The Role of Java in High Energy Physics

SLAC Colloquium - March 8th 1999

Tony Johnson

Outline Of Talk

• Introduction to Java
  • Features, Pro’s and Con’s

• Applicability to HEP
  • GUI’s and Event Displays
    • Wired - Babar Event Display- CMS event display
  • Offline Simulation and Reconstruction
    • hep.lcd package for Linear Collider Detector studies
  • Data Analysis
    • Java Analysis Studio and Related tools
  • Conclusion

History of Java

• 1991 James Gosling at Sun creates Java language (née Oak)
  • Targeted at consumer electronics - cable top boxes, VCR, TV etc.
  • Goal was reliability not speed

• 1994 Hot Java Web browser written (in Java)
  • Supports Applets - Downloadable programs that run inside web browser
  • Java licensed by Netscape, Oracle, Microsoft many others
    • Huge hype surrounding “Web Programming language”

• 1997 Java 1.1 released with many standard libraries
  • Sun’s mantra becomes “Write Once Run Anywhere”
  • Enthusiastically supported by all major hardware and many software vendors
  • Microsoft begins to have second thoughts

• 1998 Java 2 released, even more standard libraries
  • Now truly general purpose language
  • Sun (and DOJ) sue Microsoft
  • Java returns to its roots? - Jini

Java Architecture

• More than just a Web Tool
  • Java is a fully functional, platform independent, object-oriented language
  • Powerful set of machine independent libraries, including GUI library.

• Totally Buzzword Compliant
  • Simple, Object Orientated, Distributed, Dynamic, Robust, Secure, Architecture Neural, Portable, High Performance, Multithreaded.

• Interpreted?

• Compiled + Interpreted.
• Hotspot may make Java faster than statically compiled languages.

Java Features

• Simple
  • But not trivial…you need to read a book
    • Syntax very close to C++
      • No backwards compatibility issues
      • Some features of C++ which add undue complexity dropped.
      • Good stepping stone to (or from) C++
    • Clean and Efficient Object-Oriented Language
  • Language features guide programmer toward reliable programming habits

• Robust
  • Extensive Compile-Time checking of code
  • Second level of run-time checking of code
  • Memory management done by system, not by programmer
  • No pointers to mess up (Java uses references rather than pointers)
• Chances of program running as designed without the need for time-consuming debugging is greatly increased.

Java Features (continued)

• Highly Portable
  • Java works today on NT, Win95/98, Unix (including Linux), Mac, VMS
    • Personal Java - Windows CE, Palm Pilot
  • Programs written in Java are very portable
    • Move to another platform and it just works
      • Care needed with AWT GUI components (obsolete) and web browsers
    • Lifetime of HEP experiments > OS lifetime.
      • Lifetime of Java > Lifetime of HEP experiment??

• Encourages true modularity
  • Build entire framework for HEP experiment in Java
  • Abstract away underlying systems (batch system, IO system etc.)

Java Features (continued)

• Distributed
  • Built in support for Internet protocols, URL’s, HTTP, Remote Method Invocation, Corba, Database access etc.

• Secure
  • Bytecode “verifier”, padded cell (c.f. Web Browser)

• Multithreaded
  • Language has direct support for multithreading

• Dynamic
  • Libraries can change without recompiling programs that use them
  • Can dynamically load and unload code during program execution
  • Can move objects across the network (agents), or store them in databases and retrieve them later.

Java Libraries and API’s

• Standard Libraries and API’s
  • 2D + 3D graphics + GUI (Swing) + Imaging + Printing
  • Database connectivity (JDBC) + ODMG
  • Collections, IO (Serialization), Data Compression
  • Networking, Sockets, SSL, Corba, RMI
  • Java Beans (components), Help
  • Multimedia, Sound, Speech
  • Security, Code Signing, Cryptography
  • Math, Arbitrary Precision Math
  • Shared Data (Collaborative Applications)

• Huge “Community-Ware” software archive
  • IBM alone has hundreds of Java resources on its Alphaworks site

Java Tools

• Popularity of Java = many tools
  • And they are cheap (or even free)
• Development Environments (IDE’s)
  • Editor, Compiler, Debugger, WYSIWYG GUI designer, Source control
• Automatic Documentation generators
• Memory and CPU Optimizers
  • Since debugging time is minimal you might actually have time to use them
• Object Modelers

• Many commercial sets of components

Java Limitations?

• No operator overloading
  • Annoying for complex numbers, matrices, 3/4-vectors
  • Perhaps more often abused than sensibly used

• Floating point performance
  • Requirement for identical results on all platforms can be a problem
  • Being addressed by Java Grande Forum + Sun
    • http://www.javagrande.org/

• Bugs sometimes slow to be fixed
  • Printing, Imaging existed for ɭ year
  • Perhaps “Community Source License” will help

• Little control over Memory Allocation

• Integration with C++ could be better

Where would HEP use Java?

• GUI systems
  • online + control (not really any alternative)
  • Event Display

• Reconstruction+Simulation packages?

• Data Analysis tasks
  • Offline
  • Online

• Event Generators

Event Displays

• WIRED
  • Experiment independent event display framework developed at CERN by
    • Mark Donszelmann
  • Good example of modular design and code reusability
  • Client Server model
    • Event Display runs on desktop
      • Uses Swing and 2D API
      • Has rich library of projections (e.g. Fisheye)
    • Being used by Babar
      • Fetches data using CORBA

Java for Reconstruction/Simulation

• Dual Goals:
  • Contribute to Linear Collider Detector/Physics Studies
  • Experiment with using Java for full offline reconstruction and analysis package

LC Detector studies in US

• Goals:
  • Detailed Study of physics processes in a variety of possible LC Detectors.
    • Reference Small and Large detectors
  • Full simulation with GISMO
    • Switch to Geant4, when ready
  • Analysis using
    • Paw
    • C++ & Root
    • Java & JAS
  • Software Requirements
    • Flexibly handle different detector geometries and technologies
    • Rapid development of variety of reconstruction and analysis algorithms

Why Java for HEP Computing?

• Previous generation of experiments used Fortran + Data Management System (== Jazelle, Zebra, BOS)

• Solves Three Problems
  • Ability to Represent Complex Data Structures
  • Persistence (i.e. read in and write out complex structures)
  • Run time access to named data in structures (for analysis)

• Now time has marched on and modern experiments use C++
  • Represent Complex Data
  • Persistence
  • Run time access to data
  • Still need to build (or buy and deploy) data management system (e.g. Root, Objectivity)

• Java
  • Represent Complex Data
  • Persistence (serialization)
  • Run time access to data (reflection)
  • support built-in to language

Java package hep.lcd

• Reconstruction Processors
  • Track finder written, track fitter in progress
  • Several clustering algorithms

• Parameterized MC Processors
  • Can read generator input or Gismo output
  • Track and Cluster smearing

• Analysis Utilities
  • Event Shape + Thrust utilities
  • Jet finder [Jade, Durham]
  • Histograming

• Event Display
  • Simple 2D Event display currently
  • Plan to use WIRED later

• Framework
  • Driver framework
    • interactively control
      • calling of processors
      • debugging/histograming
    • Parameter (Constant) access
      • driven by detector geometry
    • MC event input (StdHEP format)
    • IO system based on Java IO
      • random access files
    • Can be run inside JAS or standalone

What does user have to write?

hep.lcd framework

Event Display

Event Display

Event Display

Event Display

Is Java fast Enough for HEP offline?

• Current (266Mhz PII, JDK 1.1.7)
  • Clustering .6 secs/event
    • 13.5 Million Calorimeter Cells
  • Fast MC 6 ms/event
  • Track Finding ~2secs/event
• Very competitive with Root implementation

• Getting even better!!!
  • JDK 1.2
  • HotSpot - Run-time optimization

• In real life may be faster than C++ (c.f. Babar)
  • Better, cheaper analysis tools
  • Manageable complexity

Java for Reconstruction/Simulation

• Looks very promising
  • Have been able to develop framework very fast
  • People have no problem learning and using it
  • Performance looks good

• Future
  • Standard Java interface to Geant4?
  • Real difficulty in porting offline code from platform to platform is not core reconstruction code, but framework
    • Batch System, scripting languages, setup
    • Java could also be used for this
      • Abstract interfaces to Batch System etc.

PPT Slide

What if I just want to user Java for data analysis?

Java Analysis Studio

• Experiment independent analysis tools for High Energy Physics data

What is Java Analysis Studio?

• Set of experiment independent analysis tools for event oriented (High Energy Physics) data
  • Data Access classes provide access to many common HEP data formats
  • Histogram Accumulation + Manipulation Classes
  • Plot Display classes
  • Lightweight framework for users to create physics analysis applications in Java.

• Tools work alone, in combination, or within
  • Java Analysis Studio GUI which gives:
    • Integrated editor and compiler
    • Efficient access to local and remote data
    • Extensibility via Plug-ins, Fitters, Functions etc.

Data Access Classes

• Currently Support
  • PAW n-tuples, Histoscope Files, Hippo n-tuples, any SQL database, flat-file n-tuples, StdHep MC files, Random access Java files
  • Any data format via user supplied Data Interface Module

• Experimenting with
  • Objectivity - Caltech (CMS), DESY
  • Root - see http://www-sldnt.slac.stanford.edu/tony/root
  • Direct access to MC generators

• Future
  • XML, CDF/HDF

Data Access Classes

• Supports both n-tuples and Structured Data
  • n-tuples are fast and allow for simplifications in GUI
    • Simple Interactive cuts
    • Simple plot generation
      but n-tuples ultimately limiting
  • Arbitrarily Structured Data provides maximum flexibility
    • Requires slightly more work from end-user
    • Complete Object Oriented Analysis Environment
    • Flexible enough to write (or prototype) reconstruction code

Data Access Classes

• Analyze local or remote data

• User interface independent of Data Location
• Does not assume fast network (works well at 28.8 bps]
• Analysis code moves (transparently) to data

Desktop

Client

Remote Data Analysis

GUI

Data

Analysis

Engine

Experiment

Interface

Experiment

Extensions

(Event Display)

TCP/IP Network

Padded Cell

C++ Code

Data

• Zebra
• Jazelle
• Paw
• Root
• Objectivity

Distributed Data Analysis

Network

Data Server

Desktop

Client

Network

Data Controller

Distributed Data

Data Server

DIM

Data Server

DIM

Data Server

DIM

Data Server

DIM

Data Server

DIM

Data Server

DIM

Histogram Filling+Manipulation

• Histogram delegates binning to:
  • “partition classes” [idea stolen from LHC++]
    • Map from X, Y to bin number
      • supports real, integer, string, date’s etc.
    • Calculation of contents, errors in bin
      • allows efficiency plots, mean/rms plots etc
    • Data storage method
      • immediate binning (c.f. Hbook)
      • delayed binning, allows rebinning, axis changes via GUI
    • Many standard partitions provided.
    • User can provide own partition functions

Plot Display Package

• 1-d/2-d Histogram/ScatterPlot Display
  • multiple axes, direct user interaction, overlays, fitting

Java Analysis Studio Features

• Rich, easy to use GUI

Demo

Can I Use JAS to Analyze Babar Data?

No!

JAS Availability

• 1.0 Beta currently available
  • Windows (NT, 95, 98) + Unix (Solaris+Linux)
  • Installed on Solaris at SLAC (/usr/local/bin/jas)
  • Limitations
    • Detailed documentation still under development
    • May still be some changes to user API
  • Download from: http://www-sldnt.slac.stanford.edu/jas

• 1.0 Final release in April
  • More plot types
  • More flexible control of histograms
    • Ability to easily compare multiple datasets
  • More n-tuple handling tools (c.f. HippoDraw)
  • Greatly improved printing

Collaboration

• CERN
  • WIRED (M. Donszelmann)
    • Integrate Wired event display as “Plug In”
  • LHC++
    • will use JAS as alternative GUI to Explorer
    • will provide interface to Gemini fitter

• DESY, Caltech - Objectivity interface

• FNAL, interface to histoscope, online-control

More Info

• Java Analysis Studio
  • http://www-sldnt.slac.stanford.edu/jas

• Please give us feedback
  • jas-feedback@sld-mail.slac.stanford.edu

• Mailing List:
  • http://www.slac.stanford.edu/cgi-bin/lwgate/JAS-L/

• Also general mailing list for Java in HEP:
  • http://www.slac.stanford.edu/cgi-bin/lwgate/HEP-JAVA/

Acknowledgments

• JAS Programming
  • Kevin Garwood, Jonas Gifford, Azhar Zuberi

• JAS Ideas Borrowed From
  • LHC++(YemI Adesanya), Histoscope (Paul LeBrun et al), HippoDraw (Paul Kunz et al)

• Babar Event Display/Corba/WIRED
  • Joe Perl, Serge Du, Mark Donszelmann

• CMS Event Display
  • Julian Bunn, Rick Wilkinson

• hep.lcd Programming
  • Joanne Bogart, Mike Ronan, Gary Bower

• LCD Gismo/Root Programming
  • Richard Dubois, Rob Shanks

Conclusions

• Java is a very useful language+environment that could be very beneficial to HEP in many areas.

• Could Java be used for entire offline for major experiment?
  • Technically - Yes
  • Will Java Survive long enough?
    • Need ISO standard
    • Need to see how market forces play out.

• Programming in Java is Fun!!
  • Spend time architecting an elegant solution to problem to be solved
    • Not
      • Reinventing the wheel,
      • Debugging someone else’s problem
      • Porting to different platforms