ISO/TS 19139-1:2019

TECHNICAL ISO/TS
SPECIFICATION 19139-1
First edition
2019-03
Geographic information — XML
schema implementation —
Part 1:
Encoding rules
Reference number
ISO/TS 19139-1:2019(E)
©
ISO 2019

---------------------- Page: 1 ----------------------
ISO/TS 19139-1:2019(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/TS 19139-1:2019(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 2
4.1 Abbreviated terms . 2
4.2 Namespace abbreviations . 2
4.3 UML model stereotypes. 3
4.3.1 Overview of UML model stereotypes . 3
4.3.2 Stereotypes of classes . 3
4.3.3 Stereotypes of attributes . 3
4.3.4 Stereotypes of links . 3
4.3.5 Stereotypes of packages . 4
5 Conformance . 4
6 Requirements for encoding . 4
6.1 Overview of requirements . 4
6.2 Rule-based . 4
6.3 Quality . 5
6.4 Web implementations . 5
6.5 Use of external XML implementations . 5
6.6 Polymorphism . 5
7 Encoding rules . 5
7.1 Overview of encoding rules . 5
7.2 Default encoding . 6
7.2.1 XML class type (XCT) . . 6
7.2.2 XML Class Global Element (XCGE) . 8
7.2.3 The XML Class Property Type (XCPT) . 9
7.3 Special case encodings .10
7.3.1 Overview of special case encodings .10
7.3.2 Abstract classes .11
7.3.3 Inheritance and sub-class encodings .12
7.3.4 Enumeration encodings .15
7.3.5 CodeList encoding .17
7.3.6 Union encoding .19
7.3.7 Encoding of MetaClasses .21
7.3.8 Encoding of externally identified implementations .22
7.4 XML Namespace package encoding .29
7.5 XML schema package encoding .29
8 Additional encodings .32
9 Encoding for modularity and reuse .32
9.1 UML packages and XML namespaces .32
9.2 UML model for XML implementation .32
9.3 Implementation Approach for Decoupling XML Packages .33
9.3.1 Overview .33
9.3.2 Implementation Approach Rules .33
9.3.3 Example of Decoupling .35
Annex A (normative) Abstract test suite .38
Annex B (informative) Backward compatibility .39
© ISO 2019 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO/TS 19139-1:2019(E)

Bibliography .40
iv © ISO 2019 – All rights reserved

---------------------- Page: 4 ----------------------
ISO/TS 19139-1:2019(E)

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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
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 211, Geographic information/Geomatics.
This first edition of ISO/TS 19139-1 cancels and replaces ISO/TS 19139:2007, which has been technically
revised.
A list of all parts in the ISO 19139 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.
© ISO 2019 – All rights reserved v

---------------------- Page: 5 ----------------------
ISO/TS 19139-1:2019(E)

Introduction
The importance of metadata describing digital geographic data is explained in detail in the text
of ISO 19115-1, and other International Standards, e.g. ISO 19110, ISO 19119, ISO 19157. Those
documents provide a structure for describing digital geographic data by defining metadata elements
and establishing a common set of metadata terminology, definitions and extension procedures. These
standards do not define encodings for those metadata.
To facilitate the standardization of implementations across the standards and in similar domain
schemas, this document provides a definitive set of rules for encoding ISO metadata standards in
Extensible Markup Language (XML). The resulting XML schemas are meant to enhance interoperability
by providing a common specification for describing, validating and exchanging metadata. These rules
are intended to be used in parallel to the rules in ISO 19136:2007, Annex E for encoding application
schemas into XML/GML. The difference is that those rules are for data that represents features; these
rules are for metadata about that data.
ISO 19118 describes the requirements for creating encoding rules based on UML schemas and the XML
based encoding rules as well as introducing XML. This document uses the encoding rules defined in
ISO 19118 and provides the specific details of their application with regards to deriving XML schema
for the UML models for other metadata standards.
These rules were first used in creating ISO/TS 19115-3 as an XML encoding of ISO 19115-1, i.e. ISO/
TS 19115-3 conforms to this document. They were also used to create ISO/TS 19157-2, an encoding of
ISO 19157.
The standardization target of this document is XML implementations of metadata. This includes both
other standards within the Geographic Information series and models developed by other organizations.
vi © ISO 2019 – All rights reserved

---------------------- Page: 6 ----------------------
TECHNICAL SPECIFICATION ISO/TS 19139-1:2019(E)
Geographic information — XML schema implementation —
Part 1:
Encoding rules
1 Scope
This document defines XML based encoding rules for conceptual schemas specifying types that
describe geographic resources. The encoding rules support the UML profile as used in the UML models
commonly used in the standards developed by ISO/TC 211. The encoding rules use XML schema for the
output data structure schema.
The encoding rules described in this document are not applicable for encoding UML application schema
for geographic features (see ISO 19136 for those rules).
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.
ISO 19118, Geographic information — Encoding
W3C XMLName, Namespaces in XML. W3C Recommendation
W3C XMLSchema-1, XML Schema Part 1: Structures. W3C Recommendation
W3C XMLSchema-2, XML Schema Part 2: Datatypes. W3C Recommendation
W3C XML, Extensible Markup Language (XML) 1.0, W3C Recommendation
W3C XLink, XML Linking Language (XLink) Version 1.0. W3C Recommendation
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological 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
namespace
collection of names, identified by a URI reference, which are used in XML documents as element names
and attribute names
[SOURCE: W3C XML]
3.2
package
general purpose mechanism for organizing elements into groups
EXAMPLE Identification information, metadata entity set information, constraint information.
© ISO 2019 – All rights reserved 1

---------------------- Page: 7 ----------------------
ISO/TS 19139-1:2019(E)

[SOURCE: ISO 19103:2015, 4.27 — modified: The EXAMPLE has been added.]
3.3
polymorphism
characteristic of being able to assign a different meaning or usage to something in different contexts,
specifically, to allow an entity such as a variable, a function, or an object to have more than one form
Note 1 to entry: There are several different kinds of polymorphism.
[SOURCE: https: //searchcio .techtarget .com/]
3.4
realization
specialized abstraction relationship between two sets of model elements, one representing a
specification (the supplier) and the other representing an implementation of the latter (the client)
Note 1 to entry: Realization indicates inheritance of behaviour without inheritance of structure.
[SOURCE: ISO 19103:2015, 4.29]
4 Symbols and abbreviated terms
4.1 Abbreviated terms
UML Unified Modeling Language
URI Uniform Resource Identifier
XCT XML Class Type
XCPT XML Class Property Type
XCGE XML Class Global Element
XML Extensible Markup Language
XSD XML Schema Definition
4.2 Namespace abbreviations
Table 1 presents the external namespaces used in this document. The left column shows the common
namespace prefix used to describe the elements in the namespace. The second column shows the
English description of the namespace prefix. The third column is the URI of the actual namespace.
These URIs do not correspond necessarily to the location of the schemas.
Table 1 — External namespaces used by this document
Namespace
English description of the namespace URI of the actual namespace
prefix
gml Geography Markup Language http: //www .opengis .net/gml/3 .2
xlink XML Linking Language (XLink) http: //www .w3 .org/1999/xlink
xs W3C XML base schemas http: //www .w3 .org/2001/XMLSchema
2 © ISO 2019 – All rights reserved

---------------------- Page: 8 ----------------------
ISO/TS 19139-1:2019(E)

4.3 UML model stereotypes
4.3.1 Overview of UML model stereotypes
A UML stereotype is an extension mechanism for existing UML concepts. In addition to the stereotypes
already defined for describing geographic resources, this document defines stereotypes necessary for a
rules-based encoding into XML schema.
The elements of the UML diagrams depicted in Clause 7 can carry stereotypes specifying an XML
implementation. Those stereotypes, listed in the following subclauses, are carried by classes
representing XML elements or XML types, UML attributes, UML links (realizations or dependencies)
and UML packages.
4.3.2 Stereotypes of classes
In this document the following Stereotypes of classes are used:
a) <>: The class represents an implementation type encoded as an XML choice block. Each
property of the class is implemented as an element of the choice.
b) <>: The class represents an implementation type encoded as an XML complex type.
c) <>: The class represents an implementation type encoded as an XML simple type.
d) <>: The class represents an implementation type encoded as an XML complex
type with simple content.
4.3.3 Stereotypes of attributes
In this document the following Stereotypes of attributes are used:
a) <>: The property is encoded as an XML attribute.
b) <>: The property is encoded as an XML attributeGroup.
c) <>: The property is encoded as an XML element with a name and a type ( name=”propertyName” type=”propertyType”/>).
4.3.4 Stereotypes of links
In this document, the following Stereotypes of links are used:
a) <>: (carried by realization relationships) The XCT of the abstract concept to implement is
substituted by the specified external implementation.
b) <>: (carried by realization relationships) The XCGE of the abstract concept to implement is
substituted by the specified external implementation.
c) <>: (carried by realization relationships) The XCPT of the abstract concept to implement is
substituted by the specified external implementation.
d) <>: (carried by dependency relationships) The source represents an XML schema
implementing the abstract concepts defined in the target.
e) <>: (carried by dependency relationships) The source and the target represent XML
schemas. The source includes () the target.
f) <>: (carried by dependency relationships) The source and the target represent sets of
XML objects grouped within the same namespace. The source imports () the target.
© ISO 2019 – All rights reserved 3

---------------------- Page: 9 ----------------------
ISO/TS 19139-1:2019(E)

4.3.5 Stereotypes of packages
In this document, the following Stereotypes of packages are used:
a) <>: The package represents an XML schema.
b) <>: The package represents a set of XML objects grouped within the same
namespace.
5 Conformance
The framework, concepts, and methodology for testing, and the criteria to be achieved to claim
conformance, are specified in ISO 19105. An XML schema implementation of geographic resources
conforms to this document if it passes the test modules defined in Annex A.
6 Requirements for encoding
6.1 Overview of requirements
Geographic resources are generally specified in other standards and specifications, e.g. metadata
according to ISO 19115-1 and feature catalogues according to ISO 19110. Geographic resources are
represented as conceptual schemas comprising a set of UML packages containing one or more UML
classes. These conceptual schemas provide an encoding-independent view of the related geographic
resources.
XML offers many alternatives for structuring information for exchange. Clause 7, in conformance with
ISO 19118, defines XML schema encoding rules more specifically applicable to the conceptual schemas
of geographic resources.
Even within the reduced limitations of ISO 19118 and the encoding rules defined in this document,
there are still choices for the creation of specific XML schemas.
This document provides the foundation needed to establish consistent XML schema implementations of
geographic resources, in the form of a set of standardized encoding rules to be applied to the conceptual
schemas of geographic resources to create standard XML schema.
The details of XML namespaces are not included in this document. A namespace is a collection of names
that can be used in XML documents as element or attribute names. The namespace identifier is used to
identify the names with a specific schema. A namespace identifier is a URI. A URI is often cumbersome
for reading, writing and including in human discussion, so this document will refer to common
namespace prefixes when identifying the contents of a namespace.
Before presenting the details of the encoding, it is important to understand why certain encoding
rules are used. Gaining an understanding of the rules will make clear the capabilities, limitations
and best-practice use. Some of the major goals considered when developing this encoding rule were
interoperability with other ISO 19100 series specifications, predictability, extensibility and usability.
Additional details of these goals are described in 6.2 to 6.6.
6.2 Rule-based
This document defines a rule-based encoding built from UML models, e.g. those in the ISO 19100
series of International Standards, as required by ISO 19118. Using a rule-based method achieves three
important goals:
— first, the resulting XML schemas are based directly on the conceptual models and therefore increase
the chance for interoperability;
— second, the resulting schema is predictable since any class, attribute, association, etc. is encoded
just as all other UML elements of the same type are encoded;
4 © ISO 2019 – All rights reserved

---------------------- Page: 10 ----------------------
ISO/TS 19139-1:2019(E)

— third, XML schemas using these rules can be generated in an automated or semi-automated fashion.
6.3 Quality
XML schema quality in the context of this document implies that all elements of the conceptual model
are consistently implemented and that a user can directly create and/or understand the content of
an XML instance document using the conceptual schema of the corresponding geographic resource.
Additionally, an implementer can determine the XML schema implementation of a geographic resource
by knowing its conceptual schema and the encoding rules.
Another aspect to quality is completeness. This document enables encoding the entire conceptual
schema of a geographic resource without regard to usage or application.
6.4 Web implementations
One of the goals stated in 6.1 is usability. Usability, as it pertains to the design of geographic resources,
focuses on their exchange with the understanding that this will often happen in a web-based
environment. While there is no restraint against creating instance documents that never transfer
across a network, there are many aspects to the design that are intended to aid Internet and web-like
transfer of geographic resources.
6.5 Use of external XML implementations
Another design principle that aids interoperability and usability is the re-use of existing XML schemas.
If an XML schema standard already exists that encodes a part of the ISO 19100 series pertaining to
geographic metadata, then it is advantageous to incorporate that XML schema standard. If the external
XML schema is directly used, then interoperability is enhanced. It is also likely that software already
exists that can process instance documents that conform to the external XML. Furthermore, if the
external schema is well designed, it might be more efficient than XML schema generated from a series
of encoding rules and this might help achieve the goal of usability.
While using an implementation that already exists has some important advantages, it is recommended
that the external XML schemas should not violate the primary design principles defined herein. See
7.3.8 for details and examples.
6.6 Polymorphism
The term polymorphism is formally defined in 3.3. In general terms, polymorphism means the ability to
assume different forms, i.e. to implement properties using their data type or any of its derived classes.
Polymorphism allows implementers to extend the more general format of properties within their
namespaces while still providing usable and understandable instance documents for users outside of
their organization. Polymorphism primarily derives from the property type encodings described in 7.3.
7 Encoding rules
7.1 Overview of encoding rules
General rules for transforming UML to XML schema are described below and are in accordance with the
rules defined in ISO 19118. In some cases, ISO 19118 allows for multiple methods of transforming UML to
XML schema, and the rules defined here serve to clarify which method is to be used to conform with this
document. Background on classes and how they are the building blocks for encoding all data exchange
(and in this case metadata exchange) is purposefully absent from this document since ISO 19118 covers
this in detail. This document is based on the encoding rules in ISO 19118 and a familiarity with that
document will greatly enhance comprehension of the topics described throughout Clause 7.
NOTE The way the encoding rules are described doesn’t prevent adopting best practices in generating XML
schemas.
© ISO 2019 – All rights reserved 5

---------------------- Page: 11 ----------------------
ISO/TS 19139-1:2019(E)

7.2 Default encoding
7.2.1 XML class type (XCT)
7.2.1.1 Overview of XML class type (XCT)
The class is the fundamental modelling concept in UML (ISO 19118), so the fundamental encoding rules
focus on the encoding of a UML class and build from there. A class is made up of one or more properties.
It is important to recall from ISO 19118 that a property can represent an attribute, association,
aggregation or composition (ISO 19118). For example, in Figure 1, the Class1 class has three properties:
attr1, attr2 and role1. For the sake of encoding into XML schema it is important to understand that
there is no distinction between properties that are UML attributes, associations, aggregations or
compositions.
ISO 19118 also describes the need to use identifiers (ids) and domain unique identifiers (DUIDs) as
identifiers in XML schema. There is a special XML schema type in baseTypes2014.xsd in the gco
namespace, gco: AbstractObject _Type, which provides the necessary identifiers. It is mentioned here
because it is part of the default XML Class type encoding.
7.2.1.2 XCT rule
As a worked example, the UML in Figure 1 is encoded in XML using the following requirements.
Figure 1 — Example
Requirement /req/default/XCT
A UML Class shall be encoded into XML schema as an XML complex type (xs: complexType) referred to
as t
...