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Xentara v2.0.4
User Manual
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Xentara v2.0.4
User Manual
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Data points are the main interface used in Xentara to access data. A data point represents a single item of data that be read and/or written. A data points is connected to skill data points, that are used to perform the actual reading and writing.
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 skill data points’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 skill data points 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.
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.
Data points are read and written through their attached skill data points. Please refer to Acquiring Values and Writing Values in Skill Data Points for details on reading and writing values.
Data points have at least the following members:
| key | The data point’s primary key. |
| name | The data point’s name. The name is the last component of the primary key. |
| UUID | The unique UUID of the data point. |
| type | The data point’s element type. For data points, this is always “data point”. |
| category | The data point’s category. For data points, this is always “data point”. |
| 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. |
| value | The data point’s value. This attribute may be readable and/or writable, depending on how the data point is attached to its input and output skill data points. |
Additionally, the data point will inherit attributes and events from its attached input and output. A data point will inherit all attributes and events related to the input data from its attached input, and all attributes and events related to the output data from its attached output. A data point that is attached to an input, 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 skill data point.
At least the following attributes and events are inherited from the data point’s attached input and output, if they are provided:
Each individual type of skill data point can have additional attributes and events that are inherited by data points. Please refer to the documentation of the specific skill data point for details.
Each data point provides two access points named “input” and “output”, that allow you to access the data point”s attached input and output 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”.