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Re: [ontolog-forum] Looking for some pragmatic guidance on modeling rela

To: ontolog-forum@xxxxxxxxxxxxxxxx
From: John F Sowa <sowa@xxxxxxxxxxx>
Date: Wed, 08 Apr 2015 15:24:17 -0400
Message-id: <55258061.4080107@xxxxxxxxxxx>
Steve,    (01)

Carl Adam Petri and his colleagues have been working on related
ideas for years.  He developed his widely used net theory in his
PhD dissertation in 1962, and he headed a group at a research
center in Bonn (GMD) for many years.    (02)

His general principle is that clock time is an abstraction that
uses one kind of process (called a clock) as a standard for
defining a metric for timing other processes.  But the choice
of clocks, the assumptions about their reliability, and the
assumptions about synchronizing them are problematical.    (03)

Petri noted that a metric-free theory of time is both more general
and more appropriate for a wide range of phenomena.  For metric time,
the most general ontology is to assume that    (04)

  1. Every clock is a process that measures time in linearly ordered
     units called ticks.  (Since the clock itself is the standard,
     it's meaningless to ask questions about its accuracy -- except
     in comparison to some other clock.  Note the joke about the man
     with two watches.)    (05)

  2. For any two processes timed by a given clock, their times
     can be compared to a resolution of one tick of that clock.
     Those ticks are called the _local time_ for those processes.    (06)

  3. For a global system with multiple clocks, the most general
     assumption is that clock time is partially ordered.    (07)

  4. When different local times are compared, it's important to
     to determine how and when (according to each clock's local
     time) they were synchronized.    (08)

For a brief summary of the issues and ontologies for time, see    (09)

    http://www.jfsowa.com/ontology/process.htm    (010)

For a more detailed discussion of issues related to time and causality,    (011)

    http://www.jfsowa.com/ontology/causal.htm    (012)

For a 50-year assessment of Petri's research,    (013)

http://www-dssz.informatik.tu-cottbus.de/publications/materials/silva-2013-50years-of-pn.pdf    (014)

For more references, google the keywords 'Petri', 'time',
'metric-free', and 'asynchronous' -- in various combinations.    (015)

John    (016)

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