1. Maria Grazia Pia, INFN Genova 1 Part V The lesson learned Summary and conclusions

2. Maria Grazia Pia, INFN Genova 2 The lesson learned ] Geant4 has successfully coped with a variety of challenges ] The software challenge ] The functionality challenge ] The performance challenge ] The physics challenge ] The challenge of distributed software development ] The management challenge ] The user support challenge ] What can we learn from the Geant4 experience?

3. Maria Grazia Pia, INFN Genova 3 The software challenge ] Geant4 is the first successful attempt to redesign a major package of CERN software for the next generation of HEP experiments using an Object Oriented environment ] Geant4 represents a fundamental test of the suitability of the object oriented approach to software in HEP, where performance is a crucial issue

4. Maria Grazia Pia, INFN Genova 4 The functionality challenge ] A variety of requirements come from l LHC experiments l CP violation physics l neutrino physics l cosmic ray physics l astrophysics l heavy ion physics l nuclear physics l radiation protection, l medical and biological applications l space science applications ] In order to meet such requirements a large degree of functionality and flexibility is provided

5. Maria Grazia Pia, INFN Genova 5 The performance challenge ] High performance is mandatory for large scale HEP experiments and for other complex applications  Geometry navigation  Benchmarks l Geant4 automatically optimizes the user’s geometrical description  EM Physics  Benchmarks l More than 3 times faster when using the same cuts with GEANT3 l More than a factor 10 faster when seeking the best performance in Geant4 that maintains constant the quality of the physics results l Geant4 is faster than GEANT3 in all aspects

6. Maria Grazia Pia, INFN Genova 6 The physics challenge ] Transparency ] Extended coverage of physics processes across a wide energy range for a variety of physics applications ] Alternative models ] OOAD allows to clearly expose the physics transparency ] OOAD allows to clearly separate the physics from other components ] OO technology (polymorphism and use of abstract interfaces) provide the means to easily handle alternative and complementary models ] An ample variety of physics models is provided

7. Maria Grazia Pia, INFN Genova 7 The challenge of distributed software development Geant4 has been developed by a collaboration of more than 100 scientists, from ~40 institutes, affiliated to more than 10 different experiments, located across 3 continents How has this been possible? OOAD has provided the framework for distributed parallel development l a core group of designers l well defined interfaces l clearly defined dependencies have allowed developers to work in parallel

8. Maria Grazia Pia, INFN Genova 8 The management challenge Geant4 has satisfied all the milestones and all the deadlines (defined several years ahead!) l in spite of the difficulties created by the distributed nature of the Collaboration l with manpower mostly available at a small fraction of time How has this been possible? ] A well defined, and continuously improving, software process has allowed to achieve all the goals l tasks, procedures and deliverables are clearly identified, defined and documented ] Efficient use of talents, expertise and manpower l for each of the areas of development, world experts in the specific domain have been invited to contribute l people contribute in the area(s) where they are expert l with clearly defined tasks and responsibilities l this also contributes to the high quality of software and physics

9. Maria Grazia Pia, INFN Genova 9 The user support challenge ] Geant4 user community is distributed worldwide and spans a variety of domains (HEP and nuclear physics, space science community, medical physics, hospitals etc.) ] A system of distributed user support has been put in place since 1999 ] A large number of users has received support on the most diverse areas l always with an expert (often the code author!) taking care of their problems and questions

10. Maria Grazia Pia, INFN Genova 10 Risk factors ] Performance and adequacy of C++ and OO technology for simulation were considered risk factors at the beginning of the project l it has been clearly demonstrated that the concerns were not justified ] Maturity of the HEP community? l to appreciate the need of a new simulation environment l to work in an environment based on software engineering l to invest into learning and mastering new technologies

11. Maria Grazia Pia, INFN Genova 11 Conclusions ] Geant4 is a toolkit for simulation of HEP and nuclear physics experiments, space and medical applications, radiation studies etc. ] Geant4 has been developed and is maintained by an international Collaboration with a distributed software organization ] Software engineering plays an essential role ] Object Oriented technologies represent a key factor ] The transparency of physics design and implementation contributes to the validation of physics results ] Geant4 represents a substantial progress with respect to Geant3 in many areas ] The use of Geant4 is ramping up in many domains ] Many results already available, in spite of the short time since the start of the production phase