[Nexus-developers] data type for binary data

[Tobias.Richter at diamond.ac.uk]

Hi Freddie,

I'd propose to leave NX_BINARY alone and just add NX_OPAQUE. 
Does not break any existing files or code. And developers can switch to the new functionality when ever they want.
They are only ever forced to change if they want to read a file with NX_OPAQUE. The only Nexus class that requires NX_BINARY is the data in NXnote as far as I can see. We should be able to allow NX_OPAQUE in there as well then.

Regards,

Tobias
________________________________________
From: nexus-developers-bounces at nexusformat.org [nexus-developers-bounces at nexusformat.org] on behalf of freddie.akeroyd at stfc.ac.uk [freddie.akeroyd at stfc.ac.uk]
Sent: 07 December 2011 01:10
To: nexus-developers at nexusformat.org
Subject: Re: [Nexus-developers] data type for binary data

Hi Eugen,

I think it would be good if we could use the HDF5 binary type as it properly distinguishes "UInt8" and "binary data", but we would need to add some support into NeXus to handle such data via the API and there are some compatibility issue we need to assess too.

If we change NX_BINARY to Opaque, then a recompiled nexus program that reads a previously written binary array (UInt8) and checked its type was "NX_BINARY" would fail. Similarly a newly compiled program writing NX_BINARY to read in by an hdf5 aware non-nexus program may find that changing from UInt8 to OPAQUE breaks something there. If we think these are likely, then one option is to remove NX_BINARY and add NX_OPAQUE instead - programs using NX_BINARY would then fail to compile and must decide on UInt8 or opaque (purely relinked programs would still work though via the previous UInt8 definition). What do people think?

Regards,

Freddie

-----Original Message-----
From: nexus-developers-bounces at nexusformat.org [mailto:nexus-developers-bounces at nexusformat.org] On Behalf Of Eugen Wintersberger
Sent: 05 December 2011 10:15
To: nexus-developers at nexusformat.org
Subject: [Nexus-developers] data type for binary data

Hi folks
  I am actually implementing the binary field type for my C++ API.
According to the Nexus documentation binary data is stored as UInt8
which has historical reasons.
HDF5 provides now an opaque data type which indicates already on HDF5
level that the data is uninterpreted binary. Thus I would rather use
this data type than UInt8.
Is this ok according to Nexus or shall I use UInt8 for backward
compatibility?

regards
   Eugen

_______________________________________________
NeXus-developers mailing list
NeXus-developers at nexusformat.org
http://lists.nexusformat.org/mailman/listinfo/nexus-developers
--
Scanned by iCritical.

_______________________________________________
NeXus-developers mailing list
NeXus-developers at nexusformat.org
http://lists.nexusformat.org/mailman/listinfo/nexus-developers

-- 
This e-mail and any attachments may contain confidential, copyright and or privileged material, and are for the use of the intended addressee only. If you are not the intended addressee or an authorised recipient of the addressee please notify us of receipt by returning the e-mail and do not use, copy, retain, distribute or disclose the information in or attached to the e-mail.
Any opinions expressed within this e-mail are those of the individual and not necessarily of Diamond Light Source Ltd. 
Diamond Light Source Ltd. cannot guarantee that this e-mail or any attachments are free from viruses and we cannot accept liability for any damage which you may sustain as a result of software viruses which may be transmitted in or with the message.
Diamond Light Source Limited (company no. 4375679). Registered in England and Wales with its registered office at Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire, OX11 0DE, United Kingdom