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SYSTEM ARCHITECTURE
DESCRIPTION DOCUMENT
TEMPLATE & GUIDELINES
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Preliminary
This document is a form to use and fill in order to produce the document related to a specific
system in the context of a development project.
The "System Architecture Description Document" (SysAD) presents the outcomes generated
by the performance of the System Logical Architecture Definition Process and of the System
Physical Architecture Definition Process.
It contains the selected solution in terms of Logical view of the Architecture of the system XX
(functional, behavioural, and temporal models) and of Physical view of the Architecture of the
system XX.
It does not present the justification and rationale of the selected solution; these elements are
described in the System Justification Document – refer to the corresponding template.
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CONTENT
1
INTRODUCTION....................................................................................................................... 5
1.1 PRESENTATION OF THE DOCUMENT ....................................................................................... 5
1.2 DOCUMENTS ........................................................................................................................ 5
1.2.1 Reference documents .................................................................................................. 5
1.2.2 Applicable documents .................................................................................................. 5
1.3 TERMINOLOGY: DEFINITIONS AND ABBREVIATIONS .................................................................. 6
2
PRESENTATION OF THE SYSTEM......................................................................................... 7
2.1 INTENDED USE OF THE SYSTEM ............................................................................................. 7
2.2 STAKEHOLDERS ................................................................................................................... 7
2.3 CONTEXT OF USE OF THE SYSTEM ......................................................................................... 7
2.3.1 Overview of the context and relationships .................................................................... 7
2.3.2 Functional architecture of the context ........................................................................... 8
2.3.3 Physical architecture of the context .............................................................................. 8
3
INDEPENDENT LOGICAL ARCHITECTURE OF THE SYSTEM ............................................. 9
3.1 STATIC FUNCTIONAL HIERARCHY (ORGANISED LIST OF FUNCTIONS) .......................................... 9
3.1.1 Description of Functions ............................................................................................... 9
3.1.2 Description of internal Input-output Flows and triggers ................................................. 9
3.2 INDEPENDENT LOGICAL ARCHITECTURE DESCRIPTION .......................................................... 10
3.2.1 Models of Operational Modes (if applicable) ............................................................... 10
3.2.2 Models of Scenarios of functions ................................................................................ 10
3.2.3 Model of Temporal Architecture (if applicable) ........................................................... 11
4
PHYSICAL ARCHITECTURE OF THE SYSTEM.................................................................... 12
4.1 PHYSICAL HIERARCHY OF THE SYSTEM INTO SYSTEMS AND SYSTEM ELEMENTS ..................... 12
4.1.1 Description of System Elements and of systems ........................................................ 12
4.1.2 Description of external Physical Interfaces ................................................................. 12
4.1.3 Description of internal Physical Interfaces .................................................................. 13
4.2 PHYSICAL ARCHITECTURE DESCRIPTION (THE SELECTED ONE) .............................................. 14
4.2.1 Diagrams of sub-systems Physical Architecture (optionally) ....................................... 14
4.2.2 Diagram of the Physical Architecture of the system .................................................... 14
4.2.3 Design Properties of the Physical Architecture of the system ..................................... 14
5
ALLOCATED LOGICAL ARCHITECTURE OF THE SYSTEM ............................................... 15
5.1 ALLOCATION TABLES........................................................................................................... 15
5.2 MODELS, DIAGRAMS OF THE ALLOCATED LOGICAL ARCHITECTURE ........................................ 16
6
DERIVED REQUIREMENTS................................................................................................... 17
6.1 DERIVED REQUIREMENTS WITHOUT EXTERNAL CONSEQUENCES (ASSIGNED TO THE SYSTEM) .. 17
6.2 DERIVED REQUIREMENTS WITH EXTERNAL CONSEQUENCES (ASSIGNED TO EXTERNAL SYSTEMS)
17
FIGURES AND TABLES
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1 INTRODUCTION
1.1 Presentation of the document
Present here briefly the content of the document and the system XX.
Typical introduction could be: The System Architecture Description Document presents
architectural elements of the system XX:

The independent logical architecture deduced from applicable System Requirements

The physical architecture constituted of System Elements, (sub) systems and their
Physical Interfaces (links / connectors)

The allocated logical architecture to the physical elements

The temporal architecture (optionally)
1.2 Documents
The documents referred here shall be defined precisely: complete title, reference and
version.
They have to be placed at the disposal of the readers, either directly in annexes, or by the
means of an appropriate documentation management.
1.2.1 Reference documents
Provide the list of documents having been used writing this document: System Requirement
Document, reports, minutes of meeting, others.
Reference
Document Title
1.2.2 Applicable documents
Provide the list of documents entirely or partially applicable: standards, templates,
descriptions of procedure, others.
Reference
Document Title
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1.3 Terminology: definitions and abbreviations
Provide the list of terms and their definition used in this document absent from usual
dictionaries or used with a different significance from their usual significance.
Each definition can be supplemented by the abbreviation used in the document.
Term
Definition
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2 PRESENTATION OF THE SYSTEM
If this section exists in other documents (for example in System Requirements Document),
and if its content is up to date, refer to these documents; otherwise document the present
section.
2.1 Intended use of the system
This section indicates the purpose, the intended use (or mission) and the main objectives of
the system:

Purpose: Why does the system exist? What is the usage and relevance of the system in
its context of use?

Intended use (mission): What it does? Which transformation does it perform to achieve
its purpose?

Objectives: Which are the main performances (quantified) that the system must satisfy
so that the purpose is achieved? How many inputs does it transform? How speed?
There is one purpose and one global mission for a given system. On the other hand there
may be several objectives.
2.2 Stakeholders
Point out the list of the stakeholders consulted during writing of the Stakeholder
Requirements Document and supplement with the list of the actors having taken part to the
System Requirements Document – SysRD, and/or those that have been added during
architecture and design of the system.
2.3 Context of use of the system
2.3.1 Overview of the context and relationships
This section locates the system in its context of use.
It identifies specifically:

the upper-system (context) with its functions and its system elements (components)

the enabling systems which have a relation with the system of interest
It is recommended to present the context of use in the form of diagrams of context, or
entity/relationships diagrams that show the system elements (components) of the context
and the relationships between these components and the system of interest or the
concerned system.
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2.3.2 Functional architecture of the context
This section indicates the main function of every component of the context and the main
input-output flows exchanged between the components of the context and the system of
interest or of the concerned system.
It is recommended to present the functional architecture of the context in the form of
diagrams that show clearly functions / activities and input-output flows / object nodes.
2.3.3 Physical architecture of the context
This section indicates the physical system elements/components of the context and the main
physical interfaces (links / connectors) that connect the components of the context to the
system of interest or the concerned system. The input-output flows are normally carried by
the physical interfaces (links / connectors).
It is recommended to present the physical architecture of the context in the form of diagrams
that show clearly the physical system elements (components or blocks) and the physical
interfaces (links / connectors).
The physical system elements / components / blocks of the context can be described in this
section as necessary. The description of the interfaces is located in the section "Interfaces".
Id.
Component/blocks of the context
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3 INDEPENDENT LOGICAL ARCHITECTURE OF THE SYSTEM
3.1 Static functional hierarchy (organised list of functions)
3.1.1 Description of Functions
Provide the organised / structured list of functions of the system. Normally for a given level of
system, the decomposition should not exceed 3 or 4 levels. One function should not be
decomposed in more than [5 ± 2] sub functions. Use preferably tables for a clear
presentation; or decomposition diagrams. Prefer verbs to infinitive or present tense. The
description attribute is important because semantic aspect in engineering is fundamental in
order any involved people understand well and do not interpret.
Example of presentation with a table:
Id.
Function
Description
F
Mission of the system
F.1
Function 1
F.1.1
Function 1.1
F.1.2
Function 1.2
F.2
Function 2
Etc.
3.1.2 Description of internal Input-output Flows and triggers
Provide the list of input, output, trigger or control flows attached to each function. Use
preferably tables to present these elements attached to their function. Provide any useful
description to understand clearly the meaning of these elements. One function may use
several inputs and generate several outputs.
Example of relationships table:
Input
Function
Output
Example of a description table:
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Description
Note: More sophisticated tables may present more information like attributes of these
elements. Information of previous tables may be merged into a single table.
3.2 Independent Logical Architecture description
The selected independent logical architecture (independent from implementation) generated
by the logical architecture definition process can be described using several different but
related concepts such as Operational Modes, and/or Scenarios of functions.
3.2.1 Models of Operational Modes (if applicable)
Operational Modes and Transition of Modes can be presented with state-transition diagram,
state-machine diagram, etc.
Additional tables can provide more information as shown below. Text as description may be
added as well.
Operational Mode
Active functions and/or
scenarios in this mode
Event or trigger and
conditions to enter the mode
Previous and
next modes
3.2.2 Models of Scenarios of functions
For each Operational Mode (if they exist), provide the description of related Scenarios of
functions including Input-output Flows, control flows, generic Constructs and adequate or
adapted behavioural patterns. Scenarios of functions should be presented with diagrams,
such as activity diagram, or FFBD.
If short names are given to Scenarios, provide additional useful information for better
understanding. Example of table:
Id.
Scenario
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3.2.3 Model of Temporal Architecture (if applicable)
When functions are performed on a temporal basis of defined frequency levels, describe
these temporal levels and concerned functions in each level. An example of table is provided
below:
Frequency/ duration
Trigger or event
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4 PHYSICAL ARCHITECTURE OF THE SYSTEM
4.1 Physical hierarchy of the system into systems and System
Elements
4.1.1 Description of System Elements and of systems
Provide the list of systems and of System Elements that compose the concerned system. It is
reminded that the complete physical architecture of a system of interest is generally
decomposed on several levels, but at a given level the architecture of one of the systems is
composed of a single level. One system should not contain more than 5 or 7 ± 2 systems
or System Elements.
Add Design Properties associated to each system or System Element, if the allocation has
been done within the study of the current system-block; several Design Properties
characterise a system or System Element.
Example of presentation with a table:
Id.
System or System
Element
Description
Design Properties
4.1.2 Description of external Physical Interfaces
Provide the list of Physical Interfaces between the systems and System Elements of the
concerned system and the physical system elements/components of the context. Depending
on the used modelling / representation technique, physical interfaces are called links or
connectors.
Example of presentation with a table:
System or System
Element
Links or Connectors
Or:
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Component of the context
Add Design Properties associated to each Physical Interface, if the allocation has been done
within the study of the current system-block. Example of presentation:
Physical Interface (Link
or Connector)
Design Properties
Note: Information as text format can be added.
4.1.3 Description of internal Physical Interfaces
Provide the list of internal physical interfaces between the systems and System Elements of
the concerned system.
Example of presentation with a table:
System or System
Element 1
Links or Connectors
System or System Element 2
Links or Connectors
System or System Element 1
System or System Element 2
Or:
Add Design Properties associated to each Physical Interface, if the allocation has been done
within the study of the current system-block. Example of presentation:
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Design Properties
Note: Information as text format can be added.
4.2 Physical Architecture description (the selected one)
The physical architecture of a system is generally represented with block diagrams (for
example, internal block diagram – IBD, or physical block diagram - PBD) that show the
systems and System Elements with their internal physical interfaces/connections and their
external physical interfaces/connections.
4.2.1 Diagrams of sub-systems Physical Architecture (optionally)
Sometimes, for study purpose, it could be interesting to show one more detailed level of the
decomposition. If it is the case, present the architecture of each (sub) system with their
internal and external physical interfaces.
Information as text format can be added.
4.2.2 Diagram of the Physical Architecture of the system
Provide representation of the physical architecture including its systems and System
Elements, and their internal and external physical interfaces.
Information as text format can be added.
4.2.3 Design Properties of the Physical Architecture of the system
Provide the Design Properties associated to the System (its Physical Architecture); several
Design Properties characterise the system.
Example of presentation with a table:
Id.
Design Property
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5 ALLOCATED LOGICAL ARCHITECTURE OF THE SYSTEM
The allocated logical architecture is based on the elements of the independent logical
architecture described in section 3. Inversely to this one, the allocated logical architecture is
dependent on technology choices for implementation; it presents the projection of functional
elements on physical architecture elements (systems, System Elements, Physical
Interfaces).
New and/or updated functions, input-output flows, triggers may be added in order to interface
correctly systems and System Elements, and to synchronise treatments and transformations
between systems and System Elements. Normally the independent logical architecture
describes the right order of execution of functions, and this logic must be kept within the
allocated logical architecture.
5.1 Allocation tables
Provide allocation of functions to systems or System Elements. Example of table:
System or System Element
Allocated Functions
Provide allocation of Input-output Flows and triggers to Physical Interfaces between systems
or System Elements. Example of table:
Physical Interfaces (link/connector)
Allocated input-output Flows, triggers
Inverse tables should be provided; examples:
Function
System or System Element
Input-output Flow, trigger
Physical Interface (link/connector)
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5.2 Models, diagrams of the Allocated Logical Architecture
Models of the allocated logical architecture are preferably presented here using scenarios of
functions like for the independent logical architecture. But here diagrams show how functions
are grouped around systems or System Elements. Those diagrams are based on a
concurrency construct because the systems and System Elements that compose the system
are running basically in parallel. To conform the order of execution of the Functions as
described in the independent logical architecture, they have to be synchronised using
triggers that condition the starting of the triggered Function.
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6 DERIVED REQUIREMENTS
Derived requirements may be identified during architecture and design activities, because
new necessary functions and constraints could be added depending on technologies and/or
System Elements selection. If such derived requirements are identified, they must be
incorporated to the System Requirements Documents related to the impacted systems for
traceability purposes.
6.1 Derived requirements
(assigned to the system)
without
external
consequences
List the derived requirements assigned to the current concerned system. Provide appropriate
attributes (for example the requirement type).
Example of table:
Requirement text
Attributes
Elements that induced the requirement
6.2 Derived requirements with external consequences (assigned to
external systems)
List the derived requirements assigned to external systems. Provide appropriate attributes
(for example the requirement type).
Example of table:
Impacted system
Requirement text
Attributes
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Elements that induced the
requirement