IEC 62541-17:2025
(Main)OPC unified architecture - Part 17: Alias Names
OPC unified architecture - Part 17: Alias Names
IEC 62541-17:2025 provides a definition of AliasNames functionality. AliasNames provide a manner of configuring and exposing an alternate well-defined name for any Node in the system. This is analogous to the way domain names are used as an alias to IP addresses in IP networks. Like a DNS Server, an OPC UA Server that supports AliasNames provides a lookup Method that will translate an AliasName to a NodeId of the related Node on a Server. An aggregating Server can collect these AliasNames from multiple Servers and provide a lookup Method to allow Client applications to discover NodeIds on a system wide basis. An aggregating Server could also define AliasNames for Nodes in other Servers that do not support AliasNames. A GDS can be constructed that would automatically aggregate all AliasNames that are defined on any Server that has registered with the GDS. In this case, the GDS also provides the lookup mechanism for Clients at a well-known endpoint and address.
Architecture unifiée OPC - Partie 17: Alias
IEC 62541-17:2025 donne une définition de la fonctionnalité des AliasNames. Les AliasNames permettent de configurer et d'exposer un nom alternatif bien défini pour n'importe quel Nœud du système. Il s'agit d'un principe analogue à la manière dont les noms de domaine sont utilisés comme alias pour les adresses IP dans les réseaux IP. Comme un Serveur DNS, un Serveur OPC UA qui prend en charge les AliasNames fournit une Méthode de recherche qui permet de traduire un AliasName en un NodeId du Nœud correspondant sur un Serveur. Un Serveur de regroupement peut collecter ces AliasNames auprès de plusieurs Serveurs et fournir une Méthode de recherche pour permettre aux applications du Client de découvrir les NodeIds à l'échelle du système. Un Serveur de regroupement peut également définir des AliasNames pour des Nœuds d'autres Serveurs qui ne prennent pas en charge les AliasNames. Il est possible de créer un Serveur de découverte global (GDS, Global Discovery Server) qui regroupe automatiquement tous les AliasNames définis sur tout Serveur qui s'est enregistré auprès du GDS. Dans ce cas, le GDS fournit également le mécanisme de recherche pour les Clients à un point d'extrémité et une adresse connus.
General Information
Standards Content (Sample)
IEC 62541-17 ®
Edition 1.0 2025-12
INTERNATIONAL
STANDARD
OPC unified architecture -
Part 17: Alias Names
ICS 25.040 ISBN 978-2-8327-0857-6
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CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms, definitions and abbreviated terms . 5
3.1 Terms and definitions . 5
3.2 Abbreviated terms. 5
4 Use cases . 6
4.1 Complex configuration . 6
4.2 Automatic reconfiguration . 6
4.3 Cloud based system . 6
4.4 Aggregated systems . 6
5 AliasNames Information Model overview . 6
6 OPC UA ObjectTypes . 8
6.1 Overview . 8
6.2 AliasNameType ObjectType Definition . 8
6.3 AliasNameCategoryType ObjectType Definition . 8
6.3.1 Definition . 8
6.3.2 FindAlias Method . 9
7 OPC UA DataTypes . 11
7.1 Overview . 11
7.2 AliasNameDataType . 11
8 Reference Types . 11
8.1 Overview . 11
8.2 AliasFor ReferenceType . 11
9 Instances . 12
9.1 Overview . 12
9.2 Aliases . 12
9.3 TagVariables . 12
9.4 Topics . 13
Annex A (informative) Examples . 14
A.1 Overview . 14
A.2 AliasNames used within a single Server . 14
A.3 AliasNames in an aggregating Server . 15
A.4 Standalone AliasNames Server . 16
A.5 Aggregating Server with a collection of Aggregates . 17
A.6 GDS . 18
A.7 Client use of an AliasName Server . 18
Annex B (normative) GDS functionality . 20
B.1 Overview . 20
B.2 Register a Server. 21
B.3 Unregister a Server . 21
B.4 Disconnect between a Client and an AliasName Server . 22
Bibliography . 24
Figure 1 – AliasNames Overview. 7
Figure 2 – AliasNames Example. 7
Figure A.1 – AliasNames in a Server example . 14
Figure A.2 – Aggregating AliasNames Server example . 15
Figure A.3 – AliasNames Server example . 16
Figure A.4 – Aggregating Server example 2 . 17
Figure A.5 – GDS with merged AliasNames example. 18
Figure B.1 – Example GDS aggregating AliasNames . 20
Figure B.2 – Server Registration Process . 21
Figure B.3 – Unregister Server Process . 22
Figure B.4 – Example Client Process for Server subscription with errors . 23
Table 1 – AliasNameType Definition . 8
Table 2 – AliasNameCategoryType Definition . 9
Table 3 – FindAlias Method Arguments . 10
Table 4 – FindAlias Method Error Codes . 10
Table 5 – FindAlias Method AddressSpace definition . 10
Table 6 – AliasNameDataType DataType structure . 11
Table 7 – AliasNameDataType Definition . 11
Table 8 – AliasFor Definition . 12
Table 9 – Aliases definition. 12
Table 10 – TagVariables definition . 13
Table 11 – Topics definition . 13
INTERNATIONAL ELECTROTECHNICAL COMMISSION
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OPC unified architecture -
Part 17: Alias Names
FOREWORD
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IEC 62541-17 has been prepared by subcommittee 65E: Devices and integration in enterprise
systems, of IEC technical committee 65: Industrial-process measurement, control and
automation. It is an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
65E/1042/CDV 65E/1100/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
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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 in the IEC 62541 series, published under the general title OPC Unified
Architecture, can be found on the IEC website.
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1 Scope
This part of IEC 62541 provides a definition of AliasNames functionality. AliasNames provide a
manner of configuring and exposing an alternate well-defined name for any Node in the system.
This is analogous to the way domain names are used as an alias to IP addresses in IP networks.
Like a DNS Server, an OPC UA Server that supports AliasNames provides a lookup Method
that will translate an AliasName to a NodeId of the related Node on a Server. An aggregating
Server can collect these AliasNames from multiple Servers and provide a lookup Method to
allow Client applications to discover NodeIds on a system wide basis. An aggregating Server
could also define AliasNames for Nodes in other Servers that do not support AliasNames. A
GDS can be constructed that would automatically aggregate all AliasNames that are defined on
any Server that has registered with the GDS. In this case, the GDS also provides the lookup
mechanism for Clients at a well-known endpoint and address.
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 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
IEC 62541-12, OPC Unified Architecture - Part 12: Discovery and Global Services
IEC 62541-14, OPC Unified Architecture - Part 14: PubSub
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 62541-1,
IEC 62541-3, IEC 62541-4, IEC 62541-5, IEC 62541-12, and IEC 62541-14 and the following
apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
3.1.1
AliasName
alternate well-defined name for any Node in the system
3.2 Abbreviated terms
GDS Global Discovery Server
4 Use cases
4.1 Complex configuration
For systems that are large and complex, engineering is often done in multiple tools and by
multiple individuals. The separate configurations are required to work together, but resolving
the references between these different configurations can be a significant task. A common
solution to simplify this task is a naming convention for the items that are being referenced.
Providing an automatic lookup capability for these names would greatly simplify configuration.
Each system can specify its own names and configurations can be built to just use the names,
without having to know the exact address of the items. The exact address would include the
address of the Server, the address of the tag in the Server, the required protocol for connecting
to the Server, security settings etc. OPC UA defines a GDS that can provide information about
what Servers are available in a system and how to connect to them, but it does not currently
provide information about the tags that are available in a given Server.
4.2 Automatic reconfiguration
In a system where many smaller Servers exist and these Servers could be dynamic, in that new
Servers can appear and disappear. Configuration could move between Servers. The automatic
resolution of where a specific piece of information is located would greatly simplify these
systems.
4.3 Cloud based system
Much like the previous use case, a cloud-based system, where Servers can be spun up in a
new cloud system or adjusted and split based on loading to multiple Servers. The automatic
resolution of where a specific piece of information is located would greatly simplify these
systems.
4.4 Aggregated systems
In systems where many simple devices exist, any given simple device could not have the ability
to provide name resolution, yet these systems can be much like systems in one of the previous
use cases. In a system such as this an aggregating Server could exist, where the aggregating
Server would provide the names as well as the lookup for the underlying Server. This
aggregating Server could also provide other functionality such as aggregation of values, but it
can also only provide the name definitions and resolutions. The underlying Server could have
no knowledge of the name.
5 AliasNames Information Model overview
The AliasNames functionality (illustrated in Figure 1) defines a number of ObjectTypes,
Methods, DataTypes and References. Figure 2 illustrates an example of the Object model
defined for AliasNames.
Figure 1 – AliasNames Overview
The model also includes some well-known fixed instances. The key functionality of AliasNames
is to reference the information that an AliasName is assigned to. These can be any Node. The
AliasNames can be grouped according to types of functionality. The OPC Foundation defines
some initial groups, but the groups can be extended by companion specifications, vendors or
end users to meet their needs. Examples for the use of AliasNames are in Annex A. The GDS
functionality for AliasNames is formally defined in Annex B.
Figure 2 – AliasNames Example
6 OPC UA ObjectTypes
6.1 Overview
An overview of this object model is provided in Clause 5. Figure 1 illustrates the overall
AliasName Object Model.
6.2 AliasNameType ObjectType Definition
Instances of the AliasNameType ObjectType provide alternate names for Nodes. The
AliasNameType is formally defined in Table 1.
Table 1 – AliasNameType Definition
Attribute Value
BrowseName AliasNameType
IsAbstract False
References NodeCl
...
IEC 62541-17 ®
Edition 1.0 2025-12
NORME
INTERNATIONALE
Architecture unifiée OPC -
Partie 17: Alias
ICS 25.040 ISBN 978-2-8327-0857-6
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SOMMAIRE
AVANT-PROPOS . 3
1 Domaine d'application . 5
2 Références normatives . 5
3 Termes, définitions et abréviations . 5
3.1 Termes et définitions. 5
3.2 Abréviations . 5
4 Cas d'utilisation . 6
4.1 Configuration complexe . 6
4.2 Reconfiguration automatique . 6
4.3 Système fondé sur le Cloud . 6
4.4 Regroupement de systèmes . 6
5 Vue d'ensemble du modèle d'information AliasNames . 6
6 ObjectTypes OPC UA . 8
6.1 Vue d'ensemble . 8
6.2 Définition de l'ObjectType AliasNameType . 8
6.3 Définition de l'ObjectType AliasNameCategoryType . 8
6.3.1 Définition . 8
6.3.2 Méthode FindAlias . 9
7 DataTypes OPC UA . 11
7.1 Vue d'ensemble . 11
7.2 AliasNameDataType . 11
8 Types de Références . 11
8.1 Vue d'ensemble . 11
8.2 ReferenceType AliasFor . 11
9 Instances . 12
9.1 Vue d'ensemble . 12
9.2 Aliases . 12
9.3 TagVariables . 12
9.4 Topics . 13
Annexe A (informative) Exemples . 14
A.1 Vue d'ensemble . 14
A.2 AliasNames utilisés dans un Serveur unique . 14
A.3 AliasNames dans un Serveur de regroupement . 15
A.4 Serveur AliasNames autonome . 16
A.5 Serveur de regroupement avec une collection d'Agrégats . 17
A.6 GDS . 18
A.7 Utilisation d'un Serveur AliasName par un Client. 18
Annexe B (normative) Fonctionnalité GDS . 20
B.1 Vue d'ensemble . 20
B.2 Enregistrement d'un Serveur . 21
B.3 Supprimer l'enregistrement d'un Serveur . 21
B.4 Déconnexion entre un Client et un Serveur AliasName . 22
Bibliographie . 24
Figure 1 – Vue d'ensemble des AliasNames . 7
Figure 2 – Exemple d'AliasNames . 7
Figure A.1 – AliasNames dans un exemple de Serveur . 14
Figure A.2 – Exemple de Serveur AliasNames de regroupement . 15
Figure A.3 – Exemple de Serveur AliasNames . 16
Figure A.4 – Serveur de regroupement, exemple 2. 17
Figure A.5 – Exemple de GDS avec AliasNames fusionnés . 18
Figure B.1 – Exemple de GDS regroupant des AliasNames. 20
Figure B.2 – Processus d'enregistrement d'un Serveur . 21
Figure B.3 – Processus de suppression de l'enregistrement d'un Serveur. 22
Figure B.4 – Exemple de processus Client en cas d'abonnement à un Serveur avec
des erreurs . 23
Tableau 1 – Définition d'AliasNameType . 8
Tableau 2 – Définition d'AliasNameCategoryType . 9
Tableau 3 – Arguments de la Méthode FindAlias . 10
Tableau 4 – Codes d'erreur de la Méthode FindAlias . 10
Tableau 5 – Définition de l'AddressSpace pour la Méthode FindAlias . 10
Tableau 6 – Structure du DataType AliasNameDataType . 11
Tableau 7 – Définition d'AliasNameDataType . 11
Tableau 8 – Définition d'AliasFor . 12
Tableau 9 – Définition d'Aliases . 12
Tableau 10 – Définition de TagVariables . 13
Tableau 11 – Définition de Topics . 13
COMMISSION ÉLECTROTECHNIQUE INTERNATIONALE
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Architecture unifiée OPC -
Partie 17: Alias
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Directives ISO/IEC, Partie 1 et les Directives ISO/IEC, Supplément IEC, disponibles sous
www.iec.ch/members_experts/refdocs. Les principaux types de documents développés par
l'IEC sont décrits plus en détail sous www.iec.ch/publications.
Dans l'ensemble du présent document et dans les autres parties de la série, certaines
conventions de document sont utilisées:
Le format italique est utilisé pour mettre en évidence un terme défini ou une définition qui
apparaît à l'article "Termes et définitions" dans l'une des parties de la série.
Le format italique est également utilisé pour mettre en évidence le nom d'un paramètre d'entrée
ou de sortie de service, ou le nom d'une structure ou d'un élément de structure habituellement
défini dans les tableaux.
Par ailleurs, les termes et noms en italique sont souvent écrits en camel-case (pratique qui
consiste à joindre, sans espace, les éléments des mots ou expressions composés, la première
lettre de chaque élément étant en majuscule). Par exemple, le terme défini est AddressSpace
et non Espace d'Adressage. Cela permet de mieux comprendre qu'il existe une définition unique
pour AddressSpace, et non deux définitions distinctes pour Espace et pour Adressage.
Une liste de toutes les parties de la série IEC 62541, publiées sous le titre général Architecture
unifiée OPC, se trouve sur le site web de l'IEC.
Le comité a décidé que le contenu de ce document ne sera pas modifié avant la date de stabilité
indiquée sur le site web de l'IEC sous webstore.iec.ch dans les données relatives au document
recherché. À cette date, le document sera
– reconduit,
– supprimé, ou
– révisé.
1 Domaine d'application
La présente partie de l'IEC 62541 donne une définition de la fonctionnalité des AliasNames.
Les AliasNames permettent de configurer et d'exposer un nom alternatif bien défini pour
n'importe quel Nœud du système. Il s'agit d'un principe analogue à la manière dont les noms
de domaine sont utilisés comme alias pour les adresses IP dans les réseaux IP. Comme un
Serveur DNS, un Serveur OPC UA qui prend en charge les AliasNames fournit une Méthode de
recherche qui permet de traduire un AliasName en un NodeId du Nœud correspondant sur un
Serveur. Un Serveur de regroupement peut collecter ces AliasNames auprès de plusieurs
Serveurs et fournir une Méthode de recherche pour permettre aux applications du Client de
découvrir les NodeIds à l'échelle du système. Un Serveur de regroupement peut également
définir des AliasNames pour des Nœuds d'autres Serveurs qui ne prennent pas en charge les
AliasNames. Il est possible de créer un Serveur de découverte global (GDS, Global Discovery
Server) qui regroupe automatiquement tous les AliasNames définis sur tout Serveur qui s'est
enregistré auprès du GDS. Dans ce cas, le GDS fournit également le mécanisme de recherche
pour les Clients à un point d'extrémité et une adresse connus.
2 Références normatives
Les documents suivants sont cités dans le texte de sorte qu'ils constituent, pour tout ou partie
de leur contenu, des exigences du présent document. Pour les références datées, seule
l'édition citée s'applique. Pour les références non datées, la dernière édition du document de
référence s'applique (y compris les éventuels amendements).
IEC 62541-1, Architecture unifiée OPC - Partie 1: Vue d'ensemble et concepts
IEC 62541-3, Architecture unifiée OPC - Partie 3: Modèle d'espace d'adressage
IEC 62541-4, Architecture unifiée OPC - Partie 4: Services
IEC 62541-5, Architecture unifiée OPC - Partie 5: Modèle d'information
IEC 62541-12, Architecture unifiée OPC - Partie 12: Services globaux et de découverte
IEC 62541-14, Architecture unifiée OPC - Partie 14: PubSub
3 Termes, définitions et abréviations
3.1 Termes et définitions
Pour les besoins du présent document, les termes et définitions de
l'IEC 62541-1, l'IEC 62541-3, l'IEC 62541-4, l'IEC 62541-5, l'IEC 62541-12 et l'IEC 62541-14
ainsi que les suivants s'appliquent.
L'ISO et l'IEC tiennent à jour des bases de données terminologiques destinées à être utilisées
en normalisation, consultables aux adresses suivantes:
– IEC Electropedia: disponible à l'adresse https://www.electropedia.org/
– ISO Online browsing platform: disponible à l'adresse https://www.iso.org/obp
3.1.1
AliasName
nom alternatif bien défini pour tout Nœud du système
3.2 Abréviations
GDS (Global Discovery Server) Serveur de découverte global
4 Cas d'utilisation
4.1 Configuration complexe
Pour les systèmes complexes et de grande taille, l'ingénierie est souvent réalisée à l'aide de
plusieurs outils et par plusieurs personnes. Les différentes configurations doivent fonctionner
ensemble, mais la résolution des références entre ces différentes configurations peut
représenter une tâche considérable. Une solution courante permettant de simplifier cette tâche
consiste à établir une convention de dénomination pour les éléments référencés. La mise en
place d'une capacité de recherche automatique pour ces noms simplifierait fortement la
configuration. Chaque système peut spécifier ses propres noms et les configurations peuvent
être conçues pour utiliser simplement les noms, sans avoir à connaître l'adresse exacte des
éléments. L'adresse exacte comprendrait l'adresse du Serveur, l'adresse de la balise dans le
Serveur, le protocole exigé pour se connecter au Serveur, les paramètres de sécurité, etc.
L'OPC UA définit un GDS qui peut fournir des informations sur les Serveurs disponibles dans
un système et sur la manière de s'y connecter, mais il ne fournit pas encore d'informations
concernant les balises qui sont disponibles dans un Serveur donné.
4.2 Reconfiguration automatique
Dans un système où il existe de nombreux Serveurs de taille réduite et dans lequel ces Serveurs
peuvent être dynamiques, au sens où de nouveaux Serveurs peuvent apparaître et disparaître.
La configuration peut passer d'un Serveur à un autre. La résolution automatique de
l'emplacement d'un élément d'information spécifique simplifierait considérablement ces
systèmes.
4.3 Système fondé sur le Cloud
Comme dans le cas d'utilisation précédent, un système fondé sur le Cloud, où les Serveurs
peuvent être lancés dans un nouveau système Cloud ou modifiés et divisés en fonction de la
charge vers de multiples Serveurs. La résolution automatique de l'emplacement d'un élément
d'information spécifique simplifierait considérablement ces systèmes.
4.4 Regroupement de systèmes
Dans les systèmes où il existe de nombreux dispositifs simples, tout dispositif simple donné
peut ne pas avoir la capacité d'assurer la résolution de noms, cependant ces systèmes peuvent
présenter une grande similitude avec les systèmes de l'un des cas d'utilisation précédents.
Dans un tel système, il peut exister un Serveur de regroupement, capable de fournir les noms
ainsi que d'effectuer la recherche pour le Serveur sous-jacent. Ce Serveur de regroupement
peut également fournir d'autres fonctionnalités telles que le regroupement de valeurs, mais il
peut également ne fournir que les définitions et les résolutions de noms. Il est possible que le
Serveur sous-jacent n'ait aucune connaissance du nom.
5 Vue d'ensemble du modèle d'information AliasNames
La fonctionnalité AliasNames (représentée à la Figure 1) définit un certain nombre
d'ObjectTypes, de Méthodes, de DataTypes et de Références. La Figure 2 montre un exemple
du modèle d'Objet défini pour les AliasNames.
Figure 1 – Vue d'ensemble des AliasNames
Le modèle comprend également des instances fixes connues. La principale fonctionnalité des
AliasNames est de référencer les informations auxquelles un AliasName est attribué. Il peut
s'agit de n'importe quel Nœud. Les AliasNames peuvent être regroupés en fonction des types
de fonctionnalité. La Fondation OPC définit certains groupes initiaux, mais les groupes peuvent
être élargis par des spécifications d'accompagnement, des vendeurs ou des utilisateurs finaux
afin de répondre à leurs besoins. Des exemples d’utilisation des AliasNames sont présentés à
l’Annexe A. La fonctionnalité GDS pour AliasNames est formellement définie à l’Annexe B.
Figure 2 – Exemple d'AliasNames
6 ObjectTypes OPC UA
6.1 Vue d'ensemble
Une vue d'ensemble de ce modèle d'objet est fournie à l'Article 5. La Figure 1 représente le
Modèle d'Objet AliasName dans son ensemble.
6.2 Définition de l'ObjectType AliasNameType
Les instances de l'ObjectType AliasNameType fournissent des noms alternatifs pour les
Nœuds. L'AliasNameType est défini de manière formelle dans le Tableau 1.
Tableau 1 – Définition d'AliasNameType
Attribut Valeur
BrowseName AliasNameType
IsAbstract False
Références NodeClass BrowseName DataType TypeDefinition ModellingRule
Sous-type du BaseObjectType défini dans l'IEC 62541-5
Conformance Units
AliasName Base
Cet ObjectType n'a ni Propriétés ni Variables. Le BrowseName de l'Objet est utilisé comme
a
...
IEC 62541-17 ®
Edition 1.0 2025-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
OPC unified architecture -
Part 17: Alias Names
Architecture unifiée OPC -
Partie 17: Alias
ICS 25.040 ISBN 978-2-8327-0857-6
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CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms, definitions and abbreviated terms . 5
3.1 Terms and definitions . 5
3.2 Abbreviated terms. 5
4 Use cases . 6
4.1 Complex configuration . 6
4.2 Automatic reconfiguration . 6
4.3 Cloud based system . 6
4.4 Aggregated systems . 6
5 AliasNames Information Model overview . 6
6 OPC UA ObjectTypes . 8
6.1 Overview . 8
6.2 AliasNameType ObjectType Definition . 8
6.3 AliasNameCategoryType ObjectType Definition . 8
6.3.1 Definition . 8
6.3.2 FindAlias Method . 9
7 OPC UA DataTypes . 11
7.1 Overview . 11
7.2 AliasNameDataType . 11
8 Reference Types . 11
8.1 Overview . 11
8.2 AliasFor ReferenceType . 11
9 Instances . 12
9.1 Overview . 12
9.2 Aliases . 12
9.3 TagVariables . 12
9.4 Topics . 13
Annex A (informative) Examples . 14
A.1 Overview . 14
A.2 AliasNames used within a single Server . 14
A.3 AliasNames in an aggregating Server . 15
A.4 Standalone AliasNames Server . 16
A.5 Aggregating Server with a collection of Aggregates . 17
A.6 GDS . 18
A.7 Client use of an AliasName Server . 18
Annex B (normative) GDS functionality . 20
B.1 Overview . 20
B.2 Register a Server. 21
B.3 Unregister a Server . 21
B.4 Disconnect between a Client and an AliasName Server . 22
Bibliography . 24
Figure 1 – AliasNames Overview. 7
Figure 2 – AliasNames Example. 7
Figure A.1 – AliasNames in a Server example . 14
Figure A.2 – Aggregating AliasNames Server example . 15
Figure A.3 – AliasNames Server example . 16
Figure A.4 – Aggregating Server example 2 . 17
Figure A.5 – GDS with merged AliasNames example. 18
Figure B.1 – Example GDS aggregating AliasNames . 20
Figure B.2 – Server Registration Process . 21
Figure B.3 – Unregister Server Process . 22
Figure B.4 – Example Client Process for Server subscription with errors . 23
Table 1 – AliasNameType Definition . 8
Table 2 – AliasNameCategoryType Definition . 9
Table 3 – FindAlias Method Arguments . 10
Table 4 – FindAlias Method Error Codes . 10
Table 5 – FindAlias Method AddressSpace definition . 10
Table 6 – AliasNameDataType DataType structure . 11
Table 7 – AliasNameDataType Definition . 11
Table 8 – AliasFor Definition . 12
Table 9 – Aliases definition. 12
Table 10 – TagVariables definition . 13
Table 11 – Topics definition . 13
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPC unified architecture -
Part 17: Alias Names
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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IEC 62541-17 has been prepared by subcommittee 65E: Devices and integration in enterprise
systems, of IEC technical committee 65: Industrial-process measurement, control and
automation. It is an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
65E/1042/CDV 65E/1100/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
Throughout this document and the 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 definitions”
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.
A list of all parts in 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 webstore.iec.ch in the data related to the
specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
1 Scope
This part of IEC 62541 provides a definition of AliasNames functionality. AliasNames provide a
manner of configuring and exposing an alternate well-defined name for any Node in the system.
This is analogous to the way domain names are used as an alias to IP addresses in IP networks.
Like a DNS Server, an OPC UA Server that supports AliasNames provides a lookup Method
that will translate an AliasName to a NodeId of the related Node on a Server. An aggregating
Server can collect these AliasNames from multiple Servers and provide a lookup Method to
allow Client applications to discover NodeIds on a system wide basis. An aggregating Server
could also define AliasNames for Nodes in other Servers that do not support AliasNames. A
GDS can be constructed that would automatically aggregate all AliasNames that are defined on
any Server that has registered with the GDS. In this case, the GDS also provides the lookup
mechanism for Clients at a well-known endpoint and address.
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 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
IEC 62541-12, OPC Unified Architecture - Part 12: Discovery and Global Services
IEC 62541-14, OPC Unified Architecture - Part 14: PubSub
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 62541-1,
IEC 62541-3, IEC 62541-4, IEC 62541-5, IEC 62541-12, and IEC 62541-14 and the following
apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
3.1.1
AliasName
alternate well-defined name for any Node in the system
3.2 Abbreviated terms
GDS Global Discovery Server
4 Use cases
4.1 Complex configuration
For systems that are large and complex, engineering is often done in multiple tools and by
multiple individuals. The separate configurations are required to work together, but resolving
the references between these different configurations can be a significant task. A common
solution to simplify this task is a naming convention for the items that are being referenced.
Providing an automatic lookup capability for these names would greatly simplify configuration.
Each system can specify its own names and configurations can be built to just use the names,
without having to know the exact address of the items. The exact address would include the
address of the Server, the address of the tag in the Server, the required protocol for connecting
to the Server, security settings etc. OPC UA defines a GDS that can provide information about
what Servers are available in a system and how to connect to them, but it does not currently
provide information about the tags that are available in a given Server.
4.2 Automatic reconfiguration
In a system where many smaller Servers exist and these Servers could be dynamic, in that new
Servers can appear and disappear. Configuration could move between Servers. The automatic
resolution of where a specific piece of information is located would greatly simplify these
systems.
4.3 Cloud based system
Much like the previous use case, a cloud-based system, where Servers can be spun up in a
new cloud system or adjusted and split based on loading to multiple Servers. The automatic
resolution of where a specific piece of information is located would greatly simplify these
systems.
4.4 Aggregated systems
In systems where many simple devices exist, any given simple device could not have the ability
to provide name resolution, yet these systems can be much like systems in one of the previous
use cases. In a system such as this an aggregating Server could exist, where the aggregating
Server would provide the names as well as the lookup for the underlying Server. This
aggregating Server could also provide other functionality such as aggregation of values, but it
can also only provide the name definitions and resolutions. The underlying Server could have
no knowledge of the name.
5 AliasNames Information Model overview
The AliasNames functionality (illustrated in Figure 1) defines a number of ObjectTypes,
Methods, DataTypes and References. Figure 2 illustrates an example of the Object model
defined for AliasNames.
Figure 1 – AliasNames Overview
The model also includes some well-known fixed instances. The key functionality of AliasNames
is to reference the information that an AliasName is assigned to. These can be any Node. The
AliasNames can be grouped according to types of functionality. The OPC Foundation defines
some initial groups, but the groups can be extended by companion specifications, vendors or
end users to meet their needs. Examples for the use of AliasNames are in Annex A. The GDS
functionality for AliasNames is formally defined in Annex B.
Figure 2 – AliasNames Example
6 OPC UA ObjectTypes
6.1 Overview
An overview of this object model is provided in Clause 5. Figure 1 illustrates the overall
AliasName Object Model.
6.2 AliasNameType ObjectType Definition
Instances of the AliasNameType ObjectType provide alternate names for Nodes. The
AliasNameType is formally defined in Table 1.
Table 1 – AliasNameType Definition
Attribute Value
BrowseName AliasNameType
IsAbstract False
References NodeClass BrowseName DataType TypeDefinition Modelling Rule
Subtype of the BaseObjectType defined in IEC 62541-5
Conformance Units
AliasName Base
This ObjectType has no Properties or Variables. The BrowseName of the Object is used as the
alias name. The string part of the BrowseName shall be the DisplayName with an empty locale
id and no other locale shall be provided. This Object shall have at least one AliasFor Reference
(or sub-type).
A Client shall always ignore the namespace associated with an AliasName for comparison with
other AliasNames.
The AliasName Object's BrowseName shall not be modified once it is defined. If an AliasName
is changed, it is considered as a deletion of the old AliasName and the addition of new
AliasName. This requirement allows AggregatingServers to detect new AliasNames.
6.3 AliasNameCategoryType ObjectType Definition
6.3.1 Definition
AliasNameCategoryType instances are used to organize the AliasNameType instances that a
Server defines. They can also include instances of AliasNameCategoryType to allow
hierarchical groupings of AliasNames. It includes a mandatory Method for finding instances of
AliasNameType in the AliasName hierarchy, starting at this instance of
AliasNameCategoryType. For example, if the Method call is made on the Aliases
AliasNameCategoryType instance (see 9.2), it would apply the AliasNameSearchPattern to all
AliasNames that are defined under TagVariables, Topics and any other
AliasNameCategoryType instance in the hierarchy.
The AliasNameCategoryType is a subtype of FolderType and is formally defined in Table 2.
Table 2 – AliasNameCategoryType Definition
Attribute Value
BrowseName AliasNameCategoryType
IsAbstract False
References NodeClass BrowseName DataType TypeDefinition Modelling Rule
Subtype of the FolderType from IEC 62541-5
Organizes Object AliasNameType OptionalPlaceholder
Organizes Object
eCategories> Type
HasComponent Method FindAlias Defined in 6.3.2 Mandatory
HasProperty Variable LastChange VersionTime PropertyType Optional
Conformance Units
AliasName Base
The list of AliasNames that an Object contains can be dynamic. For example, AliasNames can
be added in an aggregating Server as underlying Servers become available or can be removed
if a Server is no longer available.
represents any number of instances of AliasNameType. Each instance shall have at
least one AliasFor Reference to a Node. Multiple instances can point to the same Node.
allows the nesting or structuring of AliasNames into hierarchical
groupings.
An can appear in more than one place in the hierarchy of AliasNameCategories.
LastChange is the most recent time for any of the following activities:
• The last time an AliasName was added to or deleted from the AliasNameCategory,
• The last time an AliasNameCategory was added or deleted,
• The last time the referenced Nodes of an AliasName in the AliasNameCategory changed.
For AliasNameCategoryType instances that are nested, the value of LastChange shall always
be the latest VersionTime of all Organized AliasName and AliasNameCategories.
The LastChange shall be persisted. A Client that detects a LastChange that is older than what
it has cached, shall clear all cached AliasNameCategories and related AliasNames.
6.3.2 FindAlias Method
The FindAlias Method allows a Client to obtain the list of Nodes that match the provided
AliasName search string. The signature of this Method is specified below, the arguments are
defined in Table 3.
Signature
FindAlias(
[in] String AliasNameSearchPattern,
[in] NodeId ReferenceTypeFilter,
[out] AliasNameDataType[] AliasNodeList
);
Table 3 – FindAlias Method Arguments
Argument Description
AliasNameSearchPattern A string that can contain wild cards, use to find a list of AliasNames (see
IEC 62541-4 – "Wildcard Characters" table for supported wildcards, see the
"Like" FilterOperator in IEC 62541-4 for more details)
ReferenceTypeFilter A NodeId that represent a ReferenceType (i.e. AliasFor or one of its subtypes)
that restricts the search. Any ReferenceType includes all subtypes of that
ReferenceType.
AliasNodeList The returned list of AliasNameDataType. If no Nodes match the search string
or have the appropriate ReferenceType, the list shall be empty.
Method result codes are defined in Table 4.
Table 4 – FindAlias Method Error Codes
Result Code Description
Bad_InvalidArgument The input string is not a valid search string
Bad_UserAccessDenied The current user does not have the rights required.
Bad_ResponseToLarge The response was too large to be returned, try new filter and repeat find
The Method is formally defined in Table 5.
Table 5 – FindAlias Method AddressSpace definition
Attribute Value
BrowseName FindAlias
References Node Class BrowseName DataType TypeDefinition Modelling Rule
HasProperty Variable InputArguments Argument[] PropertyType Mandatory
HasProperty Variable OutputArguments Argument[] PropertyType Mandatory
It is important to note that there could be more than one entry for every AliasName. Multiple
Servers could provide a Node that represents an equivalent object (such as a temperature
sensor). An aggregating Server also could provide the Node. This Method will return the
AliasNames in order of preference. That is the Server will return what it recommends as the
best match first followed by the next best match etc. The criteria for ordering are Server specific.
The criteria could be based on the ServerStatus of the Server that contains the referenced
Node, it could be load balancing of Servers, it could be for off-loading of small device Servers,
or it could be some other algorithm.
Clients should use the first usable entry in the list.
7 OPC UA DataTypes
7.1 Overview
The following DataTypes are defined for the AliasNames model.
7.2 AliasNameDataType
This DataType defines a structure that can contain an array of ExpandedNodeId for a single
AliasName. Its elements are defined in Table 6. It will always have at least one entry in the
ReferencedNodes array.
Table 6 – AliasNameDataType DataType structure
Name Type Description
AliasNameDataType Structure
AliasName QualifiedName The AliasName (BrowseName of the Node)
ReferencedNodes ExpandedNodeId[] The Nodes referenced by the AliasName
Its representation in the AddressSpace is defined in Table 7.
Table 7 – AliasNameDataType Definition
Attribute Value
BrowseName AliasNameDataType
References Node Class BrowseName DataType TypeDefinition Modelling Rule
Subtype of the Structure defined in IEC 62541-5
Conformance Units
AliasName Base
8 Reference Types
8.1 Overview
The following References are defined for the AliasNames model.
8.2 AliasFor ReferenceType
This reference is a subtype of NonHierarchicalReferences.
The semantic of this ReferenceType is to link AliasNameType instances to the Nodes they
represent. The inverse reference is not required, i.e. the Nodes might not have a reference back
to instance of AliasNameType.
The SourceNode of References of this type shall be an Object of type AliasNameType.
The TargetNode of this ReferenceType can be of any NodeClass.
Figure 2 provides an illustration of how this ReferenceType is used. It is defined in Table 8.
Table 8 – AliasFor Definition
Attributes Value
BrowseName AliasFor
InverseName HasAlias
Symmetric False
IsAbstract False
References NodeClass BrowseName Comment
Subtype of NonHierarchicalReferences ReferenceType defined in IEC 62541-5
Conformance Units
AliasName Base
9 Instances
9.1 Overview
The following standard Objects are defined for maintaining the hierarchical structure of
AliasNameCategories in a Server. Server vendors are free to add additional instances of
AliasNameCategoryType under this hierarchy.
9.2 Aliases
The Aliases Node is formally defined in Table 9.
Table 9 – Aliases definition
Attribute Value
BrowseName Aliases
References NodeClass BrowseName DataType TypeDefinition
OrganizedBy by the Objects Folder defined in IEC 62541-5
HasTypeDefinition ObjectType AliasNameCategoryType Defined in 6.3
HasProperty Variable LastChange VersionTime PropertyType
Conformance Units
AliasName Hierarchy
This is the root folder for all alias related Objects. It can contain instances of AliasNameType
Objects and / or instances of AliasNameCategoryType Objects.
The LastChange Property, which is optional in the AliasNameCategoryType, shall be present
for the root Aliases instance. This property shall reflect the last time any changes to AliasName
occurred (see 6.3).
9.3 TagVariables
TagVariables is an instance of AliasNameCategoryType. TagVariables shall restrict instances
of AliasNameType to those that have an AliasFor References that point to Variables. The
TagVariables instance is formally defined in Table 10.
Table 10 – TagVariables definition
Attribute Value
BrowseName TagVariables
References NodeClass BrowseName DataType TypeDefinition
OrganizedBy by the Aliases defined in 9.2
HasTypeDefinition ObjectType AliasNameCategoryType Defined in 6.3
Conformance Units
AliasName Category Tags
This is the root folder for AliasNameType instances that contain an AliasFor reference to
Variables. It can contain additional AliasNameCategoryType Objects, which could be used to
create a hierarchy. A single instance of AliasNameType can exist in more than one location in
the Alias hierarchy.
9.4 Topics
Topics is an instance of AliasNameCategoryType. Topics shall restrict instances of
AliasNameType to only have AliasFor References that point to PublishedDataSetType (or
subtypes) instances (PublishedDataSetType is defined in IEC 62541-14). The Topics Node
instance is formally defined in Table 11.
Table 11 – Topics definition
Attribute Value
BrowseName Topics
References NodeClass BrowseName DataType TypeDefinition
OrganizedBy by the Aliases defined in 9.2
HasTypeDefinition ObjectType AliasNameCategoryType Defined in 6.3
Conformance Units
AliasName Category Topics
It can contain additional AliasNameCategoryType Objects, which could be used to create a
hierarchy or other structure. A single instance of AliasNameType can exist in more than one
location in the hierarchy, but all instances in the Topics hierarchy must point to an instance of
a PublishedDataSetType.
Annex A
(informative)
Examples
A.1 Overview
A number of examples are provided to help illustrate how AliasNames function. This includes a
Client using an AliasName Server, inside of a Server, in an aggregating Server and in a GDS.
A.2 AliasNames used within a single Server
Figure A.1 illustrates how this model can be used inside of a Server. This sample includes
multiple instances of AliasNameCategoryType. The figure illustrates Objects that are
referenced by more than one instance of AliasNameType.
Figure A.1 – AliasNames in a Server example
The figure describes an information model for a well. This model contains a number of other
Objects, which have Variables that are to be available via a standardized naming scheme. The
model also includes a configuration for a Pub/Sub dataset that provides the Variables defined
in the well.
The AliasName model includes the standard organization items that are required in this
document. In addition, the model also defines an extra organizational item for grouping the well
information. The example illustrates AliasNames that are both TagVariables and Topics.
A.3 AliasNames in an aggregating Server
An aggregating Server would have much the same structure as the Server in the first example,
with the exception that in the aggregating Server the target Nodes referenced by the AliasFor
Reference could be in other Servers. Figure A.2 provides an illustration of an example
aggregating Server. The Server could have a much more complex AddressSpace than provided
in the example.
Figure A.2 – Aggregating AliasNames Server example
The aggregating Server has a choice in that it could just provide the link to the underlying Node
(blue lines) or it can provide a link to the replicated Node in the aggregated Server's
AddressSpace (red lines).
A.4 Standalone AliasNames Server
The standalone AliasNames Server illustrated in Figure A.3 provides a list of AliasNames that
reference Nodes in multiple separate Servers. This type of configuration can be used for
Servers that do not have the resources to manage AliasNames on their own. It can also be used
in a system where the configuration of AliasNames occurs after the devices that are represented
by the Servers have already been deployed or if a Server just does not have support for
AliasNames. The standalone AliasNames Server can function as a lookup Server for all of the
AliasNames defined in the system. It is the responsibility of the standalone AliasNames Server
to ensure that the mapping of AliasNames to actual Nodes is correct.
Figure A.3 – AliasNames Server example
A.5 Aggregating Server with a collection of Aggregates
An aggregating Server could also collect all of the AliasNames defined in underlying Servers
and just build a composite list of these AliasNames. Since all of the AliasNames are required
to exist under the mandatory Aliases Object, it is simple for a Server to browse the
AddressSpace and build a list. The aggregating Server would be required to merge all
AliasNames listed under the well-known Objects. Some information models could define their
own well known AliasNameCategoryType Objects, which shall be merged as well. An
aggregating Server can easily have the same AliasNames with multiple NodeIds. For example,
if a temperature sensor were to be connected to two Servers for redundancy, the same
AliasName TI101 could exist in both Servers. The aggregating Server would simple report two
ExpandedNodeIds to any Client that requested TI101.
Figure A.4 – Aggregating Server example 2
In the above example, if the Temperatures AliasNameCategoryType instance were defined
locally in the Server and not defined in a standard namespace then two instances of the
Temperatures AliasNameCategoryType will exist in the aggregating Server with different
namespaces.
A.6 GDS
The GDS can include additional optional behaviour which this example illustrates. What is
required is the availability of all AliasNames in the mandatory TagVariables and Topics folder,
but a GDS can also choose to replicate or even merge the additional AliasNameCategoryType
instances from the Servers that have registered. Figure A.5 provides an illustration of a GDS
that merged the AliasNameCategory instance into a tree. It is required that
AliasNameCategories be aggregated by the GDS, but the structure of these categories is not
defined.
Figure A.5 – GDS with merged AliasNames example
For additional information about a GDS and AliasNames, see Annex B.
A.7 Client use of an AliasName Server
AliasNames allow a Client to find TagVariables or Topics easily. Many industrial systems assign
tags to specific measurement or sensors. These tags follow established nomenclatures. An
example tag is TI101, which is a temperature indicator at a specific location in a plant. The
example nomenclature is defined in ANSI/ISA-S5.1-1984 (R 1992), but this specification does
not provide or even suggest any nomenclature. A Client could be configured to display or use
the information provided by the sensor TI101, but the actual address/location of this sensor is
often not known when the Client is configured. AliasNames can be used to resolve this tag to
the actual sensor in the system.
The Client, on start-up or when it wants to access the tag, would call FindAlias on a local Server,
aggregating Server or GDS depending on how a system is configured. A Client could select
which AliasName source to call via a configuration setting. The FindAlias Method call would
return a list of all ExpandedNodeIds that the AliasName References. It is important to note that
there could be more than one Node referenced by an AliasName and that the Client must be
prepared for this. The first Node in the list of referenced Nodes returned by FindAlias Method
is the Node that the Server feels is the best match for the requested tag. The returned list could
also return more than one instance of AliasNameType and each could have their own list of
referenced Nodes. If the Method call was on a GDS or aggregating Server, the Client shall read
the ServerArray to resolve which Server the ExpandedNodeId was referencing. This would be
the last piece of information that a Client requires to be able to follow a normal connection
pattern to obtain values from the Node.
AliasName can also be configured to provide other information, such as Pub/Sub information,
but again it would only be the information that is necessary to initially subscribe to an item.
Annex B
(normative)
GDS functionality
B.1 Overview
A Global Discovery Server (GDS) that supports AliasNames, provides AliasNames functionality,
but the target Nodes referenced are in other Servers. An example of such a GDS is illustrated
in Figure B.1.
The AliasNames are aggregated from the Servers that have registered with the GDS that
expose the "Alias" capability (for information on capabilities, see IEC 62541-12). Additional
examples on aggregating AliasNames can be found in the aggregating Server example –
Clause A.3. A GDS implementation also requires additional behaviour. Annex B describes
automatic behaviour that is required by all implementations of a GDS that supports AliasNames.
Figure B.1 – Example GDS aggregating AliasNames
The following Clauses B.2, B.3, and B.4 describe this required behaviour:
• When a Server registers with the GDS, the GDS shall merge the AliasNames of the
registering Server into a master AliasNames list on the GDS.
• Pull all AliasNameCategory instances, merge any that have identical Name part of the
BrowseNames.
• The GDS will provide the ExpandedNodeId of all of the referenced NodeIds and the
ServerUri of the Server containing the NodeId.
The details of the expected behaviour of a GDS that supports AliasNames is described in
Clauses B.2, B.3, and B.4.
B.2 Register a Server
A GDS that
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