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Time Paper Description Conceptual Focus Mode of
Sheet Operation
00:00 Gets the problem statement handed over. Says after a few
seconds that the lift control problem is a classical
task, but that it is not easy to solve.
00:01 Asks whether there are built in mechanisms to solve Platform Asking
queuing of requests from pushbuttons. The observer
answers that he initially can assume that.
00:02 Gives rise to fact that he is not satisfied with two Decentralization Explaining
properties of the problem statement. First, the aspects
of minimum waiting time is hostile towards a
decentralized solution and from his point of view this is
not good. Second, he cannot guarantee the aspect of
fairness in his future solution. It is agreed upon that
he can skip these two conditions at first hand.
00:03 Says that he will solve the problem with TOPSY. He also Complexity Explaining
says that he has never tried to solve such a problem with
TOPSY before. However, it should be possible to solve to
problem with TOPSY since the aspects of the problem are
binary and hence, he will be able to map the problem into
a solution. He will solve the problem with three floors
in order to reduce conplexity. He is quite certain that
two floors are not enough. He would normally have solved
it with two floors in order to reduce complexity even
more.
00:05 Says that he considers the elevators and the floors as Reflecting
independent entities.
00:06 #1 Starts to draw a sketch of a building with three floors Drawing
and three elevators in order to achieve a deeper
understanding of the problem involved.
00:08 Starts to specify a partial solution for one elevator. Communication Specifying
This specification involves what happens when a push Synchronization
button at the floors is pushed. He names them call
buttons. Afterwards he starts to specify the pushbuttons
in the elevators. This specification is in the form of a
given elevator wants to goto a given floor or not.
00:13 Asks if it is possible for an elevator to visit a floor Asking
with a previous registrated request.
00:14 Expresses that in his solution a given request for a Explaining
floor is that he wants to change to state of one his
conditions e.g. a no to a yes. Thereby, the system will
no longer have the same request.
00:15 Specifies the actions for an elevator to goto floor Communication Specifying
number 2. This involves the movement of the elevator, the
switching off the light in the pushbutton etc.
00:16 Assumes that the underlying features turn off the light Platform Reflecting
in the pushbuttons when a request has been fulfilled. He
does not think that this assumption is unfair. He says,
however, that it could be solved in his solution by
inserting another layer for handling this aspect, but he
does not find it important in this particular problem.
00:18 Gives expression to the fact that he is about to specify Communication Explaining
some actions which have to express that when a pushbutton Specifying
has a request, the elevator has to move to that given
floor. The actions have a form that says that if an
elevator has a request for going to a given floor (this
is expressed on one side of his equation) then the other
side will express that the elevator is now of that floor
and that the request is gone. This could be expressed as
follows: (a, not b) -> (not a, b)
00:19 Observer points out that it is also interesting which
elevator goes to which floors.
00:20 Realizes that he misses a censor (a censor is one of the Specifying
entities used in his paradigm to indicate states) to
indicate which floor the elevator is currently located
at. Starts to specify the actions to indicate on which
the elevator is located.
00:22 Starts to specify the actions at a general level. He is, Specifying
however, uncertain whether is able to succeed in this
specifying. After approximately 30 seconds he stops this
specification because he realizes that the activity is
not leading anywhere.
00:23 Assumes that more than one elevator can visit a floor Independence Reflecting
upon request. This in hand means that the elevators are
completely independent.
00:24 Starts to specify again at a more specific level. The Communication Specifying
generel actions outlined just above cannot be used so Synchronization
these were erased. Gives rise to the fact that his
current problem is getting the elevators to move between
the floors. Writes down a action which says that if the
elevator is on floor 1 then it is not at floor 2, and on
the other side of the equation he writes that if the
elevator is not at floor 1 then it could be at floor 2.
And so furth with the other floors. Furthermore he says
that he will not consider the fact that an elevator can
be located between two floors due to the complexity of
his solution.
00:28 Says that his action expresses that if he is on floor 1 Distribution Explaining
he can negotiate the action and then his elevator is
located at floor 2. Furthermore, he says that this
automatically gives a distributed solution. This was also
stated at the beginning of the experiment.
00:29 Specifies further on the movement of elevators. After one Specifying
minute he realizes that his latest action is ok, but also
that it is unimportant.
00:30 He gives expression to the fact that he is problem is Complexity Explaining
that the censors outlined at the top of paper sheet #1
can be combined in 2^9 - 1 (511) ways (this is only true
when he has 2 attributes in each side of the actions.
More attributes would give more ways of combination). He
now has to find the necesary actions. Normally, TOPSY
could observe these things. He stresses that this is very
difficult to do manually.
00:31 Starts to specify again but realizes once more that his Specifying
actions are of a trivial nature. Says that he has to
incorporate 3 actions.
00:33 #2 Tries to incorporate 3 attributes in the actions. This
involves both the actual movement of elevators and the
servicing of requests from floors.
00:36 Stops up and expresses that he has now found the two Communication Specifying
basic forms of actions. First, the elevator movement Synchronization
action describes that the elevator has an internal desire
to goto a floor. Second, the elevator call action
describes that a floor has a request for an elevator in
an up-ward or down-ward direction.
00:39 He realizes that he has too much information on each Complexity Reflecting
sensor. Instead of having the up or down he maybe should
have had up or not up etc. He also says that there is
always a potentiel danger in using these methods since
people are found to put too much information on the
sensors. But it is difficult nor to put this information
into the actions due to the problems with complexity.
00:40 Starts to specify again. Says that since the system is Distribution Specifying
distributed it is hard to have in your mind and therefore
he starts to draw some state diagrams with his sensors
illustrated at the middle of paper sheet #2.
00:44 After a couple of minutes of consideration he realizes Communication Explaining
that the above mentioned problem with the #of sensors is
serious. As a direct consequence he has to redefine the
sensors in his solution. He then suddenly realizes that
the up or down-going thing is not needed in his solution.
Whether the elevator is going up or down is not important
what is important is that an elevator is wanted or not.
The up and down thing is only useful for human beings. He
then wants to redefine the call buttons to wanted or not
wanted. Notes wrong mapping at the top of paper sheet #2.
00:47 Expresses that the wanted or not wanted is at a higher Priority Reflecting
level of abstraction than the going up or down. Basically
he views the system as a system where elevators are
moving sequentially between the floors and his concern is
whether the elevator should stop or not. However, he is
of the opinion that the people in the elevator should
have higher priority than the people on the floors.
00:49 Says that he will view the situation from another Explaining
perspective. If one views the call buttons and the
movement buttons as entering goals into the system then
the only thing he has to worry about is to move the
elevators in the right direction. The problem with the so
far outlined solution is that no goals enter the system
and then nothing will happen. Specifies this new insight
on paper sheet #2.
00:50 Discovers that he might have some problems in keeping the
elevator going in the same direction until it has reached
its goal. He gives expression to the fact that it is
possible to achieve sequencing in TOPSY by specifying
that one action establish pre-conditions for another
action.
00:52 Starts to simulate some specific examples in order to Priority Experimenting
achieve the sequencing of actions. He has major
difficulties in solving this particular problem. He says
that his problem is that which floor should the elevator
visit when it is located at the second floor and it is
asked for at the third floor and has a request for the
first floor. He wants to honour the gotos before the
wanteds (requests from elevators have higher priority
than requests from floors).
00:56 Realizes that he needs a new sensor which tells him is Reflecting
the elevator going up or down. He wants to avoid that the
elevator has to go to the top in order to reverse
direction. He says that he has to solve the task at the
meta-level. He further implies that this would be much
easier if he had this simulator to check the dynamics of
the system. Simulating these kinds of things manually is
hard on the brain.
01:00 #3 Starts to specify again. This includes actions where 3 Communication Specifying
attributes are included on each side of the equation. He
has by now incorporated the aspect of goals. The
specification is carried out on a specific level for the
going up and down for an elevator.
01:04 Translate to above specific actions into a more general Specifying
actions. Says after a couple of minutes that these
outlined actions are able to move the elevator between
successive floors. So the actions are not able to move
the elevator if the elevator is located at i and you have
a goal for i+2. He also specifies the wanted action (the
requests from floors). He is now of the opinion that he
has first version solution.
01:08 Expresses some worries about marginal conditions. He is Concurrency Reflecting
worried about aspects of concurrency because he is not
sure whether the system will cover all aspects of moving
people between floors. Starts to simulate what should
happen when a person wants to go from one floor to
another.
01:09 Says that the above outlined actions could be considerd
at machine code level.
01:09 Observer asks him on aspects of synchronization and
processes
01:10 Expresses that the actions all express aspects of Concurrency Reflecting
synchronization. The two sides of the equation Synchronization
co-excludes one another. The attributes on each side of Platform
the equation are subject to real concurrency. When the
system is running he does not have to woory about aspects
of concurrency; this is taken care of by the paradigm. He
also says that the price you have to pay for this is that
if the system has more goals it tries to satisfy them
all. States once more that he assumes that the underlying
hardware take care of turning off the light in the push
buttons.
01:13 States that he is not quite able to perceive whether his Concurrency Explaining
solution will display the right kind of behaviour. Says
that the aspect of mutual exclusion gives the peal of
sequencing and thereby he is able to determine or decide
in which direction the elevator should move. It is
difficult to perceive the dynamics of such a system.
01:16 Starts to look at the problem of having more than one Synchronization Specifying
elevator service a request. Expresses that the focus is Explaining
now on synchronization between elevators. He discovers a
problem when an elevator has requests for both going up
and down and you want to choose the nearest one. That is
messy.
01:20 States that he is trying to solve two problems. First, he Explaining
wants to avoid that more elevators satisfy the same goal.
Second, he wants the elevators to satisfy the nearest
goal. Realizes that this has to be done at the meta level.
01:23 Says that it is difficult to express these things because Specifying
even though that you have some goals, you do not know
when it is going to happen. So his specific problem is
that if one elevator is going to satisfy a goal then
others do not have to satisfy the same goal. This is
difficult. Tries to specify this fact at the buttom of
paper sheet #3. Argues that this is maybe only possible
at the meta level.
01:28 States that his head hurts.
01:29 Observer asks him on aspects of processes.
01:30 Regarding the elevator proces he states that he could Proces Interrupt Reflecting
argue for an solution with interrupts or polling. Polling
However, he stresses that certain safety aspects of an
elevator system would not be controlled by electronic
devices but with mechanical devices or that is at least
what he thinks.
01:31 #4 Starts to specify the proces for elevator processor. This Processor Specifying
includes the action for the motor and the doors.
01:33 States that it might seems that he is getting over the Synchronization Explaining
problem easily, but he stresses that he is sitting on a
pure synchronization machine which solves a lot of his
problems. All that he has to do is to write down the
conditions that have to hold during execution. An action
in his paradigm is considered to be going from one state
to another co-excluded state. But the problem with the
satisfying of goals by all elevators can not be easily
solved.
01:35 He stresses that the system in its current shape will try Commitment Explaining
to service all goals. Eventually all requests from Starvation
elevators and floors will then be serviced. He is Distribution
absolutely certain that starvation will not occur in his
solution. The aspect of commitment of request does not
work with the idea of distribution and it is not
supported by his paradigm. All actors are united in
achieving a goal. This causes problems in this particular
task.
01:36 Observer asks him on processes and communication
01:37 Stresses that this is a difficult question. On a Proces Reflecting
conceptual basis all his sensors and actions will be
considered as processes and the push buttons are the ones
that initiate goals in the system. Based on these lower
level processes one is able to identify processes at a
higher level (e.g. the meta level).
01:40 Compares the distributed systems with an ants' nest. Proces Reflecting
Finding the processes here are difficult. At the lowest Distribution
level the ants are the processes, but then you have no
informtion on how the nest was build. He stresses that
the processes found in a system are created upon the view
of the system. Again he points out that his approach to
this task may disappoint the observer.
01:42 The foundation for his system is a distributed and global Distribution Explaining
storage. So if one entity wants some information from Communication
another it has to communicate with that entity. But Centralization
accoding to him this is more a problem for the
implementation. Talks informally about centralization and
decentralization and the reliability involved in
different solutions.
01:45 He finds that there is no need for a processor at each Processor
floor. There is only a need for communication between Communication
floors. The core of the system is the movement of
elevators.
01:46 Stresses that he has no doubt that he could incorporate
the aspect of having just one elevator service a request
from a floor. But this will do some damage to his overall
design. However, he is aware of the fact that this should
be solved in a real solution.
01:47 Tries to solve it on the bottom of paper sheet #3 and Specifying
later on paper sheet #4. The action says that if one
elevator service a request then the other one does not.
He also tries to write the general action down.
01:52 Outlines the meta level solution of the commitment. He
has solved it by saying that all elevators have a copy of
the requests and thereby the elevators can say I will
take this one.