Continuing with our discussion on OPC Unified Architecture (OPC-UA) , we can dive into the intricacies of the OPC UA Information Model. As we have seen, OPC-UA is a powerful, flexible, and secure communication protocol that has become a cornerstone of industrial automation and IoT (Internet of Things) systems. In this comprehensive article, we'll explore the fundamental concepts, services, and models that make up the OPC UA Information Model, empowering the reader to better understand and leverage this versatile technology.
OPC-UA, or Open Platform Communications Unified Architecture, is a machine-to-machine (M2M) communication protocol that enables seamless data exchange between various industrial devices, systems, and applications. It was developed by the OPC Foundation, a non-profit organization dedicated to the advancement of open connectivity solutions for industrial automation.
OPC-UA is designed to overcome the limitations of its predecessor, the classic OPC (OLE for Process Control) technology, by providing a more robust, scalable, and platform-independent solution. Central to this is the OPC UA Information Model, which acts as a semantic industrial data model that goes beyond raw value exchange — it encodes the meaning, structure, and relationships of industrial data so that clients and servers from different vendors can truly interoperate. Embien serves industrial, automotive, medical, and consumer domains; our cross-domain embedded services page shows how we apply the OPC UA Information Model across diverse product programmes.
The OPC UA Information Model is a comprehensive framework that defines the structure and semantics of the data exchanged within an OPC-UA system.
OPC UA Information Model
This model consists of several key concepts:
Nodes and Node Types: The building blocks of the OPC UA Information Model, representing the various entities and their relationships. Namespaces and Address Spaces: Unique identifiers that distinguish between different information models and their associated data. Base Models: Foundational models that define the core types, objects, and relationships used throughout the OPC-UA ecosystem. OPC UA Base Services: Properties and actions associated with each node, defining its behaviour and capabilities. OPC UA Companion Specifications: Domain-specific extensions to the Base Models, tailored for various industries and applications.Understanding these concepts is crucial for designing, implementing, and integrating OPC UA Information Model-based solutions. Let us take a deeper look into each of these.
At the heart of OPC-UA lies its data model, which is responsible for structuring and organizing the information exchanged between different components. The OPC UA Information Model data model is based on a hierarchical, object-oriented approach, where data is represented as a series of interconnected nodes and their associated properties, methods, and events.
Nodes are the fundamental building blocks that represent various entities, such as devices, sensors, etc. They are the most basic addressable items and are essentially a collection of attributes. Attributes, in turn, are properties associated with each node, providing information about its state, configuration, and behaviour.
The OPC UA Information Model also defines References — the relationships that connect nodes, allowing for the navigation and exploration of the data model.
Predefined data types, such as integers, floats, strings, and arrays, define the structure and format of the information in a node.
There are different classes of nodes such as
View: Defines a subset of nodes in the OPC UA Address Space. ObjectType: Provides definition for objects. Object: Represent systems, system components, real-world objects and software objects. ReferenceType: Defines the meaning of the nodes relationship. DataType: Define simple and complex data types of the Variable values. VariableType: Provides type definition for variables. Variable: Provides the value information. Method: Represents lightweight function, whose scope is bounded by an owning object.Being a service-oriented architecture, the OPC UA Information Model defines a set of OPC UA Base Services that enable communication and interaction between clients and servers. These OPC UA Base Services provide a standardized way to perform various operations, such as discovery, browsing, reading, writing, and subscribing to data.
While the OPC UA Base Services are organized into Service Sets, each Service Set defines a set of related Services organized as a logical grouping. Some of the major OPC UA Base Services sets are described below:
Discovery Service Set: Allow a Client to discover the Endpoints implemented by a Server and to read the security configuration for each of those Endpoints. SecureChannel Service Set: Allow a Client to establish a communication channel to ensure the Confidentiality and Integrity of Messages exchanged with the Server. Session Service Set: Allow the Client to authenticate the user on whose behalf it is acting and to manage Sessions. NodeManagement Service Set: Enables the Client to add, modify and delete Nodes in the OPC UA Address Space. View Service Set: Allow Clients to browse through the OPC UA Address Space or subsets of the OPC UA Address Space called Views. Query Service Set: Allows Clients to get a subset of data from the OPC UA Address Space or the View. Attribute Service Set: Provides mechanisms for Clients to read and write Attributes of Nodes, including their historical values. Method Service Set: Allow Clients to call methods that run to completion when called. They may be called with method-specific input parameters and may return method-specific output parameters. Subscription Service Set: Allow Clients to create, modify and delete Subscriptions. Subscriptions send Notifications generated by MonitoredItems to the Client.The OPC UA Base Services are the operational backbone of any OPC UA deployment — selecting and implementing the right service sets is essential for building scalable, interoperable IIoT applications. Embien’s digital transformation services leverage OPC UA information models to enable interoperable, data-driven industrial ecosystems.
The OPC UA Address Space is a hierarchical structure that organizes the various nodes and their relationships within an OPC-UA server. The OPC UA Address Space can be thought of as a virtual representation of the underlying industrial assets, devices, and data sources. The OPC UA Address Space is divided into namespaces, and nodes are mapped inside the namespaces with Node IDs.
Clients can navigate and explore the OPC UA Address Space using the OPC UA View Services, which provide mechanisms for browsing, querying, and retrieving information about the available nodes and their properties. The OPC UA Address Space can be customized and extended through the use of OPC UA companion specifications, which we'll discuss in the next section.
Inspired by object-oriented architecture, the OPC UA Information Model defines an Object-based information model that structures the semantics for representing real-time data, such as sensor readings, process variables, and control signals.
A few Base Models are defined on top of which custom implementation and extension can be done. Each of these models has associated Variables, Variable Types (definitions of the various data types and their properties), and Access Services (standardized methods for reading, writing, and subscribing to data).
DataAccess (DA) Base Model: The DataAccess (DA) Base Model defines the structure and semantics for representing real-time data, such as sensor readings, process variables, and control signals. Alarm & Conditions (AC) Base Model: The Alarm & Conditions (AC) Base defines the structure and semantics for representing alarms, events, and other conditional states within an OPC-UA system. Historical Access (HA) Base Model: The Historical Access (HA) Base Model provides a standardized way to access and manage historical data within an OPC-UA system. Programs (Prog) Base Model: The Programs (Prog) Base Model defines the structure and semantics for representing and executing programs, scripts, and other executable logic within an OPC-UA system.While the Base Models provide a solid foundation for the OPC UA Information Model, the true power of the technology lies in its ability to be extended and customized through the use of OPC UA companion specifications. These specifications are developed by various industry groups and organizations to address the unique needs and requirements of specific domains, such as building automation, energy management, and process control.
OPC UA companion specifications define additional node types, data models, and services that can be seamlessly integrated into the OPC UA Information Model ecosystem. This allows for the creation of highly specialized and tailored OPC UA-based solutions that can effectively address the challenges and requirements of diverse industrial and IoT applications. Some examples of OPC UA companion specifications include OPC UA for Devices (DI), OPC UA for Robotics (ROB), and OPC UA for PLCopen. As OPC UA bridges IT and OT environments, robust ICS cybersecurity becomes essential for protecting industrial data and operations.
The OPC UA Information Model provides a rich semantic industrial data model that enables devices and software from different vendors to share meaning, not just raw values. Its layered design — combining the OPC UA Address Space, well-defined OPC UA Base Services, and extensible OPC UA companion specifications — makes it the most comprehensive framework for industrial interoperability available today.
Embien serves automotive, industrial, medical, and consumer electronics domains, applying OPC UA Information Model concepts and IIoT integration across a broad range of product programmes.
From sensor firmware to cloud dashboards, Embien's IoT development services cover the full stack — including OPC UA server/client implementations and secure data pipelines for industrial IoT deployments.
A case study on developing an industrial protocol converter that bridges legacy fieldbus communication with modern Ethernet-based protocols — a practical application of OPC UA Information Model principles.