qualità dei servizi – lapproccio mais b. pernici politecnico di milano dipartimento di...

Qualità dei servizi Qualità dei servizi – l’approccio MAIS– l’approccio MAIS

B. PerniciB. Pernici

Politecnico di MilanoPolitecnico di MilanoDipartimento di Elettronica e Dipartimento di Elettronica e

InformazioneInformazione

(c) B. Pernici, Process Track, Milano, April 2004(c) B. Pernici, Process Track, Milano, April 2004- - 22 - -

OutlineOutline

Qualità dei dati e qualità del servizio Qualità del servizio in MAIS Classificazione delle dimensioni Specifica di dimensioni di qualità Lavoro futuro


QUALITA’ DEI DATI E DEL SERVIZIOQUALITA’ DEI DATI E DEL SERVIZIO


Dimensioni di qualita’Dimensioni di qualita’


Modello basato su Prestazioni dei Prodotti e dei Modello basato su Prestazioni dei Prodotti e dei Servizi (PSP/IQ)Servizi (PSP/IQ)

Conforme alle specifiche

Soddisfa o supera le aspettative del consumatore

Qualità prodotto Informazione corretta-Accurata-Rappresentazione concisa-Completezza-Rappresentazione consistente

Informazione utile-quantità appropriata-Rilevanza-Comprensibilità

-Interpretabilità-obiettività

Qualità servizio Informazione affidabile-Tempestività-sicurezza

Informazione usabile-Credibilità-Accessiiblità-Facilità di manipolazione-Reputazione-Valore-aggiunto


Quality Driven compositionQuality Driven composition

Proposes a global approach to planning to optimally select component services during the execution of a composite service

Defines a quality model and a quality-driven service selection

L. Zeng, B. Benatallah, M. Dumas, J. Kalagnanam, Q.Z. Sheng,Quality Driven Web Service CompositionWWW 2003, Budapest


Quality Driven compositionQuality Driven composition

Given a composite service the execution path and the execution plan are defined

Execution paths are sequences of states

Execution plans are execution paths in which each activity is performed by a service

The problem is to select for each activity the service that not only satisfies local requirements but also the global ones


Quality modelQuality model

According to the separation between service provider and service requester perspective also the quality definition depends on them

The service provider specifies SLS, i.e. the promises

The service requester selects the more appropriate quality level

The provider and the requester agree on SLA that is a set of selected SLS


QUALITA’ IN MAISQUALITA’ IN MAIS


MAIS - Enhanced service modelMAIS - Enhanced service model

Besides the classical service model we could consider the context in which the service operates

The service context could be defined by (e.g.) The channels The time-zone The location

Two models Service provisioning model Service request model

Quality of service


Quality of serviceQuality of service

Each service provides a particular quality Even a service-based process must provide a

quality What is quality for services?

Performance issues (what it offers) Economical issues (how much it costs) Resource consuming issues (what it requires)

Quality parameters are specific to different domains


Multi-channel ADAPTIVE information Multi-channel ADAPTIVE information systemssystems

t

QoS

Accepted quality threshold


Quality parametersQuality parameters

Physical resources How many CPUs, how many disks, …

Data resources Timeliness, currency, availability, …

Channel Bandwidth, latency, jitter, …

Provider Pricing policy, payment forms , …


SLS exampleSLS example

<level id="low"> <framerate unit="fps"> <max>10fps</max><min>5fps</min> </framerate> <minresolution>320x200</minresolution> <price currency="EUR">80</price> <availability unit=“%">95</availability> </level></levels>

<levels channel="PC-Eth-RSTP"> <level id="high"> <framerate unit="fps"> <max>40</max><min>31</min> </framerate> <minresolution>1024x768</minresolution> <price currency="EUR">100</price> <availability unit="%">95</availability> </level> <level id="medium"> <framerate unit="fps"> <max>30fps</max><min>11fps</min> </framerate> <minresolution>800x600</minresolution> <price currency="EUR">90</turgia> <availability unit=“%">95</availability> </level>


General ArchitectureGeneral Architecture

Invokes the chosen service

E-Service CompositionPlatform

Chooses the best e-service accordingto user request

All the modules are placed inthe platform or in service/userdevice according to their capability.

Each profile is composed by a localand a global part.



determines QoS levels acceptable forthe user

translates logical constraints in technological ones

merges service/user/context constraints

Interaction EnablingPlatform

chooses the best n-ple for service delivering



Receives as input the acceptable QoS levels with their constraints

Tries a channel adaptation making firsta theoretical adaptation study and thentrying to change the real values

Reflective Platform

Works on a given n-ple

First phase

Second phase

Monitors the channel during service provisioning


Gestione vincoli su QOS

<abstractService name=“prenotazioneAerei”> <minAffinityValue>0.7</minAffinityValue> <qos> <parameter> <name>responseTime</name> <minValue>5</minValue> <maxValue>10</maxValue> </parameter> <parameter> <name>localization</name> <value>Italia</value> </parameter> </qos></abstractService>


MODELING QoSMODELING QoS


Quality of ServiceQuality of Service

adaptation strategies both the service and provider side depend on the QoS definition

channel deeply affects the values of the QoS parameters on the

provider side so the user can perceive different values according to the

active channel In a service oriented environment we have to

consider all the involved actors independently


Our modelOur model

Composed by: A system model: objects and actors A set of roles and rules

association of quality information to objects relationships among them

Quality information expressed by: Quality parameters Quality sets


Objects and actorsObjects and actors

Objects: Services Networks Devices

Actors: Service providers Network providers Device providers Users


Objects and actorsObjects and actors

Services networks devices

Serviceproviders

Networkproviders

Deviceproviders

Users


CommunitiesCommunities

A community exists for each object considered in the model: A community for each type of service (VoD, hotel reservation, …) A community for the network A community for each type of device (PC, PDA, SmartPhone, …)

Given an object, the related community writes the specifications which define in an unambiguous way such an object

In our work we are interested in the quality specification of the object so the object specification is a set of quality parameters


Service CommunityService Community

Quality specification:• Framerate• Colordepth• Resolution

Functional specification&

ServiceProvider A

ServiceProvider C

ServiceProvider B Service

Community

E-Video

My-movie

V@D


Quality parameterQuality parameter

quality of objects set of quality parameters Defined by the community for that object

A quality parameter is a pair: Name Admissible_values

Examples of quality parameters: <framerate, [5fps..40fps]> <colordepth, [2bit..24 bit]> <resolution, [320 × 200; 800 × 600; 1024 × 768]>

Functions best and worst are introduced to obtain the admissible value which correspond namely the best and the worst quality

More on going work on function definitions


Quality setQuality set

Quality Set: class of quality parameters identified by: a name a list of quality parameters belonging to such a set

Containment relationships QS1 QS2 holds iff: same list of quality parameters for each pair of quality parameters with the same name

QS1_name.admissible_value QS2_name.admissible_value


Roles for quality managementRoles for quality management

Quality definition performed in two steps: Specification definition phase: the community defines

a quality set for the object specification Object implementation phase: the provider operates a

restriction on the specification quality parameters Containment relationship between the object

specification and implementation quality sets for an object: QSobj QSspec


ModelModel


Roles for quality managementRoles for quality management

We are interested in three main quality sets: QoS: quality of service QoN. quality of newtork QoD: quality of device

For examples from the community specification we obtain the quality set QoSspec:

<framerate, [5fps..40fps]> <colordepth, [2bit..24 bit]> <resolution, [320×200; 800×600; 1024×768]>

From the service provider implementation the realized object is defined by the quality set QoSobj

<framerate, [5fps..30fps]> <colordepth, [2bit..24 bit]> <resolution, [320×200; 800×600]>


Quality of ExperienceQuality of Experience

Represents the quality perceived by the user Composed by the same quality parameters

belonging to the QoS where the values are affected by the QoN, and QoD

Qualityrules

QoS<framerate, [5fps..30fps]><colordepth, [2bit..24 bit]>

<resolution, [320×200; 800×600]>

QoN QoD

QoE<framerate, [5fps..20fps]><colordepth, [2bit..16 bit]><resolution, [800×600]>


Quality rulesQuality rules

Quality rules are introduced to explicitly declare how the QoS is affected by the QoN and QoD

Given two quality sets QS1 and QS2 a quality rule is a function qr(QS1, QS2)= QS3, where:

QS3 is a quality set QS3 QS1

Example of quality rule qr(QoS, QoN)=QoE: framerate * colordepth * resolution = K * bandwidth

In this way we can state that:

lution)worst(reso*rdepth)worst(colo

idth)best(bandwrate)best(frame

ution)best(resol*depth)best(color

width)worst(banderate)worst(fram


Related workRelated work

Quality of Service is a relevant topic for several researches area. In particular we analyzed:

Web Service community Telecommunication community Middleware community

In all of these efforts the definition of measurable characteristics of objects is fundamental

QoS are usually defined in a way that the are not fully under the control of the user

QoE highlights this difference and defines the subset of the QoS which is fully under control of the user

La qualità del servizio e La qualità del servizio e linguaggi per la sua linguaggi per la sua rappresentazionerappresentazione

C. CappielloC. Cappiello


Classificazione delle variabili di qualità del Classificazione delle variabili di qualità del servizio servizio

QoS

Dimensioni di qualità lato fornitore

Dimensioni di qualità negoziabili

Dimensioni di qualità intrinseche del servizio

Dimensioni di qualità relative a risorse per

l’erogazione del servizio

Lato fornitore Lato cliente

Caratteristiche device

Profiloutente


negoziazione interattiva o basata sul profilo utente

Negoziazione automatica


Esempi di dimensioni di qualitàEsempi di dimensioni di qualità

Esempi di dimensioni di qualità negoziabili lato fornitore sono:

Bandwith (Larghezza di banda) Prezzo Velocita' Grado di sicurezza Accuracy Completeness Adattività Response time Provisioning Time Service Availability Timeliness (Dati) Availability (Dati)


Linguaggio di rappresentazioneLinguaggio di rappresentazione

Il linguaggio più completo per la rappresentazione delle caratteristiche di qualità è WSOL. Esso consente di specificare:

Vincoli funzionali (pre-condizioni, post-condizioni, e condizioni future) Vincoli non funzionali (es. Vincoli di QoS) Diritti di accesso


Linguaggio di rappresentazioneLinguaggio di rappresentazione

Esempio di specifica QoS

<wsol:offeringType name=“bookflight”

service=“bookflight:bookflightService”

….

<wsol:QoSconstraints name=“MaxResponseTime”

<wsol:QoSname qname=“QoSns:responsetime”/>

<wsol:QoStype typename=“QoSns:max”/>

<wsol:qvalue> 50 </wsol:qvalue>

<wsol:qunit unitname=“QoSns:ms”/>

</wsol:QoSconstraints>


Estensioni al linguaggioEstensioni al linguaggio

Estensioni del linguaggio che saranno apportate in MAIS:

Definizione dell’insieme delle dimensioni di QoS “MAIS”

Definizione dell’insieme delle specifiche di qualità “MAIS”

Introduzione di parametri importanti in fase di negoziazione (es. priorità sul soddisfacimento dei vincoli di qualità)


Conclusions and future workConclusions and future work

This work presents a way to define the quality information in a multichannel information system

All the involved actors can separately state the quality information for the controlled object

Quality rules are introduced in order to create a relationship among the quality information defined by the different actors

Now, analyzing some case studies we aim at finding other real quality rules

A prototype which exploit this model is under development

More theoretical work on: Function definition Dependency rules (ontology of quality dimensions) (OWL)


ReferencesReferences

WSLA provides a framework to define the quality parameters, responsibilities about the monitoring, the agreement between service provider and requester

A. Mani and A. Magarajan, Understanding quality of service of your Web services, provides a list of useful parameters in Web Service context

L. Zeng et al. Quality driven web services composition. WWW 2003

Real-time CORBA enforce timeliness properties Fault-tolerant CORBA (implemented in IRL) increasing the

mean time to failure, to repair and thus between failures of CORBA objects through software replication techniques

DaQuinCIS project provides a set of data quality dimensions and infrastructure for their monitoring and improvement

Andrea Maurino, Stefano Modafferi, Barbara Pernici, Reflective architectures for adaptive information systems, ICSOC 2003:115-131

C. Marchetti, B. Pernici, P. Plebani,A Quality Model for Multichannel Adaptive Information Systems, WWW04 Conference, Alternate Track on Web Services, maggio 2004


ReferencesReferences

Carlo Marchetti, Barbara Pernici, Pierluigi Plebani, A quality model for e-Service based multi-channel adaptive information systems, WISE-WQW workshop, Dic. 2004

C. Cappiello, C. Francalanci, B. Pernici, Data quality assessment from a user perspective, Workshop SIGMOD-IQIS, giugno 2004

Carlo Marchetti, Barbara Pernici, Pierluigi Plebani, A Quality Model for Multichannel Adaptive Information Systems, WWW04 Alternate Track on Web Services, maggio 2004

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