Developments with pyExpress an open source Python binding

1
Developments with pyExpressan open source Python
binding

• Hans Peter de Koning (ESA/ESTEC D/TOS-MCV, The
  Netherlands)
• Hans-Peter.de.Koning_at_esa.int
• 6th NASA-ESA Workshop on Product Data Exchange
• April 20-23, 2004, EADS/Astrium, Friedrichshafen,
  Germany

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Objectives pyExpress

• Lower the threshold for implementation of STEP
  standards as much as possible
• Ensure full portability across all computer
  platforms / compiler combinations used for
  (space) analysis tools
• Provide an OSS environment for STEP based PDE
  converters which is comparable in power and
  effectiveness with XML OSS environments
• Ensure long term availability of STEP based data
  exchange solutions to ESA in the long term,
  without any dependency on third party STEP
  toolkit vendors
• As much automated code generation as possible

3
Why Python?

• Free of charge, very powerful open source
  environment
• Highly portable across Windows, Linux, all
  UNIXes, MacOS
• Hugh set of well-tested library modules
• Numeric computation, XML, HTTP, regular
  expressions, etc.
• Dynamic memory management / automatic garbage
  collection
• Elegant object oriented programming model
• Weakly typed but with powerful runtime type
  checking
• Very powerful text processing and reflection
  capabilities
• Easy mapping to EXPRESS almost a natural fit
• Easy to implement interfaces with C/C libraries
  (using SWIG)
• In our experience much higher productivity
  environment than C or Java
• See http//www.python.org

4
pyExpress development history

• 2002, June Decided to prototype an EXPRESS
  compiler and library code generator in Python for
  STEP-NRF and STEP-TAS
• 2002, September Completed feasibility study
  (250h) successfully
• Basic scanner / parser / Python library generator
  working
• Using SPARK lexer/parser package (purely Python)
• 2002, October Decided to go ahead with pyExpress
  code generators for industrial use in upgraded
  STEP-TAS libraries and converters
• Simulog Graitec (France) ANSI C library
  generator, C/C converters
• ESA/ESTEC Python class library generator,
  TASverter tool
• 2003, March First releases of pyExpress,
  TASverter, C libraries
• 2004, February Fifth release of TASverter (now
  used in production environment)
• 2004, March Start upgrade pyExpress and merge
  with Jex (Univ. of Manchester)

5
Current capabilities

• Handles long form EXPRESS edition 1 SCHEMA
• CONSTANTs, TYPEs, ENTITYs, FUNCTIONs
• most WHERE rules
• explicit, redeclared and DERIVEd attributes
• Has built-in Part 21 reader/writer
• Not yet implemented
• USE FROM and REFERENCE FROM
• INVERSE attributes
• UNIQUE rules and global RULEs
• complex instances
• GENERIC type and ARRAY with non-default index
  bounds
• QUERY statement and some other built-in functions

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Design approach

• Highly modular
• Support ISO 10303-111994 (i.e. EXPRESS version
  1)
• Support ISO 10303-211994 (single schema / data
  section)
• Generate early binding class libraries
• Start with Python and C
• Stay as close as possible to EXPRESS schema
  structure, but adapt to target language
  conventions
• Make extensive use of Python (class / type)
  reflection capabilities
• Defensive programming and runtime type checking
  throughout
• Python is a weakly typed language
• Tool is too large to rely on programmer
  discipline use positive asserts

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pyExpress architecture
HTML API manual for Python class library A
SPARK
pyExpress utils
EXPRESS schema A
EXPRESS MetaModel Handler
uses
Scanner / Tokenizer
Early binding Python class library for schema A
Python Code Generator
Parser
tokenlist
Early binding C class library for schema A
C Code Generator
Semantic Analyzer
abstract syntax tree
pyExpress
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Outline of converter based on pyExpress
input
contains in-memory dataset(s) conforming to
Schema A
Converter X-A-Y
File or in-memory data for Tool X
output or input
Support library for Schema A macro
convenience functions
Part 21 writer
Tool X to Schema A reader
ISO 10303-21 file for dataset conforming
to Schema A
Generic STEP repository handler
Python or C API for Schema A
output
Schema A to Tool Y writer
Generated class library for Schema A
File or in-memory data for Tool Y
To be produced by converter developer
Part 21 reader
Schema A Library provided by pyExpress
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pyExpress mapping examples
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Short DEMO with easytan SCHEMA
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Future of pyExpress

• Publish as open source, once formal ESA open
  source license is available
• Expected later in 2004
• Upgrade with support for missing EXPRESS Edition
  1 functionality
• Upgrade API and dataset handling to conform to
  SDAI (ISO 10303-22)
• Develop draft Python SDAI binding (if time
  permits)
• Complete generation of API (class library) plus
  Programmers Manual
• from XML version of a STEP application protocol
  or resource
• Merge best of pyExpress and Jex (nicknamed pyJex)
• ESA contract with Manchester Informatics Ltd.
  (UK) and University of Manchesters Dept. of
  Computer Science (Prof. Hilary Kahn) started
  March 2004
• EXPRESS schema processing using Java generates
  Python, Java, C/C APIs
• Planned to be published as open source 2005-Q2
• Use on ESATAP (ESA Thermal Analysis
  Post-processor) for ESATAN results
• Contract started in Jan 2004 with Silogic (F),
  Alcatel Space (F), Dorea (F)

12
Acknowledgements

• My co-workers at ESA/ESTEC Simon Appel, David
  Alsina
• Contractor Incka (France) Olivier Pailles,
  Arnaud Klinger
• Subcontractor GRAITEC (France) Eric Lebègue and
  co-workers
• The developers of exp-engine.sourceforge.net
  (expresso) Peter Denno, Craig Lanning, Steve
  Waterburyand osexpress.sourceforge.net Josh
  Lubell, Michael Keenan, Stephane Lardetfor
  valuable ideas and examples on how to parse
  EXPRESS schemas
• The developer of the Python SPARK module John
  Aycock (http//pages.cpsc.ucalgary.ca/aycock/spar
  k)