Blueprint RTAG comments Torre Wenaus, BNL/CERN July 3, 2002

Torre Wenaus, BNL/CERN PSI Colloquium, May Slide 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  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

Torre Wenaus, BNL/CERN PSI Colloquium, May Slide 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.

Torre Wenaus, BNL/CERN PSI Colloquium, May Slide 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.

Torre Wenaus, BNL/CERN PSI Colloquium, May Slide 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

Torre Wenaus, BNL/CERN PSI Colloquium, May Slide 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

Torre Wenaus, BNL/CERN PSI Colloquium, May Slide 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