End-to-End Delay Computation for Time Petri Nets

The specification of reactive and real-time systems must be supported by formal, mathematically-founded methods in order to be satisfactory and reliable. Temporal logics have been used to this end for several years. Temporal logics allow the specification of system behavior in terms of logical formulas, including temporal constraints, events, and the relationships between the two. In the last ten years, temporal logics have reached a high degree of expressiveness. Most of the temporal logics proposed in the last few years can be used for specifying reactive systems, although not all are suitable for specifying real-time systems. In this paper we present a series of criteria for assessing the capabilities of temporal logics for the specification, validation, and verification of real-time systems. Among the criteria are the logic's expressiveness, the logic's order, presence of a metric for time, the type of temporal operators, the fundamental time entity, and the structure of time. We examine a selection of temporal logics proposed in the literature. To make the comparison clearer, a set of typical specifications is identified and used with most of the temporal logics considered, thus presenting the reader with a number of real examples.

Among the many models proposed for the specification and verification of real-time systems, timed automata and time Petri nets are prominent. These two models which were developed independently for years bear strong relationships. In this paper we survey some of the most recent approaches about translation methods from timed automata to time Petri nets. We may apply time Petri nets specific verification methods to timed automata by using these translation methods.

Specification and verification of real-time systems are important research topics with crucial applications; however, the so-called state space explosion problem often prevents model checking to be used in practice for large systems. In this work, we present a self-contained toolkit to analyze real-time systems specified using event-recording automata (ERAs), which supports system modeling, animated simulation, and fully automatic compositional verification based on learning techniques. Experimental results show that our tool outperforms the state-of-the-art timed model checker.

Areas of computer application are being broadened rapidly due to the rapid improvement of the performance of computer hardware. Applications that were not feasible before are now becoming feasible with high-performance computers. This results in increased demands for computer applications that are large and have complex temporal characteristics. Most analysis methods available, however, cannot handle large, complex real-time systems adequately; They do not scale-up, lack formalism to represent complex features and perform analyses with mathematical rigor, do not support analyses from different viewpoints, or are too hard to learn and apply. TVe need analysis methods that support formal specification and verification of real-time systems. Incremental performance of specification and analysis of systems from different viewpoints (e.g., user, analyst ) must also be supported with languages appropriate for each different viewpoint and for the users involved. This paper introduces a real-time systems analysis method, named PARTS, that aims at providing above features. PARTS supports analyses from two viewpoints: external viewpoint, a view of the sys-Permission tern from the user's perspective, and internal viewpoint, a view from the developer's perspective. These viewpoints are specified using formal languages, which are: Real-Time Events Trace (RTET) for the external viewpoint, and Time Enriched Statecharts (TES) and PARTS Data Flow Diagram (PDFD) for the internal viewpoint. All PARTS languages are based on the Real-Time Temporal Logic (RTTL), and consistency of the specifications made from two different viewpoints are analyzed based on the same RTTL formalism. PARTS converts RTET and TES specifications to RTTL specifications, which are then integrated and analyzed for consistency. All of the PARTS specificaticm languages support the top-down strategy to handle complexity.

Real-time systems are used in many critical applications. Verification of these real-time systems is essential. Presented here is a method for modeling real-time systems and computing the model's timing characteristics automatically. From a data-driven model of the system an equivalent finite state machine representation of the system is produced by this package. To provide efficient traversal of this large state space an ordered binary decision diagram (OBDD) is used to represent the state machine using symbolic methods. Algorithms have been developed to find the largest and smallest distance (times) between any two state sets. From these algorithms schedulability of the real-time system can be determined.

RTCP-nets are high level Petri nets similar to timed colored Petri nets, but with different time model and some structural restrictions. The paper deals with practical aspects of using RTCP-nets for modeling and verification of real-time systems. It contains a survey of software tools developed to support RTCP-nets. Verification of RTCP-nets is based on coverability graphs which represent the set of reachable states in the form of directed graph. Two approaches to verification of RTCP-nets are considered in the paper. The former one is oriented towards states and is based on translation of a coverability graph into nuXmv (NuSMV) finite state model. The later approach is oriented towards transitions and uses the CADP toolkit to check whether requirements given as μ-calculus formulae hold for a given coverability graph. All presented concepts are discussed using illustrative examples

In this paper, we investigate the modeling and verification of real time systems using a case study on transmission protocol, CSMA/CD. Modeling and verification of real time systems is hot research topic which has practical implications. Such systems are considered as mission critical, as its correctness within timed constraints are of great importance. Through modeling and verifying CSMA/CD protocol using timed extension of CSP (TCSP) modeling techniques in PAT, we propose a formal model for CSMA/CD protocol and verify its critical properties like deadlock-freeness, divergence-freeness and collision detection in a given bounded delay. The integrated reduction techniques in PAT help in carrying out the verification with reasonable speed and results.

Timed process algebras are useful tools for the specification and verification of real-time systems. We study the expressiveness of (classes of) these algebras which deal with temporal aspects of concurrent systems by following very different interpretations: durational actions versus durationless actions, absolute time versus relative time, timed functional behavior versus time and functional behavior, local clocks versus global clocks, eagerness versus laziness versus maximal progress.

An important key challenge in Embedded Real Time Systems (ERTS) analysis is to provide a seamless scheduling strategy. Formal methods for checking the temporal characteristics and timing constraints at a high abstraction level have proven to be useful for making the development process reliable. In this paper, we present a Petri Net modeling formalism and an analysis technique which supports not only systems scheduling analysis but also the compositional specification of real time systems. The proposed Priority Time Petri Net gives determinism aspect to the model and accelerates its execution. Indeed, a compositional specification of a PTPN for complex application and multiprocessor architecture that solves the problem of hierarchy is presented.

The task of checking if a computer system satisfies its timing specifications is extremely important. These systems are often used in critical applications where failure to meet a deadline can have serious or even fatal consequences. This paper presents an efficient method for performing this verification task. In the proposed method a real-time system is modeled by a state-transition graph represented by binary decision diagrams. Efficient symbolic algorithms exhaustively explore the state space to determine whether the system satisfies a given specification. In addition, our approach computes quantitative timing information such as minimum and maximum time delays between given events. These results provide insight into the behavior of the system and assist in the determination of its temporal correctness. The technique evaluates how well the system works or how seriously it fails, as opposed to only whether it works or not. Based on these techniques a verification tool called Verus has been constructed. It has been used in the verification of several industrial real-time systems such as the robotics system described below. This demonstrates that the method proposed is efficient enough to be used in real-world designs. The examples verified show how the information produced can assist in designing more efficient and reliable real-time systems.

An approach to the modeling and verification of real-time systems is presented. The Specification PEARL description language is used for hardware/software modeling. It has its origins in the standard Multiprocessor PEARL language. Its usefulness has been enhanced for asymmetrical multiprocessor system modeling, and parameters for schedulability analysis have been added. It is meant to be an over-layer for PEARL programs and supports the corresponding program model. The detailed program models are represented internally by timed state transition automata. The model of the co-designed system is verified for feasibility with co-simulation. The resulting information may be used for changes in the current design to gain a feasible model of the system. After that, the program models may be enhanced to their full functionality. Schedulability analysis, which should provide the designer with more precise information, can then be done. The new information can be reused on the system model in order to discover bottlenecks or possible discrepancies with the estimated times. By utilising this methodology, the possibility of implementing a non-feasible system should be minimised.

The need of conceiving reliable real-time systems is crucial for the software engineering. This paper is dedicated to the specification and the verification of land transportation systems taken as an application domain. We present a case study in the area of transportation. The system consists of several automated vehicles called CyCab, that have to communicate with a station. The components are modeled with timed automata and some properties are expressed in the timed logic TCTL to be checked by the model checking tool Kronos. These systems, which are both distributed and embedded, require to express non functional-properties, for example a response time constrained.

The specification and design of hard real-time systems using timed and temporal petri nets

In this paper, we study the problem of accumulated tokens in a timed Petri net modeling our system and its interaction with the environment. This system consists of a robot, a programmable automaton and a computer. The execution of different tasks must be done with respect to some temporal constraints. So, we use the temporal Petri nets to model the whole system and also its verification. We describe the obtained Petri net and the constraints textually or graphically in the open source TINA environment. The studied problem is a consequence of a wrong functioning. We try two approaches to solve it: the first one is behavioral-like, it makes a review of tasks scheduling, it is based on the priorities granting to specific transitions in order to fire some transitions before others; while the second one is structural-like, and it introduces some changes to the net structure with respect of the specification of the system. The obtained results show that the problem of accumulated tokens in a Petri net is not deeply related to a scheduling problem, but it is a structural problem. These two approaches can be combined into a hybrid one. These testing results also serve for the re-design process of the system by reviewing the problem sources.

Advances in sensing, effecting, and computational technologies will change the way we design, construct, and monitor systems that interact with the physical world. Building structures will sense and respond to external loads, autonomous robots will occupy construction sites, and intelligent vehicles will monitor network flows to circumvent delays. As engineers, we must be prepared to work with the information technologies that underpin these coming systems. This paper addresses several of the prominent technical concerns in designing real-time systems that control some aspect of their environment. The view taken is that, by considering software systems to be an engineering artifact, we can begin to develop the kinds of quantitative approaches found in other areas of engineering design.