Blueprint RTAG comments

1
Blueprint RTAG comments

• Torre Wenaus, BNL/CERN
• July 3, 2002

2
How will ROOT be used?

• Rene proposes
• The existing set of ROOT libs as starting core of
  LCG software
• Review and, if necessary, evolution of library
  organization, keeping in mind effect on user base
• Email exchange, particularly Vincenzo with ROOT
  team, indicates sharply the different views on
  design between the ROOT/ALICE team and CMS (and
  LHCb and ATLAS?)
• First, we should clarify here whether LHCb and
  ATLAS generally share the views of CMS. I suspect
  they do and will assume that in the following
• If they do, I see a clear conclusion
• It is not going to work for ROOT to be taken as
  the starting core of LCG software as proposed by
  Rene
• The design differences are too great, and the
  ROOT team is not going to redesign ROOT

3
How will ROOT be used?

• What we know is going to happen is that ROOT will
  be used heavily by the LCG software and all four
  experiments
• And has been taken directly as the core
  foundation for one
• I think it would be good for design discussions
  such as has been going on to continue, but we
  cannot rely on resolving them to progress
• It looks to me like we have to accept that
• we are not going to converge anytime soon on this
  line
• the line to take up and resolve is working out an
  architecturally acceptable way to make use of a
  big grey (not black) ROOT box
• With accommodation on both sides
• changes to ROOT library organization?
• Constructively getting beyond linking in the
  kitchen sink complaints
• Agreed metrics meaningful for usability,
  maintability, modularity etc.

4
How will ROOT be used?

• If the LCG software is developed as a ROOT user
  it will be drawing on a great ROOT strength
  users are listened to very carefully!
• Much more carefully than software designers
  proposing major design changes!!
• The ROOT team has been very responsive to needs
  for new and extended functionality coming from
  the persistency effort
• And, drawing on ROOT in a user-provider
  relationship matches much better the reality of
  the ROOT development model of a very small number
  of empowered developers
• The ROOT development team is small and they like
  it that way
• While ROOT will be used at the core of much LCG
  software for the foreseeable future, I think
  there needs to be a line with ROOT proper on one
  side and LCG software on the other.

5
Some personal comments on ROOT use and integration

• I think that within the LCG software architecture
  bare ROOT should be an integral, trivially
  accessible part of the architecture
• e.g., most obviously, affording the interactive
  user the ability to easily move between a Python
  prompt (see coming slide) and a ROOT prompt with
  access to their object model from ROOT possible
  now given the foreign class support in ROOT
• As Pere emphasised, integration
• Something Rene is right about every time he says
  it
• Users vote with their feet
• The design and evolution of LCG software should
  be well attuned to the user, as is ROOT
• LCG software we develop that does not use bare
  ROOT, or ROOT at all, will live or die on its
  merits
• We should build it so that it lives on its
  merits, not on life support through
  architecturally walling off ROOT in some way
• Plenty of people have bet against ROOT in the
  past. They have all been wrong. LCG software
  should not make this mistake

6
More on ROOT

• Why have I talked so much about ROOT and not
  about (your favourite product)?
• Because Rene made an important proposal we have
  to address.
• Because I live in the real world. ROOT is going
  to have a strong, central role in LCG software.
• But, I think we are seeing that the realistic
  approach is for LCG software to use ROOT, within
  an architecture distinct from ROOT.
• If we could agree on this we could go about
  developing the architecture of the LCG software
• with the ROOT relationship in this process not
  being architecture/design wars to be fought
  through, but rather resolving how usage of ROOT
  will be handled in the LCG architecture

7
Interactivity and software buses

• Can we agree on these?
• A common object dictionary will be a key part of
  the foundation, an object bus providing access
  to data objects throughout the architecture
• A Python-based interactive environment and
  component bus will be part of the architecture
• ROOT and the ROOTCINT interpreter will be
  trivially accessible from the Python environment
  and vice versa
• Architecture provides for access to data objects
  from both Python and ROOT environments