2 questions on ROOT data storage mechanism

From: Pasha Murat (murat@cdfsga.fnal.gov)
Date: Thu Nov 06 1997 - 20:04:42 MET


	Hello,

I have a couple of questions on ROOT data storage mechanism, which could be 
interesting for many people especially from large collaborations.

- is it possible to read an event written by somebody else in the collaboration
  back without knowing *everything* about the event format?

  In "ZEBRA world" if I have an event (a set of ZEBRA banks) written out,  
  I can always read it back as a set of ZEBRA banks, and then use only those 
  banks I need, without knowing the exact format of the rest banks.

- I heard that people have encountered certain difficulties with using 
  versioning mechanism provided by Objectivity. So let me ask (I apologize 
  for not trying this feature in advance) how the versioning mechanism 
  works in ROOT?  Suppose I've written several data files out using 

ClassDef(MyClass,1)

  for MyClass. Then I changed the definition of the class (say, added one 
  more data member to it) and now am using

ClassDef(MyClass,2)

  and trying to read the data written in "old" format back. How does ROOT
  know about the differences between version 1 and version 2 of MyClass?

						Thanks a lot, Pasha.



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