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/*!
    \module QtOpcUa
    \title Qt OPC UA C++ Classes
    \ingroup modules
    \qtvariable opcua
    \since 5.7
    \brief List of C++ classes that provide the Qt OPC UA functionality.

    To link against the module, e.g. when writing a new plugin, add this line to your \l qmake \c .pro file:

    \code
    QT += opcua
    \endcode
*/

/*!
    \page qtopcua-index.html
    \since 5.7
    \title Qt OPC UA
    \brief Implements OPC UA connectivity through a Qt API.

    The Qt \l{Qt OPC UA#A short introduction to OPC UA}{OPC UA} module
    implements a Qt API to interact with OPC UA on top an external
    OPC UA stack.

    The stacks are connected via plugins and can be selected/switched at
    runtime.
    Currently, only the LGPL v3 implementation FreeOPCUA is provided.
    Other SDKs can be wrapped in additional plugins.

    An HMI focused subset of functionality is implemented in
    QOpcUaClient, which can be used to visualize data present on an OPC UA
    server.

    \section1 A short introduction to OPC UA
    OPC UA is a protocol for data modelling and secure exchange of data in
    industrial applications.
    The protocol offers built-in transport security based on certificates and
    established cryptographic algorithms.
    The data modelling system is object oriented and offers support for
    pre-made models which can be extended to fit special needs.

    \section1 Implemented features from the OPC UA protocol

    Not all features offered by the plugins can be used with all
    backends. The following table shows the current status of implementation.

    \table
    \header
    \li Feature
    \li FreeOPCUA
    \li Others to come...
    \row
    \li Reading and writing of values as array/scalar
    \li X
    \li ?
    \row
    \li Reading of value ranges
    \li
    \li ?
    \row
    \li Reading of engineering units
    \li
    \li ?
    \row
    \li Browsing and reading attributes of nodes
    \li X
    \li ?
    \row
    \li Secure connection
    \li
    \li ?
    \row
    \li User/password auth
    \li X
    \li ?
    \row
    \li Data change subscription
    \li Unstable implementation in FreeOPCUA
    \li ?
    \row
    \li Event subscription
    \li Callback is not called inside FreeOPCUA, so no signal is emitted
    \li ?
    \row
    \li Method calls
    \li Low performance
    \li ?
    \row
    \li Historical access
    \li
    \li ?
    \endtable

    Asynchronous operations, reading and writing of multiple nodes using one
    method call, filters for subscriptions, aggregates and write access for
    historical data are not implemented yet.

    \section1 Data types
    A subset of OPC UA data types are currently supported in QOpcUaClient, most
    of them are available with all backends. When writing data to the server,
    the type of the value must be specified using the QOpcUaType enum.

    \table
    \header
    \li Data type
    \li FreeOPCUA
    \li Others to come...
    \li Mapping
    \row
    \li Int8/16/32
    \li X
    \li
    \li Directly used
    \row
    \li UInt8/16/32
    \li X
    \li
    \li Directly used
    \row
    \li Double
    \li X
    \li
    \li Directly used
    \row
    \li Float
    \li X
    \li
    \li Directly used
    \row
    \li Byte String
    \li X
    \li
    \li QByteArray
    \row
    \li String
    \li X
    \li
    \li QString
    \row
    \li Date Time
    \li X
    \li
    \li QDateTime
    \row
    \li Localized Text
    \li X
    \li
    \li QString
    \row
    \li Node ID
    \li X
    \li
    \li QString
    \row
    \li XML Element
    \li Not available in FreeOPCUA
    \li
    \li QByteArray
    \endtable

    \section1 Classes and ownership
    Two important classes are exposed to the user: QOpcUaClient and QOpcUaNode.

    Objects of the type QOpcUaNode are owned by the user and must be deleted when they are no longer needed.

    \section1 Related Information

    \list
    \li \l{Qt OPC UA C++ Classes}{C++ Classes}
    \li \l{Qt OPC UA Examples}{Examples}
    \li \l{https://opcfoundation.org/about/opc-technologies/opc-ua/}{OPC UA at the OPC foundation}
    \endlist
*/