oSIST prEN IEC 62541-11:2024

OPC Unified Architecture - Part 11: Historical Access

IEC 62541-11: 2025 defines the Information Model associated with Historical Access (HA). It particularly includes additional and complementary descriptions of the NodeClasses and Attributes needed for Historical Access, additional standard Properties, and other information and behaviour. The complete AddressSpace Model including all NodeClasses and Attributes is specified in IEC 62541‑3. The predefined Information Model is defined in IEC 62541‑5. The Services to detect and access historical data and events, and description of the ExtensibleParameter types are specified in IEC 62541‑4. This document includes functionality to compute and return Aggregates like minimum, maximum, average etc. The Information Model and the concrete working of Aggregates are defined in IEC 62541‑13. Conventions for Historical Access Clients are informatively provided in Annex A.
This fourth edition cancels and replaces the third edition published in 2020. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
a) a functionality has been added to support retrieving of modified events;
b) an Event has been added to indicate when a backfill occurred;
c) a new ReferenceType that can be used to indicate an external node has been defined;
d) the text has been improved to better explain the concept of annotation and remove conflicting explanations;
e) a default historian configuration (and where to find it) has been defined;
f) HistoricalEventConfigurationType, which provides general configuration information about the historical Event storage, has been added;
g) the text has been updated and optional fields have been added to HA configuration object to allow configuration to be defined for periodic data collection, not just for exception-based collection;
h) an ObjectType that can be used for external event collection has been provided as well as an example how historians can be configured.

OPC Unified Architecture - Teil 11: Zugang zu historischen Daten

Architecture unifiée OPC - Partie 11: Accès à l'historique

IEC 62541-11: 2025 définit le Modèle d'Information associé à l'Accès à l'historique (HA, Historical Access). Elle inclut en particulier des descriptions supplémentaires et complémentaires des NodeClasses et des Attributs nécessaires pour l'Accès à l'historique, des Propriétés normalisées supplémentaires et d'autres informations et comportements. Le Modèle complet de l'AddressSpace comprenant toutes les NodeClasses et tous les Attributs est spécifié dans l'IEC 62541‑3. Le Modèle d'information prédéfini est défini dans l'IEC 62541‑5. Les Services permettant de détecter et d'accéder aux données et événements historiques, ainsi qu'une description des types ExtensibleParameter, sont spécifiés dans l'IEC 62541‑4. Le présent document inclut une fonctionnalité permettant de calculer et de renvoyer des Agrégats (minimum, maximum, moyenne, etc.). Le Modèle d'information et la fonction concrète des Agrégats sont définis dans l'IEC 62541‑13. Les conventions pour les Clients d'Accès à l'historique sont données, à titre informatif, à l'Annexe A. Cette quatrième édition annule et remplace la troisième édition parue en 2020. Cette édition constitue une révision technique.
Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) une fonctionnalité qui permet de récupérer les événements modifiés a été ajoutée;
b) un Événement qui indique quand un remplissage a eu lieu a été ajouté;
c) un nouveau ReferenceType qui peut être utilisé pour indiquer un nœud externe a été défini;
d) le texte a été amélioré afin de mieux expliquer le concept d'annotation et de supprimer les explications contradictoires;
e) une configuration d'historique par défaut (et l'endroit où la trouver) a été définie;
f) l'HistoricalEventConfigurationType, qui fournit des informations de configuration générale sur le stockage des Événements historiques, a été ajouté;
g) le texte a été mis à jour et des champs facultatifs ont été ajoutés à l'objet de configuration HA afin de permettre la définition de la configuration pour la collecte de données périodique, et pas seulement pour la collecte fondée sur les exceptions;
h) un ObjectType qui peut être utilisé pour la collecte d'événements externes a été prévu, ainsi qu'un exemple de la façon dont les historiques peuvent être configurés.

Enotna arhitektura OPC - 11. del: Zgodovinski dostop

General Information

• Status: Not Published
• Public Enquiry End Date: 30-Mar-2024
• ICS: 25.040.40 - Industrial process measurement and control
• ICS: 35.100.05 - Multilayer applications
• ICS: 35.240.50 - IT applications in industry
• Technical Committee: MOV - Measuring equipment for electromagnetic quantities
• Current Stage: 4020 - Public enquire (PE) (Adopted Project)
• Start Date: 30-Jan-2024
• Due Date: 18-Jun-2024
• Completion Date: 05-Apr-2024
• Mandate: M/490 - Standardisation mandate to the European Standardisation Organisations (ESOs) to support European Smart Grid deployment
• Ref Project: prEN IEC 62541-11:2024 - OPC Unified Architecture - Part 11: Historical Access

Relations

• Revises: SIST EN IEC 62541-11:2020 - OPC Unified Architecture - Part 11: Historical Access (IEC 62541-11:2020)
• Effective Date: 31-Jan-2023

Overview

prEN IEC 62541-11:2024 - OPC Unified Architecture (OPC UA) Part 11: Historical Access defines the information model and service usage for accessing, updating and auditing historical data and events in OPC UA servers. Published as a Committee Draft for Vote (CDV) for IEC 62541-11 (ED3), this standard specifies how historians, historian-enabled servers and clients manage time-series and event history (timestamps, modifications, annotations, bounding values and changes to the AddressSpace) for industrial automation, SCADA, MES and IIoT applications.

Key topics and technical requirements

• Historical Information Model: definitions for HistoricalNodes, HistoricalDataNodes and HistoricalEventNodes, plus configuration objects that expose how history is stored and managed.
• Data architecture and historians: concepts for historian servers, external history sources, interruption handling and preservation of data continuity.
• Timestamps and bounding values: rules and examples for time domains, timestamp semantics and bounding value construction for queries.
• History services and parameters: usage of HistoryRead/HistoryUpdate services, HistoryReadDetails types (ReadRaw, ReadProcessed, ReadAtTime, ReadEventDetails), and return types such as HistoryData and HistoryEvent.
• Update and delete operations: structures and enumerations for UpdateDataDetails, DeleteRawModifiedDetails, DeleteAtTimeDetails and related operations including bulk inserts.
• Audit and security: Historical Audit Events (update, delete, annotation changes, configuration changes) to support traceability and compliance.
• Operational behavior: status codes, operation-level results, continuation points, and handling arrays/index ranges for efficient historical queries.
• Server capabilities and exposure: HistoryServerCapabilitiesType and default configuration to advertise supported historical features to clients.

Practical applications and users

Who benefits:

• Industrial automation vendors implementing OPC UA servers with history (historians, PLC/HMI vendors)
• System integrators and software developers building SCADA/MES, analytics and IIoT platforms that consume time-series and event history
• Data historians and OT/IT architects consolidating multi-vendor historical sources
• Compliance and audit teams requiring tamper-evident historical records and event tracking

Common uses:

• Time-series retrieval for trending, reporting and machine learning
• Event history analysis for root-cause investigations
• Data reconciliation between real-time and historical systems
• Auditable updates and deletions of historical records for regulatory compliance

Related standards

This Part 11 specification integrates with other OPC UA parts such as core OPC UA overview and information model parts (e.g., Part 1, Part 5) and Data Access (Part 8) implementations - together enabling interoperable, secure access to both live and historical industrial data.

Keywords: OPC UA, IEC 62541-11, Historical Access, historian, time-series, industrial automation, SCADA, MES, IIoT, historical data, audit events.

Standards Content (Sample)

SLOVENSKI STANDARD
01-marec-2024
Enotna arhitektura OPC - 11. del: Zgodovinski dostop
OPC Unified Architecture - Part 11: Historical Access
OPC Unified Architecture - Teil 11: Zugang zu historischen Daten
Architecture unifiée OPC - Partie 11: Accès à l'historique
Ta slovenski standard je istoveten z: prEN IEC 62541-11:2024
ICS:
25.040.40 Merjenje in krmiljenje Industrial process
industrijskih postopkov measurement and control
35.240.50 Uporabniške rešitve IT v IT applications in industry
industriji
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

65E/1058/CDV
COMMITTEE DRAFT FOR VOTE (CDV)
PROJECT NUMBER:
IEC 62541-11 ED3
DATE OF CIRCULATION: CLOSING DATE FOR VOTING:
2024-01-26 2024-04-19
SUPERSEDES DOCUMENTS:
65E/983/RR
IEC SC 65E : DEVICES AND INTEGRATION IN ENTERPRISE SYSTEMS
SECRETARIAT: SECRETARY:
United States of America Mr Donald (Bob) Lattimer
OF INTEREST TO THE FOLLOWING COMMITTEES: PROPOSED HORIZONTAL STANDARD:

Other TC/SCs are requested to indicate their interest, if any, in
this CDV to the secretary.
FUNCTIONS CONCERNED:
EMC ENVIRONMENT QUALITY ASSURANCE SAFETY
SUBMITTED FOR CENELEC PARALLEL VOTING NOT SUBMITTED FOR CENELEC PARALLEL VOTING
Attention IEC-CENELEC parallel voting
The attention of IEC National Committees, members of
CENELEC, is drawn to the fact that this Committee Draft for
Vote (CDV) is submitted for parallel voting.
The CENELEC members are invited to vote through the
CENELEC online voting system.
This document is still under study and subject to change. It should not be used for reference purposes.
Recipients of this document are invited to submit, with their comments, notification of any relevant patent rights of which they
are aware and to provide supporting documentation.
Recipients of this document are invited to submit, with their comments, notification of any relevant “In Some Countries” clauses
to be included should this proposal proceed. Recipients are reminded that the CDV stage is the final stage for submitting ISC
clauses. (SEE AC/22/2007 OR NEW GUIDANCE DOC).

TITLE:
OPC Unified Architecture - Part 11: Historical Access

PROPOSED STABILITY DATE: 2026
NOTE FROM TC/SC OFFICERS:
electronic file, to make a copy and to print out the content for the sole purpose of preparing National Committee positions.
You may not copy or "mirror" the file or printed version of the document, or any part of it, for any other purpose without
permission in writing from IEC.

IEC CDV 62541-11 © IEC 2023 ii

1 CONTENTS
4 FOREWORD . vi
5 1 Scope . 1
6 2 Normative references . 1
7 3 Terms, definitions, and abbreviations . 1
8 3.1 Terms and definitions . 1
9 3.2 Abbreviated terms . 3
10 4 Concepts . 3
11 4.1 General . 3
12 4.2 Data architecture . 3
13 4.3 Historians and interruption of data collection . 4
14 4.4 Modification of Historical Data/Events . 5
15 4.5 Timestamps . 5
16 4.6 Bounding Values and time domain . 6
17 4.7 Changes in AddressSpace over time . 7
18 5 Historical Information Model . 8
19 5.1 HistoricalNodes . 8
20 5.1.1 General . 8
21 5.1.2 Annotations Property. 8
22 5.2 HistoricalDataNodes . 9
23 5.2.1 General . 9
24 5.2.2 HistoricalDataConfigurationType . 9
25 5.2.3 Attributes . 11
26 5.2.4 Historical Data Configuration Object . 11
27 5.3 References . 11
28 5.3.1 Overview . 11
29 5.3.2 HasHistoricalConfiguration ReferenceType . 12
30 5.3.3 HasCurrentData ReferenceType . 12
31 5.3.4 HasCurrentEvent ReferenceType . 13
32 5.4 HistoricalEventNodes . 13
33 5.4.1 General . 13
34 5.4.2 HistoricalEventFilter Property . 14
35 5.4.3 HistoricalEventConfigurationType . 14
36 5.4.4 HistoricalEventNode Attributes . 15
37 5.5 External History sources . 15
38 5.5.1 Introduction . 15
39 5.5.2 External Historical Event Node . 15
40 5.6 Example Object Models in Historian Servers (informative) . 16
41 5.6.1 Overview . 16
42 5.6.2 HistoricalDataNodes Address Space Model . 16
43 5.6.3 Historical data . 17
44 5.6.4 HistoricalEventNodes Address Space Model . 17
45 5.6.5 Historical Events . 18
46 5.7 Exposing supported functions and capabilities . 19
47 5.7.1 General . 19
48 5.7.2 HistoryServerCapabilitiesType . 20
49 5.7.3 Default Configuration . 22

iii IEC CDV 62541-11 © IEC 2023

50 Historical Audit Events . 23
5.8
51 5.8.1 General . 23
52 5.8.2 AuditHistoryEventUpdateEventType . 23
53 5.8.3 AuditHistoryValueUpdateEventType . 24
54 5.8.4 AuditHistoryAnnotationUpdateEventType . 25
55 5.8.5 AuditHistoryDeleteEventType . 25
56 5.8.6 AuditHistoryRawModifyDeleteEventType . 26
57 5.8.7 AuditHistoryAtTimeDeleteEventType . 27
58 5.8.8 AuditHistoryEventDeleteEventType . 27
59 5.8.9 AuditHistoryConfigurationChangeEventType . 28
60 5.8.10 AuditHistoryBulkInsertEventType . 28
61 6 Historical Access specific usage of Services . 29
62 6.1 General . 29
63 6.2 Historical Nodes StatusCodes . 29
64 6.2.1 Overview . 29
65 6.2.2 Operation level result codes . 29
66 6.2.3 Semantics changed . 31
67 6.3 Continuation Points . 31
68 6.4 Arrays, index ranges and substrings . 32
69 6.5 HistoryReadDetails parameters . 33
70 6.5.1 Overview . 33
71 6.5.2 ReadEventDetails structure . 34
72 6.5.3 ReadRawModifiedDetails structure . 37
73 6.5.4 ReadProcessedDetails structure . 39
74 6.5.5 ReadAtTimeDetails structure . 41
75 6.5.6 ReadAnnotationDataDetails structure . 42
76 6.6 HistoryData parameters returned . 42
77 6.6.1 Overview . 42
78 6.6.2 HistoryData type . 42
79 6.6.3 HistoryModifiedData type . 43
80 6.6.4 HistoryEvent DataType . 43
81 6.6.5 HistoryModifiedEvent DataType . 44
82 6.6.6 Annotation DataType . 44
83 6.7 HistoryUpdateType Enumeration . 45
84 6.8 PerformUpdateType Enumeration . 45
85 6.9 HistoryUpdateDetails parameter . 46
86 6.9.1 Overview . 46
87 6.9.2 UpdateDataDetails structure . 47
88 6.9.3 UpdateStructureDataDetails structure . 49
89 6.9.4 UpdateEventDetails structure . 50
90 6.9.5 DeleteRawModifiedDetails structure . 52
91 6.9.6 DeleteAtTimeDetails structure . 53
92 6.9.7 DeleteEventDetails structure . 53
93 Annex A (informative) Client conventions . 55
94 A.1 How clients may request timestamps . 55
95 A.2 Determining the first or last historical data point . 56
96 Bibliography . 57
IEC CDV 62541-11 © IEC 2023 iv

98 FIGURES
100 Figure 1 – Possible OPC UA Server supporting Historical Access . 4
101 Figure 2 – ReferenceType hierarchy . 12
102 Figure 3 – Historical Variable with Historical Data Configuration and Annotations . 16
103 Figure 5 – Representation of an Event with History in the AddressSpace . 18
104 Figure 7 – Server and HistoryServer Capabilities . 20
106 TABLES
108 Table 1 – Bounding Value examples . 6
109 Table 2 – Annotations Property . 8
110 Table 3 – HistoricalDataConfigurationType definition . 9
111 Table 4 – ExceptionDeviationFormat Items. 10
112 Table 5 – ExceptionDeviationFormat definition . 11
113 Table 6 – Historical Access configuration definition . 11
114 Table 7 – HasHistoricalConfiguration ReferenceType . 12
115 Table 8 – HasCurrentData ReferenceType . 13
116 Table 9 – HasCurrentEvent ReferenceType . 13
117 Table 10 – Standard Historical Events Properties . 14
118 Table 11 – HistoricalEventConfigurationType definition . 14
119 Table 12 – HistoricalExternalEventSourceType definition . 15
120 Table 13 – HistoryServerCapabilitiesType Definition . 21
121 Table 16 – AuditHistoryEventUpdateEventType definition . 24
122 Table 17 – AuditHistoryValueUpdateEventType definition . 24
123 Table 18 – AuditHistoryAnnotationUpdateEventType definition . 25
124 Table 19 – AuditHistoryDeleteEventType definition . 26
125 Table 20 – AuditHistoryRawModifyDeleteEventType definition . 26
126 Table 21 – AuditHistoryAtTimeDeleteEventType definition . 27
127 Table 22 – AuditHistoryEventDeleteEventType definition . 27
128 Table 23 – AuditHistoryConfigurationChangeEventType definition . 28
129 Table 24 – AuditHistoryBulkInsertEventType definition . 28
130 Table 25 – Bad operation level result codes . 30
131 Table 26 – Good operation level result codes . 30
132 Table 27 – HistoryReadDetails parameter Symbolic Names . 33
133 Table 28 – HistoryReadDetails definition . 34
134 Table 29 – ReadEventDetails Structure . 34
135 Table 30 – ReadEventDetails definition . 35
136 Table 31 – ReadEventDetails2 Structure . 36
137 Table 32 – ReadEventDetails2 definition . 36
138 Table 33 – ReadRawModifiedDetails structure . 37
139 Table 34 – ReadRawModifiedDetails definition . 37
140 Table 35 – ReadProcessedDetails structure . 39

v IEC CDV 62541-11 © IEC 2023
Table 36 – ReadProcessedDetails definition . 40
142 Table 37 – ReadAtTimeDetails structure . 41
143 Table 38 – ReadAtTimeDetails definition . 41
144 Table 39 – ReadAnnotationDataDetails Structure . 42
145 Table 40 – ReadAnnotationDataDetails definition . 42
146 Table 41 – HistoryData structure . 42
147 Table 42 – HistoryData definition . 43
148 Table 43 – HistoryModifiedData structure . 43
149 Table 44 – HistoryModifiedData definition . 43
150 Table 45 – HistoryEvent structure . 43
151 Table 46 – HistoryEvent definition . 44
152 Table 47 – HistoryModifiedEvent structure . 44
153 Table 48 – HistoryModifiedEvent definition . 44
154 Table 49 – Annotation Structure . 44
155 Table 50 –Annotation definition . 45
156 Table 51 – HistoryUpdateType Items . 45
157 Table 52 – HistoryUpdateType definition . 45
158 Table 53 – PerformUpdateType Items . 45
159 Table 54 – PerformUpdateType definition . 46
160 Table 55 – HistoryUpdateDetails parameter Symbolic Names . 46
161 Table 56 – HistoryUpdateDetails Structure . 47
162 Table 57 – HistoryUpdateDetails definition . 47
163 Table 58 – UpdateDataDetails Structure. 48
164 Table 59 – UpdateDataDetails definition . 48
165 Table 60 – UpdateStructureDataDetails Structure . 49
166 Table 61 – UpdateStructureDataDetails definition . 49
167 Table 62 – UpdateEventDetails Structure . 50
168 Table 63 – UpdateEventDetails definition . 51
169 Table 64 – DeleteRawModifiedDetails Structure . 52
170 Table 65 – DeleteRawModifiedDetails definition . 52
171 Table 66 – DeleteAtTimeDetails Structure . 53
172 Table 67 – DeleteAtTimeDetails definition . 53
173 Table 68 – DeleteEventDetails Structure . 53
174 Table 69 – DeleteEventDetails definition . 54
175 Table A.1 – Time keyword definitions . 56
176 Table A.2 –Time offset definitions . 56
IEC CDV 62541-11 © IEC 2023 vi

179 INTERNATIONAL ELECTROTECHNICAL COMMISSION
180 ____________
182 OPC UNIFIED ARCHITECTURE –
184 Part 11: Historical Access
186 FOREWORD
187 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all
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212 publication, use of, or reliance upon, this IEC Publication or any other IEC Publications.
213 8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is indispensable
214 for the correct application of this publication.
215 9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent rights.
216 IEC shall not be held responsible for identifying any or all such patent rights.
217 International Standard IEC 62541-11 has been prepared by subcommittee 65E: Devices and
218 integration in enterprise systems, of IEC technical committee 65: Industrial-process measurement,
219 control and automation.
220 This fourth edition cancels and replaces the third edition published in 2020. This edition constitutes a
221 technical revision.
222 This edition includes the following significant technical changes with respect to the previous edition:
223 a) Added functionality to support retrieving of modified events.
224 b) Added Event to indicate when a backfill occurred.
225 c) Defined a new ReferenceType that can be used to indicate an external node.
226 d) Improved text to better explain the concept of annotation and remove conflicting explanations.
227 e) Defined a default historian configuration (and where to find it).
228 f) Added HistoricalEventConfigurationType, which provides general configuration information about
229 the historical Event storage.
230 g) Updated text and added optional fields to HA configuration object to allow configuration to be
231 defined for periodic data collection, not just for exception-based collection.

vii IEC CDV 62541-11 © IEC 2023

h) Provided ObjectType that can be used for external event collection and also provided example
233 how histoians can be configured.
235 The text of this International Standard is based on the following documents:
CDV Report on voting
65E/XX/CDV 65E/XX/RVC
237 Full information on the voting for the approval of this International Standard can be found in the report
238 on voting indicated in the above table.
239 This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
240 Throughout this document and the other parts of the IEC 62541 series, certain document conventions
241 are used:
242 Italics are used to denote a defined term or definition that appears in the "Terms and definition" clause
243 in one of the parts of the IEC 62541 series.
244 Italics are also used to denote the name of a service input or output parameter or the name of a
245 structure or element of a structure that are usually defined in tables.
246 The italicized terms and names are, with a few exceptions, written in camel-case (the practice of
247 writing compound words or phrases in which the elements are joined without spaces, with each
248 element's initial letter capitalized within the compound). For example, the defined term is
249 AddressSpace instead of Address Space. This makes it easier to understand that there is a single
250 definition for AddressSpace, not separate definitions for Address and Space.
251 A list of all parts of the IEC 62541 series, published under the general title OPC Unified Architecture,
252 can be found on the IEC website.
253 The committee has decided that the contents of this document will remain unchanged until the stability
254 date indicated on the IEC website under "http://webstore.iec.ch" in the data related to the specific
255 document. At this date, the document will be
256 • reconfirmed,
257 • withdrawn,
258 • replaced by a revised edition, or
259 • 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.
IEC CDV 62541-11 © IEC 2023 1
262 OPC Unified Architecture
264 Part 11: Historical Access
269 1 Scope
270 This document is part of the OPC Unified Architecture standard series and defines the
271 Information Model associated with Historical Access (HA). It particularly includes additional and
272 complementary descriptions of the NodeClasses and Attributes needed for Historical Access,
273 additional standard Properties, and other information and behaviour.
274 The complete AddressSpace Model including all NodeClasses and Attributes is specified in IEC
275 62541-3. The predefined Information Model is defined in IEC 62541-5. The Services to detect
276 and access historical data and events, and description of the ExtensibleParameter types are
277 specified in IEC 62541-4.
278 This standard includes functionality to compute and return Aggregates like minimum, maximum,
279 average etc. The Information Model and the concrete working of Aggregates are defined in IEC
280 62541-13.
281 2 Normative references
282 The following documents, in whole or in part, are normatively referenced in this document and
283 are indispensable for its application. For dated references, only the edition cited applies. For
284 undated references, the latest edition of the referenced document (including any amendments
285 and errata) applies.
286 IEC 62541-1, OPC Unified Architecture - Part 1: Overview and Concepts
287 IEC 62541-3, OPC Unified Architecture - Part 3: Address Space Model
288 IEC 62541-4, OPC Unified Architecture - Part 4: Services
289 IEC 62541-5, OPC Unified Architecture - Part 5: Information Model
290 IEC 62541-7, OPC Unified Architecture - Part 7: Profiles
291 IEC 62541-8, OPC Unified Architecture - Part 8: Data Access
292 IEC 62541-13, OPC Unified Architecture - Part 13: Aggregates
293 3 Terms, definitions, and abbreviations
294 3.1 Terms and definitions
295 For the purposes of this document, the terms and definitions given in IEC 62541-1, IEC 62541-
296 3, IEC 62541-4, IEC 62541-13 and the following apply.
297 3.1.1
298 Annotation
299 metadata associated with an item at a given instance in time
300 Note 1 to entry: An Annotation is metadata that is associated with an item at a given instance in time.
301 3.1.2
302 BoundingValues
303 values associated with the starting and ending time
304 Note 1 to entry: BoundingValues are the values that are associated with the starting and ending time of a
305 ProcessingInterval specified when reading from the historian. BoundingValues may be required by Clients to
306 determine the starting and ending values when requesting RawData over a time range. If a RawData value exists at
307 the start or end point, it is considered the bounding value even though it is part of the data request. If no RawData

2 IEC CDV 62541-11 © IEC 2023
308 value exists at the start or end point, then the Server will determine the boundary value, which may require data from
309 a data point outside of the requested range. See 4.6 for details on using BoundingValues.
310 3.1.3
311 Historian
312 application storing time series data and/or time series events
313 3.1.4
314 HistoricalNode
315 Object, Variable, Property or View in the AddressSpace where a Client can access historical
316 data or Events
317 Note 1 to entry: A HistoricalNode is a term used in this document to represent any Object, Variable, Property or
318 View in the AddressSpace for which a Client may read and/or update historical data or Events. The terms
319 “HistoricalNodes’s history” or “history of a HistoricalNodes” will refer to the time series data or Events stored for this
320 HistoricalNode. The term HistoricalNode refers to both HistoricalDataNodes and HistoricalEventNodes.
321 3.1.5
322 HistoricalDataNode
323 Variable or Property in the AddressSpace where a Client can access historical data
324 Note 1 to entry: A HistoricalDataNode represents any Variable or Property in the AddressSpace for which a Client
325 may read and/or update historical data. “HistoricalDataNode history” or “history of a HistoricalDataNode” refers to
326 the time series data stored for this HistoricalNode. Examples of such data are:
327 • device data (like temperature sensors)
328 • calculated data
329 • status information (open/closed, moving)
330 • dynamically changing system data (like stock quotes)
331 • diagnostic data
332 The term HistoricalDataNodes is used when referencing aspects of the standard that apply to accessing historical
333 data only.
334 3.1.6
335 HistoricalEventNode
336 Object or View in the AddressSpace for which a Client can access historical Events
337 Note 1 to entry: “HistoricalEventNode’s history” or “history of a HistoricalEventNode” refers to the time series
338 Events stored in some historical system. Examples of such data are:
339 • Notifications
340 • system Alarms
341 • operator action Events
342 • system triggers (such as new orders to be processed)
343 The term HistoricalEventNode is used when referencing aspects of the standard that apply to accessing historical
344 Events only.
345 3.1.7
346 ModifiedValues
347 HistoricalDataNode’s value that has been changed (or manually inserted or deleted) after it was
348 stored in the historian
349 Note 1 to entry: For some Servers, a lab data entry value is not a modified value, but if a user corrects a lab value,
350 the original value would be considered a modified value, and would be returned during a request for ModifiedValues.
351 Also manually inserting a value that was missed by a standard collection system may be considered a modified value.
352 Unless specified otherwise, all historical Services operate on the current, or most recent, value for the specified
353 HistoricalDataNode at the specified timestamp. Requests for ModifiedValues are used to access values that have
354 been superseded, deleted or inserted. It is up to a system to determine what is considered a modified value.
355 Whenever a Server has modified data available for an entry in the historical collection it shall set the ExtraData bit
356 in the StatusCode.
357 3.1.8
358 RawData
359 data that is stored within the historian for a HistoricalDataNode
360 Note 1 to entry: The data may be all data collected for the DataValue or it may be some subset of the data depending
361 on the historian and the storage rules invoked when the item’s values were saved.

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362 3.1.9
363 StartTime/EndTime
364 bounds of a history request which define the time domain
365 Note 1 to entry: For all requests, a value falling at the end time of the time domain is not included in the domain,
366 so that requests made for successive, contiguous time domains will include every value in the historical collection
367 exactly once.
368 3.1.10
369 TimeDomain
370 interval of time covered by a particular request, or response
371 Note 1 to entry: In general, if the start time is earlier than or the same as the end time, the time domain is considered
372 to begin at the start time and end just before the end time; if the end time is earlier than the start time, the time
373 domain still begins at the start time and ends just before the end time, with time "running backward" for the particular
374 request and response. In both cases, any value which falls exactly at the end time of the TimeDomain is not included
375 in the TimeDomain. See the examples in 4.6. BoundingValues effect the time domain as described in 4.6.
376 All timestamps which can legally be represented in a UtcTime DataType are valid timestamps, and the Server may
377 not return an invalid argument result code due to the timestamp being outside of the range for which the Server has
378 data. See IEC 62541-3 for a description of the range and granularity of this DataType. Servers are expected to handle
379 out-of-bounds timestamps gracefully, and return the proper StatusCodes to the Client.
380 3.1.11
381 StructuredHistoryData
382 structured data stored in a history collection where parts of the structure are used to uniquely
383 identify the data within the data collection
384 Note 1 to entry: Most historical data applications assume only one current value per timestamp. Therefore, the
385 timestamp of the data is considered the unique identifier for that value. Some data or meta data such as Annotations
386 may permit multiple values to exist at a single timestamp. In such cases the Server would use one or more parameters
387 of the StructuredHistoryData entry to uniquely identify each element within the history collection. Annotations are
388 examples of StructuredHistoryData.
389 3.2 Abbreviated terms
390 DA Data Access
391 HA Historical Access
392 HDA Historical Data Access
393 UA Unified Architecture
394 4 Concepts
395 4.1 General
396 This document defines the handling of historical time series data and historical Event data in
397 the OPC Unified Architecture (in a Historian). Included is the specification of the representation
398 of historical data and Events in the AddressSpace.
399 4.2 Data architecture
400 A Server supporting Historical Access provides Clients with transparent access to different
401 historical data and/or historical Event sources (e.g., process Historians, event Historians, etc.).
402 The historical data or Events may be in a proprietary data collection, database or a short-term
403 buffer within memory. A Server supporting Historical Access will provide historical data and
404 Events for all or a subset of the available Variables, Objects, Properties or Views within the
405 Server AddressSpace.
406 Figure 1 illustrates how the AddressSpace of a UA Server might consist of a broad range of
407 different historical data and/or historical Event sources.

4 IEC CDV 62541-11 © IEC 2023
server client
Operator
Display
Operator
Event
Station 2
Logger, etc.
OPC UA
Historical Access
Server
OPC UA
Historical
Access
Server
OPC-COM
Proprietary OPC UA Other data
Server
Data Server Server source
(DA or A&E)
409 Figure 1 – Possible OPC UA Server supporting Historical Access
411 The Historian may be implemented as a standalone OPC UA Server that collects data from
412 another OPC UA Server or another data source. The Historian may also just aggregate historical
413 data from underlying Historians. The Client that references the OPC UA Server supporting
414 Historical Access for historical data may be simple trending packages that desire values over a
415 given time frame or they may be complex reports that require data in multiple formats.
416 There are general requirements for Historians, but Historians can vary in functionality. A
417 consistent requirement for all Historians is that they store Historical data including a timestamp.
418 All historical data should include status information for each value, but a Historian may
419 compress this to only storing status information that indicates a problem (Bad status) and/or
420 status change, instead of storing a status for every time series data item. The status of historical
421 data can be complex. What is required is that the values returned as part of the timeseries raw
422 data match the data that would have been observed if the Value was subscribed to at that point
423 in time.
424 Historical Events are more complicated. In a stream of Events each Event can have a different
425 list of fields. EventTypes are defined in a hierarchical manner, where each EventType inherits
426 fields from its parent type and can add additional fields. Some of these additional fields may be
427 mandatory and are required to understand or process the given EventType. A Historian that
428 stores Events, shall be configurable to store all mandatory fields for any EventTypes that it
429 historizes. If it receives for storage an EventType that it does not support all mandatory fields
430 for, it may store it as one of its supertype EventTypes (one that it does support all mandatory
431 fields for), but then it shall not claim that it supports historizing of that EventType (see 5.4.3).
432 The Historian shall also provide information about the fields that are currently being historized
433 (see 5.4.3).
434 4.3 Historians and interruption of data collection
435 When an Historian is collecting and storing data, the data collection may be interrupted. The
436 interruption may have been for collecting the current values of data or for an event stream. The
437 interruption may have been due to an interruption in the source of a value or an interruption of
438 the forwarding of historical data from an underlying Historian. The interruption might also have
439 been due to an action that stopped the collection of HistoricalData or historical Events. Some
440 of these interruptions may recover with no loss of data, others may result in data gaps. The
441 Historian shall report any gaps when a client is accessing the stored historical data with an
442 error code of Bad_DataLost.

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443 For example, if a subscription for data breaks, and the historian recovers the subscription after
444 several minutes, it can check the SourceTimestamp of the initial values in the subscription. If
445 the initial value SourceTimestamp matches the last stored value SourceTimestamp, then no
446 data was lost and nothing needs to be stored indicating the given HistoricalDataNode‘s data
447 collec
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