3.1 Terms and definitions

For the purposes of this document, the terms and definitions given in OPC 10000-1, OPC 10000-3, and OPC 10000-4 and the following apply.

3.1.1 DataItem

link to arbitrary, live automation data, that is, data that represents currently valid information

Note 1 to entry: Examples of such data are

  • device data (such as temperature sensors),
  • calculated data,
  • status information (open/closed, moving),
  • dynamically-changing system data (such as stock quotes),
  • diagnostic data.
3.1.2 AnalogItem

DataItem that represents continuously-variable physical quantities (e.g., length, temperature), in contrast to the digital representation of data in discrete items

Note 1 to entry: Typical examples are the values provided by temperature sensors or pressure sensors. OPC UA defines specific VariableTypes to identify an AnalogItem. Properties describe the possible ranges of AnalogItems.

3.1.3 DiscreteItem

DataItem that represents data that may take on only a certain number of possible values (e.g., OPENING, OPEN, CLOSING, CLOSED)

Note 1 to entry: Specific VariableTypes are used to identify DiscreteItems with two states or with multiple states. Properties specify the string values for these states.

3.1.4 ArrayItem

DataItem that represents continuously-variable physical quantities and where each individual data point consists of multiple values represented by an array (e.g., the spectral response of a digital filter)

Note 1 to entry: Typical examples are the data provided by analyser devices. Specific VariableTypes are used to identify ArrayItem variants.

3.1.5 EngineeringUnits

units of measurement for AnalogItems that represent continuously-variable physical quantities (e.g., length, mass, time, temperature)

Note 1 to entry: This standard defines Properties to inform about the unit used for the DataItem value and about the highest and lowest value likely to be obtained in normal operation.