netcdf-hdf mailing list is no longer active. The list archives are made available for historical reasons.
Hi Mike, > 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 > > Mike > > At 10:16 AM 4/19/2005, Quincey Koziol wrote: > > > Quincey Koziol <koziol@xxxxxxxxxxxxx> writes: > > > > > > > I was planning on including a hidden field to disambiguate > > objects that > > > > were created at the same time, so this wouldn't happen. Since there's > > > > no > > > > advantage to using a creation order field instead of using the > > creation time > > > > when determining the n'th object inserted into a group (when > > factoring deleted > > > > objects into the equation), I'm still leaning toward using a time > > instead of an > > > > index for this purpose. Using the time provides the same > > functionality and > > > > adds information as well. > > > > > > > > I'm still somewhat split on the issue however and would welcome > > persuasive > > > > arguments in favor of one mechanism or the other. :-) I'm also > > thinking about > > > > including both fields (creation order and creation time) and allowing > > users to > > > > create an index on either, to suit their particular needs... > > > > > > Quincey, > > > > > > What happens is a machine with an inaccurate time adds a variable to a > > > dataset? > > > > It'll get the "wrong" creation time and inserted in the index > >appropriately, as you'd expect. I don't think this is a major problem > >though, > >because I don't think that most files will get edited on multiple machines in > >a very short timeframe. > > > > Quincey > > -- > Mike Folk, Scientific Data Tech (HDF) http://hdf.ncsa.uiuc.edu > NCSA/U of Illinois at Urbana-Champaign 217-244-0647 voice > 605 E. Springfield Ave., Champaign IL 61820 217-244-1987 fax >