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Qualità dei servizi – l’approccio MAIS

Qualità dei servizi – l’approccio MAIS. B. Pernici Politecnico di Milano Dipartimento di Elettronica e Informazione. Outline. Qualità dei dati e qualità del servizio Qualità del servizio in MAIS Classificazione delle dimensioni Specifica di dimensioni di qualità Lavoro futuro.

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Qualità dei servizi – l’approccio MAIS

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  1. Qualità dei servizi – l’approccio MAIS B. Pernici Politecnico di MilanoDipartimento di Elettronica e Informazione

  2. 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 2004

  3. QUALITA’ DEI DATI E DEL SERVIZIO (c) B. Pernici, Process Track, Milano, April 2004

  4. Dimensioni di qualita’ (c) B. Pernici, Process Track, Milano, April 2004

  5. Modello basato su Prestazioni dei Prodotti e dei Servizi (PSP/IQ) (c) B. Pernici, Process Track, Milano, April 2004

  6. 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 CompositionWWW 2003, Budapest (c) B. Pernici, Process Track, Milano, April 2004

  7. 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 Driven composition (c) B. Pernici, Process Track, Milano, April 2004

  8. 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 2004

  9. QUALITA’ IN MAIS (c) B. Pernici, Process Track, Milano, April 2004

  10. 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 2004

  11. 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 2004

  12. QoS t Multi-channel ADAPTIVE information systems Accepted quality threshold (c) B. Pernici, Process Track, Milano, April 2004

  13. 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 2004

  14. <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> SLS example (c) B. Pernici, Process Track, Milano, April 2004

  15. General Architecture 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. E-Service Composition Platform Chooses the best e-service according to user request Invokes the chosen service (c) B. Pernici, Process Track, Milano, April 2004

  16. General Architecture Interaction Enabling Platform chooses the best n-ple for service delivering determines QoS levels acceptable for the user translates logical constraints in technological ones merges service/user/context constraints (c) B. Pernici, Process Track, Milano, April 2004

  17. First phase Second phase General Architecture Reflective Platform Works on a given n-ple 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 Monitors the channel during service provisioning (c) B. Pernici, Process Track, Milano, April 2004

  18. 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> (c) B. Pernici, Process Track, Milano, April 2004

  19. MODELING QoS (c) B. Pernici, Process Track, Milano, April 2004

  20. 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 actorsindependently (c) B. Pernici, Process Track, Milano, April 2004

  21. 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 2004

  22. Objects and actors • Objects: • Services • Networks • Devices • Actors: • Service providers • Network providers • Device providers • Users (c) B. Pernici, Process Track, Milano, April 2004

  23. Objects and actors Service providers Network providers Users Device providers Services networks devices (c) B. Pernici, Process Track, Milano, April 2004

  24. 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 2004

  25. Service Community Service Provider B Service Provider A ServiceCommunity V@D E-Video Functional specification & • Quality specification: • Framerate • Colordepth • Resolution My-movie Service Provider C (c) B. Pernici, Process Track, Milano, April 2004

  26. 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: • <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 (c) B. Pernici, Process Track, Milano, April 2004

  27. Quality 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 (c) B. Pernici, Process Track, Milano, April 2004

  28. 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: • QSobj QSspec (c) B. Pernici, Process Track, Milano, April 2004

  29. Model (c) B. Pernici, Process Track, Milano, April 2004

  30. 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 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]> (c) B. Pernici, Process Track, Milano, April 2004

  31. 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 QoN QoD Quality rules QoE <framerate, [5fps..20fps]> <colordepth, [2bit..16 bit]> <resolution, [800×600]> QoS <framerate, [5fps..30fps]> <colordepth, [2bit..24 bit]> <resolution, [320×200; 800×600]> (c) B. Pernici, Process Track, Milano, April 2004

  32. Quality 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: (c) B. Pernici, Process Track, Milano, April 2004

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

  34. La qualità del servizio e linguaggi per la sua rappresentazione C. Cappiello

  35. 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 l’erogazione del servizio Lato fornitore Lato cliente Caratteristiche device Profilo utente (c) B. Pernici, Process Track, Milano, April 2004

  36. negoziazione interattiva o basata sul profilo utente Negoziazione automatica (c) B. Pernici, Process Track, Milano, April 2004

  37. 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 2004

  38. 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 2004

  39. Linguaggio 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> (c) B. Pernici, Process Track, Milano, April 2004

  40. Estensioni 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) (c) B. Pernici, Process Track, Milano, April 2004

  41. 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 2004

  42. 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 2003:115-131 • C. Marchetti, B. Pernici, P. Plebani,A Quality Model for Multichannel Adaptive Information Systems, WWW04 Conference, Alternate Track on Web Services, maggio 2004 (c) B. Pernici, Process Track, Milano, April 2004

  43. References • 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 (c) B. Pernici, Process Track, Milano, April 2004

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