Rogério Campos-Rebelo

From IOPT Petri nets to C: An automatic code generator tool

This paper presents a tool for automatic generation of ANSI C code from models expressed in IOPT (Input-Output Place-Transition) Petri Nets. The inputs of the tool are PNML (Petri Nets Mark-up Language) files containing the IOPT Petri net models. The tool has two different interfaces: one relying on a simple graphical interface (amenable to be used by humans), and a second one with a command line interface (amenable to be used by humans as well as by other computational systems supporting tools interaction). The tool also allows the user to tune some parts of the automatically generated code considering some characteristics of the implementation platform improving the performance of the generated code. Generated code can be directly deployed into specific controllers; PIC low-cost microcontrollers as well as general purpose PCs have been used for validation.

An IOPT-net state-space generator tool

This paper presents the IOPT2SS tool, used to automatically generate state-space graphs associated with IOPT (Input-Output Place-Transition) Petri nets models. The new tool accounts with the non autonomous nature of the IOPT Petri net class, where transition firing is constrained by external input events and input signals (expressed in transition guards); on the other hand, transitions can trigger the occurrence of output signal events and place marking can activate output signals. To achieve the performance level necessary for the fast generation of complex state-spaces during reasonable time, the tool employs a compilation strategy, starting with the automatic creation of an optimized C program. When executed, the program will create an hierarchical XML file containing the state-space graph. The output XML file can subsequently be used for model checking and property analysis, applying standard XML query languages. Finally, the output file can be converted to SVG (Scalable Vector Graphics), enabling the graphical visualization of small to medium size state-space graphs. The new tool was implemented using a set of XSL transformations and can be used as a standalone tool or as a building block in higher level frameworks, with easy integration in Web applications and graphical integrated development environments.

IOPT Petri net state space generation algorithm with maximal-step execution semantics

This paper presents an algorithm to efficiently generate the state-space of systems specified using the IOPT Petri-net modeling formalism. IOPT nets are a non-autonomous Petri-net class, based on Place-Transition nets with an extended set of features designed to allow the rapid prototyping and synthesis of system controllers through an existing hardware-software co-design framework. To obtain coherent and deterministic operation, IOPT nets use a maximal-step execution semantics where, in a single execution step, all enabled transitions will fire simultaneously. This fact increases the resulting state-space complexity and can cause an arc “explosion” effect. Real-world applications, with several million states, will reach a higher order of magnitude number of arcs, leading to the need for high performance state-space generator algorithms. The proposed algorithm applies a compilation approach to read a PNML file containing one IOPT model and automatically generate an optimized C program to calculate the corresponding state-space.

Finding Learning Paths Using Petri Nets Modeling Applicable to E-Learning Platforms

This work proposes an approach for course modeling using Petri nets. The proposed modeling method can be applied to support development of e-learning platforms (namely learning management systems - LMS) allowing student guidance when considering reaching a specific goal. This goal could be as simple as getting a set of sequential courses (or a degree), or as complex as combining different modules from different courses having different types of dependencies in order to obtain a qualification. Each course is characterized by a set of modules and their relations. Each module is represented by a Petri net model and the module structure representing the course’s dependency relations is translated into another Petri net model. Additional courses or modules can be included into the offer as their associated Petri net models can be easily composed using net addition operation. The contribution of this paper foresees the usage of common Petri nets analysis techniques (such as state space analysis, invariants, trace finding) to constraint student’s options in order to optimize his/her path to reach a degree or a qualification. A simple example considering a scenario with a few courses and modules is used to illustrate the approach.

On Structuring Events for IOPT Net Models

This paper presents a proposal for structuring events for system models expressed using IOPT nets (Input-Output Place-Transition Petri nets). Currently, a non-autonomous event within an IOPT model is defined based on change of input signals with respect to a specific threshold, when two consecutive execution steps are considered. New types of events are proposed allowing the definition of an event activated not only by crossing a fixed threshold, but also considering a change in associated signal value on a specific amount (belonging to an interval of values). The concept is further extended allowing the definition of an event based on signal values presented on previous execution steps. The proposal results on a classification of several types of events, namely threshold events, momentum events, impetus events, as well as delayed events and logical events. Usage of these types of events allows improvements in terms of expressiveness and compactness of the resulted model.

Communication support for Petri nets based distributed controllers

This paper addresses the distributed execution of IOPT Petri nets models supported by a network of distributed controllers. Each controller is associated with a sub-model. Submodels use communication channels to exchange events allowing global evolution. Whenever controllers are interconnected through some kind of network, communication channels are implemented by communication nodes associated with each distributed controller. Communication nodes are characterized in terms of layers and buffers allowing their use with different types of communication and topologies. Their usage in a simple application example composed by a network of distributed controllers interconnected through a serial ring topology network is presented. Arduino boards are used as implementation platforms for proof-of-concept purposes.

Output events for human-system interaction modeling

In this paper, a new approach to define output actions associated with output event types for human-system interaction modeling is presented. In previous works, output events are used to affect a signal in a basic way: increment, decrement or set its value in the next time instant. This work proposes a set of new types of events to define different dependencies and behaviors for output signals. These events affect the associated signal with a specific behavior, which can be defined using specific characteristics including a function, a time window, and/or a final value. The concepts of delayed output events and zoomed output event are already proposed. Delayed events postpone the event contribution in a specific number of steps. Zoomed events change the number of steps between each contribution, allowing expanding and contracting the associated behavior. These concepts can be applied to previous types of events. Finally, the proposals are discussed, presenting some examples of usage for each type of events.

Enhanced Event Modeling for Human-System Interactions Using IOPT Petri Nets

This work presents some new ways to analyze a signal that allows the modeling of human-system interactions. In addition to the possibility of creating conditions associated with the current value of the signal, the work focuses mainly on the definition of events and on their use within Input-Output Place-Transition (IOPT) nets models. Currently, non-autonomous events can be defined in two different ways, namely as a threshold detection of a signal, or variation of the first derivative of the signal. Here, this concept is generalized, allowing the analysis of events in higher derivatives of the signal. On the other hand, a new set of types of events are defined for each derivative of the signal, improving existing UP and DOWN events. Finally, an example is used to illustrate discussed concepts.

Events for human-system interaction modeling with IOPT Petri nets

In this paper, a set of event types for human-system interaction modeling is presented, and its usage with IOPT nets (Input-Output Place-Transition Petri nets) models is illustrated. Currently, a non-autonomous event based on the computation of the change with respect to a specific threshold of input signals values on two consecutive execution steps is defined for IOPT models. Other types of events are proposed, allowing the definition of an event not only based on a threshold in the signal value, but also as a change on the variation of the signal. The concept of delayed events considers two values in different time steps (other than consecutive steps). This concept can be applied to previous types of events. The concept of composed events is also introduced, in order to create events dependent on two or more events on the same signal, at the same time step as well as at different time steps. Finally, an example is used to illustrate the concepts presented.

Elementary Events for Modeling of Human-System Interactions with Petri Net Models

This paper presents a proposal for structuring events for system models expressed using IOPT nets (Input-Output Place-Transition Petri nets). Currently, a non-autonomous event within an IOPT model is defined based on change of input signals with respect to a specific threshold, when two consecutive execution steps are considered. New types of events are proposed, allowing the definition of an event activated not only by crossing a fixed threshold, but also by considering a change in associated signal values on a specific amount (belonging to an interval of values). The concept is further extended allowing the definition of an event based on signal values presented on previous execution steps. The proposal results on a classification of several types of events, namely threshold events, momentum events, impetus events, as well as delayed events and logical events. Usage of these types of events allows improvements in terms of expressiveness and compactness of the resulted model.