A Methodology for Complex Embedded Systems Design

A Petri net meta-model to develop software components for embedded systems

“…To ensure the structural compatibility of the control unit representation in the SIPN and shobi-PN models, it is imposed that the skeleton of the shobi-PN is structurally equivalent to a SIPN without reinitializations. The following concepts used for shobi-PNs are introduced: (1) control net: set of contiguous nodes and arcs of the shobi-PN that structurally corresponds to the SIPN without reinitilizations; (2) control track: path defined by a token in the control net; (3) control nodes: nodes (places or transitions) of the control net; (4) control arcs: arcs of the control net; (5) closing track: path defined by a token outside the control net; (6) closing nodes: nodes of a closing track; (7) closing arcs: arcs of a closing track; (8) closing cycle: path defined by the movement of a token in the shobi-PN; it is composed by a control track and also, if applicable, by a closing track; it can be identified by the tracking of the colour associated with all the arcs of the cycle; (9) associated net: SIPN structurally equivalent to the control net after the introduction of the reinitilizations for the uncoloured tokens.…”

“…Hierarchy can be introduced in the specifications in two different ways: (1) the control unit is modelled by the PN structure, and to introduce the hierarchy on the controller, macronodes (representing sub-PNs) may be used; (2) the data path/plant resources are represented by the internal structure of the tokens, and the hierarchy can be introduced by aggregation (composition) of several objects inside one single token (a macrotoken) or by using the inheritance of methods and data structures.…”

“…The use of shobi-PN v1.0 meta-model to specify the behaviour an industrial controller (the HIDRO production lines [23]) has revealed some semantic fragilities of that modelling approach, namely when it is mandatory to assure: (1) the violation of levels of structural hierarchy by the introduction of tokens/objects in arbitrary zones of the PNs (this is very useful when, for some specific objects, it is crucial to bypass some levels of the controller's hierarchy); (2) the creation and destruction of objects for momentary reference of objects that are external to the system; (3) the manipulation of the original (genuine) objects and not the eventual replica that the dynamic execution of the PNs can create (this is vital to deal with critical regions in the control of multiple accesses to shared resources -for instance, the elevators in the HIDRO lines case study). To solve this three kinds of detected problems, the authors have extended the shobi-PN v1.0 meta-model (which has originated the shobi-PN v2.0 meta-model) by defining: (1) a generalised arc set (GAS) which allows the use of 16 different types of arcs, each one with specific syntactic and semantic properties within the shobi-PN v2.0 meta-model (table 1); (2) the concept of asynchronous macro-transition (AMT) as an auxiliary mechanism to the GAS, to solve the specific problem of the violations of the structural hierarchy's levels.…”

“…It is also commonly agreed that designers can enhance their efficiency and productivity if there exists a common notation that everybody is able to understand. In this context, the authors recommend the use of some UML diagrams to specify and model embedded systems, because it is a notation that covers the most relevant modelling aspects of systems and it is a standard [1].…”

“…For specifying the systems, the authors are using the main views captured by the following UML diagrams: (1) use case diagrams are utilized to catch the functional aspects of the system as viewed by its users; (2) object diagrams show the static configuration of the system, and the relations among the objects the system is composed of; (3) sequence diagrams display scenarios of common interactions amongst the objects that constitute the system or the actors that interact with it; (4) class diagrams show the information of ready-made components that can be used to construct systems and specify the hierarchical relationships among them.…”