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Introduction
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The pplSystemOverview (in the following referred to as 'Overview')
is a user-oriented middlelayer device
designed to provide an easy interface to monitor properties in a Karabo system;
several types of properties can be checked against conditions set by the users.

In the following examples the Overview devices running in the LAS systems are
used to show how the device works and how to easily configure it.

Properties can be logically grouped in three available device nodes, 'inputs',
'internal', and 'outputs'. In each grouping node a property is described by a node which
includes the property key name ('Variable'), the property device ('Device'),
whether it is monitored ('Is Monitored') and whether its value is within
specifications ('Is Ok' with key *isOk*), and its configuration parameters,
see :numref:`Fig. %s <fig-property_nodes>`.

.. _fig-property_nodes:

.. figure:: _images/scene_property_nodes.png
   :scale: 50 %
   :align: center

   The device nodes where the monitored properties are displayed.

In the device configuration editor the name of the property node key includes its
type and an increasing number, e.g. 'Analogue 00', 'Analogue_abs_range 00',
'Analogue_abs_range 01', etc. Using the autogenerated 'config' scene,
allows a more user-friendly way to access them,
see :numref:`Fig. %s <fig-vars_in_config_scene>`.

.. _fig-vars_in_config_scene:

.. figure:: _images/vars_in_config_scene.png
   :scale: 50 %
   :align: center

   The properties state and configuration can be accessed through the scene 'config'.

In case the expected conditions for a property are not fulfilled its Boolean property *isOk*
is set to False, which in turns sets the corresponding grouping node *isOk* Boolean
and the device Boolean *isOk* to False. This way, the property *isOk* of every device reflects
the state of its monitored properties.

The main interface to the system is an upper-level Overview device (in the following
referred to as 'main device') which 
monitors the *isOk* property of a series of Overview devices dedicated to monitor
parts of the system. As described above, in case one property value in a monitored device 
is not fine, the subsystem device *isOk* is set to False, resulting in 
the main device to have also its property *isOk* set to False. For users thus
it is sufficient to monitor only the *isOk* Boolean of the main Overview device to
have a view of the state for the monitored properties in their system.
A typical configuration is shown in :numref:`Fig. %s <fig-overview_system>`, where
an Overview device can monitor both standard properties in Karabo devices and
the property *isOk* of a sublevel Overview device.

.. _fig-overview_system:

.. figure:: _images/OverviewSystemExample.png
   :scale: 50 %
   :align: center

   Typical configuration of Overview devices.

In case in the main device the property *isOk* has False value, then a Zabbix alert can
be sent to the users if the corresponding Boolean is set and if the Zabbix system
has been properly configured to send notifications (previously the Nagios services were used instead of Zabbix).