OPC UA Part 1 - Overview and Concepts 1.02 Specification(16)

OPC UA Specification Part1 OverView and Concepts

OPC Unified Architecture, Part 1 8 Release 1.02 5 Overview

5.1 UA Scope

OPC UA is applicable to manufacturing software in application areas such as Field Devices, Control Systems, Manufacturing Execution Systems and Enterprise Resource Planning Systems. These systems are intended to exchange information and to use command and control for industrial processes. OPC UA defines a common infrastructure model to facilitate this information exchange OPC UA specifies the following:

∙The information model to represent structure, behaviour and semantics.

∙The message model to interact between applications.

∙The communication model to transfer the data between end-points.

∙The conformance model to guarantee interoperability between systems.

5.2 Introduction

OPC UA is a platform-independent standard through which various kinds of systems and devices can communicate by sending Messages between Clients and Servers over various types of networks. It supports robust, secure communication that assures the identity of Clients and Servers and resists attacks. OPC UA defines sets of Services that Servers may provide, and individual Servers specify to Clients what Service sets they support. Information is conveyed using OPC UA-defined and vendor-defined data types, and Servers define object models that Clients can dynamically discover. Servers can provide access to both current and historical data, as well as Alarms and Events to notify Clients of important changes. OPC UA can be mapped onto a variety of communication protocols and data can be encoded in various ways to trade off portability and efficiency.

5.3 Design goals

OPC UA provides a consistent, integrated AddressSpace and service model. This allows a single OPC UA Server to integrate data, Alarms and Events, and history into its AddressSpace, and to provide access to them using an integrated set of Services. These Services also include an integrated security model.

OPC UA also allows Servers to provide Clients with type definitions for the Objects accessed from the AddressSpace. This allows information models to be used to describe the contents of the AddressSpace. OPC UA allows data to be exposed in many different formats, including binary structures and XML documents. The format of the data may be defined by OPC, other standard organizations or vendors. Through the AddressSpace, Clients can query the Server for the metadata that describes the format for the data. In many cases, Clients with no pre-programmed knowledge of the data formats will be able to determine the formats at runtime and properly utilize the data.

OPC UA adds support for many relationships between Nodes instead of being limited to just a single hierarchy. In this way, an OPC UA Server may present data in a variety of hierarchies tailored to the way a set of Clients would typically like to view the data. This flexibility, combined with support for type definitions, makes OPC UA applicable to a wide array of problem domains. As illustrated below, OPC UA is not targeted at just the SCADA, PLC and DCS interface, but also as a way to provide greater interoperability between higher level functions.