Monotony in Service Orchestrations

📝 Abstract

Web Service orchestrations are compositions of different Web Services to form a new service. The services called during the orchestration guarantee a given performance to the orchestrater, usually in the form of contracts. These contracts can be used by the orchestrater to deduce the contract it can offer to its own clients, by performing contract composition. An implicit assumption in contract based QoS management is: “the better the component services perform, the better the orchestration’s performance will be”. Thus, contract based QoS management for Web services orchestrations implicitly assumes monotony. In some orchestrations, however, monotony can be violated, i.e., the performance of the orchestration improves when the performance of a component service degrades. This is highly undesirable since it can render the process of contract composition inconsistent. In this paper we define monotony for orchestrations modelled by Colored Occurrence Nets (CO-nets) and we characterize the classes of monotonic orchestrations. We show that few orchestrations are indeed monotonic, mostly since latency can be traded for quality of data. We also propose a sound refinement of monotony, called conditional monotony, which forbids this kind of cheating and show that conditional monotony is widely satisfied by orchestrations. This finding leads to reconsidering the way SLAs should be formulated.

💡 Analysis

Web Service orchestrations are compositions of different Web Services to form a new service. The services called during the orchestration guarantee a given performance to the orchestrater, usually in the form of contracts. These contracts can be used by the orchestrater to deduce the contract it can offer to its own clients, by performing contract composition. An implicit assumption in contract based QoS management is: “the better the component services perform, the better the orchestration’s performance will be”. Thus, contract based QoS management for Web services orchestrations implicitly assumes monotony. In some orchestrations, however, monotony can be violated, i.e., the performance of the orchestration improves when the performance of a component service degrades. This is highly undesirable since it can render the process of contract composition inconsistent. In this paper we define monotony for orchestrations modelled by Colored Occurrence Nets (CO-nets) and we characterize the classes of monotonic orchestrations. We show that few orchestrations are indeed monotonic, mostly since latency can be traded for quality of data. We also propose a sound refinement of monotony, called conditional monotony, which forbids this kind of cheating and show that conditional monotony is widely satisfied by orchestrations. This finding leads to reconsidering the way SLAs should be formulated.

📄 Content

arXiv:0804.4896v2 [cs.NI] 13 May 2008 apport

de recherche ISSN 0249-6399 ISRN INRIA/RR–6528–FR+ENG Thème COM INSTITUT NATIONAL DE RECHERCHE EN INFORMATIQUE ET EN AUTOMATIQUE Monotony in Service Orchestrations Anne Bouillard — Sidney Rosario — Albert Benveniste — Stefan Haar N° 6528 May 2008 Centre de recherche INRIA Rennes – Bretagne Atlantique IRISA, Campus universitaire de Beaulieu, 35042 Rennes Cedex Téléphone : +33 2 99 84 71 00 — Télécopie : +33 2 99 84 71 71 Monotony in Service Orchestrations ∗ Anne Bouillard, Sidney Rosario, Albert Benveniste , Stefan Haar † Theme COM — Systemes communicants ´Equipes-Projets Distribcom Rapport de recherche n° 6528 — May 2008 — 20 pages Abstract: Web Service orchestrations are compositions of different Web Ser- vices to form a new service. The services called during the orchestration guar- antee a given performance to the orchestrater, usually in the form of contracts. These contracts can be used by the orchestrater to deduce the contract it can offer to its own clients, by performing contract composition. An implicit as- sumption in contract based QoS management is: ”the better the component services perform, the better the orchestration’s performance will be”. Thus, contract based QoS management for Web services orchestrations implicitly as- sumes monotony. In some orchestrations, however, monotony can be violated, i.e., the per- formance of the orchestration improves when the performance of a component service degrades. This is highly undesirable since it can render the process of contract composition inconsistent. In this paper we define monotony for orchestrations modelled by Colored Occurrence Nets (CO-nets) and we characterize the classes of monotonic orches- trations. We show that few orchestrations are indeed monotonic, mostly since latency can be traded for quality of data. We also propose a sound refinement of monotony, called conditional monotony, which forbids this kind of cheating and show that conditional monotony is widely satisfied by orchestrations. This finding leads to reconsidering the way SLAs should be formulated. Key-words: web service, orchestrations, contracts, monotony ∗This work was partially funded by the ANR national research program DOTS (ANR-06- SETI-003), DocFlow (ANR-06-MDCA-005) and the project CREATE ActivDoc. † S.Rosario and A. Benveniste are with Irisa/Inria, Campus de Beaulieu, Rennes. A. Bouillard is with Irisa/ENS Cachan Campus de Ker Lann and S.Haar is with Alcatel-Lucent Bell Labs, Kanata, ON,Canada. Monotonie dans les orchestrations de web services R´esum´e : Les orchestrations de services web sont des compositions de ser- vices ´el´ementaires. Ces services, fournissent un ’contrat’ a l’orchestrateur, ce qui garantit une certaine performance de leur service. Ces contrats sont uti- lis´es par l’orchestrateur pour proposer un contrat a un client pour son propre service. Cela se fait par la ’compostion de contrats’. Du point vue de la perfor- mance, la composition de contrats suppose implicitement que ”L’am´elioration de la performance d’un service va rendre l’orchestration plus performante”. La composition de contrats suppose ainsi que les orchestrations sont ”monotones”. Dans quelques orchestrations, cependant, la monotonie peut ne pas ˆetre respect´ee. Lorsque la performance d’un service s’am´eliore, la performance de l’orchestration se d´egrade. Ceci est tres gˆenant car cela rend le processus de composition de contrats invalide. Dans ce rapport, nous d´efinissons la mono- tonie pour les orchestrations mod´elis´ees par des r´eseaux d’occurrence color´es (CO-nets) et nous caract´erisons la classe des orchestrations monotones. Nous d´emontrons que tres peu d’orchestrations sont monotone en pratique, ce qui est largement dˆu a la possibilit´e d’am´eliorer la latence en d´egradant la qualit´e de la r´eponse donn´e. Nous proposons ensuite un raffinement de la monotonie, la ”monotonie conditionnelle”, qui interdit ce type de ’triche’. Nous montrons que la monotonie conditionnelle est tres g´en´eralement satisfaite par les orchestra- tions. Cette ´etude nous mene a reconsid´erer la formulation des contrats dans le cadre des orchestrations de services web. Mots-cl´es : web service, orchestrations, contrats, monotonie Monotony in Service Orchestrations 3 Contents 1 Introduction 3 2 Non-monotonic patterns in CO-nets 5 3 The Orchestration Model: OrchNets 7 3.1 Petri nets, Occurrence nets . . . . . . . . . . . . . . . . . . . . . 7 3.2 Our Model: OrchNets . . . . . . . . . . . . . . . . . . . . . . . . 9 4 Characterizing monotony 12 4.1 Defining monotony . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.2 A global necessary and sufficient condition . . . . . . . . . . . . . 13 4.3 A structural condition for the monotony of workflow nets . . . . 14 4.4 Discussion regarding monotony . . . . . . . . . . . . . . . . . . . 17 5 Refined QoS and Conditional monotony 18 6 Conclusion 19 1 Introduction Web Services and their composit

This content is AI-processed based on ArXiv data.