What is Software Architecture?
Chapter 2,
Authors: Len Bass, Paul, Rick
Page Numbers: 19-45
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System description of Acoustic Simulation
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What Software Architecture Is and
What It Isn't
 What is the nature of the elements?
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What is the significance of separation?
Do they run on separate processors?
Do they run at separate times?
Do the elements consist of processes, programs or both?
Are they objects, task, functions, processes, distributed programs, …
 What are the responsibilities of the elements?
 What is it they do?
 What is their function in the system?
 What is the significance of the connections?
 Do the connections mean that the elements communicate with each other , control each other
, send data to each other , use each other, invoke each other, share some information hiding
secret with each other,
 What information flows across the mechanism?
 What is the significance of the layout?
 Why is CP on a separate level?
 Does it call the other three?
 Are others not allowed to call?
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Architecture: Definition
The Software Architecture is a structure
or structures of the system, which
comprise software elements, the
externally visible properties of those
elements, and the relationships between
them
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Architecture Definition
externally visible properties assumptions other elements can make of
an element, such as its provided services,
performance
characteristics,
fault
handling, shared resources usage
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Architecture: Definition – observation
Architecture defines software elements
 The architecture represents information about how the
elements relate to each other.
 An architecture is foremost an abstraction of a system that
suppresses details of elements that do not affect how they use,
are used by, relate to, or interact with other elements.
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Architecture: Definition – observation
Systems can and do comprise more than one structure
 All nontrivial projects are partitioned into implementation
units; these units are given specific responsibilities and are
frequently the basis of work assignments for programming
teams.
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Architecture: Definition – observation
Every computing system with software has a software architecture
 Every system can be shown to comprise elements and the relations among
them.
 Unfortunately, an architecture can exist independently of its description or
specification, which raises the importance of architecture documentation and
architecture reconstruction
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Architecture: Definition – observation
the behavior of each element is part of the
architecture
behavior can be observed from the point of
view of another element.
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Architecture: Definition – observation
the definition is indifferent as to whether the
architecture for a system is a good one or a
bad one
meaning that it will allow or prevent the
system from meeting its behavioral,
performance, and life-cycle requirements.
We do not accept trial and error as the best
way to choose an architecture for a system
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Other Points of View
Architecture is high-level design
Architecture is the overall structure of the system
Architecture is the structure of the components
of a program or system, their interrelationships,
and the principles and guidelines governing their
design and evolution over time
Architecture is components and connectors
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Architectural Patterns
An architectural pattern is a description of
element and relation types together with a
set of constraints on how they may be used
Set of constraints on an architecture
Example-C/S architecture.
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Reference Models
• A reference model is a division of functionality
together with data flow between the pieces.
• It is standard decomposition of a known problem
into parts that solves problem cooperatively
• Ex: OSI reference model..
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Reference Architectures
• A reference architecture is a reference model
mapped onto software elements (that
cooperatively implement the functionality
defined in the reference model) and the data
flows between them
• Reference model divides the functionality.
• A reference architecture is the mapping of that
functionality on to a system decomposition.
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Architecture: useful concepts
Reference
model
Reference
architecture
Architectural
pattern
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Software
architecture
Why is Software Architecture Important?
1. Communication among stakeholders
-SA represents a common abstraction of a system.
-used as a basis for mutual understanding,
negotiation, compromise, and communication
by the stakeholders.
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Why is Software Architecture Important?
2.
Early design decisions
Architecture represents earliest set of
decisions about system, they are most difficult
to get correct and the hardest to change.
It is the earliest point at which design
decisions can be analyzed.
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Why is Software Architecture Important?
Transferable abstractions of a system
Architecture is a relatively small model for
how a system is structured and how its elements
work together and this is transferable across
systems.
It can be applied to other systems exhibiting
similar functional requirements.
3.
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ARCHITECTURE IS THE VEHICLE FOR STAKEHOLDER
COMMUNICATION
 Each stakeholder of a software system (customer,
user, project, manager, coder, tester) is
concerned with different system characteristics
that are affected by the architecture.
 User is concerned that system is reliable &
available.
 Customer is concerned about schedule & budget.
 Manager: teams should work independently.
 Architect: worried about strategies to achieve
goals.
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• Architecture provides a common language in
which different concerns can be expressed,
negotiated, and resolved at a level that is
intellectually manageable even for large,
complex systems
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Architectural Structures and Views
A structure is the set of elements.
view – It is a representation of set of
architecture elements, as written by and read
by system stakeholder.
It consist of representation of a set of
elements and the relations among them
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Architectural Structures
- module structures
basic elements are modules.
they are assigned areas of functional responsibility.
Module allow us answer
What is the primary responsibility of module?
What other software does it use?
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- component-and-connector structures
elements are run-time components (units of computation) and
connectors (communication vehicles).
What are the major components & how do they interact?
How does data progress through the system?
- allocation structures
shows the relationship between the software elements and the
elements in external environment in which software is
created and executed
What is the assignment of S/W elements to development team
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Architectural Structures: Module
module
decomposition
uses
layered
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class
Architectural Structures: Component-andConnector
component-and-connector
client-server
shared data
concurrency
process
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Architectural Structures: Allocation
allocation
Work assignment
implementation
deployment
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Architectural Structures: Module
 Decomposition:
 Units are modules related to each other by “is a sub module of” relation.
 Shows how larger modules are decomposed into smaller modules
recursively till the smaller modules are easily understood.
 Modules have associated products (code, test plans).
 Provides modifiability, by ensuring that changes to small modules.
 Used for project structuring also for integration & test plans.
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Uses :
Structure are modules or procedures.
Relation is “ uses”.
One unit uses another if the correctness of the first requires the presence
of a correct version of second.
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• Layered:
• If the Uses relation is carefully controlled the a system of layer comes in
picture.
• If there are n layers. Then the nth layer will use only service from layer n-1.
• Layers are often designed as abstractions & hide implementation specifics
below from the layers above.
•
•
•
•
•
Class:
module units are called classes
Relation is “inherts- from”
Collection of similar behavior.
This allows us to reason about reuse and additional functionality.
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Architectural Structures: Component-and-Connector
• Process or communicating processes:
• Deals with dynamic aspects of a running system.
• Units here are processes or threads which communicate, synchronize with
each other.
• The relation is “attachment” how components and connecters are linked
together.
•
•
•
•
Concurrency:
Allows the architects to determine the opportunities for parallelism.
Units are components and connecters are logical threads
Logical thread is a sequence of computation, that can be allocated to a
separate physical thread in design process.
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• Shared data or repository:
• The structure comprises components and connecters that create, store
and access data
• It shows how data is produced and consumed by run time software
element.
• It is used for good performance and data integrity.
• Client and server:
• Built as a group of cooperating clients and servers.
• Components are clients and servers & Connecters are protocols and
messages
• Used for load balancing( supporting run time performance) and physical
distribution.
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Architectural Structures: Allocation
• Deployment:
• Shows how software is assigned to hardware processing and
communication elements.
• The elements are software, hardware, and communication pathways.
• Relations are “allocated to” (shows which physical units are assigns to
software elements), and “migrates to” (if allocation is dynamic)
• Helps to understand the performance ,availability, security.
• Implementation:
• shows how software elements are mapped to file structures in the
systems development, integration.
• This is critical for management of development activities.
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• Work assignment:
• This structure assigns responsibility for implementing and integrating the
modules to appropriate development teams.
• This structure which is the part of the architecture makes it clear about
the decisions “who does the work”.
• The architect will know the expertise required on each team.
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Architectural Structures: Module
Software
structure
Relations
Useful For Reason About
Decomposition
is a sub module, shares
secrets with
resource allocation, project structuring
and planning, information hiding,
encapsulation, configuration control
Uses
requires the correct
presence of
extension or extraction of functionality
layered
requires the correct
presence of, uses the
rvices of, provides
abstraction to
incremental development,
implementing systems on top of
“virtual machines”
Class
is an instance of, shares
access methods of
in OO – producing rapid almost-alike
implementations from a common
template
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RESULTS
Architectural Structures: Component-Connector
Software
structure
Relations
Useful For Reason About
client-server
communicates with,
depends on
distributed operation,
separation of concerns,
performance, load
balancing
process
runs concurrently with, may run
concurrently with, excludes, precedes
scheduling, performance
concurrency
runs on the same logical thread
locations where resource
contention exists, where
threads may fork, join,
be created or killed
shared data
produces data, consumes data
performance, data
integrity, modifiability
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RESULTS
Architectural Structures: Allocation
Software structure
Relations
Useful For Reason About
deployment
allocated to,
migrated to
performance, availability,
security
implementation
stored in
configuration control,
integration, test activities
work assignment
assigned to
project management,
best use of expertise,
management of
commonality
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RESULTS