Implementation and rigorous verification of STEPTAS interfaces

1
Implementation and rigorous verification of
STEP-TAS interfaces

• Hans Peter de Koning
• Simon Appel, David Alsina Orra, Duncan Gibson
• (European Space Agency / ESTEC, Noordwijk, The
  Netherlands)
• (ESA/ESTEC D/TEC-MCV)

2
Topics

• Where are we with STEP-TAS?
• STEP-TAS STEP-based "Thermal Analysis for
  Space" data exchange standard
• Progress over last year
• Larger picture w.r.t. other data standardization
  activities in European space
• Focus on iterative, integrated data exchange
  standard development process
• Requirements ? Standard data model ? Interface
  implementation ? Verification
• Continuous interface implementation and rigorous
  verification
• What lessons did we learn?
• General recommendations
• STEP-based and non-STEP-based
• Attempt to extract best practices / patterns
• Further development and formal standardization

3
Timeline of STEP-TAS development
4
Iterative, incremental development scheme
Currently with STEP-TAS at increment (version)
5.2 Protocol now largely frozen
5
Requirements on open data exchange standards and
implementation technology

• Shall be reliable
• Shall be easy to use and understand by end-users
• Absolute minimum number of transfer parameter
  settings
• Shall be rigorously verifiable
• Shall be complete and self-contained
• Yet achievable in reasonable time and as simple
  as possible
• Shall be designed for extension while keeping
  full backwards compatibility
• Shall be portable no computer platform
  dependencies
• Shall avoid dependence on third party proprietary
  software
• Shall be designed for low cost implementation and
  maintenance
• To minimize barriers for take-up and
  implementation by tool/interface developers

6
Main characteristics STEP-TASThermal Analysis
for Space (1)

• Supports three kinds of (thermal) models
• Thermal geometric models represented by bounded
  surfaces
• Thin shells with oriented faces, mesh and
  notional thickness
• Thermal (and thermal-hydraulic) network models
• All typical ESATAN or SINDA like data and results
• Thermal test (or flight) models with sensor
  identification and possible location
• E.g. test article with thermo-couples,
  thermistors, data acquisition channels,
• Can be used in conjunction with corresponding
  STEP AP203/AP214 CAD model
• STEP-TAS is the standard that end-users should
  be aware of but includes generic
  discipline-independent STEP-NRF protocol
• NRF provides all the general features to enable
  multi-discipline data exchange
• NRF enables modular software engineering

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Main characteristics STEP-TAS Thermal Analysis
for Space (2)

• Geometric and mathematical sub-model hierarchy
  no limitation on depth
• Full parameterization of geometric and
  mathematical model possible
• Arbitrary number and depth of coordinate system
  transformations
• Retains human-understandable sequences of
  rotations w.r.t. the major axes
• Mesh definitions on geometric faces
• Mapping from geometric faces to thermal
  mathematical model nodes
• Separation of model and case specification
• Model is the representation of the static
  structure of the object of interest
• For case think of load-case / simulation scenario
  / test-case / operation-case
• Multiple cases / sub-cases possible per model
• Named materials with their thermo-optical and
  physical properties
• Supports multiple sets of properties per material
  property environment (e.g. BOL, EOL)
• Rigid body kinematics with on-orbit pointing for
  articulated parts

8
Main characteristics STEP-TAS Thermal Analysis
for Space (3)

• Space trajectory, attitude and orientation
• Orbit arcs defined by Keplerian parameters or
  general ephemeris
• Definition of named discrete events, sequencing
  of cases, parameterized attitude, etc.
• Analysis, simulation, test or operation run
  results
• Contains complete run-execution informatione.g.
  date time stamp of execution start / end,
  tool/facility name and version, etc.
• Supports choice of SI or other unit systems (but
  requires one consistent set)
• Conversion factors and offsets w.r.t. SI
  reference units are explicitly defined
• STEP-TAS dictionary fully defines all Imperial
  units used in US projects

9
STEP-TAS Conformance Classes( complete subsets
of standard)
NOTE Conduction model means All parameters
needed to compute conductive network, like
thickness, material with conductivity,
connectivity between shells with/without
contact conductance
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Main characteristics STEP-NRF Network-model
Results Format (1)

• Generic, discipline-independent protocol to
  exchange models, cases results
• Model definition, using a discrete network
  representation
• Supports model/submodel hierarchy with no
  limitation on depth
• Classification of network models, nodes, node
  relationships through dictionary
• Results data, produced in analysis, simulation,
  test or operation
• Meta-data, which records details of executed
  actual analysis, simulation, test or operation
  run
• Provides common basis for a suite of
  multi-discipline exchange standards
• Discipline-dependent data is defined in
  runtime-loadable dictionary
• E.g. thermal-tailored NRF dictionary for STEP-TAS
• Results valued quantity types for discrete
  observable items for discrete states of the
  system
• No support for continuous fields, etc.
• Any quantity has explicit quantity type and unit
  no loose numerical values
• E.g. quantity type temperature / unit kelvin
• Data model designed to cope efficiently with
  large amounts of results data
• Designed to map well onto existing scientific
  data storage standards like HDF5

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Main characteristics STEP-NRF Network-model
Results Format (2)

• Central NRF data structure for results is the
  so-called datacube
• Each element of the datacube is a scalar, vector
  or tensor property for a specific combination of
  obervable_item, quantity_type, state
• Designed for efficient storage and retrieval of
  massive amounts of structured data
• NRF supports
• Quantity value prescriptions withliteral or
  expression values
• Real, integer, complex and string enumeration
  quantity types
• Named variables, functions, interpolation tables
  and polynomials

quantity types
observable items
states
typically sampled time or frequency
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Main characteristics STEP-NRF Network-model
Results Format (3)
Results creation pattern
analysis simulation test operation tool or
facility
Chaining results creation
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STEP-TAS standard - two parts
Note "Dictionary" is similar to "Reference Data
Library" in other STEP standards
Actually a STEP-TAS file itself

• Application Protocol contains core data model
  formalized in ARM EXPRESS schema
• Run-time Loadable Dictionary contains pre-defined
  instancesAllows for backward compatible
  extensions of standardwithout costly updates to
  protocol and implemented interface software

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STEP-TAS architecture overviewfor interfaces /
converters
pyExpress (expressik) runtime library includes
STEP file reader/writer
STEP-TAS standard
STEP-TAS application protocol Thermal Analysis
for Space
pyExpress (today)
includes STEP-NRF protocol Network-model Results
Format
STEP-TAS protocol library (generated)
loaded at runtime
STEP-TAS API
STEP-TAS support library (handcoded)
expressik (future)
STEP-TAS dictionary Predefines needed units,
quantity types, node classes, Runtime download
possible from URI http//www.estec.esa.int/therma
l/
STEP-TAS .stp exchange file ISO 10303-21
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TASverter architecturewith areas of
responsibility
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Excerpts from STEP-TAS dictionary(Part 21 file
and HTML)
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STEP-TAS real model conversion galleryISS
thermal interface model
ESARAD
THERMICA
PATRAN
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STEP-TAS real model conversion galleryAutomated
Transfer Vehicle (ATV)
ESARAD
THERMICA
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STEP-TAS real model conversion galleryAutomated
Transfer Vehicle (ATV)
Original THERMICA .SYSBAS
Generated ESARAD .erg
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STEP-TAS real model conversion galleryIntegral
THERMICA
ESARAD
PATRAN
21
STEP-TAS real model conversion galleryMETOP
stowed solar array
THERMICA
ESARAD
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STEP-TAS status today

• Stable protocol and dictionary
• v5.2 available end of April at http//www.estec.es
  a.int/thermal/tools/standards.html
• All geometry parameterized
• Large automated fully documented regression test
  suite
• 310 unit test cases (186 ESARAD, 124 THERMICA)
• 24 real analysis model test cases (14 ESARAD, 10
  THERMICA)
• pyExpress Python API generator (supports EXPRESS
  edition 1)
• With built-in full programmer's manual generator
  from protocol (using epydoc)
• Full domain and global rule validation (WHERE,
  RULE)
• Documented EXPRESS-to-Python mapping
• TASverter release 6 due end of April
• Free download from http//www.estec.esa.int/therma
  l/tools/tasverter.html
• Implements STEP-TAS CC1/CC3
• Now includes simple GUI (on Windows and Linux)
• ESATAN GFF-to-STEP-TAS model/case/results
  converter implemented

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TASverter GUI
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Relation with other European space standardization

• STEP-SPE "Space Environment Analysis"
• In progress, extension of STEP-NRF and STEP-TAS
• ECSS E-10 Part 1B "System engineering -
  Requirements and process"
• Published November 2004
• ECSS E-10 Part 7A "Product data exchange"
• Officially published October 2004
• ECSS E-10 Part 9 "Engineering Database"
• In progress, ambitious standard to integrate
  system engineering and all space disciplines
• Looking at MDA, UML2/SysML/OCL, XMI, STEP AP233,
  RDF, OWL, XML/Schema
• ECSS E-10 Part 13 "Modelling Simulation"
• In progress, focuses on space/ground segment high
  software content systems

Note ECSS standards can be freely downloaded as
PDF from http//www.ecss.nl(after simple
registration)
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Lessons learned

• Keep data models simple and robust
• Refrain from "fancy" EXPRESS constructs
• STEP-TAS uses single ONEOF inheritance throughout
  and no SELECT TYPEs
• Integrated team with incremental development
  process works best
• Data modeling without extensive interface
  implementation and verification in-the-loop is
  bound to produce mediocre quality models "the
  devil is in the details"
• Stick to ARM level models
• Already at ARM level it is a serious challenge to
  achieve rigorous verification and adequate test
  coverage
• Invest in efficient schema mapping tools to
  achieve interoperability
• Serious doubt that the STEP AIM / MIM route will
  ever be successful for interoperability
• Python is an excellent language to implement
  EXPRESS data models
• Very flexible, very short and effective
  development cycles
• Performance confirmed for datasets up to 100,000
  instances

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Recommendations

• EXPRESS data modeling
• Only use constructs that can be mapped with
  minimum semantic loss to most target programming
  languages and to other modeling environments like
  UML2, XML/Schema following the MDA
• High quality standard data models require such an
  investment that they should be transferable
  between different data modeling environments
• Avoid complex entity instances, SELECT, multiple
  inheritance, implicit ANDOR subtypes
• Check expressions and algorithms in DERIVE,
  INVERSE, UNIQUE, WHERE and RULE for performance
  using profiling on interface implementations
• Naive implementation may cause huge performance
  penalties
• Formalize model verification as much as possible
  using WHERE rules and RULEs
• They act as built-in test cases, that
  automatically get executed in any implementation
• Do graphical presentation in UML class diagrams
  rather than now outdated EXPRESS-G
• Much better communication to most implementers
• Use code generation as much as possible also for
  documentation
• Split standard into core protocol and runtime
  loadable ISO 10303-21 dictionary
• Simple approach that greatly enhances future
  extensibility at affordable cost

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STEP-TAS roll-out plan
Note Resources between square brackets, e.g.
ESA
radiative
conductive
(1) Complete CC1 3 ESA
One week training course for developers at ESTEC
ESA developers
Intermediate TASverter release
Transfer ESARAD and THERMICA modules to
developers (ESA, Alstom, Astrium)
Assist Alcatel Maya upgrade/implementation CC1
3 ESA, Alcatel, Maya
(2) Develop CC2 4-7 (kinematics mission
definition) ESA, Alstom, Astrium
(3) Develop CC8 9 (ESATAN with simple MORTRAN)
ESA, Alstom
(4) Develop CC10 11 (ESATAN with full MORTRAN)
ESA, Alstom
(5) Develop CC12 (test results data) ESA
Present results at ESTEC workshop
Present results at ESTEC workshop
Standardise STEP-NRF STEP-TAS in ECSS ISO
ECSS WG chaired by ESA
STEP-TAS interfaces in US tools (targets TRASYS,
RADCAD, TSS, SINDA/FLUINT, SINDA-G) TBD
Support TASverter external release (helpdesk)
ESA
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Closing statements

• ESA is fully committed to making STEP-TAS a
  success
• Funding and maintaining robust open data exchange
  standards and software is fully in line with the
  ESAs mandate as an Agency
• Its a key element in Thermal and Space
  Environment Analysis Software Harmonisation
• The user community as a whole will benefit from
  reliable STEP-TAS middleware
• Both end-users and developers
• Our hope is that it will create a higher level
  playing field with healthy competition between
  the analysis tools while still safeguarding the
  long term interests of end-users
• ESA open source licence agreement is in final
  stage of approval
• Official release of STEP(-TAS) support software
  as OSS expected shortly
• Licence modeled after NASA Open Source Agreement
  (see http//www.opensource.org)
• See University of Manchester presentation on
  expressik for details on upcoming OSS EXPRESS
  interface kit (supporting general EXPRESS parsing
  and C, C, Python code generation)

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References

• ISO 10303 (STEP) standardshttp//www.tc184-sc4.or
  g
• STEP-TAShttp//www.estec.esa.int/thermal/tools/st
  andards.html
• TASverterhttp//www.estec.esa.int/thermal/tools/t
  asverter.html
• Hierarchical Data Format (version 5)
  HDF5http//hdf.nsca.uiuc.edu
• European Cooperation for Space Standardizationhtt
  p//www.ecss.nl
• Python (freely available open source scripting
  language)http//www.python.org
• SWIG (freely available open source programming
  language interface generator)http//www.swig.org
• OMG Model Driven Architecturehttp//www.omg.org/m
  da
• SysML (UML2 profile for System Engineering)http/
  /www.incose.org