SHReQ: Coordinating Application Level QoS

SHReQ: Coordinating Application Level QoS

Speaker:Ivan LaneseDipartimento di Informatica Università di Pisa

Authors:Dan Hirsch & Emilio TuostoDipartimento di Informatica Università di Pisa

SEFM 2005, Koblenz, Germany, 6-9 September 2005

SEFM 2005, 5-9 September, Koblenz, Germany Hirsch, Tuosto (presented by

Lanese)

Roadmap Motivations Background: c-semiring Background: SHR SHReQ An application Final remarks


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Global computing Programming global systems is hard

because: absence of centralised control client-server not enough: P2P different administrative domains (security) interoperability

different platforms, devices (e.g. PDAs, laptops, mobile phones...)

mobility network awareness

applications are location dependent different locations have different features


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Service oriented computing (SOC) Applications are made by gluing services

interconnected but independent (local choices, independently built)

Interactions governed by programmable coordination policies

Services are searched and bound ... offline can search/bind be dynamic and at run-time?

Search and bind depend on application level QoS

not low-level performance (e.g., throughput, response time)

but application-related price of services payment mode data available in a given format


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Our approach SOC modelling is not just normal

programming + primitives for mobility or synchronization

Lifting QoS issues to application level proof techniques and tools are also needed

First steps extending Klaim [see biblio] We present SHReQ, an (hyper)graph

model which exploits c-semiring for expressing application level QoS coordinating activities by synchronisation on c-

semiring values


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Constraint semirings C-semirings for abstracting

application level QoS <A ,+ , ⋆, 0, 1> where

A is a set (containing 0 and 1), +, ⋆ : A × A A


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Constraint semirings+ ⋆

x + y = y + x x ⋆ y = y ⋆ x

(x + y) + z = x + (y + z)

(x ⋆ y) ⋆ z = x ⋆ (y ⋆ z)

x + 0 = x x ⋆ 0 = 0

x + 1 = 1 x ⋆ 1 = x

x + x = x (x + y) ⋆ z = (x ⋆ z) + (y ⋆ z)

Implicit partial order: a ≤ b a + b = b “b is better than a”


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Example: priority semiring P = <N, max, min, 0, ∞> N is the set of natural numbers

with infinity ≤ is the standard order on N


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Example: broadcast semiring B = <AA{1, 0,}, +, ⋆, 0, 1> A is a set of actions A = {a | a A} are the coactions a⋆b obeys the axioms for 0 and 1 and

a⋆a = a a⋆a = a a⋆b = otherwise

a + b obeys the axioms for 0 and 1 and a + a = a a + b = otherwise


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Other semirings <{true, false}, or, and, false, true>

(boolean): Availability <Real+, min, +, +, 0> (optimization):

Price, propagation delay <Real+, max, min, 0, +> (max/min):

Bandwidth <[0, 1], max, * , 0, 1> (probabilistic):

Performance and rates <2N, , , , N> with N set (set-based):

Capabilities and access rights


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A key property Cartesian product of c-semirings is

a c-semiring Allows to use multiple QoS

dimensions at the same time


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The hypergraph model We aim at modeling new non-functional

computational phenomena The metaphor is:

“Global computers as hypergraphs” “Global computing as SHR”

Components are represented by (hyper)edges

Systems are bunches of edges connected through common nodes some nodes are declared as local

Computing means to synchronously rewrite edges according to a synchronisation policy


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The SHR approach Productions to describe the behaviour

of single edges local effects edges rewritten into generic graphs constraints on surrounding nodes

Global constraint-solving algorithm to derive transitions to select which productions can be applied allows to define complex transformations

Finally transitions are applied


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Edge Replacement Systems

R

1

2 3 4

L

12 3 4 H

A production describes how the edge L is transformed into the graph R


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Edge Replacement Systems

A production describes how the edge L is transformed into the graph R

Many productions can be applied concurrently

R

R’

1

2 3 4

1

2

3

L

L’

12 3 4

1

2

3

H


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Adding synchronization We associate actions to nodes attached

to the rewritten edges Actions performed on the same node are

composed according to a synchronization algebra

A transition is allowed iff the synchronization constraints expressed by actions are satisfied (i.e., composition is defined)

Many synchronization models are possible (point-to-point, broadcast, …)


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Adding mobility We use synchronization algebras with

mobility [see biblio] Each action is equipped with a tuple of

node references During synchronization we

compute a fusion among nodes merging corresponding nodes from synchronized

actions mobility in the Fusion Calculus style

apply the fusion to the graph and to the references of the resulting action


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From SHR to SHReQ Graphs have weights associated to

nodes values of the semiring

Productions have an applicability condition the minimum (w.r.t. ≤) value of

resources required on each node Actions are values of the semiring

⋆is action composition


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Sample production

a<z>x x

L

y:v y

R Rz

1

Rewritten edge

Final graph


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Sample production

L

a<z>

R

x x

y:v y

Rz

1

Action

Applicability

condition

Action sending

node


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SHReQ synchronization Semiring set has the following

structure

NoSyncSync

Fin 0

1

Synchronization errors

Completed synchronizatio

ns


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Quasiproductions Obtained from productions by

renaming nodes from the LHS If nodes are merged, + is used to

compute the resulting applicability condition


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Synchronizing rules We select a quasiproduction matching

each edge same label and attachment nodes we check that the applicability condition is

satisfied We compute the product of the actions

performed on each node we check that it is not in NoSync

On local nodes we check that the resulting action is in Fin

We compute the substitution on nodes we check that no old nodes are merged


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The result Each edge is replaced by the RHS of the

corresponding quasiproduction The new values on nodes are

the result of the synchronization for old nodes

1 for new nodes We apply the induced substitution

since no old nodes are merged, values from old nodes can be used

We hide nodes if the environment is not aware of them not free before and not extruded as names in -calculus


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There is some math behind Graphs as terms in an algebra Productions and transitions as

labelled rules Inference rules to derive

transitions from productions


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TRMCS case study We apply SHReQ to Teleservice and Remote

Medical Care System (TRMCS) studied by Parco Scientifico e Tecnologico d’Abruzzo

and University of L’Aquila Hierarchical system with a server S, routers R

connected to S and users U connected to routers Functionalities

users send requests for assistance (remote or ambulance) to routers

routers forward alarms to server server provides the required assistance

Aimed at showing the rewriting mechanism for the use of c-semirings for multidimensional QoS see

the bibliography


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Modelling the system

The cartesian product of priority and broadcast is used

All nodes are local (result must be a coaction)

S

R2R1

U2U3U1


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User productions

Un

(amb,n)

waUn

x x

waUn

1

Un

xx

waUn

(amb,n)<z>

uaUn

xx:(amb,n)

z


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Router productions

R

(amb,∞)<z>

raR

x x

(amb,∞)y y

raR

(amb,∞)<z>

R

x x

(amb,∞)<z>y:(amb,0) y


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Server production

x

(amb,∞)<x>

yS

w

(rem,∞)(amb,∞)x yS

w


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Sample computation

S

R2R1

U2U3U1

(amb,1) (amb,3)

(amb,∞)

(amb,∞)<z>(amb,∞)<x>

(amb,∞) (rem,∞)x y

w

r s


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Sample computation

S

R2R1

U2waU3

waU1

x y

w

r s(amb,1)

(amb,∞)

1

(amb,∞) (rem,∞)


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Sample computation

S

R2R1

U2waU3

waU1

(amb,∞)<z>

(amb,∞)<z>(amb,∞)<x>

(amb,∞) (rem,∞)x y

w

r s(amb,1)<z>


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Sample computation

S

R2R1

U2U3uaU1

x y

w

r s


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Final remarks We have presented the idea and

an application of SHReQ The main features are

general multiparty synchronisations based on c-semirings

support for application level QoS Surprisingly, SHReQ fits the design

principles for a good calculus from Milner [see biblio]


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Future work We plan to develop formal

methods based on SHReQ for specifying distributed applications and their non-functional requirements

Hopefully, develop verification techniques (e.g., model checking) on SHReQ logic for SHReQ already exists [see

biblio]


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Bibliography On extending KLAIM with QoS:

“A formal basis for reasoning on programmable QoS”, De Nicola et al., International Symposium on Verification, LNCS 2772

“A basic calculus for modelling service level agreements”, De Nicola et al., Coordination 2005, LNCS 3454

On c-semiring: “Semiring-based constraint satisfaction and

optimization”, Bistarelli, Montanari, Rossi, JACM 44(2) On SHR:

“A model of distributed systems based on graph rewriting”, Degano, Montanari, JACM 34

“Reconfiguration of software architecture styles with name mobility”, Hirsch, Inverardi, Montanari, Coordination 2000, LNCS 1906

Ph.D. thesis of Dan Hirsch and Emilio Tuosto


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Bibliography On synchronization algebras with mobility:

“Synchronization algebras with mobility for graph transformations”, Lanese, Montanari, FGUC 2004, ENTCS, to appear

On verification techniques for QoS: “A logic for graphs with QoS”, Ferrari, Lluch-

Lafuente, VODCA 2004, ENTCS, to appear On a logic for SHReQ:

“A logic for application level QoS”, Hirsch, Lluch-Lafuente, Tuosto, submitted to QAPL 2005

On design principles for calculi: “Process constructors and interpretations”,

Milner, Information Processing, Elsevier


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SHReQ: Coordinating Application Level QoS