Andrey, the experts should chime in on the storage trade-offs. (I imagine the null dataset is stored with compact layout, but in newer versions of the file format an empty group is very "compact" as well.) At the conceptual level, the two are very different and that might tip the balance in either direction. A group leaves the door open for other descendants. A dataset is a terminal node and, despite being empty, is nevertheless typed. (A null dataset has an element type!) Of course, you could "type" a group with additional attributes, but it would be a very different kind of variable.
This might be a case where there're no right or wrong choices as far as HDF5 is concerned, and users will have to decide what makes it right for them. Best, G. -----Original Message----- From: Hdf-forum [mailto:[email protected]] On Behalf Of ?????? ????????? Sent: Thursday, October 26, 2017 6:52 AM To: [email protected] Subject: Re: [Hdf-forum] HDF5 library bug or feature? Hi Gerd! 26.10.2017 14:31, Gerd Heber пишет: > Rafal, this might be a bug. However, if you don't intend to store data > there's a cheaper and maybe less contorted option: You can create a > dataset with a dataspace of class H5S_NULL. > Think of that as a dataset whose dataspace is an empty set. > (Likewise you'd use H5S_SCALAR for a singleton.) A common desire is to store non-uniform sparse data in HDF5 (consider XML attributes as example). I tend to use empty groups which only serve as container of attributes. What do you think: would empty datasets (H5S_NULL) with attributes be more efficient (introduce less overhead)? Best wishes, Andrey Paramonov -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. _______________________________________________ Hdf-forum is for HDF software users discussion. [email protected] http://lists.hdfgroup.org/mailman/listinfo/hdf-forum_lists.hdfgroup.org Twitter: https://twitter.com/hdf5 _______________________________________________ Hdf-forum is for HDF software users discussion. [email protected] http://lists.hdfgroup.org/mailman/listinfo/hdf-forum_lists.hdfgroup.org Twitter: https://twitter.com/hdf5
