ISO/TR 14813-4:2000

TECHNICAL ISO/TR
REPORT 14813-4
First edition
2000-12-15
Transport information and control
systems — Reference model architecture(s)
for the TICS sector —
Part 4:
Reference model tutorial
Systèmes de commande et d'information des transports — Architecture(s)
du modèle de référence du secteur TICS —
Partie 4: Manuel de modèle de référence
Reference number
ISO/TR 14813-4:2000(E)
©
ISO 2000

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ISO/TR 14813-4:2000(E)
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ISO/TR 14813-4:2000(E)
Contents
Foreword.iv
Introduction.vi
1 Scope .1
2 Modelling an architecture .1
3 Why object-oriented?.2
4 The Unified Modelling Language .2
5 Object-oriented modelling elements: class and object .3
6 Abstraction.5
7 Model Views .5
7.1 Use case diagrams .5
7.2 Class diagrams .6
7.2.1 Associations .8
7.2.2 Special types of association.9
7.3 Package diagrams .11
7.4 Sequence (Interaction) diagrams.11
8 Methodology .14
9 Summary.18
10 Legend of graphic symbols.19
Bibliography.21
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ISO/TR 14813-4:2000(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 main task of technical committees is to prepare International Standards, but in exceptional circumstances a
technical committee may propose the publication of a Technical Report of one of the following types:
— type 1, when the required support cannot be obtained for the publication of an International Standard, despite
repeated efforts;
— type 2, when the subject is still under technical development or where for any other reason there is the future
but not immediate possibility of an agreement on an International Standard;
— type 3, when a technical committee has collected data of different kind from that which is normally published
as an International Standard ("state of the art", for example).
Technical Reports of types 1 and 2 are subject to review within three years of publication, to decide whether they
can be transformed into International Standards. Technical Reports of type 3 do not necessarily have to be
reviewed until the data they provide are considered to be no longer valid or useful.
Technical Reports are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Attention is drawn to the possibility that some of the elements of this part of ISO/TR 14813 may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO/TR 14813-4, which is a Technical Report of type 2, was prepared by Technical Committee ISO/TC 204,
Transport Information and Control Systems.
This document is being issued in the Technical Report (type 2) series of publications (according to
subclause G.3.2.2 of Part 1 of the ISO/IEC Directives, 1995) as a “prospective standard for provisional application”
in the field of transport information and control systems because there is an urgent need for guidance on how
standards in this field should be used to meet an identified need.
This document is not to be regarded as an “International Standard”. It is proposed for provisional application so that
information and experience of its use in practice may be gathered. Comments on the content of this document
should be sent to the ISO Central Secretariat.
A review of this Technical Report (type 2) will be carried out not later than three years after its publication with the
options of: extension for another three years; conversion into an International Standard; or withdrawal.
ISO/TR 14813 consists of the following parts, under the general title Transport Information and Control Systems —
TICS Reference Architecture:
 Part 1: TICS Fundamental Services: This document presents the definition of 32 TICS fundamental services
that are the informational products or services or applications areas provided to a TICS user.
 Part 2: Core TICS Reference Architecture: This document describes an abstract object-oriented system
architecture based on the TICS Fundamental Services.
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ISO/TR 14813-4:2000(E)
 Part 3: Example Elaboration: This document refines the Core TICS Reference Architecture (Part 2) with some
emphasis on traffic management.
 Part 4: Reference Model Tutorial: This document describes the basic terms, graphical representations and
modelling views exploited in the object-oriented definition of the architecture development of Parts 2 and 3.
 Part 5: Requirements for Architecture Description in TICS Standards: Requirements for Architecture
Description in TICS Standards: This document describes the terminology and form to be used when
documenting or referencing aspects of architecture description in TICS standards.
 Part 6: Data Presentation in ASN.1: This document establishes the use of ASN.1 as the normal syntax notation
to be used in standards for the TICS sector and a common message form for such ASN.1 based data
elements.
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ISO/TR 14813-4:2000(E)
Introduction
ISO/TC204/WG1 is a working group whose prime objectives are to provide services to ISO TC204 and its working
groups. A specific mission of WG1 is to:
“Provide ISO TC204, its working Groups, related bodies and those involved in the TICS sector, with a
reference model of Conceptual Reference Architecture(s) that show the structure and inter-relationships of the
sector .”
It is expected that there may well be more than one single TICS Architecture approach to be considered and
documented and that existing architecture approaches will have previously-produced documentation developed
according to disparate standards and conventions.
It is also implicit in the work being undertaken by WG1, that working group members will require a clear, well-
structured understanding of the work of the following participant groups:
• Other TC 204 Working Groups
• CEN TC 278 Working Groups
• Japanese initiatives
• European Road Transport and Traffic Telematics programs
• US Intelligent Transportation Systems program
• Australian initiatives
• Canadian Initiatives
Full documentation of all possible architectural approaches is obviously not feasible given the high level of
resources required to carry this out. Indeed full documentation and description of all possible approaches is
undesirable as an item for Standardisation.
A defined and consistent approach is however required to facilitate the specification of architecture requirements to
enable a clear view to be developed and presented of the work of each participant group This document is one of a
set of WG1 documents intended to respond to stated WG1 objectives regarding the production of a TICS
Reference Architecture.
In order to document an architecture, graphical and textual components of a model are required. WG1 has adopted
a methodology based on the Unified Modelling Language (UML) for documenting the TICS Reference Architecture.
A tutorial on the UML is provided in ISO/TR 14813 Part 4. UML is a visual modelling language for building object-
oriented and component-based systems. A commercially available Computer Aided Software Engineering (CASE)
tool has been used by WG1 to document the Architecture. While the tool is a commercial product, UML is open and
non-proprietary.
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TECHNICAL REPORT ISO/TR 14813-4:2000(E)
Transport information and control systems — Reference model
architecture(s) for the TICS sector — Part 4: Reference model
tutorial
1 Scope
The architecture of an information and control system merges hardware and software considerations into a
coordinated and integrated system view. The system architecture is a high level abstraction, or model, of the
system. A system architecture should embrace both today’s applications and the applications that are expected in
the future. Architecture begins with the definition of the conceptual services (e.g. Part 1 - TICS fundamental
services). There are several identifiable stages of system architecture development.
• Reference architecture
• Logical architecture
• Physical architecture
The reference architecture is generic and non-prescriptive and captures the concepts of the system. A logical
architecture elaborates the functions that will provide the conceptual behaviour, and in so doing it provides some
detail about the modularity. A physical architecture is reached when the actual distribution of the system modules is
defined, thus leading to important implications for communications.
This technical report develops a TICS Reference Architecture. The objective in defining a TICS Reference
Architecture is to provide a concise reference point which is both educational and a framework for the standards
process. The Reference Architecture will be used by the Working Groups to develop their own logical and physical
architectures in a cohesive manner.
This Part introduces the model that is applied in developing the Reference Architecture in Parts 2 and 3. A tutorial
on the application of the model is provided using examples from the TICS sector.
2 Modelling an architecture
In order to document an architecture, graphical and textual components of a model are required. A unified process
[1]
and the Unified Modelling Language (UML) developed by Ivar Jacobson, Grady Booch and James Rumbaugh
addresses this requirement for the software industry. The result is a component-based process that is use-case
driven, architecture-centric, iterative, and incremental.
In Parts 2 and 3 of this technical report the abstraction that is the TICS Reference Architecture is described in four
views of the Unified Modelling Language:
1. Use Case diagram
2. Class diagram
3. Package diagram
4. Sequence (Interaction) diagram
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The UML views have been developed to support methodologies for building systems with the object model (e.g.
systems whose software is programmed in object-oriented languages). Therefore it is necessary to begin this
tutorial by introducing some basic concepts of object-oriented (OO) modelling.
Although ISO/TR14813-5 states that architectures may be developed using either OO or process-oriented
methods, WG1 has chosen to use the OO method.
3 Why object-oriented?
The Transport Information and Control Systems (TICS) Reference Architecture is being developed by ISO/TC204
Working Group 1 (WG1) with the following objectives.
• to be a concise statement of what TICS is, and thus help develop consensus within TC204 and wider circles
• to act as a framework for the standards process in TC204
• to serve an educational purpose and lend itself to promulgation in media such as the Internet.
A reference architecture is non-prescriptive of technology and deployment organisation.
In the future, WG1 expects a number of standards developments such as data dictionaries, model sub-system
architectures, and message standards to update the reference architecture and to evolve it into various
architectures.
Thus the choice of both model and process for the architecture development were important decisions. Current and
future requirements include:
• information models
• functional models
• dynamic models
• implementation models
Older system development practices are disjoint in the way that all these requirements can be met. For example,
functional and data flow models must be combined with a separate model for information, and these two types of
model do not integrate conveniently. Object-oriented modelling accommodates these requirements harmoniously.
Modern computer based system engineering for software development automates the object-oriented model. The
process also incorporates other important models. The same tools used for system engineering are suitable for the
development of architectures.
By applying the object-oriented model and process for the Reference Architecture a highly effective base is
established for future developments.
4 The Unified Modelling Language
The Unified Modelling Language is a visual modelling language for building object-oriented and component-based
systems. The UML was recently developed by Rational Software Corporation and its partners and is the successor
to the modelling languages found in the Booch, OOSE/Jacobson, OMT, and other system engineering methods.
UML has been progressed through the Object Management Group (OMG) for adoption as an OMG standard.
The developers of the UML recognised that the choice of what model projections one creates has a profound
influence upon how a problem is approached and how a solution is shaped. They maintain that
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ISO/TR 14813-4:2000(E)
• Every complex system is best approached through a small set of nearly independent views of a model - no
single view is sufficient.
• Every model can be expressed at different levels of fidelity.
• The best models are connected to reality.
Rational Software Corporation, as well as many others, are incorporating the UML into their development process
and products, which cover disciplines such as business modelling, requirements management, analysis & design,
programming, and testing.
WG1 has adopted a methodology based on UML for developing and documenting the TICS Reference Architecture
and is using a commercially available Computer Aided Software Engineering (CASE) tool to do this. While a CASE
tool is a commercial tool, UML is open and non-proprietary.
Abstraction, which is to focus on relevant details while ignoring others, is the key to the development of a reference
architecture. This determined the selection of four particular elements from the UML for the modelling task:-
1. Use Case
2. Class
3. Package
4. Sequence (Interaction)
These elements provide the multiple perspectives of the reference architecture.
• Use case diagrams define the architecture boundary, the external actors and the services provided.
• Class diagrams define the abstract elements that comprise the reference architecture. These elements
underpin the dynamic model of the system.
• Package diagrams are the means by which model (architecture) elements can be grouped. Packages
provide a hierarchical organisation as well as a network of package references.
• Sequence (Interaction) diagrams describe how the implied objects of the system cooperate to provide the
services defined in the use case.
Each element view is presented as a diagram. The underlying model integrates these views into a self-consistent
reference architecture. The modelling elements are explained in more detail in the following sections.
It is expected that some of the other types of diagrams defined in the UML (e.g. implementation diagrams) may be
used by Working Groups to develop more detailed architectures.
5 Object-oriented modelling elements: class and object
The main purpose of modelling is to prepare generic descriptions that describe many specific particular items.  In
object-oriented modelling the most important generic description is called a class and a specific particular item
belonging to a class is called an object.
Table 1 lists three particular objects (instances of a class called Intersection). The corresponding real life situation
is depicted in the schematic of Figure 1.
There are at least three conceptual levels involved in the example. The first conceptual level is the class. This is
used in architecture and design. The second conceptual level involves the software objects belonging to the class
(e.g. Intersection) which arise in the development of a system conforming to the architecture. The third conceptual
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level is that of the real world where there is roadway pavement corresponding to the higher level intersection
concepts. The higher levels are abstractions that represent the real world objects for particular purposes such as
system architecture and system implementation.
Table 1 — Example class and objects
Class Software Objects Real World Objects
Intersection Object1{ data} Main St & Route 401
{operations & attributes}
Object2{ data} Main St & Washington St
Object3{ data} Main St & Route 20
Route 401
Washington St Route 20
Main St
Figure 1 — A map of the real world corresponding to the three Intersection objects
In the above example the class might be defined so that information about real world intersections could be stored
and updated in a system database. The reader shall see later that classes (and their implied objects) are often
invented for other purposes, such as control and system interfaces.
Only classes are presented in the Reference Architecture, however the implied objects will often be referenced in
the discussion of the architecture. A more complete definition of class is now given.
A class is the descriptor for a set of objects having similar structure, behaviour, and relationships. Class definitions
consist of attributes and operations.
Attributes are the elements used to record the state of an object (e.g. the equipment deployed at an Intersection,
or the traffic demand at an Intersection, or the current control phase). State changes of an object are recorded by
changing the attribute values. Static attributes are those that apply collectively to the entire class (e.g. a count of
Intersections). In Table 1 the state of the software objects is referred to as data.
An operation is an action that a software object performs (e.g. Change Phase at an Intersection in order to allow a
different traffic movement) when it receives a particular stimulus called a message (e.g. a request to change
phase). The collection of defined operations specifies the behaviour of a class (i.e. for all its objects). Classes may
also have static operations (e.g. list the Intersections on a given route).
The relationships that are recorded about objects are called associations (e.g. each Intersection object is
associated with a set of traffic Movements, and a Movement is associated with a set of Manoeuvres which can
occur simultaneously, i.e. in the same traffic control phase). The various types of association are defined in a later
section.
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6 Abstraction
Unlike any other model, the class-object model can be applied in every stage of the development process, from
architecture to system implementation.  The key is the use of abstraction.
Because a reference architecture is concise and it originates at the very early stages of system development, it
must use abstract classes, that is classes which reflect relevant details while ignoring others.
On the other hand, in object-oriented software design and implementation, the class element provides concrete
specifications for the attributes, operations and state transitions of the software objects that will materialise the
system.
Abstraction in the class-object model is a powerful means by which the strong connection between architecture,
implementation, and the reality found in objects is maintained.
Abstraction is also applied in the other model views of the architecture. However it is only the elements of the
class-object model which are materialised in the system implementation.
7 Model Views
Our objectives for conciseness etc. can only be met by using a graphical modelling language. We now describe
the four UML model views and their diagram notation used in developing the reference architecture.
7.1 Use case diagrams
Use case diagrams are the first step in architecture development. They model the functional system requirements
and scope. There are two primary components of a use case diagram, actor and use case.
An actor is a class external to the system. The relevant actors are those whose objects interact with the system.
Thus an actor may be a role performed by a human or it may be a type of system. Although an actor is not
necessarily a human it is always represented by a ‘stick figure’ in the use case diagrams, and labelled with its class
name.
When an actor object interacts with the system, together they perform a behaviourally related transaction
sequence. Each specific sequence is called a scenario. The abstraction of similar and closely connected scenarios
is called a use case.
Just as the idea of classification is natural to the modelling process, so is the grouping together of strongly related
use cases. This is the basis for forming a use case diagram. In the diagram a use case is represented by an
ellipsis labelled with the name of the use case.
The natural way to begin an architecture specification is to identify some of the actors and the associated use
cases. This is often referred to as developing the operational concept for the system. This process answers
questions such as why is the system being developed and what must it do. (We might then specify some of the
other types of diagrams before identifying all the actors and uses cases in iterative fashion.)
A use case diagram shows the relationships among the actors and the use cases. It is a graph consisting of
actors and use cases, the latter enclosed by the system boundary. The system boundary separates the actors from
the use cases and is shown as a dashed-line rectangle. The communication (participation) associations between
the actors and the use cases, and the relationships among the use cases are shown by different types of arc in the
graph.
The participation of an actor in a use case is shown by connecting the actor symbol to the use case symbol by a
solid path. The actor is said to communicate with the use case.
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A uses relationship between use cases is shown by a directed line from the use case drawing upon transactions
outside itself to the use case being used. The line is labelled "uses". A uses relationship from use case A to use
case B indicates that an instance of the use case A will also include the behaviour as specified by B.
The example use case diagram (see Figure 2) shows three actors and three use cases which could arise in the
requirements of traffic management. (This is not a complete description of traffic management.)
The actors Vehicle, Traffic Operator and Parking interact with the use case called Traffic Control. Traffic Control
uses two other use cases, Performance Evaluation and Performance Prediction. The relationships involving the
latter are not fully developed in this example.
An important part of the use case model view is the accompanying free text description of the use cases and the
actors. This documents in narrative form the logic of the associated transaction sequences. Other model views
(e.g. sequence diagrams) are then developed in order to translate this documentation into a more formal notation.
Vehicle Traffic Operator Parking
Traffic Control
uses uses
Performance Performance
uses
Prediction Evaluation
Figure 2 — Example use case diagram
7.2 Class diagrams
Classes are declared in class diagrams and they are used in most other diagrams.
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Class diagrams show the static structure of the model, in particular, the things that exist (such as classes and their
object sets), their internal structure, and their relationships to other things. Class diagrams do not show temporal
information, although classes may contain attributes and operations that have or describe temporal behaviour.
A class is drawn as a solid-outline rectangle with up to three compartments separated by horizontal lines. The top
“name” compartment holds the class name; the middle “list” compartment holds a list of attributes; the bottom “list”
compartment holds a list of operations.
Either or both of the attribute and operation compartments may be suppressed in a class diagram. If a
compartment is suppressed, no inference can be drawn about the presence or absence of elements in it.
The Reference Architecture does not define attributes because of its level of abstraction. This important element of
the object-oriented model is mentioned for completeness and because attributes will arise when the Reference
Architecture is elaborated by the Working Groups in conjunction with the development of data dictionaries and
message standards.
An operation is shown as a text string that can be parsed into the properties (signature) of the operation model
element. The default syntax is:
name ( parameter-list )
where name is an identifier string;
where parameter-list is a comma-separated list of formal parameters.
In some cases the operation name is used without its parameter list.
In many class diagrams of the Reference Architecture both the operation and the attribute compartments are
suppressed in order to avoid clutter, or because these elements are not yet defined. Operations occur explicitly in
the sequence (interaction) dia
...