<p>Distributed real-time databases can be used to support data sharing</p><p>for applications in wireless ad-hoc networks. In such networks, topology changes frequently and partitions may be unpredictable and last for an unbounded period. In this thesis, the existing database replication protocol PRiDe is extended to handle such long-lasting partitions. The protocol uses optimistic and detached replication to provide predictable response times in unpredictable networks and forward conflict resolution to guarantee progress.</p><p>The extension, pPRiDe, combines update and state transfer strategies. Update transfer for intra-partition communication can reduce bandwidth usage and ease conflict resolution. State transfer for inter partition conflicts removes dependency on a common state between partitions prior to the merge to apply update messages on. This makes the resource usage independent of the life span of partitions. This independence comes at the cost of global data stability guarantees and pPRiDe can thus only provide per partition guarantees. The protocol supports application specific conflict resolution routines for both</p><p>state and update conflicts. A basic simulator for mobile ad-hoc networks has been developed to validate that pPRiDe provides eventual consistency.</p><p>pPRiDe shows that a hybrid approach to change propagation strategy can be beneficial in networks where collaboration by data sharing within long lasting partitions and predictable resource usage is necessary. These types of systems already require the conflict management routines necessary for pPRiDe and can benefit from an existing protocol.</p><p>In addition to pPRiDe and the simulator this thesis provides a flexible object database suitable for future works and an implementation of PRiDe on top of that database.</p>

<p>Admission controllers in dynamic real-time systems perform traditional schedulability tests in order to determine whether incoming tasks will meet their deadlines. These tests are computationally expensive and typically run in n * log n time where n is the number of tasks in the system. An incoming task might therefore miss its deadline while the schedulability test is being performed, when there is a heavy load on the system. In our work we evaluate a new approach for admission control in firm real-time systems. Our work shows that ANNs can be used to perform a schedulability test in order to work as an admission controller in firm real-time systems. By integrating the ANN admission controller to a real-time simulator we show that our approach provides feasible performance compared to a traditional approach. The ANNs are able to make up to 86% correct admission decisions in our simulations and the computational cost of our ANN schedulability test has a constant value independent of the load of the system. Our results also show that the computational cost of a traditional approach increases as a function of n log n where n is the number of tasks in the system.</p>

<p>In a distributed database system, pessimistic concurrency control is often used to ensure consistency which implies that the execution time of a transaction is not predictable. The execution time of a transaction is not dependent on the local transactions only, but on every transaction in the system.</p><p>In real-time database systems it is important that transactions are predictable. One way to make transactions predictable is to use eventual consistency where transactions commit locally before they are propagated to other nodes in the system. It is then possible to get predictable transactions due to the fact that the execution time of the transaction only depends on concurrent transactions on the local node and not on delays on other nodes and delays from a network.</p><p>In this report an investigation is made on how a replication protocol using eventual consistency can be designed for, and implemented in, DeeDS, a distributed real-time database prototype. The protocol consists of three parts: a propagation method, a conflict detection algorithm, and a conflict resolution mechanism. The conflict detection algorithm is based on version vectors. The focus is on the propagation mechanism and the conflict detection algorithm of the replication protocol.</p><p>An implementation design of the replication protocol is made. A discussion on how the version vectors may be applied in terms of granularity (container, page, object or attribute) and how the log filter should be designed and implemented to suit the particular conflict detection algorithm is carried out. A number of test cases with focus on regression testing have been defined.</p><p>It is concluded that the feasibility of the conflict detection algorithm is dependent on the application type that uses DeeDS.</p>

<p>Real-time systems are required to answer to external stimuli within a specified time-period. For this to be possible, the systems behaviour must be predictable. The use of active databases in real-time systems introduces unpredictability in the system, e.g. due to their use of active rules. The behaviour in active databases is usually specified in ECA-rules. Sets of ECA-rules are hard to analyse, which implies that the behaviour of the ECA-rule set is hard to predict.</p><p>The purpose of this project is to evaluate the ability to support the development of a predictable ECA-rule set. Using a formal method for the specification task is desirable, since a formal specification is analysable and can be proven correct. In this project, timed-automata are used for specifying the systems behaviour. A method for deriving predictable ECA-rules from a timed-automaton specification is developed, and successfully applied on a case-study specification. For this case-study specification, a set of ECA-rules preserving the analysed behaviour of the timed-automata specification is derived.</p>

<p>To gain confidence in that a dynamic real-time system behaves correctly, we test it. Automated verification & validation can be used to conduct testing of such systems in an effective and economic way.</p><p>An event monitor can be used as a part of a test oracle to monitor the system that is being tested. The test oracle could use the data (i.e., the streams of events) derived from the tested system, to determine if an executed test case gave a positive or negative result. To do this, the test oracle compares the streams of events received from the event monitor with the event expressions derived from the formal specification, and decides if the executed test case has responded positive or negative. Any deviations between observed behaviour and accepted behaviour should be reported by the test oracle as a negative result. If the executed test case gave a negative result, the monitor part should signal this to the reporter part of the test oracle.</p><p>This work aims to investigate how the event expressions can be derived from the formal specification, and in particular, how the event specification language Solicitor can be used to represent these event expressions.</p><p>We also discuss the need for parameterized event types in Solicitor, and any other event specification languages used in event monitoring. We also show that support for parameterized event types is a significant requirement for such languages.</p>

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Timed automata are a formalism to model, verify, and synthesize real-time systems. They have the advantage of having an abstract mathematical semantics, which allow formalizing and solving several verification and synthesis problems. However, timed automata are intended to design models, rather than completely describe real systems. Therefore, once the design phase is over, it remains to check whether the behavior of an actual implementation corresponds to that of the timed automaton model. An important step before implementing a system design is ensuring its robustness. This thesis considers a notion of robustness that asks whether the behavior of a given timed automaton is preserved, or can be made so, when it is subject to small perturbations. Several approaches are considered: Robustness analysis seeks to decide whether a given timed automaton tolerates perturbations, and in that case to compute the (maximum) amount of tolerated perturbations. In robust synthesis, a given system needs to be controlled by a law (or strategy) which tolerates perturbations upto some computable amount. In robust implementation, one seeks to automatically transform a given timed automaton model so that it tolerates perturbations by construction. Several perturbation models are considered, ranging from introducing error in time measures (guard enlargement), forbidding behaviors that are too close to boundaries (guard shrinking), and restricting the time domain to a discrete sampling. We also formalize robust synthesis problems as games, where the control law plays against the environment which can systematically perturb the chosen moves, by some bounded amount. These problems are studied on timed automata and their variants, namely, timed games, and weighted timed automata and games. Algorithms for the parameterized robustness analysis against guard enlargements, and guard shrinkings are presented. The robust synthesis problem is studied for two variants of the game semantics, for timed automata, games, and their weighted extensions. A software tool for robustness analysis against guard shrinkings is presented, and experimental results are discussed. The robust implementation problem is also studied in two different settings. In all algorithms, an upper bound on perturbations that the given timed automaton tolerates can be computed.

Complexity and variety of systems that are working in real time mode need to be specified regarding all behavior conditions. The correctness of the specification, determines whether implemented system will supply conditions that were set. To ensure that specification of the described real-time system is correct, we have to do verification and validation of the specification. Traditional verification methods do not assure full real time system inspection. The main drawback, talking about them, is impossibility of system evaluation according time. In this paper a reachable states graph and its generating algorithms are described, while two time moments are compared using linear programming, Simplex method. Therefore, method for checking equivalent state in system behavioral pathway was suggested. Also, theoretical reasoning for creating computer applications, which automates generation of reachable states graph, is given. Reachable states graph fully evaluates real time system behavior.

The aim of this research is to create the modeling and simulation tool for the real time systems. The component based object oriented model of real time system is introduced as solution. This model uses JAVA and XML languages to specify one component of the real time system. The model can be used to generate source code directly from components specifications. The modeling and simulation system was created based on component model. It can be used for modeling real time systems of any domain, any abstraction level or any complexity level. The experiments show that proposed modeling technique is correct.

A real-time system is one in which the correctness of the computations not only depends upon the logical correctness of the computation but also upon the time at which the result is produced. If the timing constraints of the system are not met, system failure is said to have occurred. Real-time system consist specialized hardware an software components. Nowadays, systems are so big and complex that teams of architects, analysts, programmers, testers and users must work together to create reliable real-time system. To manage this, a number of system development life cycle models have been created. System development life cycle refers to a methodology for developing systems. It provides a consistent framework of tasks and deliverables needed to develop systems. System development consist stages, that are common for all models: project planning, requirements definition, system design, implementation, testing, deployment and maintenance. However, there still are problems, that lead project to the failure. Problems appear while iterating from design stage to the implementation or prototype creation. Thesis describes methodology, that provide a way to overcome these problems. The main idea is to transform functional structure of the real-time system, that is designed using easy to understand graphical environment, to the executable code that will be able to run on target hardware components. Thesis describe the methods of doing such transformation. Methodology allows to create... [to full text]