# Introduction

DESpot is a GUI modelling environment for Discrete Event Systems (DESs), in particular those used in hierarchical interface-based supervisory control (HISC). The environment allows the definition of DES as well as both flat and hierarchical systems of DES. Flat systems are modelled as a set of supervisor DES, a set of plant DES and a set of template DES. HISC systems are modelled as a set of subsystems and interfaces. Subsystems are modelled as a set of supervisor DES, a set of plant DES and a set of template DES. Interfaces are modelled as a set of supervisor DES and a set of interface template DES. DESpot provides an intuitive GUI for defining DES projects and provides a native implementation of HISC algorithms. DESpot supports HISC projects defined with low-data events. DESpot uses the synchronous product to combine the project DES to construct the system's closed-loop behavior.

DESpot also provides a graphical and tabular editor for defining the DES structure (states, events and transitions) and provides tools to check the consistency of the DES and its different properties (e.g. integrity, reachability, nonblocking). DES are saved by DESpot in an XML-based language into files with a *.DES extension.

DESpot provides a project editor for defining flat DES projects. The editor provides tools to verify nonblocking and controllability properties of flat projects.

DESpot provides a project editor for defining HISC projects. Using this editor the user can create high or low-level subsystems and interfaces. A subsystem is defined as a collection of plant DES that makes up the subsystem’s plant, a collection of supervisor DES that make up the subsystem’s supervisor and a collection of template DES that make up the subsystem's template. An interface is defined as a collection of interface DES and a collection of interface template DES. As part of the project editors, DESpot provides an intuitive and powerful UI for managing the project event set and the complex ownership and type rules that govern an HISC project. The project editor allows users to verify the consistency of the project as well its different properties (e.g. level-wise interface consistent, level-wise nonblocking, level-wise controllable).

In addition, DESpot provides a DES Simulation Software (DSS) module for simulating either HISC or flat DES projects.

Projects are saved by DESpot in an XML-based language into files with a *.DESP extension. Within DESpot, all available characters for use in the naming of elements (subsystems, DES, events etc) are: a-z; A-Z; 0-9; ._- . The character % is used for the naming of elements (states, DES name, events etc) in template DES and interface template DES. Note that "." is currently reserved for future applications.

Please note that many items such as DES and subsystems, offer access to related functionality via context menus. Context menus can be accessed by right-clicking on the object.

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