On the Expressiveness of Attribute-based Communication

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On the Expressiveness of Attribute-basedCommunication

Yehia Abd Alrahman,

Joint work withR. De Nicola , M. Loreti

January 29, 2016

Outline

1 Collective Adaptive Systems

2 AbC: A Process Calculus for CAS

3 Encoding other communication paradigms

4 Ongoing and Future work

Collective Adaptive Systems - CAS

CAS are software-intensive systems featuring� massively interconnected systems that are physically distributed.

� operating in open and non-deterministic environments

� dynamically adapting to new requirements and environmentalconditions

The Key Challenge of software development for CAS

Is the management of a transition from systems comprising relativelyisolated, small-scale elements to large-scale, massively interconnectedsystems that are physically distributed.

Message Passing Limitations

� Is not always practical (massive no.of distributed components ina small space).

� models are very detailed (all contributing components arespecified). shared space?

� local interactions of one component does not affect the others(limited adaptation).

� Consequently, does not scale well to model CAS!

Ants Emergent Behavior

Modeling this behavior in traditional approaches is hardly possible.

Ants Emergent Behavior

Modeling this behavior in traditional approaches is hardly possible.

Learned Lessons

� a system-as-a-whole needs to be considered more than simplythe sum of its parts.

� system models should be parametric to their workingspace/environment.

� individual sensing/modifying of the shared space/environmentmight influence co-located components (without explicitinteraction).

� individual components should have a window to their workingspace for sensing/modifying

The proposed approach

We have defined the AbC calculus with a minimal set of primitivesthat rely on attribute-based communication.

Learned Lessons

� a system-as-a-whole needs to be considered more than simplythe sum of its parts.

� system models should be parametric to their workingspace/environment.

� individual sensing/modifying of the shared space/environmentmight influence co-located components (without explicitinteraction).

� individual components should have a window to their workingspace for sensing/modifying

The proposed approach

We have defined the AbC calculus with a minimal set of primitivesthat rely on attribute-based communication.

AbC through a running example

Case Study: video. . .

AbC Components

(Components) C ::= Γ :P | C1‖C2 | νxC

� Single component Γ :P – Γ denotes sets of attributes and Pprocesses

� Parallel composition ‖ – of components

� Name restriction νx (to delimit the scope of name x) – inC1‖(νx)C2, name x is invisible from within C1

Running example (step 1/5)

� Each ant is modeled as an AbC component (Anti ) of thefollowing form (Γi :PA).

� Ants execute in parallel and collaborate.

Ant1‖ . . . ‖Antn

AbC Components

� Single component Γ :P – Γ denotes sets of attributes and Pprocesses

� Parallel composition ‖ – of components

� Name restriction νx (to delimit the scope of name x) – inC1‖(νx)C2, name x is invisible from within C1

� Each ant is modeled as an AbC component (Anti ) of thefollowing form (Γi :PA).

� Ants execute in parallel and collaborate.

Ant1‖ . . . ‖Antn

AbC Processes

P ::= 0 | Act.P | 〈Π〉P | P1 + P2 | P1|P2 | K� 〈Π〉P – blocks P until the evaluation of Π under the local

environment becomes true.

� Act – communication and attribute update actions

PA running on an ant has the following form:

PA , (Worker + Supplier)|Move

AbC Processes

P ::= 0 | Act.P | 〈Π〉P | P1 + P2 | P1|P2 | K� 〈Π〉P – blocks P until the evaluation of Π under the local

environment becomes true.

� Act – communication and attribute update actions

PA running on an ant has the following form:

PA , (Worker + Supplier)|Move

Example Cont.

AbC Actions

Act ::= Π(x) | (E )@Π | [a 7→ E ]

Worker , 〈this.Istomach = 0% ∧ this.role = worker〉(this.odour ,Freq)@(Sstomach 6= 0%).((y = meal)(x , y).[this.Istomach 7→ 100%]()@ff.Follow+ Worker )

Follow , [this.direction 7→ this.attractive, this.state 7→ move]()@ff.Dispose

Move , 〈this.state 6= stop〉()@ff.Move

Example Cont.

AbC Actions

Act ::= Π(x) | (E )@Π | [a 7→ E ]

Example Cont.

AbC Actions

Act ::= Π(x) | (E )@Π | [a 7→ E ]

Example Cont.

AbC Actions

Act ::= Π(x) | (E )@Π | [a 7→ E ]

Running example cont.

Dispose , 〈this.found 6= tt ∧ this.nest 6= tt〉()@ff.Dispose +

〈this.found = tt〉[this.state 7→ stop, this.found 7→ ff,this.Istomach 7→ 100%, this.Sstomach 7→ 100%]()@ff.Follow +

〈this.nest = tt〉Supplier

Supplier , (〈this.nest = tt ∧ this.Sstomach > 0%〉Feed +

〈this.nest = tt ∧ this.Sstomach = 0% ∧ this.drnd = 0〉Search )

Feed , (y = Freq)(x , y).(portion, meal)@(odour = x)[this.Sstomach 7→ this.Sstomach − 1%].Supplier

Search , [this.direction 7→ 2πRand(), this.state 7→ move]()@ff.Dispose

Supplier , (〈this.nest = tt ∧ this.Sstomach > 0%〉Feed +〈this.nest = tt ∧ this.Sstomach = 0% ∧ this.drnd = 0〉

Search )

AbC Calculus

(Processes) P ::=

(Inaction) 0

(Input) | Π(x).P

(Output) | (E )@Π.P

(Update) | [a 7→ E ].P

(Match) | 〈Π〉P(Choice) | P1 + P2

(Par) | P1|P2

(Call) | K

(Predicates) Π ::= tt | ff | E1 on E2 | Π1 ∧ Π2 | . . .(Data) E ::= v | x | a | this.a | . . .

Encoding other communicationparadigms

A number of alternative communication paradigms such as:

� Explicit Message Passing

� Group based Communications

� Publish-Subscribe

can be easily modelled by relying on AbC primitives

Encoding the bπ-calculus

A bπ-calculus process P is rendered as an AbC component Γ:P whereΓ = ∅.

Possible problem

Impossibility of specifying the channel along which the exchange hasto happen instantaneously.

Way out

Send the communication channel as a part of the transmitted valuesand the receiver checks its compatibility.

L ax .P M , (a, x)@(a = a).L P M

L a(x).P M , Π(y , x).L P M with Π = (y = a) and y 6∈ n(L P M)

Group based communication

Group-based interaction� A group name is encoded as an attribute in AbC.

� The constructs for joining or leaving a given group can beencoded as attribute updates.

� . . .

Γ1 : (msg , this.group)@(group = b).0‖Γ2 : (y = a)(x , y).0‖

...‖Γ7 : (y = a)(x , y) | [this.group 7→ b]()@ff.0

Let Γ1(group) = a, Γ2(group) = b, Γ7(group) = c

Publish-Subscribe

Publish-Subscribe interaction is a simple special case ofattribute-based communication:

� A Publisher sends tagged messages for all subscribers byexposing from his environment only the current topic.

� Subscribers check compatibility of messages according to theirsubscriptions.

Γ1 : (msg , this.topic)@(tt) ‖Γ2 : (y = this.subscription)(x , y) ‖

Γn : (y = this.subscription)(x , y) ‖

Observation

Dynamic updates of attributes and the possibility of controlling theirvisibility give AbC great flexibility and expressive power.

Ongoing & Future Work

We have concentrated on modelling behaviours of components andtheir interactions. We are currently tackling other research items.

� Implementing the linguistic primitives for attribute-basedcommunication.

� developing quantitative variants AbC to support components intaking decisions (e.g. via probabilistic model checking).

� Considering alternative semantics and behavioural equivalencesfor AbC

� Studying the impact of bisimulation (algebraic laws, axioms,proof techniques, . . . )

Many thanks for your time.

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On the Expressiveness of Attribute-based Communication

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