A Framework for Trusted Services

An existing challenge when selecting services to be used in a service- based system is to be able to distinguish between good and bad services. In this paper we present a trust-based service selection framework. The framework uses a trust model that calculates the level of trust a user may have with a service based on past experience of the user with the service and feedback about the service received from other users. The model takes into account different levels of trust among users, different relationships between users, and different levels of importance that a user may have for certain quality aspects of a service. A prototype tool has been implemented to illustrate and evaluate the work. The trust model has been evaluated in terms of its capacity to adjust itself due to changes in user ratings and its robustness

Decomposing ratings in service compositions

An important challenge for service-based systems is to be able to select services based on feedback from service consumers and, therefore, to be able to distinguish between good and bad services. However, ratings are normally provided to a service as a whole, without taking into consideration that services are normally formed by a composition of other services. In this paper we propose an approach to support the decomposition of ratings provided to a service composition into ratings to the participating services in a composition. The approach takes into consideration the rating provided for a service composition as a whole, past trust values of the services participating in the composition, and expected and observed QoS aspects of the services. A prototype tool has been implemented to illustrate and evaluate the work. Results of some experimental evaluation of the approach are also reported in the paper

Proactive and reactive runtime service discovery: a framework and its evaluation

The identification of services during the execution of service-based applications to replace services in them that are no longer available and/or fail to satisfy certain requirements is an important issue. In this paper we present a framework to support runtime service discovery. This framework can execute service discovery queries in pull and push mode. In pull mode, it executes queries when a need for finding a replacement service arises. In push mode, queries are subscribed to the framework to be executed proactively, and in parallel with the operation of the application, in order to identify adequate services that could be used if the need for replacing a service arises. Hence, the proactive (push) mode of query execution makes it more likely to avoid interruptions in the operation of service-based applications when a service in them needs to be replaced at runtime. In both modes of query execution, the identification of services relies on distance-based matching of structural, behavioural, quality, and contextual characteristics of services and applications. A prototype implementation of the framework has been developed and an evaluation was carried out to assess the performance of the framework. This evaluation has shown positive results, which are discussed in the paper

Configuration of service oriented architectures with semantic technologies based on non-functional requirements

Ова дисертација је фокусирана на примену семантичких технологија за решавање проблема оптималне конфигурације сервисно-оријентисаних архитектура (енгл. Service Oriented Architecture – SOA) на основу нефункционалних захтева корисника. Решење је базирано на проширењу АHP алгоритма за рад са различитим врстама захтева и развоју хеуристичког приступа заснованог на генетичким алгоритмима за решавање проблема оптималне конфигурације. Постојећа решења у овој области су показала изузетно мали ниво персонализације, тј корисницима није дозвољено дефинисање разних софистициранијих врста захтева који осликавају њихове жеље, очекивања и строге захтеве за које захтевају потпуно испуњење. Такође, постојећа решења су била перманентно фокусирана на испуњење захтева функционалности, након чега се врши одабир конфигурације сходно захтевима о смањењу вредности карактеристика које имају тенденцију раста (нпр., цена и време извршавања), односно повећању вредности карактеристика које имају тенденцију опадања (нпр., поузданост и доступност). Међутим, када се посматрају целе фамилије SOA, од посебног значаја постаје проблем конструкције конфигурације при истовременом задовољењу функционалних и нефункционалних захтева. Предложено интегрално решење под називом OptConfSOAFобезбеђује представљање различитих врста захтева (безусловни, условни, захтеви о лексикографском поретку) о нефункционалним карактеристикама и оптималну конфигурацију фамилија SOA на основу дефинисаних захтева. Приступ који се предлаже обезбеђује истовремено задовољење захтева који се тичу функционалности система као и нефункционалних захтева који могу бити различитог нивоа приоритета, односити се на поједине делове или сервисно- оријентисану архитектуру у целости. Предложено решење је опште и није ограничено само на веб сервисе, иако се појам семантичких технологија обично везује за дати домен примене. Решење се може применити у било ком домену у којем се SOA парадигма може применити посматрањем сервиса као било које компоненте (необавезно софтверске) дате функционалности...This dissertation is focused on the application of semantic technologies for solving the problem of optimal configuration of service-oriented architectures (SOA) based on stakeholders’ non-functional requirements. The proposed solution is developed as an extension of the AHP algorithm to allow for processing of different kinds of requirements. To address the problem of optimal configuration of SOA, a heuristic approach based on genetic algorithms has also been proposed and validated. Existing approaches in this field have shown low level of personalization, i.e. stakeholders are neither enabled to define sophisticated requirements that reflect their own expectations and attitudes, nor they are able to indicate hard requirements that have to be fully satisfied. Furthermore, existing approaches were primarily addressing the problem of fulfilling functional requirements, while the selection of an appropriate configuration is driven by the goal of decreasing the values of monotonically decreasing features (e.g., price and execution time) and simultaneous increasing the values of monotonically increasing features (e.g., availability and reliability). By considering the whole SOA families, the problem of configuration based on both functional and nonfunctional requirements gets special importance for research and further applications. The proposed solution, titled OptConfSOAF provides a framework for specification and processing of different kinds of requirements (unconditional, conditional, and requirements about lexicographical order) over non-functional features, and further optimal configuration of SOA families. The proposed approach provides simultaneous fulfillment of functional requirements (i.e., requirements related to the system’s functionalities) and non-functional requirements, where the latter could be defined with different level of importance, for specific parts of a SOA-based system or the system in its entirety. The proposed solution is general and is not bound to web services, even though semantic technologies are often associated with that domain. Since the solution considers a service as a component (no mandatory to be software component) with the specified functionality, it is applicable and easily adaptable to any specific application domain where SOA paradigm may be applied..