Many real-time database systems, such as military institutions and government agencies, are contained in environments that exhibit restricted access of information, where mandatory access control for security is required. Hence, in addition to timing constraints, real-time database systems have security constraints. Conventional multi-level secure database models are inadequate for time-critica...

The growing level of complexity of modern embedded systems, which are increasingly distributed and heterogeneous, calls for new design approaches able to reconcile mathematical rigour with flexibility, user– friendliness and scalability. In the last few years, Timed Automata (TA) have emerged as a very promising formalism for the availability of very effective verification tools. However, their...

Time redundancy is an effective method for achieving fault tolerance in a real-time system, when space redundancy cannot be used for cost or weight constraints. This paper presents a fault-tolerant scheduling algorithm for real-time systems consisting of firm and hard periodic tasks. Firm tasks can occasionally skip one instance according to a predefined quality-ofservice parameter, whereas har...

In real-time environments, tasks have to complete by their deadlines. As we restrict our attention to mono-processor systems, a scheduling algorithm aims to determine which task is to execute on the processor [1,2]. On-line scheduling algorithms have been designed under non-overloaded conditions. We say that a real-time system is overloaded when it is impossible to schedule it on the processor ...

The problem of extending monoprocessor methods to multiprocessors for scheduling soft aperiodic tasks has been addressed and evaluated in previous works, where the most usual goal for aperiodic tasks is minimising response times. This paper introduces a new problem where the goal for aperiodic tasks is guaranteeing their deadlines. Guaranteeing aperiodic deadlines is done using an acceptance te...

Real-time systems Practitioners categorize real-time systems as hard, firm, and soft.1 Hard real-time systems include those in which a single missed deadline might cause catastrophic repercussions. Firm real-time systems tolerate one or more missed deadlines without catastrophic repercussions. In soft real-time systems, missed deadlines only result in performance degradation. Bart Van Beneden s...

While it is imperative that all time constraints are met in hard real-time systems, firm or soft real-time systems do not have as stringent timeliness requirements, allowing for some degree of tardiness (soft) or miss ratio (firm). A significant body of research within the soft and firm real-time area has focused on minimizing tardiness and/or miss ratio, but without quantifying acceptable leve...

We explore the integration of firm real-time processing— where processing completed after its deadline has no value but some jobs may be terminated or skipped—into an integrated real-time system managing hard, soft, and non-realtime processes. We show that it is feasible to add firm realtime processing to an integrated environment and that concurrently executing soft real-time processes can ben...

In real-time systems response to a request from a controlled object must be correct and timely. Any late response to a request from such a device might lead to a catastrophy. The possibility of a task overrun, i.e., missing the deadline for completing a requested task, must be checked and removed during the design of such systems. Safe design of real-time systems running periodic tasks under th...

Real-time systems comprise computers that must generate correct results in a timely manner. This involves a wide spectrum of computing systems found in our everyday life ranging from computers in rockets to our mobile phones. The criticality of producing timely results defines the different types of realtime systems. On one hand, we have the so-called hard real-time systems, where failing to me...