IEC TR 62541-1:2010

OPC Unified Architecture - Part 1: Overview and Concepts

IEC/TR 62541-1:2010(E) presents the concepts and overview of the Unified Architecture (OPC UA) specification produced by the OPC Foundation. Reading this report enables the reader to understand the series of IEC 62541 standards. Each of the other parts is briefly explained along with a suggested reading order.

General Information

• Status: Published
• Publication Date: 17-Feb-2010
• ICS: 25.040.40 - Industrial process measurement and control
• ICS: 35.100.01 - Open systems interconnection in general
• Technical Committee: SC 65E - Devices and integration in enterprise systems
• Drafting Committee: WG 8 - TC 65/SC 65E/WG 8
• Current Stage: DELPUB - Deleted Publication
• Completion Date: 05-Oct-2016

Relations

• Revised: IEC TR 62541-1:2016 - OPC unified architecture - Part 1: Overview and concepts
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC/TR 62541-1
®
Edition 1.0 2010-02
TECHNICAL
REPORT

colour
inside
OPC Unified Architecture –
Part 1: Overview and Concepts


IEC/TR 62541-1:2010(E)

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IEC/TR 62541-1
®
Edition 1.0 2010-02
TECHNICAL
REPORT

colour
inside
OPC Unified Architecture –
Part 1: Overview and Concepts


INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
U
ICS 25.040.40; 35.100.01 ISBN 978-2-88910-759-9
® Registered trademark of the International Electrotechnical Commission

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– 2 – TR 62541-1 © IEC:2010(E)
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.7
2 Normative references .7
3 Terms, definitions, abbreviations and conventions.7
3.1 Document conventions .7
3.2 Terms and definitions .7
3.3 Abbreviations .11
4 Structure of the OPC UA series .11
4.1 Structure of the IEC 62541 series of standards.11
4.2 Core specifications.12
4.3 Access type specification parts.12
4.4 Utility specification parts .13
5 IEC 62541 standards – Overview.13
5.1 UA scope .13
5.2 Introduction .13
5.3 Design goals .13
5.4 Integrated models and services .15
5.4.1 Security model.15
5.4.2 Integrated AddressSpace model .16
5.4.3 Integrated object model .17
5.4.4 Integrated services .17
5.5 Sessions .17
5.6 Redundancy .17
6 Systems concepts .17
6.1 Overview .17
6.2 OPC UA Clients.18
6.3 OPC UA Servers .19
6.3.1 General .19
6.3.2 Real objects .19
6.3.3 OPC UA Server application .19
6.3.4 OPC UA AddressSpace .20
6.3.5 Publisher/subscriber entities.20
6.3.6 OPC UA Service interface .20
6.3.7 Server to Server interactions .21
7 Service sets .22
7.1 General .22
7.2 Discovery service set .22
7.3 SecureChannel service set.22
7.4 Session service set .23
7.5 NodeManagement Service Set .23
7.6 View Service Set .24
7.7 Query Service Set .24
7.8 Attribute Service Set .24
7.9 Method Service Set .24
7.10 MonitoredItem Service Set .24

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TR 62541-1 © IEC:2010(E) – 3 –
7.11 Subscription Service Set .25
Bibliography.26

Figure 1 – Organization of the OPC UA series of standards .11
Figure 2 – OPC UA target applications.14
Figure 3 – OPC UA system architecture.18
Figure 4 – OPC UA Client architecture.18
Figure 5 – OPC UA server architecture .19
Figure 6 – Peer-to-peer interactions between Servers.21
Figure 7 – Chained Server example .22
Figure 8 – SecureChannel and Session Services .23

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INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

OPC UNIFIED ARCHITECTURE –

Part 1: Overview and Concepts


FOREWORD

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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
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The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC 62541-1, which is a technical report, has been prepared by subcommittee 65E: Devices
and integration in enterprise systems, of IEC technical committee 65: Industrial-process
measurement, control and automation.

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TR 62541-1 © IEC:2010(E) – 5 –
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
65E/92/DTR 65E/154/RVC

Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 62541 series, under the general title OPC Unified Architecture,
can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.

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INTRODUCTION
This technical report introduces the specification for developers of OPC Unified Architecture
applications. This technical report and specification are a result of an analysis and design
process to develop a standard interface to facilitate the development of applications by
multiple vendors that inter-operate seamlessly together.

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TR 62541-1 © IEC:2010(E) – 7 –
OPC UNIFIED ARCHITECTURE –

Part 1: Overview and Concepts



1 Scope
This part of IEC 62541 presents the concepts and overview of the Unified Architecture (OPC
UA) specification produced by the OPC Foundation. Reading this report enables the reader to
understand the series of IEC 62541 standards. Each of the other parts is briefly explained
along with a suggested reading order.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 62541 (all parts), OPC Unified Architecture
3 Terms, definitions, abbreviations and conventions
3.1 Document conventions
Throughout this document and the referenced other Parts of the series, certain document
conventions are used.
Italics are used to denote a defined term or definition that appears in the “Terms and
definition” clause in one of the Parts of the series.
Italics are also used to denote the name of a service input or output parameter or the name of
a structure or element of a structure that are usually defined in tables.
The italicized terms and names are also often written in camel-case (the practice of writing
compound words or phrases in which the elements are joined without spaces, with each
element's initial letter capitalized within the compound). For example the defined term is
AddressSpace instead of Address Space. This makes it easier to understand that there is a
single definition for AddressSpace, not separate definitions for Address and Space.
3.2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.2.1
AddressSpace
collection of information that an OPC UA Server makes visible to its Clients
NOTE See IEC 62541-3 for a description of the contents and structure of the Server AddressSpace.
3.2.2
Alarm
type of Event associated with a state condition that typically requires acknowledgement
NOTE See IEC 62541-9 or a description of Alarms.

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3.2.3
Attribute
primitive characteristic of a Node
NOTE All Attributes are defined by OPC UA, and may not be defined by Clients or Servers. Attributes are the only
elements in the AddressSpace permitted to have data values.
3.2.4
Certificate
digitally signed data structure that describes capabilities of a Client or Server
3.2.5
Client
software application that sends Messages to OPC UA Servers conforming to the Services
specified in the IEC 62541 series of standards
3.2.6
Condition
generic term that is an extension to an Event
NOTE A Condition represents the conditions of a system or one of its components and always exists in some
state.
3.2.7
Communication Stack
layered set of software modules between the application and the hardware that provides
various functions to encode, encrypt and format a Message for sending, and to decode,
decrypt and unpack a Message that was received
3.2.8
Complex Data
data that is composed of elements of more than one primitive data type
3.2.9
Discovery
process by which OPC UA Client obtains information about OPC UA Servers, including
endpoint and security information
3.2.10
Event
generic term used to describe an occurrence of some significance within a system or system
component
3.2.11
EventNotifier
special Attribute of a Node that signifies that a Client may subscribe to that particular Node to
receive Notifications of Event occurrences
3.2.12
Information Model
organizational framework that defines, characterizes and relates information resources of a
given system or set of systems
NOTE The core address space model supports the representation of Information Models in the AddressSpace.
See IEC 62541-5 for a description of the base OPC UA Information Model.
3.2.13
Message
data unit conveyed between Client and Server that represents a specific Service request or
response

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TR 62541-1 © IEC:2010(E) – 9 –
3.2.14
Method
callable software function that is a component of an Object
3.2.15
MonitoredItem
Client-defined entity in the Server used to monitor Attributes or EventNotifiers for new values
or Event occurrences and that generates Notifications for them
3.2.16
Node
fundamental component of an AddressSpace
3.2.17
NodeClass
class of a Node in an AddressSpace
NOTE NodeClasses define the metadata for the components of the OPC UA Object Model. They also define
constructs, such as Views, that are used to organize the AddressSpace.
3.2.18
Notification
generic term for data that announces the detection of an Event or of a changed Attribute
value; Notifications are sent in NotificationMessages
3.2.19
NotificationMessage
Message published from a Subscription that contains one or more Notifications
3.2.20
Object
Node that represents a physical or abstract element of a system
NOTE Objects are modelled using the OPC UA Object Model. Systems, subsystems and devices are examples of
Objects. An Object may be defined as an instance of an ObjectType.
3.2.21
Object Instance
synonym for Object
NOTE Not all Objects are defined by ObjectTypes.
3.2.22
ObjectType
Node that represents the type definition for an Object
3.2.23
Profile
specific set of capabilities to which a Server may claim conformance; each Server may claim
conformance to more than one Profile
NOTE The set of capabilities are defined in IEC 62541-7.
3.2.24
Program
executable Object that, when invoked, immediately returns a response to indicate that
execution has started, and then returns intermediate and final results through Subscriptions
identified by the Client during invocation

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3.2.25
Reference
explicit relationship (a named pointer) from one Node to another
NOTE The Node that contains the Reference is the source Node, and the referenced Node is the target Node. All
References are defined by ReferenceTypes.
3.2.26
ReferenceType
Node that represents the type definition of a Reference
NOTE The ReferenceType specifies the semantics of a Reference. The name of a ReferenceType identifies how
source Nodes are related to target Nodes and generally reflects an operation between the two, such as “A Contains
B”.
3.2.27
RootNode
beginning or top Node of a hierarchy
NOTE The RootNode of the OPC UA AddressSpace is defined in IEC 62541-5.
3.2.28
Server
software application that implements and exposes the Services specified in the IEC 62541
series of standards
3.2.29
Service
Client-callable operation in an OPC UA Server
NOTE Services are defined in IEC 62541-4. A Service is similar to a method call in a programming language or an
operation in a Web services WSDL contract.
3.2.30
Service Set
group of related Services
3.2.31
Session
logical long-running connection between a Client and a Server.
NOTE A Session maintains state information between Service calls from the Client to the Server.
3.2.32
Subscription
Client-defined endpoint in the Server, used to return Notifications to the Client
NOTE ”Subscription” is a generic term that describes a set of Nodes selected by the Client (1) that the Server
periodically monitors for the existence of some condition, and (2) for which the Server sends Notifications to the
Client when the condition is detected.
3.2.33
Variable
Node that contains a value
3.2.34
View
specific subset of the AddressSpace that is of interest to the Client.

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TR 62541-1 © IEC:2010(E) – 11 –
3.3 Abbreviations
A&E Alarms and Events
API Application Programming Interface
COM Component Object Model
DA Data Access
DCS Distributed Control System
DX Data Exchange
HDA Historical Data Access
HMI Human-Machine Interface
LDAP Lightweight Directory Access Protocol
MES Manufacturing Execution System
OPC OPC Foundation (a non-profit industry association)
formerly an acronym for “OLE for Process Control”. No longer used
PLC Programmable Logic Controller
SCADA Supervisory Control And Data Acquisition
SOAP Simple Object Access Protocol
TCP Transmission Control Protocol
UA Unified Architecture
UDDI Universal Description, Discovery and Integration
UML Unified Modelling Language
WSDL Web Services Definition Language
XML Extensible Mark-up Language
4 Structure of the OPC UA series
4.1 Structure of the IEC 62541 series of standards
Figure 1 shows the division of the OPC Unified Architecture.
OPC UA Multi-Part Specification
Core Specification Parts Access Type Specification Parts
Part 1 – Overview & Concepts Part 8 – Data Access
Part 2 – Security Model Part 9 – Alarms & Conditions
Part 3 – Address Space Model Part 10 – Programs
Part 4 – Services Part 11 – Historical Access
Part 5 – Information Model
Utility Specification Parts
Part 6 – Service Mappings
Part 12 – Discovery
Part 7 – Profiles
Part 13 – Aggregates

IEC  296/10

Figure 1 – Organization of the OPC UA series of standards

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IEC 62541-1 to IEC 62541-7 specify the core capabilities of OPC UA. These core capabilities
define the structure of the OPC AddressSpace and the Services that operate on it.
IEC 62541-8 to IEC 62541-11 apply these core capabilities to specific types of access
previously addressed by separate OPC COM specifications, such as Data Access (DA),
Alarms and Events (A&E) and Historical Data Access (HDA). IEC 62541-12 describes
Discovery mechanisms for OPC UA and IEC 62541-13 describes ways of aggregating data.
Readers are encouraged to read IEC 62541-1 to IEC 62541-5 of the core specifications
before reading IEC 62541-6 to IEC 62541-13. Some parts can be skipped depending on the
needs of the reader. For example, a reader interested in Data Access should read IEC 62541-
1 to IEC 62541-5 and then IEC 62541-8.
4.2 Core specifications
IEC/TR 62541-1 – General
Part 1 (this part) presents the concepts and overview of OPC UA.
IEC 62541-2 – Security model
IEC 62541-2 describes the model for securing interactions between OPC UA Clients and OPC
UA Servers.
IEC 62541-3 – Address space model
IEC 62541-3 describes the contents and structure of the Server’s AddressSpace.
IEC 62541-4 – Services
IEC 62541-4 specifies the Services provided by OPC UA Servers.
IEC 62541-5 – Information model
IEC 62541-5 specifies the types and their relationships defined for OPC UA Servers.
IEC 62541-6 – Mappings
IEC 62541-6 specifies the transport mappings and data encodings supported by OPC UA.
IEC 62541-7 – Profiles
IEC 62541-7 specifies the Profiles that are available for OPC Clients and Servers. These
Profiles provide groups of Services or functionality that can be used for conformance level
certification. Servers and Clients will be tested against the Profiles.
4.3 Access type specification parts
IEC 62541-8 – Data access
IEC 62541-8 specifies the use of OPC UA for data access.
IEC 62541-9 – Alarms and conditions
IEC 62541-9 specifies the use of OPC UA support for access to Alarms and Conditions. The
base system includes support for simple Events; this specification extends that support to
include support for Alarms and Conditions.

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TR 62541-1 © IEC:2010(E) – 13 –
IEC 62541-10 – Programs
IEC 62541-10 specifies OPC UA support for access to Programs.
IEC 62541-11 – Historical access
IEC 62541-11 specifies use of OPC UA for historical access. This access includes both
historical data and historical Events.
4.4 Utility specification parts
IEC 62541-12 – Discovery
IEC 62541-12 specifies how Discovery Servers operate in different scenarios and describes
how UA Clients and Servers should interact with them. It also defines how UA related
information should be accessed using common directory service protocols such as UDDI and
LDAP.
IEC 62541-13 – Aggregates
IEC 62541-13 specifies how to compute and return aggregates like minumum, maximum,
average etc. Aggregates can be used with base (live) data as well as historical (HDA) data.
5 IEC 62541 standards – 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
sin
...