[OPC 10000-8] defines a DataItem as a link to arbitrary, live automation data, i.e. data that represents currently valid information. 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), and diagnostic data.
AnalogItems are DataItems that represent continuously-variable physical quantities. Typical examples are the values provided by temperature sensors or pressure sensors. OPC UA defines AnalogItemType VariableType to identify an AnalogItem.
The ADI Information Model extends the Variable model defined in OPC UA specification [OPC 10000-3], [OPC 10000-5] and [OPC 10000-8], It introduces VariableTypes, which are specifically utilized for the process analytical domain.
Parameters which hold simple data like a single numerical value, string value or a time-stamp value are represented by BaseDataVariableType defined in [OPC 10000-5] or one of its subtypes.
For more details see paragraph C.1.
Parameters which hold array data that may be acquired during normal analyser operation or used as inputs (e.g. background, calibration) are represented by VariableTypes, which are direct subtypes of DataItemType and described in [OPC 10000-8].
For more details on DataItemType and its relationship with ADI Parameters see paragraph C.2