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Maximally Permissive Composition of Actors in Ptolemy II
Marten Lohstroh

Citation
Marten Lohstroh. "Maximally Permissive Composition of Actors in Ptolemy II". Technical report, EECS Department, University of California, Berkeley, March, 2013.

Abstract

The "Cyber" and "Physical" worlds are merging. Cyber-Physical Systems (CPS) are no longer isolated, but start to reach into the Cloud, thereby composing a network which realizes the concept that became known as The Internet of Things. The dynamic nature of the applications in this domain poses significant technical challenges concerning the assurance of important system properties like reliability, robustness, adaptability, and security. Modeling has proven itself to be a valuable tool in gaining better understanding of complex systems, but existing modeling platforms may lack the expressivity to model these new, much more dynamic, and opportunistically composed systems in which the data they handle typically does not conform to a rigid structure.

This thesis addresses the problem of handling dynamic data, in the statically typed, actor-oriented modeling environment called Ptolemy II. It explores the possibilities of using type inference to statically type dynamic data and leverage dynamic type checking to invoke error handling strategies that enhance robustness. The goal is to achieve maximally permissive composition, and the presented solution comes in the form of backward type inference. Backward inferred types are specific enough not to limit composability and general enough not to impose unnecessary constraints on the data. The type constraints imposed by downstream actors determine the type of the otherwise underdetermined output ports of actors that mediate access to untyped resources. This is achieved using additional type constraints, without changing Ptolemy II's original type resolution algorithm, and with no significant impact on the run-time of type resolution. The proposed solution was implemented successfully and has been adopted as an extension of the Ptolemy II type system.

As a byproduct, this thesis gives a thorough case study of the Ptolemy II type system. It uncovers two (independent) obscurities: interference between automatic type conversion and dynamic dispatch; and unsafe access to record elements. Both issues are discussed extensively and possible improvements are suggested.

Electronic downloads

Citation formats  
  • HTML
    Marten Lohstroh. <a
    href="http://chess.eecs.berkeley.edu/pubs/974.html"
    ><i>Maximally Permissive Composition of Actors in
    Ptolemy II</i></a>, Technical report,  EECS
    Department, University of California, Berkeley, March, 2013.
  • Plain text
    Marten Lohstroh. "Maximally Permissive Composition of
    Actors in Ptolemy II". Technical report,  EECS
    Department, University of California, Berkeley, March, 2013.
  • BibTeX
    @techreport{Lohstroh13_MaximallyPermissiveCompositionOfActorsInPtolemyII,
        author = {Marten Lohstroh},
        title = {Maximally Permissive Composition of Actors in
                  Ptolemy II},
        institution = {EECS Department, University of California, Berkeley},
        month = {March},
        year = {2013},
        abstract = {<p>The "Cyber" and "Physical" worlds are merging.
                  Cyber-Physical Systems (CPS) are no longer
                  isolated, but start to reach into the Cloud,
                  thereby composing a network which realizes the
                  concept that became known as The Internet of
                  Things. The dynamic nature of the applications in
                  this domain poses significant technical challenges
                  concerning the assurance of important system
                  properties like reliability, robustness,
                  adaptability, and security. Modeling has proven
                  itself to be a valuable tool in gaining better
                  understanding of complex systems, but existing
                  modeling platforms may lack the expressivity to
                  model these new, much more dynamic, and
                  opportunistically composed systems in which the
                  data they handle typically does not conform to a
                  rigid structure.</p> <p>This thesis addresses the
                  problem of handling dynamic data, in the
                  statically typed, actor-oriented modeling
                  environment called Ptolemy II. It explores the
                  possibilities of using type inference to
                  statically type dynamic data and leverage dynamic
                  type checking to invoke error handling strategies
                  that enhance robustness. The goal is to achieve
                  maximally permissive composition, and the
                  presented solution comes in the form of backward
                  type inference. Backward inferred types are
                  specific enough not to limit composability and
                  general enough not to impose unnecessary
                  constraints on the data. The type constraints
                  imposed by downstream actors determine the type of
                  the otherwise underdetermined output ports of
                  actors that mediate access to untyped resources.
                  This is achieved using additional type
                  constraints, without changing Ptolemy II's
                  original type resolution algorithm, and with no
                  significant impact on the run-time of type
                  resolution. The proposed solution was implemented
                  successfully and has been adopted as an extension
                  of the Ptolemy II type system.</p> <p>As a
                  byproduct, this thesis gives a thorough case study
                  of the Ptolemy II type system. It uncovers two
                  (independent) obscurities: interference between
                  automatic type conversion and dynamic dispatch;
                  and unsafe access to record elements. Both issues
                  are discussed extensively and possible
                  improvements are suggested.</p>},
        URL = {http://chess.eecs.berkeley.edu/pubs/974.html}
    }
    

Posted by Marten Lohstroh on 20 Mar 2013.
Groups: ptolemy
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