Data points form a layer of semantic abstraction between the physical hardware and the data. The primary key can be freely chosen to represent the function of the data it provides access to, whereas the I/O point’s primary key is determined by the way the data is physically acquired. A bearing temperature reading may, for example, be available as an analog input on a Modbus device on a serial bus. The primary key of the I/O point might then be something like “Shop Floor Server.Serial Bus 3.Line A Controller.AI 11a”. This key is not easily recognizable as a bearing temperature, so the value could additionally be exposed as a data point with primary key “Shop Floor.Line A.Drive.Bearing Temperature”. This makes understanding the meaning of the value much easier, and also protects against the case where the physical location of the input might change.

Data points can also join separate inputs and outputs point into a single read/write data point. A data point might, for example, read its value from an input on an analog input module, and write its value to an output on a separate analog output module.

Display Information

Data points can have some attributes attached to them that determine how the data point should be displayed to the user. The following types of display information are supported:

Units: These are the physical units of the data point’s value, e.g. “kg” or “°C”.
Display Name: This is a name that can be used instead of the primary key to identify the data point to the user. This display name may be used as a label in a GUI, for example.

Xentara does not use these attributes itself. They are meant to be used by clients to present the data point to the user in a more human friendly way.

Reading and Writing Data Points

Data points are read and written through their attached I/O points. Please refer to Acquiring Values and Writing Values in I/O Points for details on reading and writing values.

Accessing Data Points

Data points have at least the following members:

Attributes

key	The data point’s primary key.
name	The data point’s name. The name is the last component of the primary key.
units	The physical units of the data point’s value, like “kg” or “°C”. If the data point’s value has no units, this attribute contains an empty string.
displayName	The name that should be used to identify the data point to the user instead of the primary key. If no special display name has been specified for the data point, this attribute will be the same as the primary key.
UUID	The unique UUID of the data point.
value	The data point’s value. This attribute may be readable and/or writable, depending on how the data point is attached to its I/O points.

Additionally, the data point will inherit attributes and events from its I/O points. A data point will inherit all attributes and events related to the input data from its input I/O point, and all attributes and events related to the output data from its output I/O point. A data point that is attached to an input I/O point, will, for example, inherit the “quality” and “updateTime” attributes from the input. This means that the data point will also have a “quality” and an “updateTime” attribute with the same values as the I/O point.

At least the following attributes and events are inherited from the data point’s I/O points, if they are provided:

value (attribute)
updateTime (attribute)
sourceTime (attribute)
changeTime (attribute)
quality (attribute)
error (attribute)
writeTime (attribute)
writeError (attribute)
changed (event)

Any change events for the attributes listed above are also inherited. The meaning of these members is described in detail in Accessing I/O Points.

Each individual type of I/O point have additional attributes and events that are inherited by data points. Please refer to the documentation of the specific I/O point for details.

To refer to a member, use its primary key. The primary key of the value attribute of an I/O component called “My.Data.Point” is “My.Data.Point.value”.

Accessing the I/O Points of a Data Point Directly

Each data point provides two access points named “input” and “output”, that allow you to access the data point”s input and output I/O point directly. To refer to the input of a data point named “My.Data.Point”, use the key “My.Data.Point.input”. This key can be used wherever a primary key would normally be used.

You can also access attributes, events, and tasks of the input and output through these access points. To get the “key” attribute of the input of a data point named “My.Data.Point”, use the key “My.Data.Point.input.key”.

Table of Contents

Display Information

Reading and Writing Data Points

Accessing Data Points

Accessing the I/O Points of a Data Point Directly