• Source: Pepa

      • Pepa may refer to:

      Pepa, Democratic Republic of the Congo, a village
      Pepa Airport, an airstrip
      PEPA or Performance Evaluation Process Algebra, a stochastic process algebra
      PEPA (drug), an ampakine drug that is a potential nootropic
      Pepa (musical instrument), a flute-like musical instrument from Assam
      La Pepa or the Spanish Constitution of 1812


      People with the nickname


      Pepa (footballer) (born 1980), Portuguese footballer
      Pepa (rapper), Jamaican-American rap & hip-hop artist, member of Salt-N-Pepa
      Pepa Fernández (born 1965), Spanish journalist
      Pepa Rus (born 1985), Spanish actress, humorist, and singer


      People with the surname


      Avni Pepa (born 1988), Kosovar footballer
      Brunild Pepa (born 1990), Albanian footballer


      Fictional characters


      Pepa Madrigal from Encanto


      See also


      Joseph (name)
      Pepe (disambiguation)

    • Source: PEPA

      • Performance Evaluation Process Algebra (PEPA) is a stochastic process algebra designed for modelling computer and communication systems introduced by Jane Hillston in the 1990s. The language extends classical process algebras such as Milner's CCS and Hoare's CSP by introducing probabilistic branching and timing of transitions.
      Rates are drawn from the exponential distribution and PEPA models are finite-state and so give rise to a stochastic process, specifically a continuous-time Markov process (CTMC). Thus the language can be used to study quantitative properties of models of computer and communication systems such as throughput, utilisation and response time as well as qualitative properties such as freedom from deadlock. The language is formally defined using a structured operational semantics in the style invented by Gordon Plotkin.
      As with most process algebras, PEPA is a parsimonious language. It has only four combinators, prefix, choice, co-operation and hiding. Prefix is the basic building block of a sequential component: the process (a, r).P performs activity a at rate r before evolving to behave as component P. Choice sets up a competition between two possible alternatives: in the process (a, r).P + (b, s).Q either a wins the race (and the process subsequently behaves as P) or b wins the race (and the process subsequently behaves as Q).
      The co-operation operator requires the two "co-operands" to join for those activities which are specified in the co-operation set: in the process P < a, b> Q the processes P and Q must co-operate on activities a and b, but any other activities may be performed independently. The reversed compound agent theorem gives a set of sufficient conditions for a co-operation to have a product form stationary distribution.
      Finally, the process P/{a} hides the activity a from view (and prevents other processes from joining with it).


      Syntax


      Given a set of action names, the set of PEPA processes is defined by the following BNF grammar:




      P
      ::=
      (
      a
      ,
      λ
      )
      .
      P




      |




      P
      +
      Q




      |




      P






      L




      ▹


      ◃




      Q




      |




      P

      /

      L




      |




      A


      {\displaystyle P::=(a,\lambda ).P\,\,\,|\,\,\,P+Q\,\,\,|\,\,\,P{\stackrel {\triangleright \!\!\triangleleft }{\scriptstyle {L}}}Q\,\,\,|\,\,\,P/L\,\,\,|\,\,\,A}


      The parts of the syntax are, in the order given above

      action
      the process



      (
      a
      ,
      λ
      )
      .
      P


      {\displaystyle (a,\lambda ).P}

      can perform an action a at rate



      λ


      {\displaystyle \lambda }

      and continue as the process P.
      choice
      the process P+Q may behave as either the process P or the process Q.
      cooperation
      processes P and Q exist simultaneously and behave independently for actions whose names do not appear in L. For actions whose names appear in L, the action must be carried out jointly and a race condition determines the time this takes.
      hiding
      the process P behaves as usual for action names not in L, and performs a silent action



      τ


      {\displaystyle \tau }

      for action names that appear in L.
      process identifier
      write



      A


      =



      d
      e
      f




      P


      {\displaystyle A{\overset {\underset {\mathrm {def} }{}}{=}}P}

      to use the identifier A to refer to the process P.


      Tools


      PEPA Plug-in for Eclipse
      ipc: the imperial PEPA compiler
      GPAnalyser for fluid analysis of massively parallel systems


      References




      External links


      PEPA: Performance Evaluation Process Algebra

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