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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
/*!
\page qtscxml-overview.html
\title Qt SCXML Overview
\brief Describes the Qt SCXML module.
\ingroup explanation
The Qt SCXML module provides classes for embedding state machines created
from State Chart XML (SCXML) files in Qt applications. The SCXML files
can be created using any suitable tool, such as a text editor or a
simulator, as long as they comply to the \l {SCXML Specification}, with the
restrictions and extensions described in \l{SCXML Compliance}.
Parts of the application logic can be replaced with an encapsulated SCXML
file. This enables creating a clear division between the application logic
and the user interface implementation by using Qt Quick or Qt Widgets.
The Qt SCXML module differs from the \l {Qt State Machine Overview}
{State Machine framework} in the \l{Qt State Machine} module in that Qt SCXML provides a
\e {conforming processor} that can parse and process \e {conforming SCXML
documents}. In Qt SCXML, state machines are read from separate SCXML files
and integrated to Qt applications by instantiating the QScxmlStateMachine
class and loading an SCXML file dynamically or by using the Qt SCXML
Compiler to generate a subclass of QScxmlStateMachine that is instantiated.
The communication with the SCXML document is provided by the signals and
methods of the QScxmlStateMachine class.
The basic state machine concepts, \e state, \e transition, and \e event are
based on those in the SCXML Specification. State charts provide a graphical
way of modeling how a system reacts to stimuli. This is done by defining the
possible states that the system can be in, and how the system can move from
one state to another (transitions between states). A key characteristic of
event-driven systems (such as Qt applications) is that behavior often
depends not only on the last or current event, but also the events that
preceded it. With state charts, this information is easy to express.
Qt SCXML integrates tightly with Qt's meta-object system; for example,
transitions between states can be triggered by signals, and states can be
configured to set properties and invoke methods on \l{QObject}{QObjects}.
Qt's event system is used to drive the state machines.
The state graph in Qt SCXML is hierarchical. States can be nested inside
other states, and the current configuration of the state machine consists of
the set of states that are currently active.
\section1 Data Models
Qt SCXML supports the null data model, which must be supported by conforming
SCXML processors, and the ECMAScript data model. In addition, Qt SCXML
provices its own C++ data model that is implemented by the
QScxmlCppDataModel class. The class enables writing C++ code for \e expr
attributes and \c <script> elements. The \e {data part} of the data model is
backed by a subclass of QScxmlCppDataModel, for which the Qt SCXML compiler
will generate the dispatch methods.
\section1 Qt SCXML Compiler
The Qt SCXML Compiler, \c qscxmlc, reads an .scxml file and produces C++
source and header files that contain a class that implements a state
machine as defined in SCXML. For more information about using the compiler,
see \l{Using the Qt SCXML Compiler (qscxmlc)}.
Both the dynamically created and the compiled state machines behave in the
same way, have the same properties, states, data model, and so on. They only
differ in the way they are instantiated. For more information, see
\l{Instantiating State Machines} and \l{Qt SCXML Examples}.
\section1 Logging Categories
The Qt SCXML module exports the following logging categories:
\table
\header
\li Logging Category
\li Description
\row
\li qscxmlLog
\li Enables Qt SCXML module log
\row
\li scxmlLog
\li Enables log of SCXML documents
\endtable
*/
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