Multi-Agent Systems (MAS) and Event-Based Systems (EBS) are two fundamental paradigms for the engineering of complex software systems. In this talk, we summarise the most important features of the MAS and EBS, and discuss how they could be integrated within a unified conceptual framework. The resulting framework could work as the foundation of a principled discipline for the engineering of complex software systems, by promoting a coherent integration of agent-based and event-based abstractions, languages, technologies, and methods.

1. Event-Based vs. Multi-Agent Systems:
Towards a Uni

2. ed Conceptual Framework
Preliminary Notes
Andrea Omicini
Dipartimento di Informatica { Scienza e Ingegneria (DISI)
Alma Mater Studiorum|Universita di Bologna, Italy
Short Course @ WOA 2014 Mini-school
Workshop nazionale Dagli Oggetti agli Agenti
Universita di Catania, Italy
25 Settembre 2014
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 1 / 62

3. Outline
1 Programming Paradigms for Complex System Engineering
2 Engineering MAS as Event-Based Systems
3 Conclusion
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 2 / 62

4. Programming Paradigms for Complex System Engineering
Outline
1 Programming Paradigms for Complex System Engineering
2 Engineering MAS as Event-Based Systems
3 Conclusion
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 3 / 62

5. Programming Paradigms for Complex System Engineering Complexity in Software Systems
Outline
1 Programming Paradigms for Complex System Engineering
Complexity in Software Systems
Mixing Paradigms
Agent-Based vs. Event-Based Systems
2 Engineering MAS as Event-Based Systems
Essentials of Event-Based Systems
MAS as Event-Based Systems
MAS Coordination: An Event-driven View
A Case Study in MAS Coordination as EBS: TuCSoN
3 Conclusion
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 4 / 62

6. Programming Paradigms for Complex System Engineering Complexity in Software Systems
Accidental Complexity I
Accidental complexity (originally called accidental diculty
[Brooks, 1987]) is not related to the application problem, but rather
to our lack of appropriate abstractions and tools to directly handle
the essence of the problem (essential complexity)
Whereas [Brooks, 1987] claims that software engineers nowadays
mostly deal with essential complexity due to the high-level languages
and frameworks available, new application scenarios have generated
new forms of accidental complexity
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 5 / 62

7. Programming Paradigms for Complex System Engineering Complexity in Software Systems
Accidental Complexity II
Sources of accidental complexity [Milicevic et al., 2013]
distributed interaction | the distributed architecture of multiple servers
running on the cloud (server farms) interacting with clients
running on dierent platforms (e.g., smartphones, web
browsers, desktop widgets, etc.)
abstraction gap | between the problem-domain level (high-level, often
event-driven) and the implementation-level (low-level
messages, queues, schedulers, asynchronous callbacks)
shared data consistency | many sources of data are replicated and
distributed, and accessed concurrently|as well as distributed
resources, more generally
concurrency issues | such as data races, atomicity violations, deadlocks,
etc.
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 6 / 62

8. Programming Paradigms for Complex System Engineering Complexity in Software Systems
Distributed Event-Based Systems
Nowadays, applications are increasingly distributed and event-driven
[Milicevic et al., 2013]
According to [Fiege et al., 2002], the event-based architectural style
has become prevalent for large-scale distributed applications due to the
inherent loose coupling of the participants
facilitates the clear separation of communication from computation
carries the potential for easy integration of autonomous, heterogeneous
components into complex systems that are easy to evolve and scale
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 7 / 62

9. Programming Paradigms for Complex System Engineering Complexity in Software Systems
Object Event-Based Systems
Object-oriented languages, frameworks, and platforms are still
dominating the SE landscape
The same application

10. eld (human-computer graphical interfaces)
that made object-oriented languages mainstream is where
event-driven programming fully developed

11. rst
So, object-oriented and event-driven programming represent a good
match
However, distributed computing with object-oriented programming
suers from an abstraction gap: distributed objects requires either
the design of distributed control or total transparency
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 8 / 62

12. Programming Paradigms for Complex System Engineering Complexity in Software Systems
Agent-Based Event-Based Systems
Agent-based engineering for complex software systems
Encapsulation of control makes agents overcome the abstraction gap
of OOP [Odell, 2002]
Agent abstractions inherently deal with distribution [Jennings, 2000]
Agent autonomy {{ along with the associated agent features such as
sociality, pro-activeness, situatedness, and the like { make
agent-oriented software engineering (AOSE) a viable approach for
engineering complex software systems [Jennings, 2001]
Extra agent features such as mobility and intelligence make AOSE
the most eective approach available for the engineering of intelligent
and pervasive distributed systems [Zambonelli and Omicini, 2004]
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 9 / 62

13. Programming Paradigms for Complex System Engineering Mixing Paradigms
Outline
1 Programming Paradigms for Complex System Engineering
Complexity in Software Systems
Mixing Paradigms
Agent-Based vs. Event-Based Systems
2 Engineering MAS as Event-Based Systems
Essentials of Event-Based Systems
MAS as Event-Based Systems
MAS Coordination: An Event-driven View
A Case Study in MAS Coordination as EBS: TuCSoN
3 Conclusion
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 10 / 62

14. Programming Paradigms for Complex System Engineering Mixing Paradigms
Agent-Oriented vs. Object-Oriented Computing
Agents are not objects [Graesser, 1996], but they can mixed up with
objects|e.g., by wrapping objects as agents [Odell, 2002]
Agent middleware can build upon object middleware to enable the
paradigm shift|e.g., Jade [Bellifemine et al., 2007], TuCSoN
[Omicini and Zambonelli, 1999]
The artefact notion works as a conceptually-coeherent bridge between
agents and objects [Omicini et al., 2008]
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 11 / 62

15. Programming Paradigms for Complex System Engineering Mixing Paradigms
The AA Metamodel
In the agents artefacts (AA) meta-model [Omicini et al., 2008], in
short
agents are autonomous computational entities, encapsulating control
along with a criterion to govern it
artefacts are computational entities aimed to be used by agents
By extending the reach of the object notion to artefacts, agents can use
objects in a MAS, thus making agent / object interaction sound from both
a conceptual and a technical viewpoint
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 12 / 62

16. Programming Paradigms for Complex System Engineering Agent-Based vs. Event-Based Systems
Outline
1 Programming Paradigms for Complex System Engineering
Complexity in Software Systems
Mixing Paradigms
Agent-Based vs. Event-Based Systems
2 Engineering MAS as Event-Based Systems
Essentials of Event-Based Systems
MAS as Event-Based Systems
MAS Coordination: An Event-driven View
A Case Study in MAS Coordination as EBS: TuCSoN
3 Conclusion
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 13 / 62

17. Programming Paradigms for Complex System Engineering Agent-Based vs. Event-Based Systems
Agents-Events Integration?
Either indirectly, since
objects-oriented programming straightforwardly couples with
event-driven systems
agents can mixup with objects|by either wrapping objects, or using
them as artefacts
or directly, since
agents are supposed to be reactive to change
[Wooldridge and Jennings, 1995]
agents and MAS are supposed to be situated [Weyns et al., 2007]
agents and events could cope well, in principle, thus allowing for a
seamless integration
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 14 / 62

18. Programming Paradigms for Complex System Engineering Agent-Based vs. Event-Based Systems
Examples I
Integrating MAS with event-based system (EBS)
Most of the agent architectures adopts some eective notion of event, in order to
provide for agent reactiveness|e.g., BDI architectures [Rao and George, 1991]
Most of the agent middlewares provide some event-based abstractions and
mechanisms so as to deal with asynchronous message passing and environment
change{{{such as Jade [Bellifemine et al., 2007] and TuCSoN
[Omicini and Zambonelli, 1999]
[Aiello et al., 2011] presents an agent-based architecture for coordinating event
streams from WBSN
ELDA is an event-driven agent meta-model [Fortino et al., 2010]
eXAT [Di Stefano and Santoro, 2005] is an agent programming platform exploiting
the Erlang concurrent language [Armstrong et al., 1996]
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19. Programming Paradigms for Complex System Engineering Agent-Based vs. Event-Based Systems
Examples II
Integrating actors with event-based system
Event-based actors allow for event-based programming without
inversion of control [Haller and Odersky, 2006]
Scala actors unify event-based with thread-based programming
[Haller and Odersky, 2009]
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 16 / 62

20. Programming Paradigms for Complex System Engineering Agent-Based vs. Event-Based Systems
Issues
However, the above examples just emphasise the need for the integration
of the two paradigms, without providing a coherent and uniform
conceptual framework for both
Should we be content with the mere integration of technologies?
What about conceptual integrity?
Could we aim at a whole, coherent
uniform conceptual framework for MAS and EBS
?
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 17 / 62

21. Engineering MAS as Event-Based Systems
Outline
1 Programming Paradigms for Complex System Engineering
2 Engineering MAS as Event-Based Systems
3 Conclusion
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 18 / 62

22. Engineering MAS as Event-Based Systems Essentials of Event-Based Systems
Outline
1 Programming Paradigms for Complex System Engineering
Complexity in Software Systems
Mixing Paradigms
Agent-Based vs. Event-Based Systems
2 Engineering MAS as Event-Based Systems
Essentials of Event-Based Systems
MAS as Event-Based Systems
MAS Coordination: An Event-driven View
A Case Study in MAS Coordination as EBS: TuCSoN
3 Conclusion
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 19 / 62

23. Engineering MAS as Event-Based Systems Essentials of Event-Based Systems
Caveat Lector
The notions of event-based systems, event-based programming,
event-driven programming are more or less ubiquitous in Computer
Science literature
Neither terminology is uniform, nor the many diverse ontologies are
overall fully consistent
What is considered essential, or, fundamental by researchers and
teachers often does not coincide
However, some shared ideas and terms can be pointed out to provide
for a common ontology and terminology for event-based systems
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 20 / 62

24. Engineering MAS as Event-Based Systems Essentials of Event-Based Systems
Terminology for Event-Based Systems
De

25. nition
According to [Fiege et al., 2002], an event-based systems (EBS) is
a system in which the integrated components communicate by
generating and receiving event noti

26. cations
An event is an occurrence of a happening relevant for the system, e.g.
a state change in some component
A noti

27. cation is the rei

28. cation of an event within the system, and
provides for its description
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29. Engineering MAS as Event-Based Systems Essentials of Event-Based Systems
Event Models
Dierent event models can be supported by dierent sorts of noti

30. cations,
e.g. [Fiege et al., 2002]
name/value pairs [Carzaniga et al., 2001]
objects [Eugster et al., 2001]
semi-structured data [Fiege et al., 2003]
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 22 / 62

31. Engineering MAS as Event-Based Systems Essentials of Event-Based Systems
Middleware and Events
At the middleware level, noti

32. cations may take the form of messages,
or, of any speci

33. c form adopted / promoted by the middleware
services
Being transmitted in the same way and format of messages does not
make them messages in all aspects
Event noti

34. cation service
An event noti

35. cation service, or event system for short, applies dierent
techniques and data and

36. lter models to distribute noti

37. cations between
the components of an event-based system [Fiege et al., 2002]
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 23 / 62

38. Engineering MAS as Event-Based Systems Essentials of Event-Based Systems
Event-Based Architectures
Components in event-based systems act as either producers or
consumers of noti

39. cations
Producers publish noti

40. cations, and provide an output interface for
subscription
Consumers subscribe to noti

41. cations as speci

42. ed by producers
Being not real messages, noti

43. cations have not a designed receiver:
they are distributed by the event noti

44. cation service to consumers
that subscribed to that sort of noti

45. cation
Expressiveness of subscriptions depends on the data model and

46. lter
language used
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 24 / 62

47. Engineering MAS as Event-Based Systems Essentials of Event-Based Systems
Issues in Event-Based Systems
Mechanisms [Fiege et al., 2002]
noti

48. cation

49. ltering
noti

50. cation distribution
Software engineering
inversion of control [Haller and Odersky, 2006]
coordination of events [Milicevic et al., 2013]
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 25 / 62

51. Engineering MAS as Event-Based Systems MAS as Event-Based Systems
Outline
1 Programming Paradigms for Complex System Engineering
Complexity in Software Systems
Mixing Paradigms
Agent-Based vs. Event-Based Systems
2 Engineering MAS as Event-Based Systems
Essentials of Event-Based Systems
MAS as Event-Based Systems
MAS Coordination: An Event-driven View
A Case Study in MAS Coordination as EBS: TuCSoN
3 Conclusion
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 26 / 62

52. Engineering MAS as Event-Based Systems MAS as Event-Based Systems
Rethinking MAS Meta-Model
The MAS triad: agents, society, environment
agents are the autonomous computational entities encapsulating the
designed (sub)goals for the MAS, which are expressed through their
own course of actions
environment captures the unpredictability of the MAS context, by
modelling the external resources and features that are relevant for the
MAS, along with their change over time
societies represent the ensembles where the collective behaviours of
the MAS are regulated towards the achievement of the overall system
goals
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 27 / 62

53. Engineering MAS as Event-Based Systems MAS as Event-Based Systems
Agents Environment as Event Sources
From a SE viewpoint, agents and environment are the abstractions
representing the only sources of events in a MAS
agents represent the designed source of events, autonomously driving
control towards their own goals, and producing internal events
through their actions
environment models the external events which are relevant for the
MAS, whose dynamics is in principle unpredictable, through
abstractions of some sorts { environment resources, sensors
actuators, probes { that also capture the diversity of environment
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 28 / 62

54. Engineering MAS as Event-Based Systems MAS as Event-Based Systems
An Event-based View of MAS
MAS can be seen as event-based systems, where
agents encapsulate internal events|more generally, they encapsulate
the activities in MAS that generate events according to some
application criterion
environment models external events through dedicated
abstraction|thus capturing the dynamics of the unpredictable events
external but relevant to MAS
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 29 / 62

55. Engineering MAS as Event-Based Systems MAS as Event-Based Systems
Bene

56. ts of MAS as EBS
since agents encapsulate control along with the criteria for control {
expressed in terms of high level abstractions such as beliefs, goals,
intentions, plans { articulated events histories are modelled along
with their motivations in MAS as EBS
since environment is modelled as a

57. rst-class event-based abstraction,
all causes of change and disruption in a MAS are modelled in a
uniform way as event pro-sumers
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 30 / 62

58. Engineering MAS as Event-Based Systems MAS as Event-Based Systems
Architectural Requirements for MAS as EBS
agent autonomy | boundary artefacts for agents
environment diversity | boundary artefacts for probes
As a resulting bene

59. t, boundary artefacts can deal with diversity of all
sorts of events, and translate them all according to a common general
event model
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 31 / 62

60. Engineering MAS as Event-Based Systems MAS Coordination: An Event-driven View
Outline
1 Programming Paradigms for Complex System Engineering
Complexity in Software Systems
Mixing Paradigms
Agent-Based vs. Event-Based Systems
2 Engineering MAS as Event-Based Systems
Essentials of Event-Based Systems
MAS as Event-Based Systems
MAS Coordination: An Event-driven View
A Case Study in MAS Coordination as EBS: TuCSoN
3 Conclusion
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 32 / 62

61. Engineering MAS as Event-Based Systems MAS Coordination: An Event-driven View
An Event-based View of MAS as Interacting Systems
MAS can be seen as event-based systems, where
agents encapsulate internal events
environment models external events through dedicated abstraction
! social abstractions of some sort take care of dealing with interaction
agent-agent interaction
agent-environment interaction
environment-environment interaction
and, any other more complex pattern of interaction
taking care of their mutual dependencies, by coordinating the many
resulting
ows of events [Malone and Crowston, 1994]
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 33 / 62

62. Engineering MAS as Event-Based Systems MAS Coordination: An Event-driven View
Harnessing the Complexity of Interaction
An essential source of complexity for computational systems is
interaction [Wegner, 1997]
Coordination models work by constraining the space of interaction
[Wegner, 1996]
So, in principle, coordination abstractions and technologies can help
harnessing the intricacies of interaction in the engineering of complex
software systems
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 34 / 62

63. Engineering MAS as Event-Based Systems MAS Coordination: An Event-driven View
The Nature of Coordination Models
According to [Ciancarini, 1996],
A coordination model provides a framework in which the
interaction of active and independent entities called agents can
be expressed
Coordination: a meta-model [Ciancarini, 1996]
The components of a coordinated system are
Coordination entities | the entities whose mutual interaction is ruled by
the model, also called the coordinables, or agents
Coordination media | the abstractions enabling and ruling interaction
among coordinables
Coordination laws | the rules governing the observable behaviour of
coordinables, the behaviour coordination media, as well as
their interactions of any sort
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64. Engineering MAS as Event-Based Systems MAS Coordination: An Event-driven View
Coordination as Constrained Interaction [Wegner, 1996]
Coordination models harness the complexity of interaction by disciplining
the space of admissible interactions [Omicini, 1999]
the coordination primitives provided by a coordination model
constrain the possibile agent actions
the coordination media provided by a coordination model constrain
the possible targets of agent actions
Coordination models as constrainers of interaction
A coordination model constrains its coordinables (agents) to interact via a
limited yet (possibly) expressive set of primitives acting on a class of
pre-de

65. ned media of coordination, whose computational behaviour de

66. nes
the laws of coordination
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 36 / 62

67. Engineering MAS as Event-Based Systems MAS Coordination: An Event-driven View
Event-Based Coordination
The potential of event-based coordination has been recognized
both in academia and industry and there exists a considerable
amount of work on event noti

68. cation systems [Fiege et al., 2002]
a number of event-based middleware providing such services, such as
JEDI [Cugola et al., 2001]
a number of event-based coordination models
[Papadopoulos and Arbab, 1998, Viroli et al., 2002], technologies
[Freeman et al., 1999], and formalisms
[Omicini, 1999, Viroli and Ricci, 2002]
witness the role of event-based middleware in the engineering of complex
distributed systems, as well as the event-based nature of the most relevant
coordination models, such as tuple-based ones [Omicini, 1999]
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 37 / 62

69. Engineering MAS as Event-Based Systems MAS Coordination: An Event-driven View
Coordination in MAS
Given that
artefacts are the reactive abstractions in MAS [Omicini et al., 2008]
coordination artefacts are the social abstractions in charge of
managing dependencies [Malone and Crowston, 1994]
the social abstractions in charge of coordinating multiple event
ow
according to their mutual dependencies in MAS are the coordination
artefacts [Omicini et al., 2004]
Coordination models in MAS
The role of coordination models in MAS [Ciancarini et al., 2000] is to
provide event-driven coordination media as the coordination artefacts
governing event coordination in MAS
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70. Engineering MAS as Event-Based Systems MAS Coordination: An Event-driven View
Bene

71. ts of MAS Coordination as EBS
Since all events are uniformly represented through the same general
event model { the same language for noti

72. cations {, coordination
artefacts can be used to deal with both social and situated
dependencies, governing agent-agent, agent-environment,
environment-environment interaction through the same set of
coordination abstractions, languages, and mechanisms
[Mariani and Omicini, 2014]
Coordination artefacts provide a speci

73. c, event-based computational
model for dealing with event observation, manipulation, and
coordination
Coordination artefacts encapsulate the logic for the coordination of
multiple related
ows of events, thus counterfeiting inversion of
control
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 39 / 62

74. Engineering MAS as Event-Based Systems A Case Study in MAS Coordination as EBS: TuCSoN
Outline
1 Programming Paradigms for Complex System Engineering
Complexity in Software Systems
Mixing Paradigms
Agent-Based vs. Event-Based Systems
2 Engineering MAS as Event-Based Systems
Essentials of Event-Based Systems
MAS as Event-Based Systems
MAS Coordination: An Event-driven View
A Case Study in MAS Coordination as EBS: TuCSoN
3 Conclusion
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 40 / 62

75. Engineering MAS as Event-Based Systems A Case Study in MAS Coordination as EBS: TuCSoN
TuCSoN Architecture I
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76. Engineering MAS as Event-Based Systems A Case Study in MAS Coordination as EBS: TuCSoN
TuCSoN Architecture II
agents | Any computational entity willing to exploit TuCSoN
coordination services. Agents should request and obtain an
ACC from the TuCSoN node. Any action from any agent
towards the MAS { either social or situated { is then
mediated by its associated ACC.
ACC | Agent coordination contexts [Omicini, 2002] are TuCSoN
boundary artefacts devoted to agents. ACC both enable and
constraint agents interactions: in particular, ACCs map every
agent operation into events asynchronously dispatched to
tuple centres. ACCs thus decouple agents from MAS in
control, reference, space, and time.
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 42 / 62

77. Engineering MAS as Event-Based Systems A Case Study in MAS Coordination as EBS: TuCSoN
TuCSoN Architecture III
probes | Environmental resources in TuCSoN are called probes.
They are dealt with as sources of perceptions (aka sensors)
or makers of actions (aka actuators) in a uniform way.
Probes do not directly interact with the MAS, but through
mediation of their associated transducer.
transducers | TuCSoN transducers [Casadei and Omicini, 2009] are the
boundary artefacts devoted to probes. Each probe is
assigned to a transducer, which is specialised to handle
events from that probe, and to act on probes through
situation operations. Transducers thus decouple in control,
reference, space and time probes from tuple centres.
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78. Engineering MAS as Event-Based Systems A Case Study in MAS Coordination as EBS: TuCSoN
TuCSoN Architecture IV
events | TuCSoN adopts and generalises the ReSpecT event
model. Events are the run-time data structure representing
both activities and change in a uniform way. ACC and
transducers translate external events (activities and change)
into internal events (operations and situations) that tuple
centres can handle to implement the policies required for
MAS coordination
tuple centres | TuCSoN architectural component implementing
coordination artefacts, thus in charge of managing
dependencies. As such, they are meant to govern both social
and situated interactions [Omicini and Mariani, 2013]. By
adopting ReSpecT tuple centres, TuCSoN relies on (i) the
ReSpecT language to program coordination laws, and (ii)
the ReSpecT situated event model to implement events
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79. Engineering MAS as Event-Based Systems A Case Study in MAS Coordination as EBS: TuCSoN
TuCSoN Event Model I
hEventi ::= hStartCausei , hCausei , hEvaluationi
hStartCausei ; hCausei ::= hActivityi j hChangei , hSourcei , hTargeti , hTimei , hSpace:Placei
hSourcei ; hTargeti ::= hAgentIdi j hCoordArtefactIdi j hEnvResIdi j ?
hEvaluationi ::= ? j fhResultig
Table: ReSpecT situated event model
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80. Engineering MAS as Event-Based Systems A Case Study in MAS Coordination as EBS: TuCSoN
TuCSoN Event Model II
hActivityi ::= hOperationi j hSituationi
hOperationi ::= out( hTuplei ) j (in j rd j no j inp j rdp j nop) ( hTemplatei [, hTermi] )
hSituationi ::= getEnv( hKeyi , hValuei ) j setEnv( hKeyi , hValuei )
hChangei ::= env( hKeyi , hValuei ) j time( hTimei ) j
from( hSpacei , hPlacei ) j to( hSpacei , hPlacei )
Table: ReSpecT triggering events
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81. Engineering MAS as Event-Based Systems A Case Study in MAS Coordination as EBS: TuCSoN
Event-Based TuCSoN: Summing Up
In a TuCSoN-coordinated MAS
ACCs and transducers represent agents and environment,
respectively, in the MAS, by translating activities and changes in a
common event model
Tuple centres deals with both social and situated dependencies by
making it possible to program the coordination of all sort of event in
a uniform way
In essence, TuCSoN seemingly provides both a model and a technology to
engineer coordinated MAS as EBS
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 47 / 62

82. Conclusion
Outline
1 Programming Paradigms for Complex System Engineering
2 Engineering MAS as Event-Based Systems
3 Conclusion
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 48 / 62

83. Conclusion
Summing Up
A unifying conceptual framework for MAS and EBS
is possible
could work as the foundation of a principled discipline for the
engineering of complex software systems
by promoting a coherent integration of agent-based and event-based
abstractions, languages, technologies, and methods
Interaction
is a key issue as far as system complexity is concerned
requires the availability of suitably-expressive event-driven
coordination models and middleware for a disciplined engineering of
complex MAS as EBS
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 49 / 62

84. References
References I
Aiello, F., Bellifemine, F. L., Fortino, G., Galzarano, S., and Gravina, R. (2011).
An agent-based signal processing in-node environment for real-time human activity
monitoring based on wireless body sensor networks.
Engineering Applications of Arti

85. cial Intelligence, 24(7):1147{1161.
Armstrong, J., Virding, R., Wikstrom, C., and Williams, M. (1996).
Concurrent Programming in Erlang.
Prentice Hall International, 2nd edition.
Bellifemine, F. L., Caire, G., and Greenwood, D. (2007).
Developing Multi-Agent Systems with JADE.
Wiley.
Brooks, F. P. (1987).
No Silver Bullet Essence and Accidents of Software Engineering.
Computer, 20(4):10{19.
Carzaniga, A., Rosenblum, D. S., and Wolf, A. L. (2001).
Design and evaluation of a wide-area event noti

86. cation service.
ACM Transactions on Computer Systems, 19(3):332{383.
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 50 / 62

87. References
References II
Casadei, M. and Omicini, A. (2009).
Situated tuple centres in ReSpecT.
In Shin, S. Y., Ossowski, S., Menezes, R., and Viroli, M., editors, 24th Annual ACM
Symposium on Applied Computing (SAC 2009), volume III, pages 1361{1368, Honolulu,
Hawai'i, USA. ACM.
Ciancarini, P. (1996).
Coordination models and languages as software integrators.
ACM Computing Surveys, 28(2):300{302.
Ciancarini, P., Omicini, A., and Zambonelli, F. (2000).
Multiagent system engineering: The coordination viewpoint.
In Jennings, N. R. and Lesperance, Y., editors, Intelligent Agents VI. Agent Theories,
Architectures, and Languages, volume 1757 of LNAI, pages 250{259. Springer.
6th International Workshop (ATAL'99), Orlando, FL, USA, 15{17 July 1999. Proceedings.
Cugola, G., Di Nitto, E., and Fuggetta, A. (2001).
The JEDI event-based infrastructure and its application to the development of the OPSS
WFMS.
IEEE Transactions on Software Engineering, 27(9):827{850.
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 51 / 62

88. References
References III
Di Stefano, A. and Santoro, C. (2005).
Supporting agent development in Erlang through the eXAT platform.
In Unland, R., Calisti, M., and Klusch, M., editors, Software Agent-Based Applications,
Platforms and Development Kits, Whitestein Series in Software Agent Technologies, pages
47{71. Birkhauser Basel.
Eugster, P. T., Guerraoui, R., and Damm, C. H. (2001).
On objects and events.
ACM SIGPLAN Notices, 36(11):254{269.
16th ACM SIGPLAN Conference on Object-oriented Programming, Systems, Languages,
and Applications (OOPSLA'01), Tampa Bay, FL, USA. Proceedings.
Fiege, L., Gartner, F. C., Kasten, O., and Zeidler, A. (2003).
Supporting mobility in content-based publish/subscribe middleware.
In Middleware 2003, Lecture Notes in Computer Science, pages 103{122. Springer Berlin
Heidelberg.
ACM/IFIP/USENIX International Middleware Conference Rio de Janeiro, Brazil, June
16{20, 2003 Proceedings.
Fiege, L., Muhl, G., and Gartner, F. C. (2002).
Modular event-based systems.
The Knowledge Engineering Review, 17(4):359{388.
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 52 / 62

89. References
References IV
Fortino, G., Garro, A., Mascillaro, S., and Russo, W. (2010).
Using event-driven lightweight DSC-based agents for MAS modelling.
International Journal of Agent-Oriented Software Engineering, 4(2):113{140.
Freeman, E., Hupfer, S., and Arnold, K. (1999).
JavaSpaces Principles, Patterns, and Practice: Principles, Patterns and Practices.
The Jini Technology Series. Addison-Wesley Longman.
Graesser, S. F. A. (1996).
Is it an agent, or just a program?: A taxonomy for autonomous agents.
In Muller, J. P., Wooldridge, M. J., and Jennings, N. R., editors, Intelligent Agents III
Agent Theories, Architectures, and Languages: ECAI'96 Workshop (ATAL) Budapest,
Hungary, August 12{13, 1996 Proceedings, volume 1193 of Lecture Notes In Computer
Science, pages 21{35. Springer.
Haller, P. and Odersky, M. (2006).
Event-based programming without inversion of control.
In Lightfoot, D. E. and Szyperski, C., editors, Modular Programming Languages. 7th Joint
Modular Languages Conference, JMLC 2006 Oxford, UK, September 13-15, 2006
Proceedings, number 1 in Lecture Notes in Computer Science, pages 4{22, Oxford, UK.
Springer Berlin Heidelberg.
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 53 / 62

90. References
References V
Haller, P. and Odersky, M. (2009).
Scala actors: Unifying thread-based and event-based programming.
Theoretical Computer Science, 410(2-3):202{220.
Jennings, N. R. (2000).
On agent-based software engineering.
Arti

91. cial Intelligence, 117(2):277{296.
Jennings, N. R. (2001).
An agent-based approach for building complex software systems.
Communications of the ACM, 44(4):35{41.
Malone, T. W. and Crowston, K. (1994).
The interdisciplinary study of coordination.
ACM Computing Surveys, 26(1):87{119.
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 54 / 62

92. References
References VI
Mariani, S. and Omicini, A. (2014).
Coordination in situated systems: Engineering mas environment in TuCSoN.
In Fortino, G., Di Fatta, G., Li, W., Ochoa, S., Cuzzocrea, A., and Pathan, M., editors,
Internet and Distributed Computing Systems, volume 8729 of Lecture Notes in Computer
Science, pages 99{110. Springer International Publishing.
7th International Conference on Internet and Distributed Computing Systems (IDCS
2014), Calabria, Italy, 22-24 September 2014, Proceedings.
Milicevic, A., Jackson, D., Gligoric, M., and Marinov, D. (2013).
Model-based, event-driven programming paradigm for interactive Web applications.
In 2013 ACM International Symposium on New Ideas, New Paradigms, and Re
ections on
Programming Software (Onward!'13), pages 17{36, New York, NY, USA. ACM Press.
Odell, J. J. (2002).
Objects and agents compared.
Journal of Object Technology, 1(1):41{53.
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 55 / 62

93. References
References VII
Omicini, A. (1999).
On the semantics of tuple-based coordination models.
In 1999 ACM Symposium on Applied Computing (SAC'99), pages 175{182, New York,
NY, USA. ACM.
Special Track on Coordination Models, Languages and Applications.
Omicini, A. (2002).
Towards a notion of agent coordination context.
In Marinescu, D. C. and Lee, C., editors, Process Coordination and Ubiquitous Computing,
chapter 12, pages 187{200. CRC Press, Boca Raton, FL, USA.
Omicini, A. and Mariani, S. (2013).
Coordination for situated MAS: Towards an event-driven architecture.
In Moldt, D. and Rolke, H., editors, International Workshop on Petri Nets and Software
Engineering (PNSE'13), volume 989 of CEUR Workshop Proceedings, pages 17{22. Sun
SITE Central Europe, RWTH Aachen University.
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 56 / 62

94. References
References VIII
Omicini, A., Ricci, A., and Viroli, M. (2008).
Artifacts in the AA meta-model for multi-agent systems.
Autonomous Agents and Multi-Agent Systems, 17(3):432{456.
Special Issue on Foundations, Advanced Topics and Industrial Perspectives of Multi-Agent
Systems.
Omicini, A., Ricci, A., Viroli, M., Castelfranchi, C., and Tummolini, L. (2004).
Coordination artifacts: Environment-based coordination for intelligent agents.
In Jennings, N. R., Sierra, C., Sonenberg, L., and Tambe, M., editors, 3rd international
Joint Conference on Autonomous Agents and Multiagent Systems (AAMAS 2004),
volume 1, pages 286{293, New York, USA. ACM.
Omicini, A. and Zambonelli, F. (1999).
Coordination for Internet application development.
Autonomous Agents and Multi-Agent Systems, 2(3):251{269.
Papadopoulos, G. A. and Arbab, F. (1998).
Coordination models and languages.
In Zelkowitz, M. V., editor, The Engineering of Large Systems, volume 46 of Advances in
Computers, pages 329{400. Academic Press.
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 57 / 62

95. References
References IX
Rao, A. S. and George, M. P. (1991).
Modeling rational agents within a BDI architecture.
In Allen, J. F., Fikes, R., and Sandewall, E., editors, 2nd International Conference on
Principles of Knowledge Representation and Reasoning (KR'91), pages 473{484, San
Mateo, CA. Morgan Kaufmann Publishers.
Viroli, M., Omicini, A., and Ricci, A. (2002).
On the expressiveness of event-based coordination media.
In Arabnia, H. R., editor, International Conference on Parallel and Distributed Processing
Techniques and Applications (PDPTA'02), volume III, pages 1414{1420, Las Vegas, NV,
USA. CSREA Press.
Viroli, M. and Ricci, A. (2002).
Tuple-based coordination models in event-based scenarios.
In 22nd International Conference on Distributed Computing Systems, pages 595{601. IEEE
CS.
Proceedings of the Workshops.
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 58 / 62

96. References
References X
Wegner, P. (1996).
Coordination as constrained interaction.
In Ciancarini, P. and Hankin, C., editors, Coordination Languages and Models. First
International Conference, COORDINATION '96 Cesena, Italy, April 15{17, 1996.
Proceedings, Lecture Notes in Computer Science, pages 28{33, Cesena, Italy. Springer
Berlin Heidelberg.
Wegner, P. (1997).
Why interaction is more powerful than algorithms.
Communications of the ACM, 40(5):80{91.
Weyns, D., Omicini, A., and Odell, J. J. (2007).
Environment as a

97. rst-class abstraction in multi-agent systems.
Autonomous Agents and Multi-Agent Systems, 14(1):5{30.
Wooldridge, M. J. and Jennings, N. R. (1995).
Intelligent agents: Theory and practice.
Knowledge Engineering Review, 10(2):115{152.
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 59 / 62

98. References
References XI
Zambonelli, F. and Omicini, A. (2004).
Challenges and research directions in agent-oriented software engineering.
Autonomous Agents and Multi-Agent Systems, 9(3):253{283.
Special Issue: Challenges for Agent-Based Computing.
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 60 / 62

99. Extras
URLs
Slides
On APICe
http://apice.unibo.it/xwiki/bin/view/Talks/EbsmasWoa2014
On SlideShare
http://www.slideshare.net/andreaomicini/
event-based-vs-multi-agent-systems-towards-a-unified-conceptual-framework-
preliminary-notes
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100. Event-Based vs. Multi-Agent Systems:
Towards a Uni

101. ed Conceptual Framework
Preliminary Notes
Andrea Omicini
Dipartimento di Informatica { Scienza e Ingegneria (DISI)
Alma Mater Studiorum|Universita di Bologna, Italy
Short Course @ WOA 2014 Mini-school
Workshop nazionale Dagli Oggetti agli Agenti
Universita di Catania, Italy
25 Settembre 2014
A. Omicini (DISI, UniBO) Event-Based vs. Multi-Agent Systems WOA 2014 { 25/9/2014 62 / 62