Subject:
History objects 0.1
From:
David Adams <dladams@bnl.gov>
Date:
Wed, 17 Oct 2001 13:11:01 -0400
To:
Paolo Calafiura <PCalafiura@lbl.gov>, Srini Rajagopalan <srinir@bnl.gov>
CC:
David Adams <dladams@bnl.gov>

Paolo and Srini:

I read through your document "History Objects" document (dated 16oct01, version 0.1) and I have the following comments:

1. I think it would be useful to state use cases and requirements in advance of
   your design. I would be glad to get more input and have you work from the
   requirements that I posted.

2. You speak of an event history and show the event history pointing back to
   its parent event history. This implies the existence of an "event" consisting
   of all the data produced in a particular job for a particular event ID. This
   event would consist of pointers to all its data objects. The event history
   and event would reference one another and might be combined into a single
   object. The event class should be made explicit or the list of data objects
   added to the event history.

3. A job can take output from two other jobs. I.e. a new event can be be built 
   from two input events. (All three events correspond to the same event
   identifier and raw data). Your event history should allow for multiple event
   history inputs. It should also allow for no history for the case of raw data.

4. Your data object history omits pointers back to parent data objects.
   I agree that we can regenerate the data by rerunning the original job when 
   the original events (i.e. all their data) exist. But I would like the data to 
   be reproducible at a finer granularity: we should be able to reproduce a data 
   object from its parents (or equivalents!) without requiring that any other part
   of the events still be accessible. This requires pointers back to the parent
   data objects or a way to generate these pointers. Perhaps you can recover them
   using the job and event history but it seems simplest and most reliable to keep
   them in the data object history. If nothing else this provides an important
   check. If you don't want to add these pointers, then you should clarify the
   implied requirements for the job and event histories.

da

P.S. If you don't mind, I would like to include a copy of your document and
future revisions on my data model page.

-- 
David Adams                      desk: 631-344-6049
Brookhaven National Lab          fax: 631-344-5078
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