OPC Unified Architecture - Part 8: Data Access

IEC 62541-8:2020 is available as IEC 62541-8:2020 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.
IEC 62541-8:2020 is part of the overall OPC Unified Architecture (OPC UA) standard series and defines the information model associated with Data Access (DA). It particularly includes additional VariableTypes and complementary descriptions of the NodeClasses and Attributes needed for Data Access, additional Properties, and other information and behaviour.
The complete address space model, including all NodeClasses and Attributes is specified in IEC 62541-3. The services to detect and access data are specified in IEC 62541-4.
This third edition cancels and replaces the second edition published in 2015. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
a) added new VariableTypes for AnalogItems;
b) added an Annex that specifies a recommended mapping of OPC UA Dataccess to OPC COM DataAccess;
c) changed the ambiguous description of "Bad_NotConnected";
d) updated description for EUInformation to refer to latest revision of UNCEFACT units.

Architecture unifiée OPC - Partie 8: Accès aux données

IEC 62541-8:2020 est disponible sous forme de IEC 62541-8:2020 RLV qui contient la Norme internationale et sa version Redline, illustrant les modifications du contenu technique depuis l'édition précédente.
L'IEC 62541-8:2020 fait partie intégrante de la série de normes générales sur l'architecture unifiée OPC (OPC UA). Elle définit le modèle d'information associé à l'Accès aux données (DA). Elle spécifie notamment des VariableTypes supplémentaires et fournit des descriptions complémentaires concernant les NodeClasses et attributs nécessaires pour l'Accès aux données, ainsi que des propriétés supplémentaires et d'autres paramètres relatifs aux informations et au comportement.
Le modèle d'espace d'adresses complet, comprenant toutes les NodeClasses et tous les Attributs, est spécifié dans l'IEC 62541-3. Les services de détection et d'accès aux données sont spécifiés dans l'IEC 62541-4.
Cette troisième édition annule et remplace la deuxième édition parue en 2015. Cette édition constitue une révision technique.
Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) ajout de nouveaux VariableTypes pour les AnalogItems;
b) ajout d'une annexe qui spécifie le mapping recommandé entre OPC UA DataAccess et OPC COM DataAccess;
c) modification de la description ambiguë de "Bad_NotConnected";
d) mise à jour de la description de EUInformation pour renvoyer à la dernière révision des unités CEFACT-ONU.

General Information

Status
Published
Publication Date
21-Jun-2020
Current Stage
PPUB - Publication issued
Completion Date
22-Jun-2020
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IEC 62541-8
Edition 3.0 2020-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
OPC unified architecture –
Part 8: Data access
Architecture unifiée OPC –
Partie 8: Accès aux données
IEC 62541-8:2020-06(en-fr)
---------------------- Page: 1 ----------------------
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IEC 62541-8
Edition 3.0 2020-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
OPC unified architecture –
Part 8: Data access
Architecture unifiée OPC –
Partie 8: Accès aux données
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 25.040.40; 35.100.05 ISBN 978-2-8322-8464-3

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® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC 62541-8:2020 © IEC 2020
CONTENTS

FOREWORD ........................................................................................................................... 5

1 Scope .............................................................................................................................. 7

2 Normative references ...................................................................................................... 7

3 Terms, definitions and abbreviated terms ........................................................................ 7

3.1 Terms and definitions .............................................................................................. 7

3.2 Abbreviated terms ................................................................................................... 8

4 Concepts ......................................................................................................................... 8

5 Model .............................................................................................................................. 9

5.1 General ................................................................................................................... 9

5.2 SemanticsChanged ............................................................................................... 10

5.3 Variable Types ...................................................................................................... 10

5.3.1 DataItemType ................................................................................................ 10

5.3.2 AnalogItem VariableTypes ............................................................................. 11

5.3.3 DiscreteItemType .......................................................................................... 14

5.3.4 ArrayItemType ............................................................................................... 17

5.4 Address Space model ........................................................................................... 23

5.5 Attributes of DataItems ......................................................................................... 24

5.6 DataTypes ............................................................................................................ 25

5.6.1 Overview ....................................................................................................... 25

5.6.2 Range ............................................................................................................ 25

5.6.3 EUInformation ............................................................................................... 25

5.6.4 ComplexNumberType .................................................................................... 27

5.6.5 DoubleComplexNumberType ......................................................................... 27

5.6.6 AxisInformation .............................................................................................. 28

5.6.7 AxisScaleEnumeration ................................................................................... 28

5.6.8 XVType ......................................................................................................... 29

6 Data Access specific usage of Services ......................................................................... 29

6.1 General ................................................................................................................. 29

6.2 PercentDeadband ................................................................................................. 29

6.3 Data Access status codes ..................................................................................... 30

6.3.1 Overview ....................................................................................................... 30

6.3.2 Operation level result codes .......................................................................... 30

6.3.3 LimitBits ........................................................................................................ 32

Annex A (informative) OPC COM DA to UA mapping ........................................................... 33

A.1 Overview............................................................................................................... 33

A.2 Security considerations ......................................................................................... 33

A.3 COM UA wrapper for OPC DA Server ................................................................... 33

A.3.1 Information Model mapping ............................................................................ 33

A.3.2 Data and error mapping ................................................................................. 37

A.3.3 Read data ...................................................................................................... 40

A.3.4 Write Data ..................................................................................................... 41

A.3.5 Subscriptions ................................................................................................. 42

A.4 COM UA proxy for DA Client ................................................................................. 42

A.4.1 Guidelines ..................................................................................................... 42

A.4.2 Information Model and Address Space mapping ............................................ 42

A.4.3 Data and error mapping ................................................................................. 46

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IEC 62541-8:2020 © IEC 2020 – 3 –

A.4.4 Read data ...................................................................................................... 48

A.4.5 Write data ...................................................................................................... 49

A.4.6 Subscriptions ................................................................................................. 49

Figure 1 – OPC DataItems are linked to automation data ........................................................ 9

Figure 2 – DataItem VariableType hierarchy ......................................................................... 10

Figure 3 – Graphical view of a YArrayItem ............................................................................ 19

Figure 4 – Representation of DataItems in the AddressSpace ............................................... 24

Figure A.1 – Sample OPC UA Information Model for OPC DA ............................................... 34

Figure A.2 – OPC COM DA to OPC UA data and error mapping ............................................ 38

Figure A.3 – Status Code mapping........................................................................................ 39

Figure A.4 – Sample OPC DA mapping of OPC UA Information Model and Address

Space ................................................................................................................................... 43

Figure A.5 – OPC UA to OPC DA data & error mapping ........................................................ 46

Figure A.6 – OPC UA Status Code to OPC DA quality mapping ............................................ 48

Table 1 – DataItemType definition ........................................................................................ 11

Table 2 – BaseAnalogType definition .................................................................................... 12

Table 3 – AnalogItemType definition ..................................................................................... 13

Table 4 – AnalogUnitType definition ...................................................................................... 13

Table 5 – AnalogUnitRangeType definition ........................................................................... 14

Table 6 – DiscreteItemType definition ................................................................................... 14

Table 7 – TwoStateDiscreteType definition ........................................................................... 15

Table 8 – MultiStateDiscreteType definition .......................................................................... 15

Table 9 – MultiStateValueDiscreteType definition ................................................................. 16

Table 10 – ArrayItemType definition ...................................................................................... 17

Table 11 – YArrayItemType definition ................................................................................... 18

Table 12 – YArrayItem item description................................................................................. 20

Table 13 – XYArrayItemType definition ................................................................................. 20

Table 14 – ImageItemType definition .................................................................................... 21

Table 15 – CubeItemType definition ...................................................................................... 22

Table 16 – NDimensionArrayItemType definition ................................................................... 23

Table 17 – Range DataType structure ................................................................................... 25

Table 18 – Range definition .................................................................................................. 25

Table 19 – EUInformation DataType structure ....................................................................... 25

Table 20 – EUInformation definition ...................................................................................... 26

Table 21 – Examples from UNECE Recommendation N° 20 .................................................. 26

Table 22 – ComplexNumberType DataType structure ........................................................... 27

Table 23 – ComplexNumberType definition ........................................................................... 27

Table 24 – DoubleComplexNumberType DataType structure ................................................. 27

Table 25 – DoubleComplexNumberType definition ................................................................ 28

Table 26 – AxisInformation DataType structure ..................................................................... 28

Table 27 – AxisScaleEnumeration values.............................................................................. 28

Table 28 – AxisScaleEnumeration definition ......................................................................... 29

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– 4 – IEC 62541-8:2020 © IEC 2020

Table 29 – XVType DataType structure ................................................................................. 29

Table 30 – XVType definition ................................................................................................ 29

Table 31 – Operation level result codes for BAD data quality ................................................ 31

Table 32 – Operation level result codes for UNCERTAIN data quality ................................... 31

Table 33 – Operation level result codes for GOOD data quality ............................................. 31

Table A.1 – OPC COM DA to OPC UA Properties mapping ................................................... 36

Table A.2 – DataTypes and mapping .................................................................................... 39

Table A.3 – Quality mapping ................................................................................................. 40

Table A.4 – OPC DA Read error mapping ............................................................................. 41

Table A.5 – OPC DA Write error code mapping ..................................................................... 41

Table A.6 – DataTypes and Mapping .................................................................................... 47

Table A.7 – Quality mapping ................................................................................................. 48

Table A.8 – OPC UA Read error mapping ............................................................................. 49

Table A.9 – OPC UA Write error code mapping ..................................................................... 49

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IEC 62541-8:2020 © IEC 2020 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPC UNIFIED ARCHITECTURE –
Part 8: Data access
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

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indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent

rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 62541-8 has been prepared by subcommittee 65E: Devices and

integration in enterprise systems, of IEC technical committee 65: Industrial-process

measurement, control and automation.

This third edition cancels and replaces the second edition published in 2015. This edition

constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous

edition:
a) added new VariableTypes for AnalogItems;

b) added an Annex that specifies a recommended mapping of OPC UA Dataccess to OPC

COM DataAccess;
c) changed the ambiguous description of "Bad_NotConnected";

d) updated description for EUInformation to refer to latest revision of UNCEFACT units.

---------------------- Page: 7 ----------------------
– 6 – IEC 62541-8:2020 © IEC 2020
The text of this International Standard is based on the following documents:
FDIS Report on voting
65E/708/FDIS 65E/726/RVD

Full information on the voting for the approval of this International Standard can be found in the

report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

Throughout this document and the other parts of the IEC 62541 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 IEC 62541 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, with a few exceptions, 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.

A list of all parts of the IEC 62541 series, published under the general title OPC Unified

Architecture, can be found on the IEC website.

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to

the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

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.

---------------------- Page: 8 ----------------------
IEC 62541-8:2020 © IEC 2020 – 7 –
OPC UNIFIED ARCHITECTURE –
Part 8: Data access
1 Scope

This part of IEC 62541 is part of the overall OPC Unified Architecture (OPC UA) standard series

and defines the information model associated with Data Access (DA). It particularly includes

additional VariableTypes and complementary descriptions of the NodeClasses and Attributes

needed for Data Access, additional Properties, and other information and behaviour.

The complete address space model, including all NodeClasses and Attributes is specified in

IEC 62541-3. The services to detect and access data are specified in IEC 62541-4.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements 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 TR 62541-1, OPC Unified Architecture – Part 1: Overview and Concepts
IEC 62541-3, OPC Unified Architecture – Part 3: Address Space Model
IEC 62541-4, OPC Unified Architecture – Part 4: Services
IEC 62541-5, OPC Unified Architecture – Part 5: Information Model
UN/CEFACT: UNECE Recommendation N° 20, Codes for Units of Measure Used in
International Trade, available at
https://www.unece.org/cefact/codesfortrade/codes_index.html
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC TR 62541-1,

IEC 62541-3, and IEC 62541-4 and the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1.1
DataItem

link to arbitrary, live automation data, that is, data that represents currently valid information

Note 1 to entry: Examples of such data are
• device data (such as temperature sensors),
---------------------- Page: 9 ----------------------
– 8 – IEC 62541-8:2020 © IEC 2020
• calculated data,
• status information (open/closed, moving),
• dynamically changing system data (such as stock quotes),
• diagnostic data.
3.1.2
AnalogItem

DataItem that represents continuously variable physical quantities (e.g. length, temperature),

in contrast to the digital representation of data in discrete items

Note 1 to entry: Typical examples are the values provided by temperature sensors or pressure sensors. OPC UA

defines a specific VariableType to identify an AnalogItem. Properties describe the possible ranges of AnalogItems.

3.1.3
DiscreteItem

DataItem that represents data that may take on only a certain number of possible values (e.g.

OPENING, OPEN, CLOSING, CLOSED)

Note 1 to entry: Specific VariableTypes are used to identify DiscreteItems with two states or with multiple states.

Properties specify the string values for these states.
3.1.4
ArrayItem

DataItem that represents continuously variable physical quantities and where each individual

data point consists of multiple values represented by an array (e.g., the spectral response of a

digital filter)

Note 1 to entry: Typical examples are the data provided by analyser devices. Specific VariableTypes are used to

identify ArrayItem variants.
3.1.5
EngineeringUnits

units of measurement for AnalogItems that represent continuously variable physical quantities

(e.g. length, mass, time, temperature)

Note 1 to entry: This standard defines Properties to inform about the unit used for the DataItem value and about

the highest and lowest value likely to be obtained in normal operation.
3.2 Abbreviated terms
DA data access
EU engineering unit
UA Unified Architecture
4 Concepts
Data Access deals with the representation and use of automation data in Servers.

Automation data can be located inside the Server or on I/O cards directly connected to the

Server. It can also be located in sub-servers or on other devices such as controllers and

input/output modules, connected by serial links via field buses or other communication links.

OPC UA Data Access Servers provide one or more OPC UA Data Access Clients with
transparent access to their automation data.

The links to automation data instances are called DataItems. The categories of automation data

are provided is completely vendor-specific. Figure 1 illustrates how the AddressSpace of a

Server may consist of a broad range of different DataItems.
---------------------- Page: 10 ----------------------
IEC 62541-8:2020 © IEC 2020 – 9 –
OPC UA Server
Root
AddressSpace
with data items
IEC
Figure 1 – OPC DataItems are linked to automation data

Clients may read or write DataItems, or monitor them for value changes. The Services needed

for these operations are specified in IEC 62541-4. Changes are defined as a change in status

(quality) or a change in value that exceeds a client-defined range called a Deadband. To detect

the value change, the difference between the current value and the last reporte
...

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