Data Access

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Introduction

Data Access is an information model for real-time data, i.e. data that represent current state and behaviour of the underlying industrial or business process. Access is provided with Read, Write and Subscription Services. Typical sources are sensors, control devices, position transducers and more.

Such information is typically used by Clients for user displays, or to monitor and control the process.

Examples include:

  • device data such as sensor measurement or actuator state
  • energy consumption, energy price
  • calculated data
  • business data
  • dynamically-changing system data (such as stock quotes)
  • diagnosis data

In automation systems the data is often located on I/O cards or on other devices such as controllers and input/output modules, connected by serial links via field buses or other communication links. The DA model therefore also defines codes that specify the quality of the physical connection.
Note – Data Access is specified in OPC UA Part 8.

Required Data Access Capabilities

OPC UA Data Access is represented by a set of advanced capabilities. The key functionalities for Data Access, however are already part of the required Information Access capabilities (see InfoAccess All).

Advanced Data Access Capabilities

Data Access

URN:          https://opcfoundation.org/wiki/index.php/Data_Access#Data_Access

Discovery ID: DA


Description
DataAccess in general is the ability to access real-time data. The data are Variables with a type that reflects the main classification (e.g., analog or discrete).

Usage Considerations

  • User Displays
  • Process monitoring and control

Conformance Testing

Client Server

Array Data

URN:          https://opcfoundation.org/wiki/index.php/Data_Access#Array_Data

Discovery ID: DA


Description
Array Data refer to continuously-variable physical quantities where each individual data point consists of multiple values represented by an array (e.g., the spectral response of a digital filter).

Usage Considerations
Typical examples are the data provided by process and laboratory analyser devices like Particle Size Monitor or Gas Chromatograph.


Conformance Testing

Client Server

Client is able to process the array data defined in the OPC UA Data Access specification.

Provide access to Variables with array data as defined in the OPC UA Data Access specification.