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> At 07:07 PM 4/20/2005, you wrote:
> > > This question came up today at the NASA briefing, when we were talking
> > > about the netCDF 4 project. There was a weak but immediate and negative
> > > reaction to using time as a proxy for creation order. The reason given
> > was
> > > that many applications would want to use the creation time as an
> > attribute,
> > > but that the times used would not necessarily give the same ordering as
> > > creation time because different times might be relative to different time
> > > zones. I have a feeling there were other cases, given the reaction
> > people had.
> > >
> > > Of course this could only happen if people were allowed to change the
> > > "creation time." And one could also argue that creation time is a
> > > different attribute -- it's the time the link was created, not the time
> > the
> > > data was collected. But I have a feeling this would just lead to
> > confusion.
> > >
> > > So at best, I think there is concern that this could led to confusion. I
> > > tend to agree.
> >
> > Ok, I think we've heard enough customer push-back on this that we
> > ought to
> >provide both options and allow people to choose which they'd like. Here's a
> >list of the fields that I'm planning on storing on storing for each link:
> > - Name (indexable, must be unique, modifiable)
> > - Creation time (indexable, may be non-unique, modifiable)
> > - Creation order (indexable, unique, monotonicly increasing,
> > non-modifiable)
> > - Character set (i.e. ASCII, UTF-8, etc.) (non-indexable?, non-unique,
> > modifiable)
> > - Object address/link target (for hard/soft links) (non-indexable, may
> > be
> > non-unique (for multiple links to same object), modifiable?)
> >
> > Applications can determine which of the three indexable fields they'd
> > like
> >to have an index maintained for with a group creation property. They will
> >choose an index for iteration, etc. with a group access property.
> >
> > Quincey
>
> It will be tough, if even possible, to do Creation order in parallel systems.
> You would need to maintain this shared Creation Order Index (COI) quantity
> across multiple processes dealing with racing conditions. Will there be
> a COI per group (thus many COI's per file)
> or a COI per file (thus multiple COI's per execution)
> or one COI per execution?
>
> I think the second one, a COI per file, is the best (or least bad) choice.
The first one (COI per group). I don't think it's a problem, since our
metadata modification code requires collective calls by the application.
Quincey
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