Qualità dei servizi – lapproccio MAIS B. Pernici Politecnico di Milano Dipartimento di Elettronica e Informazione

(c) B. Pernici, Process Track, Milano, April Outline Qualità dei dati e qualità del servizio Qualità del servizio in MAIS Classificazione delle dimensioni Specifica di dimensioni di qualità Lavoro futuro

(c) B. Pernici, Process Track, Milano, April QUALITA DEI DATI E DEL SERVIZIO

(c) B. Pernici, Process Track, Milano, April Dimensioni di qualita

(c) B. Pernici, Process Track, Milano, April Modello basato su Prestazioni dei Prodotti e dei Servizi (PSP/IQ) Conforme alle specifiche Soddisfa o supera le aspettative del consumatore Qualità prodottoInformazione corretta - Accurata - Rappresentazione concisa - Completezza - Rappresentazione consistente Informazione utile - quantità appropriata - Rilevanza - Comprensibilità - Interpretabilità - obiettività Qualità servizioInformazione affidabile - Tempestività - sicurezza Informazione usabile - Credibilità - Accessiiblità - Facilità di manipolazione - Reputazione - Valore-aggiunto

(c) B. Pernici, Process Track, Milano, April Quality 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 Composition WWW 2003, Budapest

(c) B. Pernici, Process Track, Milano, April Quality 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

(c) B. Pernici, Process Track, Milano, April Quality 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

(c) B. Pernici, Process Track, Milano, April QUALITA IN MAIS

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

(c) B. Pernici, Process Track, Milano, April Quality 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

(c) B. Pernici, Process Track, Milano, April Multi-channel ADAPTIVE information systems t QoS Accepted quality threshold

(c) B. Pernici, Process Track, Milano, April Quality parameters Physical resources How many CPUs, how many disks, … Data resources Timeliness, currency, availability, … Channel Bandwidth, latency, jitter, … Provider Pricing policy, payment forms, …

(c) B. Pernici, Process Track, Milano, April SLS example 10fps 5fps 320x x fps 11fps 800x

(c) B. Pernici, Process Track, Milano, April General Architecture Invokes the chosen service E-Service Composition Platform Chooses the best e-service according to user request All the modules are placed in the platform or in service/user device according to their capability. Each profile is composed by a local and a global part.

(c) B. Pernici, Process Track, Milano, April General Architecture determines QoS levels acceptable for the user translates logical constraints in technological ones merges service/user/context constraints Interaction Enabling Platform chooses the best n-ple for service delivering

(c) B. Pernici, Process Track, Milano, April General Architecture Receives as input the acceptable QoS levels with their constraints Tries a channel adaptation making first a theoretical adaptation study and then trying to change the real values Reflective Platform Works on a given n-ple First phase Second phase Monitors the channel during service provisioning

(c) B. Pernici, Process Track, Milano, April Gestione vincoli su QOS 0.7 responseTime 5 10 localization Italia

(c) B. Pernici, Process Track, Milano, April MODELING QoS

(c) B. Pernici, Process Track, Milano, April Quality 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

(c) B. Pernici, Process Track, Milano, April Our 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

(c) B. Pernici, Process Track, Milano, April Objects and actors Objects: Services Networks Devices Actors: Service providers Network providers Device providers Users

(c) B. Pernici, Process Track, Milano, April Objects and actors Servicesnetworks devices Service providers Network providers Device providers Users

(c) B. Pernici, Process Track, Milano, April Communities 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

(c) B. Pernici, Process Track, Milano, April Service Community Quality specification: Framerate Colordepth Resolution Functional specification & Service Provider A Service Provider C Service Provider B Service Community E-Video My-movie

(c) B. Pernici, Process Track, Milano, April Quality 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: 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

(c) B. Pernici, Process Track, Milano, April Quality set Quality Set: class of quality parameters identified by: a name a list of quality parameters belonging to such a set Containment relationships QS 1 QS 2 holds iff: same list of quality parameters for each pair of quality parameters with the same name QS 1_name.admissible_value QS 2_name.admissible_value

(c) B. Pernici, Process Track, Milano, April Roles 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: QS obj QS spec

(c) B. Pernici, Process Track, Milano, April Model

(c) B. Pernici, Process Track, Milano, April Roles 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 QoS spec : From the service provider implementation the realized object is defined by the quality set QoS obj

(c) B. Pernici, Process Track, Milano, April Quality 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 Quality rules QoS QoNQoD QoE

(c) B. Pernici, Process Track, Milano, April Quality rules Quality rules are introduced to explicitly declare how the QoS is affected by the QoN and QoD Given two quality sets QS 1 and QS 2 a quality rule is a function qr(QS 1, QS 2 )= QS 3, where: QS 3 is a quality set QS 3 QS 1 Example of quality rule qr(QoS, QoN)=QoE: framerate * colordepth * resolution = K * bandwidth In this way we can state that:

(c) B. Pernici, Process Track, Milano, April Related 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 linguaggi per la sua rappresentazione C. Cappiello

(c) B. Pernici, Process Track, Milano, April Classificazione delle variabili di qualità del servizio QoS Dimensioni di qualità lato fornitore Dimensioni di qualità negoziabili Dimensioni di qualità intrinseche del servizio Dimensioni di qualità relative a risorse per lerogazione del servizio Lato fornitoreLato cliente Caratteristiche device Profilo utente

(c) B. Pernici, Process Track, Milano, April negoziazione interattiva o basata sul profilo utente Negoziazione automatica

(c) B. Pernici, Process Track, Milano, April Esempi 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)

(c) B. Pernici, Process Track, Milano, April Linguaggio 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

(c) B. Pernici, Process Track, Milano, April Linguaggio di rappresentazione Esempio di specifica QoS <wsol:offeringType name=bookflight service=bookflight:bookflightService …. <wsol:QoSconstraints name=MaxResponseTime 50

(c) B. Pernici, Process Track, Milano, April Estensioni al linguaggio Estensioni del linguaggio che saranno apportate in MAIS: Definizione dellinsieme delle dimensioni di QoS MAIS Definizione dellinsieme delle specifiche di qualità MAIS Introduzione di parametri importanti in fase di negoziazione (es. priorità sul soddisfacimento dei vincoli di qualità)

(c) B. Pernici, Process Track, Milano, April Conclusions 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)

(c) B. Pernici, Process Track, Milano, April References 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: C. Marchetti, B. Pernici, P. Plebani,A Quality Model for Multichannel Adaptive Information Systems, WWW04 Conference, Alternate Track on Web Services, maggio 2004

(c) B. Pernici, Process Track, Milano, April References Carlo Marchetti, Barbara Pernici, Pierluigi Plebani, A quality model for e-Service based multi-channel adaptive information systems, WISE-WQW workshop, Dic 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