SIST ISO 19108:2003

INTERNATIONAL ISO
STANDARD 19108
First edition
2002-09-01
Geographic information — Temporal
schema
Information géographique — Schéma temporel

Reference number
©
ISO 2002
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ii © ISO 2002 – All rights reserved

Contents Page
Foreword . v
Introduction. vi
1 Scope. 1
2 Conformance. 1
2.1 Conformance classes and requirements. 1
2.2 Application schemas for data transfer. 1
2.3 Application schemas for data with operations . 1
2.4 Feature catalogues. 1
2.5 Metadata element specifications . 1
2.6 Metadata for data sets . 1
3 Normative references. 1
4 Terms, definitions and abbreviated terms. 2
4.1 Terms and definitions. 2
4.2 Abbreviated terms. 6
5 Conceptual schema for temporal aspects of geographic information. 6
5.1 Structure of the schema . 6
5.2 Geometry of time. 7
5.2.1 Time as a dimension. 7
5.2.2 Temporal objects. 7
5.2.3 Temporal geometric primitives. 8
5.2.4 Temporal topological objects . 13
5.3 Temporal reference systems . 16
5.3.1 Types of temporal reference systems. 16
5.3.2 Calendars and clocks. 17
5.3.3 Temporal coordinate systems. 19
5.3.4 Ordinal temporal reference systems. 20
5.4 Temporal position. 21
5.4.1 Introduction. 21
5.4.2 TM_Position. 21
5.4.3 TM_TemporalPosition. 21
5.4.4 Position referenced to calendar and clock. 23
5.4.5 Position referenced to a temporal coordinate system. 23
5.4.6 Position referenced to an ordinal temporal reference system.24
5.5 Time and components of geographic information . 24
5.5.1 Temporal aspects of geographic information components . 24
5.5.2 Temporal feature attributes. 25
5.5.3 Temporal feature operations. 26
5.5.4 Time and feature associations. 27
5.5.5 Temporal metadata elements. 29
Annex A (normative) Abstract test suite . 31
A.1 Application schemas for data transfer. 31
A.2 Application schemas for data with operations . 31
A.3 Feature catalogues. 31
A.4 Metadata element specifications . 32
A.5 Metadata for data sets . 32
Annex B (informative) Use of time in application schemas . 33
B.1 Temporal feature attributes. 33
B.1.1 TM_GeometricPrimitive as a data type . 33
B.1.2 TM_GeometricPrimitive as a temporal attribute . 33
B.1.3 TM_TopologicalComplex as an attribute . 34
B.1.4 Recurring attribute values. 34
B.2 Temporal feature associations. 35
B.2.1 Simple temporal associations. 35
B.2.2 Feature succession. 36
B.3 Feature associations with temporal characteristics. 37
Annex C (normative) Describing temporal reference systems in metadata. 38
C.1 Metadata for temporal reference systems . 38
Annex D (informative) Description of calendars. 41
D.1 Internal structure of calendars. 41
D.2 Describing a calendar. 42
D.3 Examples. 43
D.3.1 Julian calendar. 43
D.3.2 Modern Japanese calendar . 44
D.3.3 Ancient Babylonian calendar . 45
D.3.4 Global Positioning System calendar. 47
Bibliography. 48

iv © ISO 2002 – All rights reserved

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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
The main task of technical committees is to prepare International Standards. Draft International Standards adopted
by the technical committees are circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 19108 was prepared by Technical Committee ISO/TC 211, Geographic information/Geomatics.
Annexes A and C form a normative part of this International Standard. Annexes B and D are for information only.
Introduction
This International Standard defines the standard concepts needed to describe the temporal characteristics of
geographic information as they are abstracted from the real world. Temporal characteristics of geographic
information include feature attributes, feature operations, feature associations, and metadata elements that take a
value in the temporal domain.
The widespread application of computers and geographic information systems has led to the increased analysis of
geospatial data within multiple disciplines. Geographic information is not confined to a three-dimensional spatial
domain. Many geographic information systems require data with temporal characteristics. A standardized
conceptual schema for temporal characteristics will increase the ability of geographic information to be used for
certain types of applications such as simulations and predictive modelling.
As a fundamental physical reality, time is of interest to the whole range of scientific and technical disciplines. Many
of the concepts described in this International Standard are applicable outside of the field of geographic
information. ISO/TC 211 does not intend to develop independent standards for the description of time, but the
technical committee believes that it is necessary to standardize the way to describe the temporal characteristics of
geographic data sets and features. Geographic information system and software developers and users of
geographic information will use this schema to provide consistently understandable temporal data structures.
Historically, temporal characteristics of features have been treated as thematic feature attributes. For example, a
feature "Building" may have an attribute "date of construction". However, there is increasing interest in describing
the behaviour of features as a function of time. This can be supported to a limited extent when time is treated
independently of space. For example, the path followed by a moving object can be represented as a set of features
called "way point", each of which is represented as a point and has an attribute that provides the time at which the
object was at that spatial position. Behaviour in time may be described more easily if the temporal dimension is
combined with the spatial dimensions, so that a feature can be represented as a spatiotemporal object. For
example, the path of a moving object could be represented as a curve described by coordinates in x, y and t. This
International Standard has been prepared in order to standardize the use of time in feature attributes. Although it
does not describe feature geometry in terms of a combination of spatial and temporal coordinates, it has been
written to establish a basis for doing so in a future standard within the ISO 19100 series.

vi © ISO 2002 – All rights reserved

INTERNATIONAL STANDARD ISO 19108:2002(E)

Geographic information — Temporal schema
1 Scope
This International Standard defines concepts for describing temporal characteristics of geographic information. It
depends upon existing information technology standards for the interchange of temporal information. It provides a
basis for defining temporal feature attributes, feature operations, and feature associations, and for defining the
temporal aspects of metadata about geographic information. Since this International Standard is concerned with
the temporal characteristics of geographic information as they are abstracted from the real world, it emphasizes
valid time rather than transaction time.
2 Conformance
2.1 Conformance classes and requirements
This International Standard defines five conformance classes, which depend upon the nature of the test item.
2.2 Application schemas for data transfer
To conform to this International Standard, an application schema for data transfer shall satisfy the requirements of
A.1 of the Abstract Test Suite in annex A.
2.3 Application schemas for data with operations
To conform to this International Standard, an application schema that supports operations on data shall satisfy the
requirements of A.2 of the Abstract Test Suite in annex A.
2.4 Feature catalogues
To conform to this International Standard, a feature catalogue shall satisfy the requirements of A.3 of the Abstract
Test Suite in annex A.
2.5 Metadata element specifications
To conform to this International Standard, a metadata specification shall satisfy the requirements of A.4 of the
Abstract Test Suite in annex A.
2.6 Metadata for data sets
To conform to this International Standard, metadata for a data set shall satisfy the requirements of A.5 of the
Abstract Test Suite in annex A.
3 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 31-1:1992, Quantities and units — Part 1: Space and time
ISO 1000:1992, SI units and recommendations for the use of their multiples and of certain other units
ISO 8601:2000, Data elements and interchange formats ― Information interchange ― Representation of dates and
times
ISO/IEC 11404:1996, Information technology ― Programming languages, their environments and system software
interfaces ― Language-independent data types
1)
ISO/TS 19103: , Geographic information — Conceptual schema language
1)
ISO 19107: , Geographic information — Spatial schema
1)
ISO 19109: , Geographic information — Rules for application schema
1)
ISO 19110: , Geographic information — Methodology for feature cataloguing
1)
ISO 19111: , Geographic information — Spatial referencing by coordinates
1)
ISO 19115: , Geographic information — Metadata
4 Terms, definitions and abbreviated terms
4.1 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
4.1.1
calendar
discrete temporal reference system that provides a basis for defining temporal position to a resolution of one
day
4.1.2
calendar era
sequence of periods of one of the types used in a calendar, counted from a specified event
4.1.3
UTC
Coordinated Universal Time
time scale maintained by the Bureau International des Poids et Mesures (International Bureau of Weights and
Measures) and the International Earth Rotation Service (IERS) that forms the basis of a coordinated dissemination
of standard frequencies and time signals [ITU-R Rec.TF.686-1 (1997)]
4.1.4
day
period having a duration nominally equivalent to the periodic time of the Earth's rotation around its axis

1) To be published.
2 © ISO 2002 – All rights reserved

4.1.5
edge
one-dimensional topological primitive [ISO 19107]
NOTE The geometric realization of an edge is a curve. The boundary of an edge is the set of one or two nodes associated
to the edge within a topological complex.
4.1.6
event
action which occurs at an instant
4.1.7
feature
abstraction of real world phenomena [ISO 19101]
NOTE A feature may occur as a type or an instance. Feature type or feature instance should be used when only one is
meant.
4.1.8
feature association
relationship between features [ISO 19109]
NOTE 1 A feature association may occur as a type or an instance. Feature association type or feature association instance
is used when only one is meant.
NOTE 2 Feature associations include aggregation of features.
4.1.9
feature attribute
characteristic of a feature [Adapted from ISO 19110]
NOTE A feature attribute has a name, a data type, and a value domain associated to it.
4.1.10
feature division
feature succession in which a previously existing feature is replaced by two or more distinct feature instances of
the same feature type
EXAMPLE An instance of the feature type “land parcel” is replaced by two instances of the same type when the parcel is
legally subdivided.
4.1.11
feature fusion
feature succession in which two or more previously existing instances of a feature type are replaced by a single
instance of the same feature type
EXAMPLE Two instances of the feature type “pasture” are replaced by a single instance when the fence between the
pastures is removed.
4.1.12
feature operation
operation that every instance of a feature type may perform [ISO 19110]
EXAMPLE An operation upon a “dam” is to raise the dam. The results of this operation are to raise the height of the “dam”
and the level of water in a “reservoir”.
NOTE Feature operations provide a basis for feature type definition.
4.1.13
feature substitution
feature succession in which one feature instance is replaced by another feature instance of the same or different
feature type
EXAMPLE An instance of feature type “building” is razed and replaced by an instance of feature type “parking lot”.
4.1.14
feature succession
replacement of one or more feature instances by other feature instances, such that the first feature instances
cease to exist
4.1.15
geometric primitive
object representing a single, connected, homogeneous element of space [ISO 19107]
NOTE Geometric primitives are non-decomposed objects that present information about geometric configuration. They
include points, curves, surfaces, and solids.
4.1.16
Gregorian calendar
calendar in general use; first introduced in 1582 to define a year that more closely approximated the tropical year
than the Julian calendar [adapted from ISO 8601:2000]
NOTE 1 The introduction of the Gregorian calendar included the cancellation of the accumulated inaccuracies of the Julian
year. In the Gregorian calendar, a calendar year is either a common year or a leap year; each year is divided into 12 sequential
months.
4.1.17
instant
0-dimensional geometric primitive representing position in time
NOTE The geometry of time is discussed in 5.2.
4.1.18
interval scale
scale with an arbitrary origin which can be used to describe both ordering of values and distances between values
NOTE Ratios of values measured on an interval scale have no meaning.
4.1.19
Julian date
Julian day number followed by the decimal fraction of the day elapsed since the preceding noon
4.1.20
Julian day number
number of days elapsed since Greenwich mean noon on 1 January 4713 BC, Julian proleptic calendar
4.1.21
life span
period during which something exists
NOTE Valid-time life span is the period during which an object exists in the modelled reality. Transaction-time life span is
the period during which a database object is current in the database.
4.1.22
month
period approximately equal in duration to the periodic time of a lunar cycle
4 © ISO 2002 – All rights reserved

NOTE The duration of a month is an integer number of days. The number of days in a month is determined by the rules of
the particular calendar.
4.1.23
node
0-dimensional topological primitive [ISO 19107]
NOTE The boundary of a node is the empty set.
4.1.24
ordinal era
one of a set of named periods ordered in time
4.1.25
ordinal scale
scale which provides a basis for measuring only the relative position of an object
4.1.26
ordinal temporal reference system
temporal reference system composed of ordinal eras
4.1.27
period
one-dimensional geometric primitive representing extent in time
NOTE A period is bounded by two different temporal positions.
4.1.28
periodic time
duration of one cycle [adapted from ISO 31-2:1992]
4.1.29
point
0-dimensional geometric primitive, representing a position [ISO 19107]
NOTE The boundary of a point is the empty set.
4.1.30
temporal coordinate
distance from the origin of the interval scale used as the basis for a temporal coordinate system
4.1.31
temporal coordinate system
temporal reference system based on an interval scale on which distance is measured as a multiple of a single
unit of time
4.1.32
temporal feature association
feature association characterized by a reference to time or to a temporal constraint
4.1.33
temporal feature operation
feature operation specified as a function of time
4.1.34
temporal position
location relative to a temporal reference system
4.1.35
temporal reference system
reference system against which time is measured
4.1.36
topological complex
collection of topological primitives that is closed under the boundary operations [ISO 19107]
NOTE Closed under the boundary operations means that if a topological primitive is in the topological complex, then its
boundary objects are also in the topological complex.
4.1.37
topological primitive
topological object that represents a single, non-decomposable element [ISO 19107]
NOTE A topological primitive corresponds to the interior of a geometric primitive of the same dimension in a geometric
realization.
4.1.38
transaction time
time when a fact is current in a database and may be retrieved [Jensen et al. (1994)]
4.1.39
valid time
time when a fact is true in the abstracted reality [Jensen et al. (1994)]
4.2 Abbreviated terms
For the purposes of this International Standard, the following abbreviations apply.
AD Anno Domini
BC Before Christ
GPS Global Positioning System
TOW Time of Week
UML Unified Modeling Language
UTC Coordinated Universal Time
WN Week Number
5 Conceptual schema for temporal aspects of geographic information
5.1 Structure of the schema
This clause presents a conceptual schema for describing temporal aspects of geographic information. The schema
is specified in the Unified Modeling Language (UML) [Object Management Group (1999)]. ISO/TS 19103 describes
the way in which UML is used in this family of standards. The three primary aspects of a UML class are attributes,
operations, and associations. This schema uses all three. This schema is an abstract model; to conform to this
International Standard, an implementation shall provide the capabilities described by these elements of the abstract
model, but it need not implement them in the same way.
6 © ISO 2002 – All rights reserved

The schema consists of two packages (see Figure 1). The package Temporal Objects (described in 5.2) defines
temporal geometric and topological objects that shall be used as values for the temporal characteristics of features
and data sets. The temporal position of an object shall be specified in relation to a temporal reference system. The
package Temporal Reference System (5.3, 5.4) provides elements for describing temporal reference systems.
Subclause 5.5 describes how the concepts specified in 5.2 through 5.4 shall be used in the context of geographic
information.
Figure 1 — Structure of the temporal schema
Names of UML classes defined in the ISO 19100 series of standards begin with a two-letter prefix followed by an
underscore to identify the specific standard, and possibly the package, in which they are defined. TM_ is used to
identify classes defined in this International Standard.
5.2 Geometry of time
5.2.1 Time as a dimension
Time is a dimension analogous to any of the spatial dimensions. Like space, time has geometry and topology. A
point in time occupies a position that can be identified in relation to a temporal reference system. Distance can be
measured. Unlike space, however, time has a single dimension — temporal reference systems are analogous to
the linear referencing systems that are used to describe spatial position for some kinds of applications. Although
time has an absolute directionality — movement in time is always forward — time can be measured in two
directions.
NOTE Although time always has geometry and topology at a conceptual level, sometimes it is possible or desirable to
describe geometry alone, or topology alone.
Time is measured on two types of scales, ordinal and interval. An ordinal scale provides information only about
relative position in time, while an interval scale offers a basis for measuring duration.
5.2.2 Temporal objects
Temporal geometric and topological objects shall be used as values for the temporal characteristics of features and
data sets. See 5.5 and annex B for an explanation and examples. TM_Object (see Figure 2) is an abstract class
that has two subclasses. TM_Primitive is an abstract class that represents a non-decomposed element of geometry
or topology of time. There are two subclasses of TM_Primitive. A TM_GeometricPrimitive (5.2.3) provides
information about temporal position. A TM_TopologicalPrimitive (5.2.4.2) provides information about connectivity in
time. A TM_Complex is an aggregation of TM_Primitives. TM_TopologicalComplex (5.2.4.5) is the only subclass of
TM_Complex that is defined in this International Standard; it is an aggregation of connected
TM_TopologicalPrimitives.
Figure 2 — Temporal objects
5.2.3 Temporal geometric primitives
5.2.3.1 Temporal geometric primitive classes
The two geometric primitives in the temporal dimension are the instant and the period. These primitives are defined
analytically in the case of time measured on an interval scale, and analogically in the case of time measured on an
ordinal scale. TM_GeometricPrimitive is an abstract class with two subclasses, TM_Instant represents an instant
and TM_Period represents a period (see Figure 3). TM_GeometricPrimitive inherits from TM_Primitive a
dependency on the interface TM_Order, and also has a dependency on the interface TM_Separation. The «uses»
stereotype on the dependency means that the class may support any of the operations defined for the interface,
but need not support all of them.
8 © ISO 2002 – All rights reserved

Figure 3 — Temporal geometric primitives
5.2.3.2 TM_Instant
An instant is a zero-dimensional geometric primitive that represents position in time. It is equivalent to a point in
space. In practice, an instant is an interval whose duration is less than the resolution of the time scale.
Attributes:
TM_Instant has one attribute.
a) position: TM_TemporalPosition shall provide the position of this TM_Instant. The TM_TemporalPosition shall
be associated with a single temporal reference system, as specified in 5.3. An instance of TM_Instant is an
identifiable object, while an instance of TM_TemporalPosition is a data value. The TM_TemporalPosition of a
given TM_Instant may be replaced by an equivalent TM_TemporalPosition associated with a different temporal
reference system.
5.2.3.3 TM_Period
The period is a one-dimensional geometric primitive that represents extent in time. The period is equivalent to a
curve in space. Like a curve, it is an open interval bounded by beginning and end points (instants), and has length
(duration). Its location in time is described by the temporal positions of the instants at which it begins and ends; its
duration equals the temporal distance between those two temporal positions.
Since it is impossible to measure duration on an ordinal scale, an instant cannot be distinguished from a period on
this basis. In practice, the time at which a single event occurs can be considered an instant when time is measured
on an ordinal scale. A series of consecutive events must occupy an interval of time, which is a period. The term
period is commonly applied to sequences of events that have distinctive characteristics in common.
Associations:
a) Beginning links the TM_Period to the TM_Instant at which it starts.
b) Ending links the TM_Period to the TM_Instant at which it ends.
For a variety of reasons, the position of the TM_Instant designated by begin or end may be indeterminate. See
5.4.3 for a discussion of indeterminate temporal positions.
Constraints:
a) {self.begin.position < self.end.position} states that the temporal position of the beginning of the period must be
less than (i.e. earlier than) the temporal position of the end of the period.
5.2.3.4 TM_Order
TM_GeometricPrimitives inherit a dependency on TM_Order from TM_Primitive. TM_Order provides an operation
for determining the position of this TM_Primitive relative to another TM_Primitive.
Operation:
a) relativePosition (other:TM_Primitive): TM_RelativePosition shall accept another TM_Primitive as input and
return a value for TM_RelativePosition as specified in 5.2.3.5.
5.2.3.5 TM_RelativePosition
Values for relative positions are provided by the enumerated data type TM_RelativePosition (see Figure 4) and are
based on the 13 temporal relationships identified by Allen (1983). For TM_Primitives, the operation
TM_Order.relativePosition shall return a value of the TM_RelativePosition as follows:
a) If both this TM_Primitive and other are TM_Instants, the operation shall return a value for TM_RelativePosition
as follows:
Returns: If:
Before self.position Equals self.position=other.position
After self.position>other.position

b) If this TM_Primitive is a TM_Period and other is a TM_Instant, the operation shall return a value for
TM_RelativePosition as follows:
Returns: If:
Before self.end.position < other.position
EndedBy self.end.position = other.position
Contains self.begin.position < other.position AND self.end > other.position
BegunBy self.begin.position = other.position
After self.begin.position > other.position

10 © ISO 2002 – All rights reserved

c) If this TM_Primitive is a TM_Instant and other is a TM_Period, the operation shall return a value for
TM_RelativePosition as follows:
Returns: If:
Before self.position < other.begin.position
Begins
self.position = other.begin.position
During
self.position > other.begin.position AND self.position < other.end.position
Ends
self.position = other.end.position
After
self.position > other.end.position

Figure 4 — TM_RelativePosition
d) If both this TM_Primitive and other are TM_Periods, the operation shall return a value for TM_RelativePosition
as follows:
Returns: If:
Before
self.end.position < other.begin.position
Meets
self.end.position = other.begin.position
Overlaps
self.begin.position < other.begin.position AND self.end.position > other.begin.position
AND self.end.position < other.end.position
Begins
self.begin.position = other.begin.position AND self.end.position < other.end.position
BegunBy
self.begin.position = other.begin.position AND self.end.position > other.end.position
During self.begin.position > other.begin.position AND self.end.position < other.end.position
Contains self.begin.position < other.begin.position AND self.end.position > other.end.position
Equals
self.begin.position = other.begin.position AND self.end = other.end.position
OverlappedBy
self.begin.position > other.begin.position AND self.begin.position < other.end.position
AND self.end.position > other.end.position
Ends
self.begin.position > other.begin.position AND self.end.position = other.end.position
EndedBy
self.begin.position < other.begin.position AND self.end.position = other.end.position
MetBy
self.begin.position = other.end.position
After self.begin.position > other.end.position

This operation shall raise an exception if any input value of TM_TemporalPosition is indeterminate.
5.2.3.6 TM_Separation
TM_GeometricPrimitive also has a dependency on the interface TM_Separation, which provides operations for
calculating length and distance. TM_Duration (see Figure 5) is a data type that contains return values for those
operations.
a) length(): TM_Duration shall return the duration of this TM_GeometricPrimitive. The length of a TM_Instant is
zero by definition. When the TM_GeometricPrimitive is a TM_Period, the operation shall return the distance
between the temporal positions provided by TM_Period.begin and TM_Period.end. This operation shall raise
an exception if the value of either TM_TemporalPosition is indeterminate, or if the TM_TemporalPositions are
referenced to a TM_OrdinalReferenceSystem.
b) distance (other:TM_GeometricPrimitive): TM_Duration shall return the distance from this
TM_GeometricPrimitive to another TM_GeometricPrimitive, i.e. the absolute value of the difference between
their temporal positions. The distance shall be the distance between the two closest TM_TemporalPositions of
the two TM_GeometricPrimitives. If either TM_GeometricPrimitive is connected to, overlaps, or is contained
within the other, the operation shall return a value of zero. The operation shall raise an exception if: (1) either
of the two TM_TemporalPositions is indeterminate, (2) the TM_TemporalPositions are not both associated with
the same TM_ReferenceSystem, or (3) either TM_TemporalPosition is associated with a
TM_OrdinalReferenceSystem.
5.2.3.7 TM_Duration
TM_Duration (see Figure 5) is a data type to be used for describing length or distance in the temporal dimension. It
has two subtypes.
TM_PeriodDuration uses the format specified by ISO 8601 for exchanging information about the duration of a
period. It allows duration to be expressed in terms of multiple units of time, specifically years, months, days, hours,
minutes, and seconds. Although individual values are optional, a value shall be provided for at least one unit.
Attributes:
a) designator: CharacterString = P is a mandatory element which designates that the following characters
represent the duration of a period.
b) years [0.1]: CharacterString is a positive integer, followed by the character “Y” which indicates the number of
years in the period.
c) months [0.1]: CharacterString is a positive integer followed by the character “M” which indicates the number of
months in the period.
d) days [0.1]: CharacterString is a positive integer followed by the character “D” which indicates the number of
days in the period.
e) timeIndicator [0.1]: CharacterString = “T” shall be included whenever the sequence includes values for units of
less than a day.
f) hours [0.1]: CharacterString is a positive integer followed by the character “H” which indicates the number of
hours in the period.
g) minutes [0.1]: CharacterString is a positive integer followed by the character “M” which indicates the number
of minutes in the period.
h) seconds [0.1]: CharacterString is a positive integer followed by the character “S” which indicates the number
of seconds in the period.
The value for the rightmost unit may be expressed as a positive decimal fraction rather than as a positive integer.
EXAMPLE A duration of five days, four hours, and 30,7 minutes is represented as P5DT4H30.7M.
12 © ISO 2002 – All rights reserved

NOTE Although this format is defined in ISO 8601 for use with dates in the Gregorian calendar and times in UTC,
TM_PeriodDuration may be used as the data type for expressing length or distance whenever temporal positions are referenced
to a calendar that describes dates in terms of years, months and days and a clock that describes times in hours, minutes and
seconds.
Figure 5 — TM_Duration
TM_IntervalLength is a data type specified by ISO/IEC 11404 for intervals of time, represented here in UML. It
supports the expression of duration in terms of a specified multiple of a single unit of time.
Attributes:
a) unit: CharacterString is the name of the unit of measure used to express the length of the interval.
b) radix: Integer is a positive integer that is the base of the multiplier of the unit.
c) factor: Integer is an integer that is the exponent of the base.
(-factor)
d) value: Integer is the length of the time interval as an integer multiple of one radix of the specified unit.
EXAMPLE Unit = “second,” radix = 10, factor = 3, value = 7 specifies a time interval length of 7 ms.
5.2.4 Temporal topological objects
5.2.4.1 Introduction
Topology provides information about connectivity between objects in time, and may incidentally provide information
about the ordering of objects in time. It does not provide information about temporal position. Topological
relationships can often be derived from geometric information. However, data about temporal position is sometimes
inadequate for doing this, so topology may need to be described explicitly. Topology may also be used in
applications that have a requirement to describe topological relationships explicitly, even though they could be
derived.
EXAMPLE It may be possible to observe the order of several events or states within a single ordinal era, but the ordinal
temporal reference system does not support assignment of distinct temporal positions to these events or states. The order can
be described by modelling these events or states with topological primitives.
5.2.4.2 TM_TopologicalPrimitive
A topological primitive represents a single non-decomposable element of topology and its relationships to other
topological primitives within a topological complex. The two topological primitives relevant for temporal information
are the node, which is 0-dimensional, and the edge, which is one-dimensional. In the temporal schema, there are
presented by two subclasses of TM_TopologicalPrimitive: TM_Node and TM_Edge (see Figure 6). When an
application includes information about temporal position as well as connectivity, a TM_TopologicalPrimitive may be
associated with a TM_GeometricPrimitive of the same dimension. Because topological primitives are intended to
provide information about connectivity, their most significant characteristics are the associations that link them to
each other. Another consequence is
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