Hi all -
Are there any existing practices (either established or experimental)
for the use of the "history" attribute when dealing with complex,
branching processing histories?
Given the "history" attribute is only intended to be human readable, I
suspect the answer is "no". In which case, what would be more palatable:
inventing a new syntax, or throwing away everything prior to the last
linear sequence?
I'm not sure how many existing practices there are, but a new
syntax is *definitely* preferable to loss of this information.
The standard lets you continuously append processing 'events' to
the global history, using a timestamp; in theory you can append
all the branching histories, adding information about which
component was modified (maybe going from datestamp/action to
datestamp/component/action ?). The component identifiers would
need to include enough information to let the user know what
slice, and what variable, was modified by each action.
John's SSDS example shows an interesting way to accumulate
this information, which could be expanded for branched provenance.
It's not quite the same as the NetCDF-defined history attribute,
but it looks like a great way to make this field machine readable.
By the way, here's the definition, from the NetCDF Users' Guide:
history
A global attribute for an audit trail. This is a character array with
a line for each invocation of a program that has modified the
dataset. Well-behaved generic netCDF applications should append a
line containing: date, time of day, user name, program name and
command arguments.
and a snippet from the CF standard:
2.6.2. Description of file contents
The NUG defines title and history to be global attributes. We wish
to allow the newly defined attributes, i.e., institution, source,
references, and comment, to be either global or assigned to
individual variables. When an attribute appears both globally and as
a variable attribute, the variable's version has precedence. ...
history
Provides an audit trail for modifications to the original data.
Well-behaved generic netCDF filters will automatically append their
name and the parameters with which they were invoked to the global
history attribute of an input netCDF file. We recommend that each
line begin with a timestamp indicating the date and time of day that
the program was executed.
- Nan
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