Dejan Škvorc

Programming Languages for End-User Personalization of Cyber-Physical Systems

The increased usage of smart devices and appliances opens new venues to build applications that integrate physical and virtual world into consumer-oriented context-sensitive cyber-physical systems (CPS). Since physical processes are dynamic, concurrent, event-driven, and powered by various sensors, controllers, and actuators, a combination of service-oriented architecture (SOA) and event-driven architecture (EDA) is the most promising software architecture for virtualization of heterogeneous components into interoperable application building blocks. In this paper, we propose a CPS design paradigm where devices, such as sensors, controllers, and actuators, are virtualized into environmental services. To support event-driven workflow coordination, we designed special-purpose coopetition services that provide fundamental EDA characteristics, such as decoupled interactions, many-to-many communication, publish/subscribe messaging, event triggering, and asynchronous operations. Based on these two groups of services, we present a design of event-driven service composition languages that target two distinct groups of developers. Using Python as an example, we present a transformation of arbitrary general-purpose programming language into an event-driven service composition language for developers familiar with parallel programming using operating system kernel mechanisms. On the other hand, we present the design and cognitive evaluation of an end-user language, whose 2D tabular workspace resembles the process of sketching an automation application on a sheet of paper.

Performance evaluation of Websocket protocol for implementation of full-duplex web streams

Besides traditional synchronous HTTP request-response communication paradigm that was used on the Web for decades, modern Web services require more flexible communication system that enables asynchronous messaging between clients and servers, as well as server-initiated data delivery. Among several Web-based asynchronous communication paradigms emerged recently, the Websocket protocol and corresponding Websocket API are accepted as a pivotal framework for implementation of full-duplex asynchronous Web streams. In this paper, we evaluate the performance of the Websocket protocol with respect to underlying TCP protocol. We compare the two against the latency and amount of generated network traffic. The results show that, except a small overhead imposed due to initial handshaking, Websocket-based communication does not consume any more network traffic than plain TCP based communication. However, it is still slightly inferior in terms of latency.

Virtual Network for Development and Execution of Service-Oriented Applications

Service-oriented computing represents an emerging paradigm where software functionalities are delivered to consumers as services rather than products. Service-oriented applications consist of services available on the Internet and the coordination logic that binds independent services into the application-specific workflow. Execution of distributed applications in shared and dynamic Internet environments faces two open issues: security of service invocation and dependence of coordination logic on physical distribution of services. In this paper, we propose a model for development and execution of service-oriented applications based on a virtual network. Virtual network provides the environment for secure execution of service-oriented applications independent of the physical network configuration. Virtual network is based on service-oriented architecture, which enables run-time management of virtual network by users and distributed applications

Formal Model for Data Dependency Analysis between Controls and Actions of a Graphical User Interface

1 Abstract—End-user development is an emerging computer science discipline that provides programming paradigms, techniques, and tools suitable for users not trained in software engineering. One of the techniques that allow ordinary computer users to develop their own applications without the need to learn a classic programming language is a GUI-level programming based on programming-by-demonstration. To build wizard-based tools that assist users in application development and to verify the correctness of user programs, a computer-supported method for GUI-level data dependency analysis is necessary. Therefore, formal model for GUI representation is needed. In this paper, we present a finite state machine for modeling the data dependencies between GUI controls and GUI actions. Furthermore, we present an algorithm for automatic construction of finite state machine for arbitrary GUI application. We show that proposed state aggregation scheme successfully manages state explosion in state machine construction algorithm, which makes the model applicable for applications with complex GUIs.

Geospatial publish / subscribe systems for the Internet of Things

The concept of the Internet of Things (IoT) describes the physical objects (smart mobile devices, various types of sensor devices) which have a range of sensors and are connected to the Internet. One of the main challenges for data processing in the Internet of things is to quickly and effectively provide the delivery of sensor data to interested parties in real time. Publish/subscribe systems are seen as appropriate for this purpose as they offer an infrastructure for almost immediate delivery of notifications to interested subscribers. In traditional publish/subscribe systems, subscriptions define content which is interesting to the user and that is usually a multidimensional interval of an attribute space in which the notifications are defined. This type of subscriptions is not appropriate to the Internet of things, where the sensor data, except for the value of the measured quantity, usually include a geospatial component (e.g. a point, line or polygon) which refers to the geographical area in which the measurement was made. Therefore, the subscription should also consist of a geospatial object that represents a geographic area of interest to subscribers and additional data in the form of traditional attribute space intervals that are used for continuous comparison with the upcoming notifications. This paper presents the existing centralized and distributed publish/subscribe systems, and proposes the idea of geospatial publish/subscribe systems.

Object-oriented programming model for synthesis of domain-specific application development environment

Domain-specific languages are becoming increasingly popular allowing experts to focus on solving their specific problems instead of focusing on the means needed. Various domain-specific tools have been developed that allow experts to design systems and workflows by connecting graphical elements together. These elements have to either be predefined by a developer, or created by the expert by combining simpler objects together. The issue of bridging the gap between the semantics of the problem and the technology used to implement the solution therefore stays with the software developer. In this article, we propose an enhancement of the object oriented programming paradigm that is aimed at easier conversion of the technology (objects, classes) into their visual representation. We propose a high-level implementation domain to expert domain compiler that is able to automatically generate domain-specific representations of available technical components. The compiler is designed as a general-purpose domain-agnostic agent, which generates appropriate domain-specific representations of the technology using technical data obtained from the system and domain-specific data provided as a set of rules. This paper discusses the requirements placed on the architecture of the input system, the design requirements for the domain-agnostic compiler and the data needed for a complete description of the domain specifics.

Android-powered web server for volunteer-based environment sensing

Many people today are using smartphones and similar forms of mobile computers in every aspect of their lives as a standard and undetachable personal outfit. Besides the significant amount of computing power, storage capacity, and communication capabilities, these devices are equipped with a set of embedded sensors. This makes them not only sufficient for being a reliable on-site assistants, but also powerful enough to deliver sensory information collected from the environment to the remote users through the Internet. Having an open community of smartphone users involved as data sources into the environment sensing program reduces the need for a dedicated sensory infrastructure preinstalled throughout the environment, yet providing a satisfactory level of territory coverage. The necessary prerequisite is, however, that users can contribute effortlessly, with minimum or no overhead compared to a normal smartphone usage. In this paper, we present a prototype implementation of an Android-powered web server for autonomous capture and delivery of sensory information from a mobile device to the remote users. A modular software framework is described for seamless extension of the server with support for new types of sensors as new models of devices appear on the market, while still providing basic level of interoperability with these sensors until the server gets upgraded.

Designing the programming assignment for a university compiler design course

This paper analyzes the key properties of a programming assignment for a university compiler design course. After an overview of popular choices used at several universities in the world, we describe the assignment given to students of the Programming Language Translation undergraduate course at the University of Zagreb, Faculty of Electrical Engineering and Computing, and provide the rationale behind several design decisions through an analysis of its evolution in recent years. While most compiler programming assignments are based on tools like lexer and parser generators, our students actually build slightly simplified versions of these tools themselves. We discuss our experiences with this programming assignment over the last three years and qualitative differences in the results between this assignment and the tool based assignment we had been using before.