ISO 15926-6:2024

International
Standard
ISO 15926-6
First edition
Industrial automation systems
2024-12
and integration — Integration of
life-cycle data for process plants
including oil and gas production
facilities —
Part 6:
Rules for the development and
validation of reference data of ISO/
TS 15926-4
Systèmes d'automatisation industrielle et intégration —
Intégration de données de cycle de vie pour les industries de
"process", y compris les usines de production de pétrole et de gaz —
Partie 6: Règles relatives à l'élaboration et à la validation des
données de référence de l'ISO/TS 15926-4
Reference number
© ISO 2024
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Published in Switzerland
ii
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, symbols and abbreviated terms . 2
3.1 Terms and definitions .2
3.2 Symbols .5
3.3 Abbreviated terms .5
4 General principles for the content of a reference data library (RDL) . 5
4.1 Structure of the rules for attributes in this document .5
4.2 Naming convention for attributes .6
4.3 Presentation convention .6
4.4 Defining a reference data library .6
4.4.1 Definition and content of a reference data library .6
4.4.2 Reference data library and reference data item .6
4.4.3 Minimum information about a reference data item .6
4.4.4 Reference data library .7
4.5 Reference data item identification . .7
4.5.1 Category of reference data item identification .7
4.5.2 Types of reference data item identification .7
4.5.3 Types of text definitions and notes of a reference data item .8
4.6 Classifications .8
4.6.1 General .8
4.6.2 Class of inheritance relationship (Attribute: Superclass#) .10
4.6.3 Grouping based on ISO 15926-2 entities .10
4.7 Attributes for units of measure (UoM) .10
5 Reference data item attributes .11
5.1 Attribute: URI .11
5.1.1 General .11
5.1.2 Assignment of URI.11
5.1.3 Syntax of URI .11
5.2 Attribute: UniqueNumber . 12
5.3 Attribute: UniqueName . 13
5.4 Attribute: Synonym1 . 13
5.5 Attribute: Synonym2 . . .14
5.6 Attribute: TextDefinition .14
5.6.1 Content of a reference data item text definition .14
5.6.2 Reference data item definition by explicit text .14
5.6.3 Reference data item text definition by explicit text taken from a source . 15
5.6.4 Reference data item text definition by document reference .17
5.6.5 Requirements for a reference data item text definition .18
5.6.6 Use of a reference data item human-interpretable identifier in a text definition .18
5.6.7 Standard forms for a reference data item text definition .19
5.7 Attribute: Source . 22
5.8 Attribute: Notes . 22
5.9 Attribute: Superclass1 . 22
5.10 Attribute: Superclass2 . 23
5.11 Attribute: Superclass3 . 23
5.12 Attribute: Superclass4 . 23
5.13 Attribute: Superclass5 . 23
5.14 Attribute: ISO15926-2Entity . 23
5.15 Attribute: Classification1 . 23
5.16 Attribute: Classification2 . 23

iii
5.17 Attribute: Classification3 . 23
5.18 Attribute: Classification4 . 23
5.19 Attribute: Symbol .24
5.20 Attribute: Operator . .24
5.21 Attribute: FirstOperand .24
5.22 Attribute: SecondOperand .24
5.23 Attribute: Factor.24
5.24 Attribute: Prefix .24
5.25 Attribute: Exponent . 25
6 Representation of a reference data library .25
Annex A (normative) Representation of a reference data library in spreadsheet format .27
Annex B (informative) Correspondence between versions of ISO/TS 15926-4 and ISO 15926-6
(this document) .31
Annex C (informative) Recommendations for a reference data item text definition .32
Bibliography .33

iv
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 184, Automation systems and integration,
Subcommittee SC 4, Industrial data.
This first edition cancels and replaces the first edition of ISO/TS 15926-6:2013, which has been technically
revised.
The main changes are:
— update of the normative references;
— deletion of Clause 8 on the administration of a reference data library;
— deletion of rules for external reference data libraries;
— grouping of all rules under one clause with the subclause numbers in the order of the attributes to
improve readability;
— improvement of the separation between the factual rule for an attribute and the options that would exist
to choose from;
— improvement of Clause 4 for providing the general principles of the attributes to navigate the user;
— deletion of pieces of text that would be more appropriate in a separate knowledge document.
A list of all parts in the ISO 15926 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

v
Introduction
The ISO 15926 series provides a representation process of industry facility life-cycle information. This
representation is specified by a generic, conceptual data model that is suitable as the basis for implementation
in a shared database or data warehouse. The data model is designed to be used in conjunction with reference
data, i.e. standard instances that represent information common to a number of users, production facilities,
or both.
Most reference data are in ISO/TS 15926-4. This document specifies the rules that are required for the
development and validation of reference data items of ISO/TS 15926-4. This document also contains
examples of reference data items.
Some reference data are in ISO/TS 15926-11, ISO/TS 15926-12, or ISO 15926-13. The support for a specific
life-cycle activity depends on the use of appropriate reference data in conjunction with the data model.
NOTE A reference data library used with the ISO 15926 series can be standardized or proprietary. A reference
data library which is initially proprietary can subsequently be submitted for standardization. Classes contained
within a reference data library can be more or less generic. Generic core classes and commodity classes are likely to be
standardized, but specific manufactured product classes are unlikely to be standardized.

vi
International Standard ISO 15926-6:2024(en)
Industrial automation systems and integration — Integration
of life-cycle data for process plants including oil and gas
production facilities —
Part 6:
Rules for the development and validation of reference data of
ISO/TS 15926-4
1 Scope
This document specifies technical requirements for the structure and content of a reference data library for
ISO/TS 15926-4.
NOTE This document can also be applied to reference data libraries other than ISO/TS 15926-4.
The following are within the scope of this document:
— identification of a reference data item as specified in ISO/TS 15926-4;
— information that defines a reference data item;
— the way identifying and defining information is recorded using ISO 15926-2;
— the reference data library that contains the reference data items necessary to record identification and
defining information;
— the representation of the reference data library that is defined by this document as a spreadsheet.
The following are outside the scope of this document:
— administrative information about the source, the history of changes, and the current status of a reference
data item and a reference data library;
— the way administrative information is recorded using ISO 15926-2;
— the reference data library that contains the reference data items necessary to record administrative
information;
— defining the scope of reference data libraries within the ISO 15926 series;
— methods and guidelines for implementing ISO 15926-2;
— procedures for maintaining reference data libraries;
— requirements for the representation of a proprietary reference data library.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
the 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.

ISO 15926-2, Industrial automation systems and integration — Integration of life-cycle data for process plants
including oil and gas production facilities — Part 2: Data model
ISO 80000-1:2022, Quantities and units — Part 1: General
3 Terms, definitions, symbols and abbreviated terms
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 Terms and definitions
3.1.1
administrative information
information (3.1.5) about the administration of an item in a reference data library (3.1.17)
EXAMPLE Creation date, last change date, origin, change description, explanatory comment.
[SOURCE: ISO/IEC 11179-3:2023, 3.2.67, modified — The domain has been removed and "registry" has been
replaced by "reference data library".]
3.1.2
attribute
data (3.1.4) element for the computer-sensible description of a property (3.1.10), a relation or a class (3.1.3)
Note 1 to entry: An attribute describes only one detail of a property, class, or relation.
EXAMPLE The name of a property, the code of a class, the measure unit in which values of a property are provided.
[SOURCE: ISO 13584-42:2010, 3.3]
3.1.3
class
category or division of things (3.1.22) based on one or more criteria for inclusion and exclusion
Note 1 to entry: A class need not have any members (things that satisfy its criteria for membership).
Note 2 to entry: Because a spatio-temporal paradigm is used to define individuals in this document, all classes are
non-well-founded sets. These are explained in ISO 15926-2:2003, D.2.4.
[SOURCE: ISO 15926-1:2004, 3.1.1]
3.1.4
data
representation of information (3.1.5) in a formal manner suitable for communication, interpretation, or
processing by human beings or computers
[SOURCE: ISO 10303-2:2024, 3.1.207]
3.1.5
information
facts, concepts, or instructions
[SOURCE: ISO 10303-2:2024, 3.1.227]

3.1.6
instance
data (3.1.4) that represents, in computer-processable form, some real-world thing (3.1.22)
[SOURCE: ISO 15926-1:2004, 3.1.13]
3.1.7
maintenance organization
organizational unit that is responsible for the maintenance of the reference data library (3.1.17)
Note 1 to entry: Procedure for the maintenance of ISO/TC 184/SC 4 reference data (3.1.11) is described in
[12]
ISO/TC 184/SC4 N2591 .
Note 2 to entry: The maintenance organization in this document represents the combination of the ISO/TC 184/SC 4
secretariat, the ISO/TC 184/SC 4/WG 3 and the ISO/TC 184/SC 4/WG 22 together carrying out the task of maintenance
of ISO/TS 15926-4 reference data library published as a database using the procedure. The maintenance team (MT) is
defined by the ISO/TC 184/SC 4/WG 3 and the validation team (VT) is defined by the ISO/TC 184/SC 4/WG 22.
3.1.8
possible individual
thing (3.1.22) that exists in space and time
Note 1 to entry: This definition is taken from ISO 15926-2, in which “possible_individual” is an entity but not a defined term.
3.1.9
power class
set of all subclasses (3.1.21) of a class (3.1.3), including the class itself and the empty set
Note 1 to entry: A subclass of a power class selects subclasses that satisfy a specific context. A restricted set of
subclasses can be a “facet” or “aspect”.
3.1.10
property
aspect or quality of something that can be determined by measurement or observation
Note 1 to entry: The term “property” is used in ISO 15926-2.
3.1.11
reference data
process plant life-cycle data (3.1.4) that represents information (3.1.5) about classes (3.1.3) or individuals
which are common to many process plants or of interest to many users
[SOURCE: ISO 15926-1:2004, 3.1.18]
3.1.12
reference data item
thing (3.1.22) that is defined within a reference data library (3.1.17)
3.1.13
reference data item definition by text
text, and optionally equations and figures that are intended to be understood by a human, and that is the
normative definition of a reference data item (3.1.12)
3.1.14
reference data item definition by document reference
normative reference to a document that provides the normative definition of a reference data item (3.1.12)
3.1.15
reference data item non-human-interpretable identifier
text that is a unique identifier for a reference data item (3.1.12) and that is not intended to be interpreted
by a human
Note 1 to entry: The use of a reference data item non-human-interpretable identifier is defined in 5.2.

3.1.16
reference data item human-interpretable identifier
text that is a unique identifier for a reference data item (3.1.12) and that is intended to be interpreted by a human
Note 1 to entry: The use of a reference data item human-interpretable identifier is defined in 5.3.
Note 2 to entry: If a reference data item is a class (3.1.3), then its reference data item human-interpretable identifier
can be a term.
Note 3 to entry: The reference data item human-interpretable identifier is used for all references to a reference data
item in natural language text definitions.
Note 4 to entry: Names in natural language and terms in dictionaries are often unique only within a context. A reference
data item can be used in many contexts. Hence, a reference data item human-interpretable identifier can be longer
than a name in a natural language and contain words that qualify a natural language name to ensure that it is unique.
Note 5 to entry: A reference data library (3.1.17) can contain additional terms for a reference data item which are not
unique and which are used within particular contexts.
3.1.17
reference data library
RDI
managed collection of reference data (3.1.11)
[SOURCE: ISO 15926-1:2004, 3.1.19]
3.1.18
reference data library module
collection of reference data items (3.1.12) within a reference data library (3.1.17) that shares the same subject area
EXAMPLE Electrical is a reference data library module, represented by a specific spreadsheet, which contains
reference data library items (classes) that are of direct interest to the electrical engineering discipline, which in this
case is the subject area. In the context of ISO 15926-2, the reference data library module is a class (3.1.3) of class with
as members all classes contained by the corresponding spreadsheet.
[SOURCE: ISO/TS 15926-4:2024, 3.1.14]
3.1.19
relationship
connection among model elements
Note 1 to entry: In this document, a relationship is one of: an association, a generalization or a specialization.
[SOURCE: ISO/IEC 11179-3:2023, 3.1.4, modified — The domain has been deleted.]
3.1.20
superclass
class (3.1.3) that is a generalization of one or more other classes
Note 1 to entry: The classes being generalized are known as subclasses (3.1.21).
Note 2 to entry: A particular class can be a superclass with respect to one relationship (3.1.19) and simultaneously a
subclass with respect to another relationship.
[SOURCE: ISO/IEC 11179-3:2023, 3.1.9, modified — The domain and note 2 to entry have been deleted.]
3.1.21
subclass
class (3.1.3) that is a specialization of another class
Note 1 to entry: The class being specialized is known as a superclass (3.1.20).
Note 2 to entry: A particular class can be a subclass with respect to one relationship (3.1.19) and simultaneously a
superclass with respect to another relationship.

[SOURCE: ISO/IEC 11179-3:2023, 3.1.10, modified — The domain and note 2 to entry have been deleted.]
3.1.22
thing
anything that is, or can be thought about, or perceived
Note 1 to entry: This definition is taken from ISO 15926-2, in which thing is an entity but not a defined term, including
material and non-material objects, ideas, and actions.
3.1.23
upper camel-case notation
naming convention in which compound words are joined together without spaces, and the first letter of
every word is uppercase
[SOURCE: ISO/IEC 39794-5:2019, 3.56]
3.2 Symbols
Symbols used in this document are given in Table 1.
Table 1 — Symbols for set theory operations
Symbol Usage Meaning of usage
∪ A∪B union of sets A and B
∩ A∩B intersection of sets A and B
¬ ¬A complement of set A
* A* power set of set A
3.3 Abbreviated terms
CR Change Request
MT Maintenance Team
OED Oxford English Dictionary
OWL Web Ontology Language
RDL Reference Data Library
UML Unified Modelling Language
UoM Units of Measure
URN Uniform Resource Name
URI Uniform Resource Identifier
VT Validation Team
4 General principles for the content of a reference data library (RDL)
4.1 Structure of the rules for attributes in this document
This document has been structured such that the rules for the attributes are listed in the subclauses of
Clause 5. The number of the subclause corresponds to the number of the attribute. The numbering of
attributes corresponds to the “Attribute numbers” given in Annex A, where all attributes are listed with the
proper reference to the rule’s subclauses. Each reference data item shall be defined by assigning values to

the mandatory attributes defined by Table A.1. An explanation of each attribute name is given in Table A.1,
together with examples of the attribute.
NOTE Detailed requirements for using attributes are specified in 4.4.3 and subclauses corresponding to each
attribute.
Attributes for defining reference data items are categorized into three groups. Those are described in 4.5,
4.6, and 4.7.
4.2 Naming convention for attributes
Attribute names for a reference data item shall be denoted in the upper camel-case notation.
4.3 Presentation convention
For ease of identification, ISO 15926-2 entities, their subclasses and human-interpretable identifiers are
formatted using bold font in this document.
EXAMPLE Usage of bold font for ISO 15926-2 entities and their subclasses in the explanations:
In a representation of a reference data library in accordance with ISO 15926-2, a human-interpretable identifier is
represented by an instance of reference_data_item_human-interpretable_identification (subclass of ISO 15926
entity class_of_identification).
4.4 Defining a reference data library
4.4.1 Definition and content of a reference data library
This subclause includes the rules for the reference data library as a whole:
— a reference data library;
— minimum information about a reference data item;
— attribute.
4.4.2 Reference data library and reference data item
A reference data library is a collection of reference data items.
A reference data item is a class corresponding to a typical thing that appears in industry data, which can
be repeatedly used in engineering documents or various data in information systems in that life cycle. A
reference data item is specified with several reference data, and the ISO/TS 15926-4 reference data library
is characterized by 25 reference data.
One of the mandatory reference data is an identifier defined in 5.2, and another optional reference data is
notes defined in 5.8.
NOTE A reference data item is usually a class but can be a member of possible_individual.
EXAMPLE A “pump” is a typical physical thing in the engineering phase, and “maintenance” is also a typical
abstract thing in the O&M phase.
4.4.3 Minimum information about a reference data item
A reference data item shall be characterised by minimum information which corresponds to specific
attributes as follows:
— a URI for the reference data item;
— a unique non-human-interpretable identifier for the reference data item;

— a unique human-interpretable identifier for the reference data item;
— a definition that is either a text definition or a formal definition using a set theory relationship;
— at least one superclass;
— at least one ISO 15926-2 entity;
— at least one classification;
— units of measure (UoM) attributes if the reference data items are units of measure classes.
The unique non-human-interpretable and human-interpretable identifiers shall be assigned by the
maintenance organization.
NOTE The URI need not be assigned by the maintenance organization. If a URI is assigned to the reference data
item by a source which can be normatively referenced, then that URI can be used.
4.4.4 Reference data library
A reference data library shall have a reference data item or reference data items.
A reference data library may be grouped into modules, as defined in 3.1.17. A module shall be named after
its classification with additional information depending on the representation of a reference data library.
This document defines the rules for the attributes of the representation of the ISO/TS 15926-4 modules as
spreadsheets. In future versions of this document, rules for other representations, such as database format,
may be added where necessary.
NOTE The reference data library of ISO/TS 15926-4 are all grouped into separate modules as spreadsheets in
which reference data items have the same classifications respectively.
EXAMPLE Both the class “centrifugal pump” and “dynamic pump”, which have “rotating equipment class” for
Classification1, are grouped into the same module, and the name of the module is “rotating_equipment-v1.xls” where
“-v1.xls” is an additional information specific for a spreadsheet representation as described in Clause 6.
4.5 Reference data item identification
4.5.1 Category of reference data item identification
This category includes the following definitions:
— types of reference data item identification;
— types of text definition and notes of a reference data item;
— formal relationships for definition.
4.5.2 Types of reference data item identification
The reference data item identification shall consist of the following:
— one URI, as specified in 5.1;
— a single non-human-interpretable identifier, as specified in 5.2;
— a single human-interpretable identifier, as specified in 5.3.
The reference data item identification can include any number of synonyms if there are two synonyms, as
specified in 5.4 and 5.5.
NOTE 1 5.2 and 5.3 require both the non-human-interpretable and the human-interpretable identifiers to be
unique. This implements ISO/IEC 11179-6.

NOTE 2 This document does not specify how an identifier of a reference data item is used in proprietary reference
data libraries.
EXAMPLE Within ISO/TS 15926-4, the class centrifugal pump is identified by the human-interpretable identifier
“centrifugal pump” and by the non-human-interpretable identifier “7436”. The human-interpretable identifier is
more memorable.
NOTE 3 The appropriate human-interpretable identifier for a reference data item cannot be known when it is first
identified by the maintaining organization for the reference data library. Hence, a reference data item can be identified
only by its non-human-interpretable identifier.
4.5.3 Types of text definitions and notes of a reference data item
Text about a reference data item shall be as follows:
— Attribute: TextDefinition.
If a reference data item has a normative definition as defined in 5.6.7, then a reference data item shall not
have a text definition.
In case a reference data item is a superclass, the text definition is defined by the superclass statement with
distinguishing characteristics. This is explained in 5.6.7. In all other cases, a definition of a reference data
item needs to be given, which will be normative. This is defined in 5.6.1:
— Attribute: Source;
— Attribute: Note.
There can be any number of notes about a reference data item, as described in 5.8.
4.6 Classifications
4.6.1 General
A classification of a class plays several roles in the management of classes, as follows:
a) a classification of a class can be based on the way in which a class is defined;
EXAMPLE 1 The members of the class of functional objects have only function as a criterion. In some cases,
there are classification aspects, such as type of pipe fitting, pressure rating of pipe fitting, size of pipe fitting, and
material of pipe fitting. Each aspect can be organized using a class of class, typically done in a project RDL.
b) a classification can be based upon a level in a classification hierarchy;
EXAMPLE 2 Classes in other RDLs, such as project RDLs, which are extensions of ISO/TS 15926-4, can be
classified according to the level in the following hierarchy:
— core classes;
— de facto classes;
— standard classes;
— commodity product classes;
— proprietary product classes.
c) a classification can be based on domain.
EXAMPLE 3 The rotating equipment class has classes relevant to rotating equipment as members. The division of
the reference data library into modules is a class classification.
NOTE 1 All classes in ISO/TS 15926-4 are core classes. Other classifications of class are possible.

A class_of_class is a class whose members are instances (see 3.1.6) of the class. A class_of_class is a means
of classifying the subdivisions of a class membership, i.e., they can be used to identify types of subdivisions
in ISO 15926-2.
For these purposes, three types of relationships between reference data item and other reference data
item(s) or an ISO 15926-2 entity shall be prepared as follows:
— an attribute for inheritance relationship (Attribute: Superclass#);
— an attribute for grouping based on an ISO 15926-2 entity (Attribute: ISO15926-2ENTITY);
— an attribute for grouping based on business use cases (Attribute: Classification1).
NOTE 2 # of Superclass # can be 1, 2, 3, 4 and 5 (See 5.9, 5.10, 5.11, 5.12 and 5.13).
Classifications can be theoretically explained by a power class (see 3.1.9), as shown in Figure 1.
Usually, a class in the reference data library is an instance of the same ISO 15926 entity as its superclass. An
exception is where a class in the reference data library is a subclass of an instance of a class of functional
objects. This is because a subclass lower down the hierarchy does not necessarily have only function as its
criterion. Moreover, classifying a class as a member of a power class of one of its superclasses provides no
additional information.
NOTE 3 ISO/TS 15926-4 does not contain the power class. It is represented here because the concept is useful in a
project RDL.
NOTE 4 In a project RDL, a class of class can be used to affect the use of members of that class of class since the
range of a relationship can be restricted to only members of a specific class of class. When a class is not a member of
the class of class that is defined as a range for a specific relationship, instances of that class cannot be used as a range
for that specific relationship on the project data level.
EXAMPLE 4 The class “DOCUMENT TYPE” can have a power class “DOCUMENT_TYPE_CLASSIFICATION”.
“correspondence”, “multimedia”, “permit”, “contract”, and “requisition” classes are subclasses of “DOCUMENT_
TYPE”. “DOCT” (Document type) and “CONT” (Content type) are subclasses of “DOCUMENT_TYPE_CLASSIFICATION”.
“correspondence”, “multimedia”, and “permit” classes are members of “DOCT”. “contract” and “requisition” classes
are members of “CONT”. Those relationships are shown in Figure 1.
Figure 1 — A UML class diagram related to classifications
NOTE 5 In an EXPRESS implementation of the ISO 15926 series, each class in a reference data library must explicitly
be an instance of an entity in the ISO 15926 data model. The choice of this entity is effectively a classification of the class.

4.6.2 Class of inheritance relationship (Attribute: Superclass#)
A reference data item that is a class can have any number of superclasses; thus, multiple inheritance is
allowed.
EXAMPLE 1 The class “centrifugal pump” has the class “dynamic pump” as a superclass.
EXAMPLE 2 The class “shell and tube condenser” has the classes “condenser” and “shell and tube heat exchanger”
as superclasses.
NOTE The maximum number of superclasses is five in a spreadsheet representation.
4.6.3 Grouping based on ISO 15926-2 entities
A reference data item shall be a member of an entity in ISO 15926-2 and shall have one
Attribute: ISO15926-2Entity.
4.7 Attributes for units of measure (UoM)
This category includes the following definition:
— attributes related to UoM, which are introduced by this document, based on the ISO 80000 series;
— relationships among those attributes.
The UoM data used in industry projects come from various sources. The reason is the UoM data sets are
applied to projects in all parts of the world. To date, in practice, there are several UoM data sets that are
being used in projects, such as the ISO 80000 series, QUDT, and NASA sets.
The current content of ISO/TS 15926-4 only contains UoMs coming from the ISO 80000 series.
The notations of UoM RDIs shall be in accordance with the ISO 80000 series, and the base unit for RDIs in
ISO/TS 15926-4 follows SI units as specified in the ISO 80000 series. In addition to those principles, this
document also introduced seven specific attributes to represent UoMs of the ISO 80000 series in a computer-
sensible manner.
Those seven attributes are as follows:
— Attribute: Symbol, as defined in 5.19;
— Attribute: Operator as defined in 5.20;
— Attribute: FirstOperand as defined in 5.21;
— Attribute: SecondOperand as defined in 5.22;
— Attribute: Factor as defined in 5.23;
— Attribute: Prefix as defined in 5.24;
— Attribute: Exponent as defined in 5.25.
Those are only applicable for UoM reference data items registered in the UoM module of ISO/TS 15926-4
reference data library. There are two types of reference data items. One type is unit classes, which are
subclasses of class property_quantification of ISO 15926-2, and the other types are unit reference data
items, which are subclasses of scale. Those seven attributes are only applicable to the latter. Attributes for
UoM are mandatory, as specified in Table 2 if a reference data item is a member of a unit of measure class.

Table 2 — Possible combination of attributes of UoM
First Second
Attribute
Symbol Operator Factor Prefix Exponent
names
operand Operand
If the unit If the operator
Explanation Possible combination is
type is type is
Prefix
Symbol
name
speci-
(real num- of ISO (natural
Data type fied in UniqueName UniqueName
ber) 80000- number)
ISO 80000
1:2022,
series
Table 4
(base unit) (empty) (n/a) (n/a) (n/a) (n/a) (n/a)
multiply M M (n/a) (n/a) (n/a)
Possible
divide M M (n/a) (n/a) (n/a)
attribute com-
bination based factor M (n/a) M (n/a) (n/a)
(derived
on symbol and
unit)
prefix M (n/a) (n/a) M (n/a)
operator
exponentiate M (n/a) (n/a) (n/a) M
reciprocal M (n/a) (n/a) (n/a) (n/a)
Key
M/O  data
...