Showing papers presented at "International Symposium on Object/Component/Service-Oriented Real-Time Distributed Computing in 2006"

Model-driven development: its essence and opportunities

Abstract: This paper gives a short overview of model-driven development - an approach to software development in which high-level models play a fundamental role. First, the problems that plague current programming approaches are analyzed. This is followed by a short description of the essential features of model-driven development and the potential benefits that it can bring. The results achieved in industrial practice are reviewed briefly, followed by an analysis of current impediments towards greater levels of adoption of this approach and what needs to be done about to overcome them.

RTSTREAM: real-time query processing for data streams

Abstract: Many real-time applications, such as traffic control systems, surveillance systems and health monitoring systems, need to operate on continuous unbounded streams of data. These applications also have inherent real-time performance requirements that have to be met under high-volume, time-varying incoming data streams. In this paper, we present a real-time data stream query model named PQuery, which provides periodic real-time queries on data streams for the aforementioned real-time applications. To support the PQuery model, a real-time data stream management prototype system named RTSTREAM is developed to provide deadline miss ratio guarantees for periodic queries over continuous and unbounded data streams. We describe the periodic query semantics and discuss why the periodic query model is appropriate for real-time applications. To handle irregular data arrival patterns and query workloads, we propose data admission as an overload protection mechanism. We conduct performance studies with synthetic workloads as well as real workloads from network traffic monitoring applications. The experimental results show that the proposed periodic query model suits the need of the real-time applications and the data admission overload protection approach is effective in managing the workload fluctuations.

Architecture classification for SOA-based applications

Abstract: The architecture of SOA-based applications is different from traditional software architecture where the architecture is mainly static. The architecture of an SOA-based application is dynamic, i.e., the application may be composed at runtime using existing services. Thus SOA has provided a new direction for software architecture study, where the architecture is determined at runtime and architecture can be dynamically changed at runtime to meet the new software requirements. This paper proposes an architecture classification scheme for SOA-based applications. Using this classification, several well-known SOA-based applications are reviewed including the architectures proposed and adopted by major computer companies and standard organizations. The architecture classification provides a unified way to evaluate a variety of architectures for SOA-based applications.

Real-time garbage collection for Java

Abstract: Automatic memory management or garbage collection greatly simplifies the development of large systems. However, garbage collection is usually not used in real-time systems due to the unpredictable temporal behavior of current implementations of a garbage collector. In this paper we propose a concurrent collector that is scheduled periodically in the same way as ordinary application threads. We provide an upper bound for the collector period so that the application threads never run out of memory.

Load balancing techniques for distributed stream processing applications in overlay environments

Abstract: Service overlays that support distributed stream processing applications are increasingly being deployed in wide-area environments. The inherent heterogeneous, dynamic and large-scale nature of these systems makes it difficult to meet the quality of service (QoS) requirements of the distributed stream processing applications. In this paper we address the load balancing problem for distributed stream processing applications and present a decentralized and adaptive algorithm that allows the composition of distributed stream processing applications on the fly across a large-scale system, while satisfying their QoS demands. The algorithm fairly distributes the load on the resources and adapts dynamically to changes in the resource utilization or the QoS requirements of the applications. Our experimental results demonstrate the scalability, efficiency and performance of our approach.

Dependability driven integration of mixed criticality SW components

Abstract: Mapping of software onto hardware elements under platform resource constraints is a crucial step in the design of embedded systems. As embedded systems are increasingly integrating both safety-critical and non-safety critical software functionalities onto a shared hardware platform, a dependability driven integration is desirable. Such an integration approach faces new challenges of mapping software components onto shared hardware resources while considering extra-functional (dependability, timing, power consumption, etc.) requirements of the system. Considering dependability and real-time as primary drivers, we present a systematic resource allocation approach for the consolidated mapping of safety critical and non-safety critical applications onto a distributed platform such that their operational delineation is maintained over integration. The objective of our allocation technique is to come up with a feasible solution satisfying multiple concurrent constraints. Ensuring criticality partitioning, avoiding error propagation and reducing interactions across components are addressed in our approach. In order to demonstrate the usefulness and effectiveness of the mapping, the developed approach is applied to an actual automotive system.

Tree-based WCET analysis on instrumentation point graphs

Abstract: This paper presents a framework for combining low-level measurement data through high-level static analysis techniques on instrumented programs in order to generate WCET estimates, for which we introduce the instrumentation point graph (IPG). We present the notion of iteration edges, which are the most important property of the IPG from a timing analysis perspective since they allow more path-based information to be integrated into tree-based calculations on loops. The main focus of this paper, however, is an algorithm that performs a hierarchical decomposition of an IPG into an Itree to permit tree-based WCET calculations. The Itree representation supports a novel high-level structure, the meta-loop, which enables iteration edges to be merged in the calculation stage. The timing schema required for the Itree is also presented. Finally, we outline some conclusions and future areas of interest.

Dynamically deploying Web services on a grid using Dynasoar

Abstract: Dynasoar is an infrastructure for dynamically deploying Web services over a grid or the Internet. It enables an approach to grid computing in which distributed applications are built around services instead of jobs. Dynasoar automatically deploys a service on an available host if no existing deployments exist, or if performance requirements cannot be met by existing deployments. This is analogous to remote job scheduling, but offers the opportunity for improved performance as the cost of moving and deploying the service can be shared across the processing of many messages. A key feature of the architecture is that it makes a clear separation between Web service providers, who offer services to consumers, and host providers, who offer computational resources on which services can be deployed, and messages sent to them processed. Separating these two components and defining their interactions, opens up the opportunity for interesting new organisational/business models.

Incorporating situation awareness in service specifications

Abstract: Service-oriented architecture has the major advantage of enabling rapid composition of distributed applications from various services, and has become increasingly popular for many large-scale service-based systems in various application areas, including scientific collaboration, e-business, health care, military, and homeland security. Situation awareness (SAW) is the capability of the entities in a service-based system to be aware of the situation changes and automatically adapt themselves to such changes to satisfy user requirements, including security and privacy. The continuing evolutions of the entities and environment makes SAW one of the most desired features to support dynamic adaptive computing in service-based systems. In this paper, the relationship between contexts/situations and services in situation-aware service-based systems is identified and an extension of OWL-S with situation ontology, called SAW-OWL-S, incorporates SAW in service specifications is presented. An approach to generating service specifications for situation-aware service-based systems using SAW-OWL-S and the system diagram of situation-aware service-based systems using SAW-OWL-S are presented.

Looking ahead in open multithreaded transactions

Abstract: Open multithreaded transactions constitute building blocks that allow a developer to design and structure the execution of complex distributed systems featuring cooperative and competitive concurrency in a reliable way. In this paper we describe an optimization to the standard open multithreaded transaction model that does not impose any participant synchronization when committing a transaction, but still provides the same execution semantics. This optimization - letting participants "look ahead" and continue their execution on the outside of the transaction - makes it possible to speed up the execution of in individual transaction with multiple participants tremendously. The paper describes all technical issues that had to be solved, e.g. adapting concurrency control of transactional objects to be look-ahead aware, adapting joining rules for look-ahead participants, and re-defining exception handling in the presence of look-ahead.

Predictability of earliest deadline zero laxity algorithm for multiprocessor real-time systems

Abstract: Validation methods for hard real-time jobs are usually performed based on the maximum execution time. The actual execution time of jobs are assumed to be known only when the jobs arrive or not known until they finish. A predictable algorithm must guarantee that it can generate a schedule for any set of jobs such that the finish time for the actual execution time is no later than the finish time for the maximum execution time. It is known that any job-level fixed priority algorithm (such as earliest deadline first) is predictable. However, job-level dynamic priority algorithms (such as least laxity first) may or may not. In this paper, we investigate the predictability of a job-level dynamic priority algorithm EDZL (earliest deadline zero laxity). We show that EDZL is predictable on the domain of integers regardless of the knowledge of the actual execution times. Based on this result, furthermore, we also show that EDZL can successfully schedule any periodic task set if the total utilization is not greater than (m + 1)/2, where m is the number of processors.

A space-efficient caching mechanism for flash-memory address translation

Abstract: While flash memory has been widely adopted for various embedded systems, space efficiency with reasonable performance has become a critical issue for the design of the flash-memory translation layer. The target of this paper is to improve the performance of existing designs by proposing a search-tree-like caching mechanism for efficient address translation. A replacement strategy with a low time complexity is presented to monitor the access status of recently used LBA's. The proposed caching mechanism and replacement strategy were shown being highly effective in the reducing of the address translation time over popular translation layer designs, such as NAND, where realistic workloads were used for experiments.

Scheduling non-preemptive periodic tasks in soft real-time systems using fuzzy inference

Abstract: Many scheduling algorithms have been studied to guarantee the time constraints of real-time processes. Scheduling decision of these algorithms is usually based on parameters which are assumed to be crisp. However, in many circumstances the values of these parameters are vague. The vagueness of parameters suggests that we make use of fuzzy logic to decide in what order the requests should be executed to better utilize the system and as a result reduce the chance of a request being missed. We have proposed a new fuzzy algorithm called highest fuzzy priority first. The performance of this algorithm is compared with the well-known earliest deadline first algorithm through simulation. For both algorithms, tasks are considered to be non-preemptable. Simulation results show that this fuzzy approach outperforms the earliest deadline first has algorithm in that it decreases the number of missed deadlines and serves more important tasks better.

Accounting system: a fine-grained CPU resource protection mechanism for embedded system

Abstract: In ubiquitous computing environments, our daily lives will be made convenient by embedded intelligent devices. Those devices, such as car navigation systems, personal digital assistances, and cellular phones, provide various kinds of the complex services. Those devices are networked with each other and provide complicated services, through the Internet. While they provide useful services, there is an increasing possibility of security attacks, which include the unexpected execution of unsecure codes. Current information appliances have not yet fully embodied a resource protection mechanism that prevents misbehaved applications from consuming the whole CPU capacity of system resources. In this paper, we propose accounting system, and describe its design and implementation. The system is a resource monitoring and restriction system that has the purpose of improving the system's reliability and security. We developed the system on Linux. Our system is a very generic to offer various services, such as security improvement, overload control, and class-based accounting, that require CPU resource control.

An infrastructure for adaptive fault tolerance on FT-CORBA

Abstract: The fault tolerance provided by FT-CORBA is basically static, that is, once the fault tolerance properties of a group of replicated processes are defined, they cannot be modified in runtime. A support for dynamic reconfiguration of the replication would be highly advantageous since it would allow the implementation of mechanisms for adaptive fault tolerance, enabling FT-CORBA to adapt to the changes that can occur in the execution environment. In this paper, we propose a set of extensions to the FT-CORBA infrastructure in the form of interfaces and object service implementations, enabling it to support dynamic reconfiguration of the replication.

Complexity management for composable real-time systems

Abstract: Embedded real-time systems are becoming increasingly complex due to ever increasing size and functionality so that complexity management is of growing importance, especially in dependable hard real-time systems development, where errors caused by complexity can have fatal consequences. This paper systematically characterizes different kinds of complexity: system-level complexity, component interface complexity, and component implementation complexity. The effects of the different kinds of complexity are described and it is explained why minimizing system-level complexity should be a principal goal of any distributed embedded real-time systems architecture. The concept of system-level components is introduced as a solution to the problem of system-level complexity during the integration process.

Embedded sensor networked operating system

Abstract: Recently, the availability of cheap and small micro sensor node and low power wireless communication give a contribution of enhanced developments of wireless sensor network application in real society. Furthermore, middlewares and operating systems for convenience on development of sensor network application are essentially needed. In this paper, we introduce a sensor network operation system, Nano-Qplus platform, which is flexible, dynamic, and easy manageable for sensor network application programmers. Furthermore, for the purpose of performance evaluation, we compare Nano-Qplus to other sensor network operating systems related to memory read/write time and task creation latency. The results of performance analysis shows that Nano-Qplus offers enhanced advantages that other sensor network operating systems, so we can notice Nano-Qplus is easily applied to real sensor network applications.

Using the FOMDA approach to support object-oriented real-time systems development

Abstract: This paper tackles the problem of ever changing embedded systems non-functional requirements, specially the architectural ones. It proposes a solution based on features model and MDA standards, which is called features-oriented model-driven architecture (FOMDA). This proposal can be used to help application designer in defining the mappings and transformations of UML models to as many target platforms as wished. This is done by configuring model-to-model and model-to-code transformations over tiers, where every tier represents some target platform properties that the system must be mapped and transformed to. To validate the proposal a case study related to the development of an embedded real-time system is presented, detailing how to transform a generic high-level UML model to a model specific for a given target platform. Obtained results are optimistic and conclude that the FOMDA approach can make designers re-think their current development process to make it more decoupled from a specific target platform.

FP/FIFO feasibility conditions with kernel overheads for periodic tasks on an event driven OSEK system

Abstract: In this paper we show how to take into account kernel overheads in classical real-time feasibility conditions for fixed priority (FP) scheduling where tasks having the same fixed priority are scheduled FP/FIFO. We consider the periodic task model with arbitrary deadlines and an event driven OSEK kernel. The feasibility conditions are based on the worst case response time computation of the tasks. We identify the sources of kernel overheads that influence the response time of the tasks. In such a system the overheads are due to the context switching that activates/terminates and reschedules tasks and to the granularity of the periodic timer used to implement the periodic task model. We show how to take into account those overheads in the classical FP/FIFO feasibility conditions. We compare the worst case response time obtained with kernel overhead to the response time obtained on a real event driven OSEK implementation. We show that the kernel overheads cannot be neglected and that the theoretical results are valid and can be used for a real-time dimensioning.

Java Virtual Machine monitoring for dependability benchmarking

Abstract: A monitoring infrastructure is a key component in each task aimed at evaluating the dependability of a system. This paper presents a monitoring infrastructure for the Java Virtual Machine (JVM), which is starting to be employed in mission and safety critical application, often with real-time requirements. This infrastructure, named JVMMon, collects data about both the state and the failures of the monitored Virtual Machine. The state of the JVM was defined according to the Java Virtual Machine specification. JVMMon is constituted by three components: a monitoring agent which collects data from the monitored VM; a local monitor daemon that receives data from such agent and updates the state of the JVM; a data collector, which stores events and state snapshots in a database. The impact on the performance of the JVM has been evaluated running the SPEC JVM98 benchmark suite.

A fault-tolerant model of wireless sensor-actor network

Abstract: In a wireless sensor and actor network (WSAN), a group of sensors, actors, and actuation devices are geographically distributed and linked by wireless networks. Sensors gather information for an event occurring in the physical world and send them to actors. Actors can perform appropriate actions on actuation devices by making a decision on receipt of sensed information from sensors. Sensors are low cost, low powered devices with limited energy, computation, and wireless communication capabilities. Sensors may not only stop by fault but also suffer from arbitrary faults. Furthermore, wireless communication is less reliable due to noise and shortage of power of sensors. Reliable realtime communication among sensors, actors, and actuation devices is required in WSAN applications. In order to realize the reliability and realtimeness, we newly propose a multi-actor/multi-sensor (MAMS) model where each sensor sends sensed information to multiple actors and each actor receives sensed information from multiple sensors in an event area. Actors are required to causally/totally order events from multiple sensors and actions on actuation devices. In addition, multiple actors may perform actions on receipt of sensed information. Multiple redundant executions of an action on each device have to be prevented and conflicting actions on each device from multiple actors have to be serialized. In this paper, we discuss how to realize reliable, ordered delivery of sensed information to actors from sensors on the basis of global time and how to reliably and non-redundantly perform actions with realtime constraints.

Java framework for distributed real-time embedded systems

Abstract: This paper presents the evaluation of a multithread distributed real-time object-oriented platform. A communication API was developed to increase functionalities of an API that implements the real-time specification for Java standard, extending it to cover embedded distributed applications. Real-time restrictions of the communication are ensured by a time-out mechanism. The API can be adapted to be used with different underlying network and physical mediums. The development focused on restrictive embedded platforms with low performance and small memory. An evaluation in terms of the fulfillment of timing constraints, and memory footprint is presented for a CAN-bus network. The results also demonstrate the timely correctness provided by the communication API running over an RTSJ implementation.

Formal modeling and analysis of the AFDX frame management design

Abstract: The Avionics Full Duplex Switched Ethernet (AFDX) has been developed to provide reliable data exchange with strong data transmission time guarantees in internal communication of the aircraft. The AFDX design is based on the principle of a switched network with physically redundant links to support availability and be tolerant to transmission and link failures in the network. In this work, we develop a formal model of the AFDX frame management to ascertain the reliability properties of the design. To capture the precise temporal semantics, we model the system as a network of timed automata and use Uppaal to model-check for the desired properties expressed in CTL. Our analysis indicates that the design of the AFDX frame management is vulnerable to faults such as network babbling which can trigger unwarranted system resets. We show that these problems can be alleviated by modifying the original design to include a priority queue at the receiver for storing the frames. We also suggest communicating redundant copies of the reset message to achieve tolerance to network babbling.

Getting more flexible scheduling in the RTSJ

Abstract: This paper illustrates how the real-time specification for Java (RTSJ) can be modified to allow applications to implement more flexible scheduling. The proposed approach is a two-level scheduling mechanism where the first level is the RTSJ priority scheduler and the second level is under application control. Minimum, backward-compatible changes to the RTSJ specification are discussed to motivate the required interface. The only assumptions made about the underlying real-time operating system are that it supports pre-emptive priority-based dispatching and that changes to priorities have immediate effect.

MDA-based development in the DECOS integrated architecture - modeling the hardware platform

Abstract: Reduced time-to-market in spite of increasing the system's functionality, reuse of software on different hardware platforms, and the demand for performing validation activities earlier in the development phase raise the need for revising the state-of-the-art development methodologies for distributed embedded systems. The model driven architecture is a design methodology addressing these emerging requirements. Developing embedded systems according to this model-based paradigm requires a platform-independent representation of the functionality of the application as well as a precise model of the targeted hardware platform. In this paper we introduce a meta-model for capturing the resources of hardware platforms realizing the DECOS architecture, which is an integrated time-triggered architecture aimed at the development of distributed embedded systems. Furthermore, we present a tool chain based on this meta-model that speeds up the modeling process and reduces the likelihood of human errors by facilitating the reuse of hardware building blocks from libraries.

Interaction-based behavior modeling of embedded software using UML 2.0

Abstract: Many prior approaches in UML-based embedded software design incorporate state-based behavior modeling. However, interaction-based behavior modeling provides more intuitive view of a system. In this paper, we propose an approach to interaction-based behavior modeling of embedded software using UML 2.0. We use the interaction overview diagrams and the sequence diagrams to model the behavior. We present the method of constructing interaction-based behavior model with an example. We also briefly describe the idea of generating executable code from it.

A diagnostic framework for integrated time-triggered architectures

Abstract: Integrated architectures promise substantial technical and economic benefits in the development of distributed embedded real-time systems. In the context of diagnosis new diagnostic strategies can be applied by taking the physical and functional structure of an integrated system into account. In this paper we present a diagnostic framework that is designed to tackle prevalent diagnostic problems industry is currently facing, such as the trouble-not-identified phenomenon in electronic systems. So-called out-of-norm assertions (ONAs) are employed that combine diagnostic information to correlate experienced failures in order to decide on the type fault (e.g., transient vs. permanent, internal vs. external) affecting the system. Based on a prototype implementation of the integrated time-triggered DECOS architecture we show the feasibility of this diagnostic strategy.

Modeling behavioral patterns of concurrent objects using Petri nets

Abstract: Object-oriented software development practices are being rapidly adopted within increasingly complex systems, including reactive, real-time and concurrent system applications. While data modeling is performed very well under current object-oriented development practices, behavioral modeling necessary to capture critical information in real-time, reactive, and concurrent systems is often lacking. Addressing this deficiency, we offer an approach for modeling and analyzing concurrent object-oriented software designs through the use of behavioral patterns captured through colored Petri nets.

Automated logging of mobile phones failures data

Abstract: The increasing complexity of mobile phones directly affects their reliability, while the user tolerance for failures becomes to decrease, especially when the phone is used for business- or mission-critical applications. Despite these concerns, there is still little understanding on how and why these devices fail and no techniques have been defined to gather useful information about failures manifestation from the phone. This paper presents the design of a logger application to collect failure-related information from mobile phones. Preliminary failure data collected from real-world mobile phones confirm the proposed logger is a useful instrument to gain knowledge about mobile phone failure's dynamics and causes.

Individual contour extraction for robust wide area target tracking in visual sensor networks

Abstract: In this paper, we propose an approach to collaboratively track motion of a moving target in a wide area utilizing camera-equipped visual sensor networks, which are expected to play an essential role in a variety of applications such as surveillance and monitoring. A genetic fitting method for efficient contour extraction is used as inter-scene approach to detect and track the target. We also considered the existence of faulty sensors in the network which deteriorate the difficulty of target tracking problem, and proposed a robust sensor collaboration method. The experimental results have shown that the proposed target tracking approach produces very successful target tracking compared with the existing method especially in case that the target is adjacent to neighboring objects of background.