Eva Kühn

VIP-MDBS: a logic multidatabase system

We present a multidatabase management system built in Vienna Integrated Prolog (VIP) for cooperative management of autonomous databases. Data in different databases may differ with respect to naming, structures and value types. VIP-MDBS (VIP MultiDataBase System) allows the ability to manipulate them jointly and in a non-procedural way. Its features are similar to those of the relational multidatabase language MSQL, but adapted to logic programming. We introduce the concept of so-called semantic relations, a concept which stems from the extension of global views by deductiveness. VIP-MDBS allows for representation of intentional data and formulation of recursive multiple queries.

General purpose work flow languages

Work flow management requires language support for work flow specification and task specification. Many approaches and systems for work flow management therefore offer at least one new language for work flow specification; task specification is usually done in a traditional language. This is motivated in particular by the fact that many components already exist and the task of the work flow tool is the specification of the interaction between these components. The intention of this article is to demonstrate that a general purpose programming language can serve both aspects. We do not really see the need to develop yet another language that a user or application programmer must learn. If an existing programming language like C or Prolog is extended towards work flow capabilities, it is easy to reuse autonomous existing software components and to build interfaces among them.

Automated measurement of API usability

ContextUsability is an important software quality attribute for APIs. Unfortunately, measuring it is not an easy task since many things like experienced evaluators, suitable test users, and a functional product are needed. This makes existing usability measurement methods difficult to use, especially for non-professionals. ObjectiveTo make API usability measurement easier, an automated and objective measurement method would be needed. This article proposes such a method. Since it would be impossible to find and integrate all possible factors that influence API usability in one step, the main goal is to prove the feasibility of the introduced approach, and to define an extensible framework so that additional factors can easily be defined and added later. MethodA literature review is conducted to find potential factors influencing API usability. From these factors, a selected few are investigated more closely with usability studies. The statistically evaluated results from these studies are used to define specific elements of the introduced framework. Further, the influence of the user as a critical factor for the frameworks feasibility is evaluated. ResultsThe API Concepts Framework is defined, with an extensible structure based on concepts that represent the users actions, measurable properties that define what influences the usability of these concepts, and learning effects that represent the influence of the users experience. A comparison of values calculated by the framework with user studies shows promising results. ConclusionIt is concluded that the introduced approach is feasible and provides useful results for evaluating API usability. The extensible framework easily allows to add new concepts and measurable properties in the future.

Algebraic foundation of a data model for an extensible space-based collaboration protocol

Space-based computing middleware offers a data driven style for the coordination of processes. The interaction requirements between these processes can be complex, and the template matching coordination law of the Linda and JavaSpaces model is not sufficient. Moreover, the usage should not be limited to a single platform. Several authors have proposed coordination extensions, but besides the suggestion to use XML or RDF based query facilities, a formalization of a general and extensible space-based coordination model has not yet been realized. In this paper we present the algebraic data structures and the coordination model based on a navigational query language for the extensible virtual shared memory architecture, and show how they can be adapted to support arbitrary coordination laws by the introduction of user-definable matchmaker and selector functions. The platform independence is achieved through a language independent communication protocol. The formal specification of the data model is the necessary basis for this protocol.

Towards an Architectural Framework for Agile Software Development

One of the ideas of agile software development is to respond to changes rather than following a plan. Constantly changing businesses result in changing requirements, to be handled in the development process. Therefore, it is essential that the underlying software architecture is capable of managing agile business processes. However, criticism on agile software development states that it lacks paying attention to architectural and design issues and therefore is bound to engender suboptimal design-decisions. In this paper we propose an architectural framework for agile software development, that by explicitly separating computational, coordinational, and communicational models offers a high degree of flexibility regarding architectural and design changes introduced by agile business processes. The framework strength is facilitated by combining the characteristics and properties of state-of-the-art middleware architectural styles captured in a simple API. The benefit of our approach is a clear architectural design with minimized effects of changes the models have on each other, accompanied by an efficient realization of new business requirements.

An Execution Model for Distributed Database Transactions and Its Implementation in VPL

We present an execution model for distributed transactions that can be employed for multidatabase systems. We use the Flex Transaction model that has been proposed as a highly general and flexible tool for the specification of distributed transactions and extend it by allowing nested and possibly recursive transaction specifications. We show how a given transaction specification and its execution model can be mapped into a representation in a new concurrent Prolog language, the VPL (Vienna Parallel Logic) language. The representation in VPL can be considered as an executable specification. We show some optimizations concerning this mapping and define a significant subclass of Flex Transactions with a declarative representation in VPL that can be modeled by AND/OR structures. We argue that it is more advantageous to use VPL directly for the transaction specification because it provides more flexibility and more control aspects than the Flex Transaction model.

Peer-Based Programming Model for Coordination Patterns

Modern distributed software systems must integrate in near-time parallel processes and heterogeneous information sources provided by active, autonomous software systems. Such lively information sources are e.g. sensory data, weather data, traffic data, or booking data, operated by independent distributed sites. The complex integration requires the coordination of these data flows to guarantee consistent global semantics. Design, implementation, analysis and control of distributed concurrent systems are notoriously complex tasks. Petri Nets are widely used to model concurrent activities. However, a higher-level programming abstraction is needed. We propose a new programming model for modeling concurrent coordination patterns, which is based on the idea of “peer workers” that represent re-usable coordination and application components. These components encapsulate behavior, structure distributed data and control flow, and allow integration of pre-existing service functions. A domain-specific language is presented. The usability of the peer-based programming model is evaluated with the Split/Join pattern.

Space-Based Architectures as Abstraction Layer for Distributed Business Applications

For constantly changing businesses, it is essential that the underlying software architecture is capable of managing agile business processes and meeting future business needs. Decoupling between applications and services in distributed systems is addressed by e. g., service-oriented architectures. On the other hand, applications and its underlying middleware are still tightly coupled with respect to the middlewares architectural style. As a result of the tight coupling middleware adaptations introduced due to e. g., new business requirements can affect the application as well. In this paper we propose the concept of space-based architecture (SBA), that allows decoupling distributed applications with respect to the underlying middleware architecture by combining the characteristics and properties of state-of-the-art middleware architectural styles captured in a simple API. The benefit of our approach is minimal application adaptations in case of changing the underlying middleware architectural style, which allows for more efficient realization of new business requirements.

Foundations for a Model-Driven Integration of Business Services in a Safety-Critical Application Domain

Current architectures for systems integration provide means for forming agile business processes by manually or dynamically configuring the components.However, a major challenge in the safety-critical Air Traffic Management (ATM) domain is to interconnect business services taking into account service level agreements regarding the underlying network infrastructures. In such domains, manual configuration is forbidden due to the resulting error-prone and time-consuming tasks, while dynamic configuration is not allowed due to nondeterministic decision making. In this paper we propose a model-driven system configuration approach (MDSC),which explicitly models the components of the network infrastructures and their capabilities to automatically generate a logical network configuration. Based on an industry application example, we show the feasibility of the proposed integration platform in the ATM domain and discuss the advantages and limitations.

Applying Swarm Intelligence Algorithms for Dynamic Load Balancing to a Cloud Based Call Center

Load-Balancing is a significant problem in heterogeneous distributed systems. Nowadays we face an extreme growth of computer systems and their complexities requiring advanced intelligent solutions for load-balancing that lead to autonomic self-organizing infrastructures. There is still a need to prove that real use cases can benefit from self-* approaches. We developed a pattern, called SILBA, for such an infrastructure based on decentralized control, intelligent and exchangeable policies for load-balancing, and black-board based communication mechanisms. Different types of algorithms (both intelligent and unintelligent) were plugged into SILBA. In this paper, we present one particular use-case – a Call Center that is operated in a Cloud environment.