- From: Manfred Hauswirth <manfred.hauswirth@deri.org>
- Date: Tue, 22 Dec 2009 19:24:35 +0000
- To: Michael Compton <Michael.Compton@csiro.au>
- CC: Semantic Sensor Network Incubator Group WG <public-xg-ssn@w3.org>
Michael Compton wrote:
> my conceptions/preconceptions/misconceptions are as follows.
>
> - A sensor need not be a physical device. Kevin's definition of "An
> entity capable of observing a phenomenon and returning an observed
> value." seems ok to me.
+1
> - A Sensor need not be a single entity - it can be composed of any
> number of sub sensors, each perhaps of their own identity, each
> perhaps measuring different things that get combined into the whole.
+1
> - The following things 'are' sensors
> *a temperature sensor (i.e. a physical device) at location l
> *a program on a computer (far away from location l) that can read in
> the temperature at location l and a wind speed estimate for location l
> and calculate the windchill at l
+1
> More correctly, in both cases something has acted as a sensor for a
> particular phenomenon: a device in the first instance, and the program
> in the second - if I wrote down the temperature and wind speed
> measurements on a piece of paper and calculated the wind chill myself,
> then I have acted as the sensor.
>
> - The example of the wind chill sensor means that sensors can have
> multiple components, and I guess the components may themselves be
> interesting.
+1
What we use in GSN (Global Sensor Network middleware, gsn.sf.net) is the
following (this is clearly insufficient, so I am interested in using
what we define): Everything is a VirtualSensor which has a name,
properties and provides you an access abstraction, e.g.,
- a temperature sensor (device), say, t_1
- another temperature sensor (device), say, t_2)
- any combination of t_1 and t_2, e.g., avg(t_1, t_2) called, e.g., t_3
- a camera filming the location where t_3 was measured, c_1
- a "structured" virtual sensor returning (t_3, c_1)
- etc. (you get the idea :-)
> - A device (a physical piece of hardware) can also be broken down into
> components (presumably other devices, but perhaps also systems -
> software systems etc) but I don't see that as having anything to do
> with sensors or their decomposition into parts. For example, imagine
> a device that can measure wind speed and temperature, that has a small
> inbuilt chip that can calculate wind chill, round measurements,
> compute averages and a radio to communicate its readings. It's
> physical decomposition into its components is different from its
> decomposition into the roles it can play as a sensor. So the two
> sorts of decomposition may be related, but not equivalent.
The question also is: Is this relevant for all domains. For some it is
of premiere importance to know exactly how the sensor measured for
others it is an unnecessary detail. Also it depends on the measurement,
e.g., when you count cars, it does not really matter how you counted.
> - I'm also unsure about the word system and in particular it's
> relationship to process.
+1 !!! (confuses me a lot as well)
> - partly I see the problem as linguistic: i.e. we are using the word
> sensor in two different contexts. We think of things in terms of 'ah
> this thing is a sensor', but we also say 'a sensor is a process'. Is
> what we are really saying that to sense something is to follow a
> process that leads to a value as an estimate of a phenomenon. In
> which case a sensor isn't a thing at all it's really a 'to sense
> do...' or 'was sensed by doing...'. So if we take it that to sense
> something is to follow a process that estimates a value, then what is
> a system and why is a sensor one? To think of a system as a
I think "estimate" in itself is problematic linguistically as if it
comes to counting, for example, in many domains the counts are actually
exact.
> collection of components in some technical sense and then make sensor
> one of these is to take the 'ah this thing is a sensor' approach, but
> then we also agree on 'a sensor is a process' which now seems to make
> a sensor not a system. So is the biggest problem here simply that we
> (copying from SWE) have decided that systems have components and
> sensors are also made up of things, so it must be a system - where as
> there are actually two hierarchies here and we should represent them
> with different relationships?
>
> So how about....
>
> a System is a device/computer system/software system that is made up
> of components
>
> a Sensor is a process (a description of inputs/outputs, some steps and
> data flows) which may also be made up of sub sensors
Hmm, when I count items in a production line via a photo sensor, how is
that a process?
Best regards,
Manfred
> a System may play the role of a sensor for phenomenon X.
>
>
>
> Michael
>
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>
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>
>
> On 17/12/2009, at 19:11 , John Graybeal wrote:
>
> >
> > On Dec 16, 2009, at 12:00, Manfred Hauswirth wrote:
> >
> >> Hi John,
> >>
> >> thanks for your insightful comments. Some more comments from my side.
> >>
> >> John Graybeal wrote:
> >>>> Regarding "all systems are processes": Honestly, I would not >
> >>> understand this (I stated this at the F2F). For me, you have
> >>> systems > which include one ore more processes. If systems are
> >>> processes, why > have systems at all. My notion of systems would
> >>> informally consist > of processes, scenarios, deployments, etc.
> >>> The question "why have systems at all?" is the crux here. Can we
> >>> state clearly when a process is not a system? Or in other words,
> >>> how is a system more narrow than a process?
> >>> Incidentally, my notion of processes would informally consist of
> >>> the same list. I am also having trouble drawing the distinction.
> >>
> >> Interesting! I think this may be due to our different background (I
> >> assume your are not a computer scientist like myself - without
> >> evidence I may add).
> >
> > Computer Science and Statistics. 30 years software and systems
> > support. (No worries!)
> >
> >> In my area (computer science, information systems) systems would be
> >> defined as I do and a system would consist of software and hardware
> >> and the processes would clearly be "inside" the system as part of
> >> the software, so there is a clear distinction between "system" and
> >> "process" (other CS/IS people - please feel free to contradict me),
> >> whereas you seem to define this more from the viewpoint of an
> >> experiment which is being observed (?) where processes come into
> >> play as part of the observation process (please correct me - I am
> >> guessing here).
> >
> > I'm using one of the general meanings of the word 'process', which
> > applies not just to what's happening in side the computer or
> > component, but what happens as all the software and components
> > interact with each other. There are local processes and there are
> > external processes.
> >
> > It isn't driven by experiment orientation but by broader CS
> > orientation -- dealing with engineering systems of systems, and
> > including the human component in those systems, and modeling all the
> > above as processes (which may, or may not, then be computerized in the
> > new version of the system). Anyway, just a different viewpoint,
> > neither right nor wrong.
> >
> >> The problem here seems to lie in different conceptualizations in
> >> different communities - all of which done according to the specific
> >> needs of a community. Now, while this may complicate things, I think
> >> it is also a useful and actually mandatory exercise. While I may
> >> claim, that I need to understand the conceptualization because as an
> >> CS/IS person I will have to build (software/hardware) systems
> >> (sorry! no other term comes to mind) which need to manage
> >> information coming out of observations, you may claim exactly the
> >> same from you point of view (and rightfully so). The question now
> >> for me is: Who are our users and how to serve them best? Where's the
> >> sweet spot?
> >
> > Concur. I presumed from the start that the group was interested in
> > modeling hardware elements, but I have found it useful to consider
> > those hardware components as processes in a larger system of systems.
> > They take data in and transform it to other data that is spit out.
> > This is one useful definition of a process, as Luis notes.
> >
> > Oops, got off track there! But our agreed point is to agree on which
> > type of devices (= which group of users) we want to make the ontology
> > for. My assumption/preference was the group that used physical
> > devices to transform measurable phenomena into digital data (because
> > that's the easiest to model and the most immediately useful). But I
> > can go with whatever on this, as long as we all understand.
> >
> >>>> PhysicalSystem: I don't remember the exact reason for this. Did
> >>> we > mean deployment?
> >>> I assume this is to distinguish it from a software system.
> >>>> Sensor as subclass of Device: I think this is too narrow. I can
> >>>> think of sensors which are not devices at all, e.g., human
> >>> "sensors" > in the context of social sensing (which is an accepted
> >>> concept in > many domains including CS by now). Making sensors a
> >>> subclass of > device limits us to purely technical systems in
> >>> hardware, IMHO. Is > an RSS feed a device? I can clearly use it as
> >>> a sensor. I think that > Device should be a subclass of Sensor.
> >>> Even in existing middelware > systems like our GSN we followed
> >>> that path (without having an > ontology in mind at all).
> >>> This gets to purpose of the ontology. As I understood it, the
> >>> group was originally constructed to model hardware sensors. (May
> >>> have just been a wrong assumption on my part. More precisely, what
> >>> we clearly were not doing is modeling samplers, that is, devices
> >>> that return a physical sample.)
> >>
> >> Agreed. But "sensors" do not necessarily manifest themselves as
> >> hardware. If I want to detect user activity / inactivity on a
> >> computer in an experiment, one of my sensors may be a the keyboard,
> >> another one running processes (not waiting for user input), etc. It
> >> is very hard to draw the line here. My question: Do I have to have
> >> this distinction at all? Essentially I convert an X into a Y and Y
> >> should be usable in a computer. Whether X a is a physical phenomenon
> >> or not depends on the domain, IMHO.
> >
> > Sure, that works for me too. If you make a sensor too general,
> > though, it can have components. What do we call those components --
> > are not at least some of them sensors? So now, what is different from
> > the sensor that can have sensors, and a device, which has the same
> > recursion into smaller devices; and a system, which can have systems
> > (and a process, that can have processes)?
> >
> > I'm being a little silly of course. All I mean to do is call
> > attention to the need to define the terms according to what makes them
> > different from each other, not just whether they are higher or lower
> > in a hierarchy. I think we haven't done that well enough yet.
> >
> >>> So using one definition of sensor ("anything that senses") makes
> >>> Sensor very broad, and other things would subclass to it. (Since
> >>> some devices (a hammer) don't sense things, we'll have to define
> >>> Device narrowly to make it a subclass Sensor.) Using another
> >>> definition of sensor ("a component that detects (measures) a
> >>> physical phenomenon, converting it into a digital representation
> >>> that can be output to other components"), a Sensor is clearly a
> >>> specific type of Device, and is also a component of any sensing
> >>> device.
> >>
> >> If you see software as a Device, I would agree to it, but then again
> >> Device has the connotation of hardware.
> >
> > Ah, I said a Sensor was hardware in my original world, so I didn't
> > have any problem here -- since my Sensor was hardware and my Device
> > had a sensor, I was already on board with Device being hardware.
> >
> >>> Do we have a set of definitions by any chance, so we can all use
> >>> these (or some) terms the same way?
> >>
> >> I don't think we have.
> >>
> >>>> Why is a Device a subclass of a Process? A Process can use
> >>> Sensors > which are manifested as Devices to do/measure something,
> >>> IMHO. Again > this is a quite narrow notion of the concepts.
> >>> I'm not following your argument here. Yes, a Process can use
> >>> Sensors as you say. So can a Device. There is no inconsistency
> >>> that I can see. This suggests a Device is in fact a type of
> >>> Process.
> >>
> >> Sorry, but I don't understand how a Device can be a Process.
> >
> > The "Process: something that receives an input and produces an output"
> > is not a sufficient explanation or model of that?
> >
> > John
> >
> >>
> >> Best regards,
> >>
> >> Manfred
> >>
> >
> >
>
>
--
Prof. Manfred Hauswirth
Digital Enterprise Research Institute (DERI)
National University of Ireland, Galway (NUIG)
http://www.manfredhauswirth.org/
Received on Tuesday, 22 December 2009 19:25:15 UTC