1. Common Application Software for the LHC experiments NEC’2007 International Symposium, Varna, Bulgaria 10-15 September 2007 Pere Mato, CERN

2. Pere Mato, CERN/PH 2 Foreword “Common software” is the is the software that is used by at least two experiments –In general, common software would be of a generic nature and non- specific to one experiment –The borderline between generic and specific is somehow arbitrary »It depends very much on the willingness of re-using (i.e. trusting) software developed by others and adapting own requirements to fit it –Sharing software has become a necessity »HEP experiments cannot afford developing complete specific solutions from scratch

3. Pere Mato, CERN/PH 3 Outline  Main software requirements  Software structure  Programming languages  Non-HEP packages  HEP generic packages  Experiment’s software frameworks  The LCG Applications Area  Summary

4. Pere Mato, CERN/PH 4 Main Software Requirements  The new software being developed by the LHC experiments must cope with the unprecedented conditions and challenges that characterizes these experiments (trigger rate, data volumes, etc.)  The software should not become the limiting factor for the trigger, detector performance and physics reach for these experiments  In spite of its complexity it should be easy-to-use –Each one of the ~ 4000 LHC physicists (including people from remote/isolated countries, physicists who have built the detectors, software-old-fashioned senior physicists) should be able to run the software, modify part of it (reconstruction,...), analyze the data, extract physics results

5. Pere Mato, CERN/PH 5 individual physics analysis batch physics analysis batch physics analysis detector Event Summary Data (ESD) raw data event reconstruction event reconstruction event simulation event simulation event filter (selection & reconstruction) event filter (selection & reconstruction) processed data Processing Stages and Datasets Analysis Object Data (AOD) (extracted by physics topic)

6. Pere Mato, CERN/PH 6 Software Structure non-HEP specific software packages Experiment Framework Event Det Desc. Calib. Applications Core Libraries Simulation Data Mngmt. Distrib. Analysis Every experiment has a framework for basic services and various specialized frameworks: event model, detector description, visualization, persistency, interactivity, simulation, calibrarion, etc. General purpose non-HEP libraries Applications are built on top of frameworks and implementing the required algorithms Core libraries and services that are widely used and provide basic functionality Specialized domains that are common among the experiments

7. Pere Mato, CERN/PH 7 Programming Languages  Object-Oriented (O-O) programming languages have become the norm for developing the software for HEP experiments  C++ is in use by (almost) all Experiments –Pioneered by Babar and Run II (D0 and CDF) –LHC experiments with an initial FORTRAN code base have basically completed the migration to C++  Large common software projects in C++ have been in production for many years aready –ROOT, Geant4, …  FORTRAN still in use mainly by the MC generators –Large developments efforts are put for the migration to C++ (Pythia8, Herwig++, Sherpa,…)

8. Pere Mato, CERN/PH 8 Scripting Languages  Scripting has been an essential component in the HEP analysis software for the last decades –PAW macros (kumac) in the FORTRAN era –C++ interpreter (CINT) in the C++ era –Python recently introduced and gaining momentum  Most of the statistical data analysis and final presentation is done with scripts –Interactive analysis –Rapid prototyping to test new ideas –Driving complex procedures  Scripts are also used to “configure” complex C++ programs developed and used by the LHC experiments –“Simulation” and “Reconstruction” programs with hundreds or thousands of options to configure

9. Pere Mato, CERN/PH 9 Python Role  Python language is interesting for two main reasons: –High level programming language »Simple, elegant, easy to learn language »Ideal for rapid prototyping »Used for scientific programming (www.scipy.org) –Framework to “glue” different functionalities »Any two pieces of software can be glued at runtime if they offer a Python interface  A word of caution: –Python is interpreted: not for computation

10. Pere Mato, CERN/PH 10 Non-HEP Packages widely used in HEP  Non-HEP specific functionality required by HEP programs can be implemented using existing packages –Favoring free and open-source software –About 30 packages are currently in use by the LHC experiments  Here are some examples –Boost »Portable and free C++ source libraries intended to be widely useful and usable across a broad spectrum of applications –GSL »GNU Scientific Library –Coin3D »High-level 3D graphics toolkit for developing cross-platform real-time 3D visualization –XercesC »XML parser written in a portable subset of C++ non-HEP specific software packages Experiment Framework Applications Core Libraries Simulation Data Mngmt. Distrib. Analysis

11. Pere Mato, CERN/PH 11 HEP Generic Packages (1)  Core Libraries –Library of basic types (e.g. 3-vector, 4-vector, points, particle, etc.) –Extensions to C++ Standard Library –Mathematical libraries –Statistical libraries  Utility Libraries –Operating system isolation libraries –Component model and plugin management –Database interfaces –C++ Reflexion  Examples: ROOT, CLHEP, etc. non-HEP specific software packages Experiment Framework Applications Core Libraries Simulation Data Mngmt. Distrib. Analysis

12. Pere Mato, CERN/PH 12 HEP Generic Packages (2)  MC Generators –This is the best example of common code used by all the experiments »Well defined functionality and fairly simple interfaces  Detector Simulation – Presented in form of toolkits/frameworks (Geant4, FLUKA) »The user needs to input the geometry description, primary particles, user actions, etc.  Data Persistency and Management –To store and manage the data produced by experiments  Data Visualization –GUI, 2D and 3D graphics  Distributed and Grid Analysis –To support end-users using the distributed computing resources (PROOF, Ganga,…) non-HEP specific software packages Experiment Framework Applications Core Libraries Simulation Data Mngmt. Distrib. Analysis

13. Pere Mato, CERN/PH 13 ROOT - Core Libraries and Services  ROOT provides the basic functionality needed by any application –Used basically by all HEP experiments  Current ROOT work packages –BASE: Foundation and system classes, documentation and releases –DICT: Reflexion system, meta classes, CINT and Python interpreters –I/O: Basic I/O, trees, queries –PROOF: parallel ROOT facility, xrootd –MATH: Mathematical libraries, histogramming, fitting –GUI: Graphical User interfaces and Object editors –GRAPHICS: 2-D and 3-D graphics –GEOM: Geometry system

14. Pere Mato, CERN/PH 14 ROOT - Core Integrating Elements  The common application software should facilitate the integration of independently developed components to build a coherent application  Dictionaries –Dictionaries provide meta data information (reflection) to allow introspection and interaction of objects in a generic manner –The ROOT strategy is to evolve to a single reflection system (Reflex)  Scripting languages –Interpreted languages are ideal for rapid prototyping –They allow integration of independently developed software modules (software bus) –Standardizing on CINT(C++) and Python scripting languages  Component model and Plugin Management –Modeling the application as components with well defined interfaces –Loading the required functionality at runtime

15. Pere Mato, CERN/PH 15 ROOT I/O  ROOT provides support for object input/output from/to platform independent files –The system is designed to be particularly efficient for objects frequently manipulated by physicists: histograms, ntuples, trees and events –I/O is possible for any user class. Non-intrusive, only the class “dictionary” needs to be defined –Extensive support for “schema evolution”. Class definitions are not immutable over the life-time of the experiment  The ROOT I/O area is still moving after 10 years –Recent additions: Full STL support, data compression, tree I/O from ASCII, tree indices, etc.  All new experiments rely on ROOT I/O to store its data

16. Pere Mato, CERN/PH 16 Persistency Framework  FILES - based on ROOT I/O –Targeted for complex data structure: event data, analysis data –Management of object relationships: file catalogues –Interface to Grid file catalogs and Grid file access  Relational Databases – Oracle, MySQL, SQLite –Suitable for conditions, calibration, alignment, detector description data - possibly produced by online systems –Complex use cases and requirements, multiple ‘environments’ – difficult to be satisfied by a single solution –Isolating applications from the database implementations with a standardized relational database interface »facilitate the life of the application developers »no change in the application to run in different environments »encode “good practices” once for all

17. Pere Mato, CERN/PH 17 POOL - Persistency framework  The POOL project is delivering a number of “products” –POOL – Object and references persistency framework –CORAL – Generic database access interface –ORA – Mapping C++ objects into relational database Oracle SQLite MySQL ROOT I/O RDBMS STORAGE MGR COLLECTIONS FILE CATALOG POOL API USER CODE COOL API COOL CORAL –COOL – Detector conditions database  Object storage and references successfully used in large scale production in ATLAS, CMS, LHCb  Need to focus on database access and deployment in Grid –basically starting now

18. Pere Mato, CERN/PH 18 MC Generators  Many MC generators and tools are available to the experiments provided by a solid community –Each experiment chooses the tools more adequate for their physics  Example: ATLAS alone uses currently –Generators »AcerMC: Zbb~, tt~, single top, tt~bb~, Wbb~ »Alpgen (+ MLM matching): W+jets, Z+jets, QCD multijets »Charbydis: black holes »HERWIG: QCD multijets, Drell-Yan, SUSY... »Hijing: Heavy Ions, Beam-gas.. »MC@NLO: tt~, Drell-Yan, boson pair production »Pythia: QCD multijets, B-physics, Higgs production... –Decay packages »TAUOLA: Interfaced to work with Pythia, Herwig and Sherpa, »PHOTOS: Interfaced to work with Pythia, Herwig and Sherpa, »EvtGen: Used in B-physics channels.

19. Pere Mato, CERN/PH 19 Detector Simulation - Geant4  Geant4 has become an established tool, in production for the majority of LHC experiments during the past two years, and in use in many other HEP experiments and for applications in medical, space and other fields  On going work in the physics validation  Good example of common software LHCb : ~ 18 million volumes ALICE : ~3 million volumes

20. Pere Mato, CERN/PH 20 PROOF – Parallel ROOT Facility  PROOF aims to provide the necessary functionality that allows to run ROOT data analysis in parallel –A major upgrade of the PROOF system has been started in 2005. –The system is evolving from processing interactive short blocking queries to a system that also supports long running queries in a stateless client mode. –Currently working with ALICE to deploy it on the CERN Analysis Facility (CAF)

21. Pere Mato, CERN/PH 21 Experiment Data Processing Frameworks  Experiments develop Software Frameworks –General Architecture of any Event processing applications (simulation, trigger, reconstruction, analysis, etc.) –To achieve coherency and to facilitate software re-use –Hide technical details to the end-user Physicists –Help the Physicists to focus on their physics algorithms  Applications are developed by customizing the Framework –By the “composition” of elemental Algorithms to form complete applications –Using third-party components wherever possible and configuring them  ALICE: AliROOT; ATLAS+LHCb: Athena/Gaudi  CMS: moved to a new framework 2 years ago non-HEP specific software packages Experiment Framework Applications Core Libraries Simulation Data Mngmt. Distrib. Analysis

22. Pere Mato, CERN/PH 22 Example: The GAUDI Framework  User “algorithms” consume event data from the “transient data store” with the help of “services” and “tools” with well defined interfaces and produce new data that is made available to other “algorithms”.  Data can have various representations and “converters” take care of their transformation  The GAUDI framework is used by LHCb, ATLAS, Harp, Glast, BES III

23. Pere Mato, CERN/PH 23 Software Configuration  Re-using existing software packages saves on development effort but complicates “software configuration”  We need to hide this complexity  A configuration is a combination of packages and versions that are coherent and compatible  E.g. LHC experiments build their application software based on a given “LCG/AA configuration”, which is decided by the “architects” –Interfaces to the experiments configuration systems (SCRAM, CMT) –Concurrent different configurations are everyday situation

24. Pere Mato, CERN/PH 24 LCG Applications Area  The Applications Area is one of the six activity areas of the LHC Computing Project (LCG) that should deliver the common physics applications software for the LHC experiments  The area is organized to ensure focus on real experiment needs –Experiment-driven requirements and monitoring –Architects in management and execution –Open information flow and decision making –Participation of experiment developers –Frequent releases enabling iterative feedback  Success is defined by adoption and validation of the developed products by the experiments –Integration, evaluation, successful deployment

25. Pere Mato, CERN/PH 25 Applications Area Organization AA Manager AliceAtlasCMSLHCb Architects Forum Application Area Meeting MBLHCC External Collaborations Geant4 ROOT Work plans Quarterly Reports Reviews Resources LCG AA Projects EGEE Chairs Decisions SIMULATION SPI WP1 WP2 ROOT WP3 WP1 POOL WP1 WP2 WP1 Subproject 1

26. Pere Mato, CERN/PH 26 AA Projects  SPI – Software process infrastructure (S. Roiser) –Software and development services: external libraries, savannah, software distribution, support for build, test, QA, etc.  ROOT – Core Libraries and Services (R. Brun) –Foundation class libraries, math libraries, framework services, dictionaries, scripting, GUI, graphics, SEAL libraries, etc.  POOL – Persistency Framework (D. Duellmann) –Storage manager, file catalogs, event collections, relational access layer, conditions database, etc.  SIMU - Simulation project (G. Cosmo) –Simulation framework, physics validation studies, MC event generators, Garfield, participation in Geant4, Fluka.

27. Pere Mato, CERN/PH 27 Summary  The next generation of software for experiments needs to cope with more stringent requirements and new challenging conditions –The software should not be the limiting factor and should allow the physicists extract the best physics from the experiment –The new software is more powerful but at the same time more complex  Some techniques and tools allow us to integrate functionality developed independently into a single and coherent application –Dictionaries, scripting languages, component models and plugin management  Substantial effort is put in software configuration to provide stable and coherent set of software versions of the packages needed by the experiments  The tendency is to push the line of what is called common software upwards –LCG project is helping in this direction by organizing the requirements gathering, the development and the adoption by the experiments of the common software products