Complex Distributed Software Systems Research Articles

Improving Conformance of Web Services: A Constraint-based Model-driven Approach

Web services have been widely used to develop complex distributed software systems in the context of Service Oriented Architecture (SOA). As a standard for describing Web services, the Web Service Description Language (WSDL) provides a universal mechanism to describe the service’s functionalities for the service consumers. However, the current WSDL only provides the description of the interfaces to a Web Service without any restrictions or assumptions on how to properly invoke the service, resulting in divergent understanding of the Web service’s behavior between the service developer and service consumer. A particular challenge is how to make explicit the various behavior assumptions and restrictions of a service (for the user), and make sure that the service implementation conforms to them (for the developer). In this article, we propose a constraint-based model-driven approach to improving the behavior conformance of Web services. In our approach, constraints are introduced in an extended WSDL, called CxWSDL, to formally and explicitly express the implicit restrictions and assumptions on the behavior of a Web service, and then the predefined constraints are used to derive test cases in a model-driven manner to test the service implementation’s conformance to its behavior constraints from the user’s perspective. An empirical study involving four real-life Web services was conducted to evaluate the effectiveness of our approach, and four actual inconsistencies were discovered.

Mind Your Outcomes: The ΔQSD Paradigm for Quality-Centric Systems Development and Its Application to a Blockchain Case Study

This paper directly addresses a long-standing issue that affects the development of many complex distributed software systems: how to establish quickly, cheaply, and reliably whether they can deliver their intended performance before expending significant time, effort, and money on detailed design and implementation. We describe ΔQSD, a novel metrics-based and quality-centric paradigm that uses formalised outcome diagrams to explore the performance consequences of design decisions, as a performance blueprint of the system. The distinctive feature of outcome diagrams is that they capture the essential observational properties of the system, independent of the details of system structure and behaviour. The ΔQSD paradigm derives bounds on performance expressed as probability distributions encompassing all possible executions of the system. The ΔQSD paradigm is both effective and generic: it allows values from various sources to be combined in a rigorous way so that approximate results can be obtained quickly and subsequently refined. ΔQSD has been successfully used by a small team in Predictable Network Solutions for consultancy on large-scale applications in a number of industries, including telecommunications, avionics, and space and defence, resulting in cumulative savings worth billions of US dollars. The paper outlines the ΔQSD paradigm, describes its formal underpinnings, and illustrates its use via a topical real-world example taken from the blockchain/cryptocurrency domain. ΔQSD has supported the development of an industry-leading proof-of-stake blockchain implementation that reliably and consistently delivers blocks of up to 80 kB every 20 s on average across a globally distributed network of collaborating block-producing nodes operating on the public internet.

A METHODOLOGY FOR MODELING MULTI-AGENT SYSTEMS USING NESTED PETRI NETS

In the past two decades, multi-agent systems have emerged as a new paradigm for conceptualizing large and complex distributed software systems. Even though there are many conceptual frameworks for using multi-agent systems, there is no well established and widely accepted method for the representation of multi-agent systems. We adapt a well-known formal model, predicate transition nets, to include the notions of dynamic structure, agent communication and coordination to address the representation problems. This paper presents a comprehensive methodology for modeling multi-agents based on the extensions. We demonstrate our modeling approach with an example. Several case studies on different application domains from our previous works are also discussed.

Distributed embedded control system design with verification support

The problem of integrating a method of formal model verification into the process of designing complex distributed software systems is considered. It is proposed to use a platform-independent model as the central object of the design. It is developed on the basis of a system core responsible for logical management of the entire system. The proposed approach makes it possible to increase the quality of the software and to guarantee the specification compliance. The proposed method is tested on a real control system of a vessel’s power supply.

Berlin Brain–Computer Interface—The HCI communication channel for discovery

The investigation of innovative Human–Computer Interfaces (HCI) provides a challenge for future interaction research and development. Brain–Computer Interfaces (BCIs) exploit the ability of human communication and control bypassing the classical neuromuscular communication channels. In general, BCIs offer a possibility of communication for people with severe neuromuscular disorders, such as amyotrophic lateral sclerosis (ALS) or complete paralysis of all extremities due to high spinal cord injury. Beyond medical applications, a BCI conjunction with exciting multimedia applications, e.g., a dexterity discovery, could define a new level of control possibilities also for healthy customers decoding information directly from the user's brain, as reflected in EEG signals which are recorded non-invasively from the scalp. This contribution introduces the Berlin Brain–Computer Interface (BBCI) and presents set-ups where the user is provided with intuitive control strategies in plausible interactive bio-feedback applications. Yet at its beginning, BBCI thus adds a new dimension in HCI research by offering the user an additional and independent communication channel based on brain activity only. Successful experiments already yielded inspiring proofs-of-concept. A diversity of interactive application models, say computer games, and their specific intuitive control strategies are now open for BCI research aiming at a further speed up of user adaptation and increase of learning success and transfer bit rates. BBCI is a complex distributed software system that can be run on several communicating computers responsible for (i) the signal acquisition, (ii) the data processing and (iii) the feedback application. Developing a BCI system, special attention must be paid to the design of the feedback application that serves as the HCI unit. This should provide the user with the information about her/his brain activity in a way that is intuitively intelligible. Exciting discovery applications qualify perfectly for this role. However, most of these applications incorporate control strategies that are developed especially for the control with haptic devices, e.g., joystick, keyboard or mouse. Therefore, novel control strategies should be developed for this purpose that (i) allow the user to incorporate additional information for the control of animated objects and (ii) do not frustrate the user in the case of a misclassification of the decoded brain signal. BCIs are able to decode different information types from the user's brain activity, such as sensory perception or motor intentions and imaginations, movement preparations, levels of stress, workload or task-related idling. All of these diverse brain signals can be incorporated in an exciting discovery scenario. Modern HCI research and development technologies can provide BCI researchers with the know-how about interactive feedback applications and corresponding control strategies.

Agent oriented programming with Ada'95

This paper shows the suitability of Object Oriented Programming language Ada'95 for Agent Oriented Programming. Agent oriented programming relies on the assumption, that a complex distributed software system can be programmed as a set of communicating, interacting, knowledge base entities called (software) agents. In this work we study the financial market case by introducing new modeling and implementation tools in order to simulate and understand some properties of the market evolution process. Object -Oriented modeling of social systems requires the integration of new concepts related to mental processes such as learning, planning, knowledge representation and communication. If one defines an agent as an object combination of mental state to perceive its environment and achieve some goals, a knowledge base to hold its memory and an interfacing communication with other entities then all the above properties could be fulfilled. In this paper we describe a method for the use of Ada object Oriented Programming language for the implementation of a MAS plate-form. The results obtained in the experimental part lead to some parameters of the model validation, like the agent's performance in increasing their own wealth and their adapted behavior throughout the evolving market.