of metadata.
This would just be an integer that incremented for each new HDF5
object, or maybe several such sequences for different kinds of

There are some advantages of sequence numbers over times:
 - you don't have to worry about clock resolution and the possibility
   that creation times of two objects are equal
 - you can use gaps in the sequence numbers to tell that objects have
   been deleted, something not possible with times
 - adding 1 is cheaper than the system call necessary to access the
   system clock
 - in distributed systems, there is not necessarily a well-defined
   time ordering for events (only a partial ordering)

I don't foresee any need for knowing the actual creation time of a
netCDF-4 object, but if there are other applications for this kind of
information, than feel free to ignore this suggestion ...


Mike Folk, Scientific Data Tech (HDF)
NCSA/U of Illinois at Urbana-Champaign          217-244-0647 voice
605 E. Springfield Ave., Champaign IL 61820 217-244-1987 fax

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