Space-aware Coordination in RespecT

Space-aware Coordination in ReSpecT

Stefano Mariani Andrea Omicini{s.mariani, andrea.omicini}@unibo.it

DISIAlma Mater Studiorum—Universita di Bologna

WOA 2013Torino, Italy

2 December 2013

Mariani, Omicini (DISI, Alma Mater) Space-aware ReSpecT WOA 2013, 2/12/2013 1 / 42

Outline

1 Motivations & Goals

2 Space-aware Coordination MediaSpatial issuesSpace-aware tuple centres

3 Spatial ReSpecTBasic ReSpecTLanguage extensionVirtual Machine extension

4 Expressiveness via Examples

5 Conclusion, Ongoing & Future Work


Motivations & Goals

Outline







Motivations & Goals

The Need for Spatial Coordination

Spatial issues are fundamental in many sorts of complex software systems,including intelligent, multi-agent, adaptive, and self-organising ones[Beal et al., 2011].

Spatial coordination

Understanding the basic mechanisms of spatial coordination is afundamental issue for coordination models and languages in order togovern situated interaction in the spatio-temporal fabric.


Motivations & Goals

Goal of the Work

In this work we aim at

devising out

the fundamental abstractionsthe basic mechanismsthe linguistic constructs

required to generally enable and promote space-aware coordination

defining their embodiment in terms of

the tuple centre coordination mediumthe ReSpecT coordination language


Motivations & Goals

Outline of the Work

Along this line, we

discuss the issues of spatial coordination

devise out the general requirements for space-aware coordinationmedia

introduce the specific notion of space-aware tuple centre

show how the ReSpecT coordination language can be extended so asto support space-aware coordination


Space-aware Coordination Media

Outline







Space-aware Coordination Media Spatial issues

Outline








Situatedness & Awareness I

Spatial coordination requires

spatial situatedness

spatial awareness

of the coordination media

This translates in a number of technical requirements



Situatedness & Awareness II

Situatedness

A space-aware coordination abstraction should at any time be associatedto an absolute positioning, both physical and virtual

In fact,

software abstractions may move along a virtual space – typically, thenetwork – which is usually discrete

whereas physical devices move through a physical space, which ismostly continuous

However, software abstractions may also be hosted by mobile physicaldevices, thus share their motion.



Situatedness & Awareness III

Awareness

The position of the coordination medium should be available to thecoordination laws it contains in order to make them capable of reasoningabout space—so, to implement space-aware coordination laws.

Also, space has to be embedded into the working cycle of the coordinationmedium:

a spatial event should be generated within a coordination medium,conceptually corresponding to changes in space

then, such events should be captured by the coordination medium,and used to activate space-aware coordination laws


Space-aware Coordination Media Space-aware tuple centres

Outline








Tuple Centres

Technically, a tuple centre is a programmable tuple space, i.e., a tuplespace whose behaviour in response to (coordination) events can beprogrammed so as to specify and enact any coordination policy[Omicini and Denti, 2001b, Omicini, 2007].

General-purpose coordination media

Tuple centres can then be thought as general-purpose coordinationabstractions, which can be suitably forged to provide specific coordinationservices.



Space-aware Tuple Centres I

The location of a tuple centre is obtained through the notion ofcurrent place

i.e., the absolute position of the computational device where thecoordination medium is running, or the domain name of node hostingthe tuple centre

Motion is conceptually represented by two sorts of spatial events:

leaving from a starting placestopping at an arrival place

in any sort of space / place

Analogously to (coordination) operation and time events, it ispossible to specify reactions triggered by spatial events—the so-calledspatial reactions



Space-aware Tuple Centres II

Space-aware coordination policies

As a result, a spatial tuple centre

can be programmed to react to motion in either a physical or a virtualspace

so as to enforce space-aware coordination policies.


Spatial ReSpecT

Outline







Spatial ReSpecT Basic ReSpecT

Outline








ReSpecT I

ReSpecT tuple centres

ReSpecT tuple centres are based on first-order logic (FOL), which isadopted both for the communication language (logic tuples), and for thebehaviour specification language (ReSpecT) [Omicini and Denti, 2001a].

Basically, reactions in ReSpecT are defined as Prolog-like facts(reaction specification tuples) of the form

reaction(Activity , Guards , Reactions )

A reaction specification tuple specifies the list of the operations(Reactions ) to be executed when a given event occurs (calledtriggering event, caused by an Activity ) and some conditions on theevent hold (Guards evaluate to true).



ReSpecT II


Spatial ReSpecT Language extension

Outline








Spatial Observation Predicates

current place(@S ,?P ) succeeds if P unifies with the position of the nodewhich the tuple centre belongs to

event place(@S ,?P ) succeeds if P unifies with the position of the nodewhere the triggering event was originated

start place(@S ,?P ) succeeds if P unifies with the position of the nodewhere the event chain that led to the triggering event wasoriginated

The node position can be specified as either

S =ph its absolute physical position

S =ip its IP number

S =dns its domain name

S =map its geographical location—as typically defined by mapping serviceslike Google Maps

S =org its organisational position—that is, a location within anorganisation-defined virtual topology



Spatial Guard Predicates

at(@S ,@P ) succeeds when the tuple centre is currently executing at theposition P , specified according to S

near(@S ,@P ,@R ) succeeds when the tuple centre is currently executing atthe position included in the spatial region with centre P andradius R , specified according to S



Spatial Event Descriptors

from(?S ,?P ) matches a spatial event raised when the device hosting thetuple centre starts moving from position P , specifiedaccording to S .

to(?S ,?P ) matches a spatial event raised when the device hosting thetuple centre stops moving and reaches position P , specifiedaccording to S .

As a result, the following are admissible reaction specification tuplesdealing with spatial events:

reaction(from(?Space ,?Place ), Guards , Reactions ).

reaction(to(?Space ,?Place ), Guards , Reactions ).



Spatial Extension


Spatial ReSpecT Virtual Machine extension

Outline








Extended Event Model I

The first fundamental extension to the event model is clearly depictedin Table II: a new sort of spatial 〈Activity〉 is introduced

! In particular, the notion of 〈Situation〉 activity is extended with the twospatial activities from( 〈Space〉〈Place〉 ), to( 〈Space〉〈Place〉 )

Another issue is represented by spatial qualification of events, that is,making all ReSpecT events featuring spatial properties—in the sameway as for temporal properties in [Omicini et al., 2005]

! This is represented by the 〈Space:Place〉 property featured by 〈Cause〉– and 〈StartCause〉, of course –, as shown in Table III, where theextended ReSpecT event model is depicted.



Extended Event Model II



Extended Transition System I

The operational semantics of a ReSpecT tuple centre is expressed bya transition system over a state represented by the labelled tripleOpE ,SitE〈Tu,Re,Op〉OutE

n [Casadei and Omicini, 2009]—abstractingaway from the specification tuples Σ

OutE is automatically emptied by emitting the outgoing events

In the same way, OpE and SitE are automatically extended whenevera new incoming (either operation or situation) event enters a tuplecentre

! In particular, SitE is added new environment events by the associatedtransducers [Casadei and Omicini, 2009], new time events by the flowof time [Omicini et al., 2005], and also new spatial events wheneversome sort of motion takes place



Extended Transition System II

The behaviour of a ReSpecT tuple centre is modelled by a transitionsystem composed of four different transitions[Casadei and Omicini, 2009]: reaction (−→r ), situation (−→s),operation (−→o), log (−→l)

! Quite intuitively, spatial events are handled – in the same way as timeand environment events – by the situation transition, which triggersReSpecT spatial reactions


Expressiveness via Examples

Outline








Spheric Broadcasting I

Requirements:

a message has to be locally spread in the environment (e.g. networkof nodes), so as to be perceived only by nearby agents

you want to do so through a distributed, collaborative disseminationprocess

the distance defining “locally” can be thought of as a “straight-line”radius, identifying a three-dimensional sphere around the point wherethe message is firstly created



Spheric Broadcasting II

1 % 1) Get agent message

2 % 1.1) Delete garbage tuple

3 ...

4 % 1.2) Check range then forward

5 reaction( out(spheric(Msg,Radius )),

6 (operation,completion),

7 ( current_place(ph,RecPos), % Current position

8 start_place(ph,SendPos), % Starting position

9 in_range(RecPos,SendPos,Radius), % Prolog computation

10 start_source(Sender), start_time(Time),

11 out(msg(Msg,Sender,Time )),

12 rd(neighbours(Nbrs)), List of neighbours

13 out(forward(Nbrs,Msg,Radius )) )).

14 % 2) Forward to every neighbour

15 % 2.1) Delete garbage tuple

16 ...

17 % 2.2) Neighbour list not empty

18 reaction( out(forward ([Nbr|Nbrs],Msg,Radius )),

19 internal,

20 ( Nbr ? out(spheric(Msg,Radius )), % Forward

21 out(forward(Nbrs,Msg,Radius )) )). % Iterate



Spheric Broadcasting III

Given a virtual topology is reified in the tuple neighbours, we getthat any message embedded in a spheric tuple is autonomouslyspread solely to Radius-reachable neighbouring tuple centres

This is made possible by the start place/1 observation predicate,inspecting the place where the first spheric broadcast request wasissued—regardless of the number of tuple centre hops taken toforward the request

“Basic”, spatial-coordination mechanisms

? What if we replace current place(ph,RecPos) withcurrent place(dns,RecPos)?

? What if we replace start place with event place?



Monitored Motion I

Requirements:

you have an autonomous mobile device – e.g. a simplewheel-equipped robot – that has to reach a given destination

this implies that the mobile device should

start moving when asked to do somonitor its own position so as to understand when given destination isreached, if obstacles are on its way, etc.finally stop when due



Monitored Motion II

1 % 1) Compute motion vector then start moving

2 reaction( out(move(Dest,TStep )), (operation,completion),

3 ( current_place(ph,Here), current_time(Now),

4 Check is Now+TStep,

5 direction(Dest,Here,Vec), % Prolog computation

6 out_s( ... ), % Schedule monitoring (Reaction 2)

7 current_target(_@Node), % Get node id

8 motion_dev@Node <- env(dir,Vec), % Set direction

9 motion_dev@Node <- env(engine, ’on’) )). % Move on

10 % 2) Monitor destination arrival

11 reaction( time(Check), internal, % Time to check

12 ( current_place(ph,Here),

13 rd(move(Dest,TStep )),

14 ( check(Here,Dest), % Prolog computation

15 current_target(_@Node), % Get node id

16 motion_dev@Node <- env(engine, ’off’)

17 ; % Prolog ’if-then-else ’

18 current_time(Now), Check is Now+TStep,

19 out_s( ... ) ))). % Schedule monitoring (Reaction 2)

20 % 3) Arrival clean-up

21 reaction( to(Dest), internal, in(move(Dest,_ )) ). % Dest. reached


Conclusion, Ongoing & Future Work

Outline








Conclusion

Spatial situation is a requirement for many advanced applicationscenarios

Coordination models should be enhanced to handle situatedinteraction

Coordination media should be enhanced to address all the need ofspace-aware coordination

Tuple centres can be extended to become space-aware coordinationmedia

ReSpecT can be extended to enable space-aware coordination policies



Ongoing & Future Work

Implementation of space-aware ReSpecT tuple centres completed

ReSpecT tuple centres provided as coordination media of theTuCSoN coordination middleware [TuCSoN, 2013]

Android version in beta version

Experiments on Android devices and mobile computers

Spatial transducers for a range of diverse mobile sensors & devices


References

References I

Beal, J., Michel, O., and Schultz, U. P. (2011).

Spatial computing: Distributed systems that take advantage of our geometricworld.

ACM Trans. Auton. Adapt. Syst., 6(2):11:1–11:3.

Casadei, M. and Omicini, A. (2009).

Situated tuple centres in ReSpecT.

In Shin, S. Y., Ossowski, S., Menezes, R., and Viroli, M., editors, 24th AnnualACM Symposium on Applied Computing (SAC 2009), volume III, pages1361–1368, Honolulu, Hawai’i, USA. ACM.

Omicini, A. (2007).

Formal ReSpecT in the A&A perspective.

Electronic Notes in Theoretical Computer Science, 175(2):97–117.

5th International Workshop on Foundations of Coordination Languages andSoftware Architectures (FOCLASA’06), CONCUR’06, Bonn, Germany,31 August 2006. Post-proceedings.


References

References II

Omicini, A. and Denti, E. (2001a).

Formal ReSpecT.

Electronic Notes in Theoretical Computer Science, 48:179–196.

Declarative Programming – Selected Papers from AGP 2000, La Habana, Cuba,4–6 December 2000.

Omicini, A. and Denti, E. (2001b).

From tuple spaces to tuple centres.

Science of Computer Programming, 41(3):277–294.

Omicini, A., Ricci, A., and Viroli, M. (2005).

Time-aware coordination in ReSpecT.

In Jacquet, J.-M. and Picco, G. P., editors, Coordination Models and Languages,volume 3454 of LNCS, pages 268–282. Springer-Verlag.

7th International Conference (COORDINATION 2005), Namur, Belgium,20–23 April 2005. Proceedings.


References

References III

TuCSoN (2013).

Home page.

http://tucson.unibo.it/.


Space-aware Coordination in ReSpecT

Stefano Mariani Andrea Omicini{s.mariani, andrea.omicini}@unibo.it

DISIAlma Mater Studiorum—Universita di Bologna

WOA 2013Torino, Italy

2 December 2013


Space-aware Coordination in RespecT

Technology

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￼￼￼￼￼￼￼Space-aware Coordination in RespecT

Technology

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Space-aware Coordination in RespecT

Transcript of Space-aware Coordination in RespecT