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

• http://www.eecs.berkeley.edu/Pubs/TechRpts/2013/EECS-2013-19.html

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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