Re: [netcdf-java] Replacing variable-length dimensions in CDM with ArraySequence

I don't know what to say. I think there are several groups reading and
writing variable length arrays. I hope this doesn't prevent me/others from
reading existing files or change the way their files are written since
collections would then be a mix.

On Sunday, November 6, 2016, dmh@xxxxxxxx <dmh@xxxxxxxx> wrote:

> Clarification 1:
>
> I was probably too terse in my previous message about variable-length
> dimensions. Let me elaborate a bit.
>
> All existing dimensions (including UNLIMITED) have
> (at any point in time) a fixed known size and every use of that dimension
> has that size. Note that an UNLIMITED dimension's size may change over
> time, but it is still the case that all occurrences of it have the same
> size at any point in time.
>
> A variable-length dimension (often represented by "*") has potentially
> a different size for every occurrence at any given point in time.
> The pretense that a variable-length dimension is a dimension causes
> significant code and use complications in the CDM data model.
>
> An ArraySequence is particular form of CDM Array, similar to an
> Array Structure, that encapsulates the fact the the length of the sequence
> can differ for each ArraySequence instance. The goal of the proposed change
> is to isolate/encapsulate true variable-length objects within an
> ArraySequence object.
>
> So, if we have, for example,
>         int x(5,*)
> then this would be represented as a 5 element array of
> ArraySequence objects, and each ArraySequence object
> contains a variable length vector of integers.
> Using the netcdf-4 model, this would be:
>         types:    int(*) sequence_t
>         variables: sequence_t x(5)
>
> The requirement on e.g. IOSP developers is that they create ArraySequence
> objects, and the requirement on the client users of CDM (via the
> netcdf-Java library) is that they recognize ArraySequence objects.
>
> My speculation is that anyone who uses variable-length dimensions already
> has to make code exceptions to process it, and it is probable that only
> that code would need to be changed to deal with ArraySequence.
>
> Note: ArraySequences actually already exist in the CDM code, but are
> currently not used (AFAIK).
>
> =Dennis Heimbigner
>  Unidata
>
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-- 
Sincerely,

Bob Simons
IT Specialist
Environmental Research Division
NOAA Southwest Fisheries Science Center
99 Pacific St., Suite 255A      (New!)
Monterey, CA 93940               (New!)
Phone: (831)333-9878            (New!)
Fax:   (831)648-8440
Email: bob.simons@xxxxxxxx

The contents of this message are mine personally and
do not necessarily reflect any position of the
Government or the National Oceanic and Atmospheric Administration.
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