Ljam Lou Somers

Yasper: a tool for workflow modeling and analysis

This paper presents Yasper, a tool for modeling, analyzing and simulating workflow systems, based on Petri nets. Yasper puts Petri net modeling in the hands of business analysts and software architecture designers. They can specify systems in familiar terms (XOR choice, workflow, cases, roles, processing time and cost), and can directly run manual and automatic simulations on the resulting models to analyze correctness and performance. Yasper was designed to cooperate with other tools, such as Petri net analyzers, and off-the-shelf software for data (color) handling and forms handling

Consistency in model integration

State-of-the-art systems engineering uses many models reflecting various aspects of the modeled system. A major task of system engineers is to ensure consistency between the many models. We present an approach to the engineering of complex systems based on the modeling of use cases and object life cycles as Petri nets. Synchronization by place fusion allows the derivation of an integrated model that can be verified and validated. We illustrate our approach by a case study.

Z and High Level Petri Nets

High level Petri nets have tokens with values, traditionally called colors, and transitions that produce tokens in a functional way, using the consumed tokens as arguments of the function application. Large nets should be designed in a topdown approach and therefore we introduce a hierarchical net model which combines a data flow diagram technique with a high level Petri net model. We use Z to specify this net model, which is in fact the metamodel for specific systems. Specific models we specify partly by diagrams and partly in Z. We give some advantages and disadvantages of using Z in this way. Finally we show how to specify systems by means of an example.

Integrated model-driven design-space exploration for embedded systems

Embedded systems and their design trajectories are becoming increasingly complex, and there is a growing demand for performance, reliability, energy efficiency and low cost. To cope with these challenges, decision making early in the development trajectory needs to be supported by appropriate modeling and analysis. To achieve this support, we need to find the modeling abstractions that allow extensive design-space exploration, tune these modeling abstractions towards the users, and integrate support for different types of modeling and analysis.

Message exchange in the building industry

A process model is described for exchanging information in the building industry. In this model participants send and receive messages. On receipt of a message an activity is executed if all required information is available. Otherwise a message will be sent to another participant to obtain the missing information. After execution of an activity a reply is sent with the desired data. In a building project an agreement is defined with all activities that will be executed by each of the participants. An executable implementation of the process model is built in ExSpect. In ExSpect the message exchange process can be simulated and analyzed for a specific building project.

A re-entrant flowshop heuristic for online scheduling of the paper path in a large scale printer

A Large Scale Printer (LSP) is a Cyber Physical System (CPS) printing thousands of sheets per day with high quality. The print requests arrive at run-time requiring online scheduling. We capture the LSP scheduling problem as online scheduling of reentrant flowshops with sequence dependent setup times and relative due dates with makespan minimization as the scheduling criterion. Exhaustive approaches like Mixed Integer Programming can be used, but they are compute intensive and not suited for online use. We present a novel heuristic for scheduling of LSPs that on average requires 0.3 seconds per sheet to find schedules for industrial test cases. We compare the schedules to lower bounds, to schedules generated by the current scheduler and schedules generated by a modified version of the classical NEH (MNEH) heuristic [1], [2]. On average, the proposed heuristic generates schedules that are 40% shorter than the current scheduler, have an average difference of 25% compared to the estimated lower bounds and generates schedules with less than 67% of the makespan of schedules generated by the MNEH heuristic.

Use cases as workflows

In requirements engineering we have to discover the user requirements and then we have to transform them into precise system specifications. There are two essential aspects to be modeled: the data aspect and the process aspect of the system. There are many techniques available to describe these aspects but it is always difficult to integrate these views in a consistent way. Last decade two techniques are used frequently in requirements engineering: use cases and workflow models. We show that these techniques can be integrated in a natural way, using the framework of colored Petri nets. We only sketch the underlying formal framework and focus on the practical application of the approach by a case study.

Online heuristic for the Multi-Objective Generalized traveling salesman problem

Todays manufacturing systems are typically complex cyber-physical systems where the physical and control aspects interact with the scheduling decisions. Optimizing such facilities requires ordering jobs and configuring the manufacturing system for each job. This optimization problem can be described as a Multi-Objective Generalized TSP where conflicting objectives lead to a trade-off space. This is the first work to address this TSP variant, introducing a compositional heuristic suitable to online application.

Online Scheduling of 2-Re-entrant Flexible Manufacturing Systems

Online scheduling of operations is essential to optimize productivity of flexible manufacturing systems (FMSs) where manufacturing requests arrive on the fly. An FMS processes products according to a particular flow through processing stations. This work focusses on online scheduling of re-entrant FMSs with flows using processing stations where products pass twice and with limited buffering between processing stations. This kind of FMS is modelled as a re-entrant flow shop with due dates and sequence-dependent set-up times. Such flow shops can benefit from minimization of the time penalties incurred from set-up times. On top of an existing greedy scheduling heuristic we apply a meta-heuristic that simultaneously explores several alternatives considering trade-offs between the used metrics by the scheduling heuristic. We identify invariants to efficiently remove many infeasible scheduling options so that the running time of online implementations is improved. The resulting algorithm is much faster than the state of the art and produces schedules with on average 4.6% shorter makespan.

Adaptivity in Professional Printing Systems

There is a constant pressure on developers of embedded systems to simultaneously increase system functionality and to decrease development costs. Aviable way to obtain a better system performance with the same physical hardware is adaptivity: a system should be able to adapt itself to dynamically changing circumstances. The development of adaptive embedded systems has been the topic of the Octopus project, an industry-as-laboratory project of the Embedded Systems Institute, with the professional printer domain of Oce-Technologies B.V.as an industrial carrier. The project has resulted in techniques and tools for model-based development of adaptive embedded systems including component-level and system-level control strategies, system architecting tools, and automatic generation of system software. This introductory chapter presents the Octopus project and provides a reading guide for this book, which presents the results of the Octopus project.