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Software Engineering
Devon M. Simmonds
University of North Carolina, Wilmington
Some slides adapted from various sources
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Outline
Requirements Analysis
Software Design
Implementation
Systems Engineering
Evolution
Deployment
Testing
 This lecture will provide:
 An introduction to software architecture.






A definition of software architecture
Architectural styles
Architecture as a process
Architectural views
Benefits of software architecture
summary
Software Design – bridging the gap between requirements & Implementation
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Outline
Requirements Analysis
Software Design
Implementation
Systems Engineering
Evolution
Deployment
Testing
 In this session we address:
 An introduction to software architecture.






A definition of software architecture
Architectural styles
Architecture as a process
Architectural views
Benefits of software architecture
Summary
Software Design – bridging the gap between requirements & Implementation
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What is Software Design?
• Software design expresses a solution to a
problem in programming language
independent terms.
– This permits a design to be implemented in any
programming language.
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Moving from problem to
Architecture
Requirements Spec
Design Spec
System attributes, anticipated
changes, design constraints
Design goals
Use Cases
Contracts
Class Diagrams
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Architecture
• subsystem structure
• subsystem interfaces
•etc.
Other models
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The Place of Architecture in
Design Phases
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• Architectural Design
– Identify subsystems and the services they provide
– Describe interactions across subsystems
• Subsystem Design:
– Define classes
– Describe how objects interact to accomplish subsystem services
• Sequence diagrams, state machines, etc.
• User Interface Design
• Data structures/Database Design
• Algorithm Design
– Pre and post conditions
• Test Case Design
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UML Diagram Types for
Architectural Design
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• Architectural Design
– Package diagrams
– Component diagrams
– Deployment diagrams
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Architecture defined
 Architecture n (1555)
 1: the art or science of building; specifically: the
art or practice of designing and building
structures and esp. habitable ones.
 2 a: formation or construction resulting from or
as if from a conscious act <the architecture of the
garden>
 b: a unifying or coherent form or structure <the
novel lacks architecture>
 4: a method or style of building.
Merriam Webster’s Collegiate Dictionary
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Can be built by one person
Requires
Minimal modeling
Simple process
Simple tools
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Built most efficiently and timely by a team
Requires
Modeling
Well-defined process
Power tools
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The more complex the problem the greater the need for:
Teams of developers
Modeling
Well-defined processes
Significant tool support
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Computer Architecture
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is not Software Architecture
• The assembly of logical elements into a computing device.
• Specifying the relations between parts of a computer system.
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What is Software Architecture?
• (a model that) describes the overall
structure of the software subsystems, the
relationships among subsystems and the
behavior of subsystems (i.e. how
subsystems interact).
A
P
K
M
B
C
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What are the goals of Software
Architecture?
• The goal of architectural design is to meet
present and future demands on the
architecture.
A
P
K
M
B
C
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Software Architecture in UML
• In UML, the architecture of a software may
be described using:
– Package diagrams
– Component diagrams
– Deployment diagrama
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Outline
Requirements Analysis
Software Design
Implementation
Systems Engineering
Evolution
Deployment
Testing
 In this session we address:
 An introduction to software architecture.
 A definition of software architecture
Architectural styles




Architecture as a process
Architectural views
Benefits of software architecture
Summary
Software Design – bridging the gap between requirements & Implementation
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How do we go about creating an
architecture for a system?
• Exploring architectural Styles
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Architectural Styles
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Architectural styles
• An architecture style is a specification of how
subsystems in a software may be organized.
– Specification of architectural components
– Specification of architectural connectors
Component N
Component N-1
– Specification of constraints on how components can
be combined
• Specification of component interaction (data exchange)
– Specification of component configuration to form a
system
• Specification of one or more semantic models that specify
how a system’s overall properties can be determined from the
properties of its parts
Component 2
Component 1
• Each architectural style defines a class of
architectures.
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Components & Connectors
• What is an architectural
component/subsystem?
– A modular unit with well defined
provided and required interfaces that is
replaceable.
Component N
Component N-1
• What is an architectural connector?
– A mechanism that mediates
communication, coordination or
cooperation among components.
Component 2
Component 1
• e.g. remote procedure calls, message passing
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Popular architecture styles
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• Layered
• Client-server
– Peer-to-peer
• Model-view controller
• Pipe and Filter
• Shared Repository
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Layered Architectures,
cont.
A Layered Architectural Style
• Figure 2-1. Tanenbaum et al.
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Rationale for Layered
Architectures
• Separate presentation and application
logic, and other areas of concern.
UI Layer
“Domain” or “Application Logic” Layer
Services Layer
Persistence
Subsystem
Logging
Subsystem
...
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Layered Architectures, cont.
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Classical Three-Tiered Architecture
• Figure 2-4 (Tanenbaum). The simplified organization
of an Internet search engine into three different layers.
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Layered Architectures, cont.
Benefits of layered Architectures
• Clear separation of parts/roles/subsystems.
• Easy to plug and play components.
• Relatively simple to implement as either a concurrent or
sequential system.
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Popular architecture styles
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• Layered
• Shared Repository
• Client-Server
– Peer-to-peer
• Model-view controller
• Pipe and Filter
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Shared repository architectures
K
A
T
• Multiple sub-systems share a common
database.
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Repository model characteristics
• Advantages
– Efficient way to share large amounts of data;
– Sub-systems need not be concerned with how data is produced
Centralised management e.g. backup, security, etc.
– Sharing model is published as the repository schema.
• Disadvantages
– Sub-systems must agree on a repository data model. Inevitably a
compromise;
– Data evolution is difficult and expensive;
– No scope for specific management policies;
– Difficult to distribute efficiently.
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Popular architecture styles
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• Layered
• Shared Repository
• Client-Server
– Peer-to-peer
• Model-view controller
• Pipe and Filter
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Client-server (“two-tier”)
architectures
• A network architecture in which each
computer or process on the network is either
a client or a server.
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Architectural Styles
•The client/Server Model
Client
invocation
result
Server
invocation
result
Server
Client
Key:
Proc ess :
Computer:
Fig. 2.2 Coulouris et al.: Clients invoke individual servers
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Coulouris etal.Distributed Systems: Concepts and Design Edn. 3 © Addison-Wesley Publishers 2000
Client/Server Model, cont.
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A service provided by multiple servers
Servic e
Server
Client
Server
Client
Server
Fig. 2.3 Coulouris et al.
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Coulouris etal.Distributed Systems: Concepts and Design Edn. 3 © Addison-Wesley Publishers 2000
Client/Server Model, cont.
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Web proxy servers and caches
Web
s erver
Client
Proxy
s erver
Web
s erver
Client
Fig. 2.4 Coulouris et al.: Web proxy servers
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Peer-to-peer (P2P) architectures
• Each network node has equivalent
responsibilities – is both a client and a
server.
B
A
C
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Coulouris etal.Distributed Systems: Concepts and Design Edn. 3 © Addison-Wesley Publishers 2000
Client/Server Model, cont.
Client-server characteristics
• Advantages
– Distribution of data is straightforward;
– Makes effective use of networked systems. May require cheaper hardware;
– Easy to add new servers or upgrade existing servers.
• Disadvantages
– No shared data model so sub-systems use different data organisation.
Data interchange may be inefficient;
– Redundant management in each server;
– No central register of names and services - it may be hard to find out
what servers and services are available.
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Popular architecture styles
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• Layered
• Shared Repository
• Client-Server
– Peer-to-peer
• Model-view controller
• Pipe and Filter
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The Model-view-controller architecture
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Data
Functionality
Model
change
notifies
Controller
query
View
change
User Interface
• Separates the application object (model) from
• The way it is presented to the user (view), from
• The way in which the user controls it (controller).
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Popular architecture styles
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• Layered
• Shared Repository
• Client-Server
– Peer-to-peer
• Model-view controller
• Pipe and Filter
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Pipe and Filter architectures
A
K
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T
• Input to one subsystem is processed and the output is
passed to another subsystem for processing.
• E.g. program compilation using the multi-phase translator architecture
Compilation of a program is divided into
– Lexical analysis
» lex
– Syntax analysis
– Semantic analysis
– optimization
– Code generation
» yacc – a tool for generating compilers
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Pipe and Filter Characteristics
• Advantages
– Supports transformation reuse.
– Intuitive organization for stakeholder
communication.
– Easy to add new transformations.
– Relatively simple to implement as either a
concurrent or sequential system.
• Disadvantages
– Requires a common format for data transfer along
the pipeline and difficult to support event-based
interaction.
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Architecture styles Summary
• An architecture style provides a standardized
vocabulary for communication
• An architecture style defines a family of systems
sharing similar characteristics.
• An awareness of these styles can simplify the
problem of defining system architectures.
• However, large systems are heterogeneous and
may use a combination of architectural styles.
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Architectural Design Process
•
•
•
•
Identify potential subsystems
Select architectural styles
Arrange subsystems to fit architectural styles
Identify subsystem dependencies
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Architectural Design Exercise
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• Draw layered, client-server, shared repository and pipeand-filter architectures using this description
– The BirdCage Corporation needs software to aid the management of its
business. The corporation builds its business around domestic birds. BirdCage
arranges its business around different services with each service being
managed by a different company making BirdCage a group of companies.
Companies are divided into departments. Services include veterinary services,
safekeeping of birds, bird calisthenics and a bird competitions service. In order
to streamline its business, BirdCage classifies the veterinary and safekeeping
services as medical services. The other two services are regarded as
entertainment services. In the future the company hopes to add a number of
“Nutritional” services to address the production and sales of food for birds. The
corporation classifies birds as either exotic or non-exotic. BirdCage does not
provide entertainment services for exotic birds. Owls and crows are non-exotic
birds, while macaws, cockatoos and green quakers are exotic. BirdCage seeks
to maintain a minimum stock of at least 10 of each type of exotic bird.
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Outline
Requirements Analysis
Software Design
Implementation
Systems Engineering
Evolution
Deployment
Testing
 In this session we address:
 An introduction to software architecture.
 A definition of software architecture
 Architectural styles
 Architecture as a process
 Architectural views
 Benefits of software architecture
 Summary
Software Design – bridging the gap between requirements & Implementation
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Mary Shaw, CMU
Grady Booch,
Philippe Kruchten,
Rich Reitman
Kurt Bittner, Rational
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Architecture as a process
• Software architecture encompasses the set of
significant decisions about the organization of a
software system
– selection of the structural elements and their interfaces by
which a system is composed
– behavior as specified in collaborations among those
elements
– composition of these structural and behavioral elements
into larger subsystem
– architectural style that guides this organization
• The output of this design process is a description of the software
architecture.
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Outline
Software Design
Requirements Analysis
Implementation
Systems Engineering
Evolution
Deployment
Testing
 In this session we address:
 An introduction to software architecture.
 A definition of software architecture
 Architectural styles
 Architecture as a process
 Architectural views
 Benefits of software architecture
 Summary
Software Design – bridging the gap between requirements & Implementation
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Many stakeholders, many views
• Architecture is many things to many different
interested parties
–
–
–
–
–
–
customer
project manager
architect
developer
maintainer
etc.
• Multiple stakeholders  many views
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Architectural view
• An architectural view is a simplified
description (an abstraction) of a system from a
particular perspective or vantage point,
covering particular concerns, and omitting
entities that are not relevant to this
perspective.
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A model is a complete description of a system from a particular perspective
Models, Views, and Diagrams
Use Case
Use Case
Diagrams
Use Case
Diagrams
Diagrams
State
State
Diagrams
Class
Diagrams
Diagrams
State
State
Diagrams
Object
Diagrams
Diagrams
Use Case
Use Case
Diagrams
Sequence
Diagrams
Diagrams
Scenario
Scenario
Diagrams
Collaboration
Diagrams
Diagrams
Scenario
Scenario
Diagrams
Statechart
Diagrams
Diagrams
State
State
Diagrams
Component
Diagrams
Diagrams
Models
Component
Component
Diagrams
Deployment
Diagrams
Activity
Diagrams
Diagrams
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Diagrams
• A diagram is a view into a model
– Presented from the aspect of a particular
stakeholder
– Provides a partial representation of the system
– Is semantically consistent with other views
• UML diagrams
– Static views: use case, class, object, component,
deployment
– Dynamic views: sequence, statechart, activity
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The 4 + 1 View Model – Philippe Kruchten(95)
Development view
Logical view
Programmers
Software management
End-user Functionality
.
Use case view
Process view
System integrators:
Performance, Scalability, Throughput
Conceptual
Physical view
System topology,
Delivery, installation
Physical
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Example Logical Architecture
bill order
Customer Care
Accounts Receivables
System Static Structural Diagram
invoice
Order Processing
customer update
Domain
query order
order update
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Deployment Diagram
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• Captures the topology of a system’s hardware
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Outline
Requirements Analysis
Software Design
Implementation
Systems Engineering
Evolution
Deployment
Testing
 In this session we address:
 An introduction to software architecture.




A definition of software architecture
Architectural styles
Architecture as a process
Architectural views
 Benefits of software architecture
 summary
Software Design – bridging the gap between requirements & Implementation
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Advantages of explicit architecture
• Stakeholder communication
– Architecture may be used as a focus of discussion
by system stakeholders.
• System analysis
– Means that analysis of whether the system can
meet its non-functional requirements is possible.
• Large-scale reuse
– The architecture may be reusable across a range
of systems.
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Architecting system characteristics
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 Performance
 Localize critical operations and minimize communications. Use large
rather than fine-grain components.
 Security
 Use a layered architecture with critical assets in the inner layers.
 Safety
 Localize safety-critical features in a small number of sub-systems.
 Availability
 Include redundant components and mechanisms for fault tolerance.
 Maintainability
 Use fine-grain, replaceable components.
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Outline
Requirements Analysis
Software Design
Implementation
Systems Engineering
Evolution
Deployment
Testing
 In this session we address:
 An introduction to software architecture.






A definition of software architecture
Architectural styles
Architecture as a process
Architectural views
Benefits of software architecture
Summary
Software Design – bridging the gap between requirements & Implementation
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Summary
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Architectural design decisions
•
•
•
•
•
•
•
•
Is there a generic application architecture that can be used?
How will the system be distributed?
What architectural styles are appropriate?
What approach will be used to structure the system?
How will the system be decomposed into modules?
What control strategy should be used?
How will the architectural design be evaluated?
How should the architecture be documented?
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Summary
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Key points
• The software architecture is the fundamental framework for
structuring the system.
• Architectural design decisions include decisions on the
application architecture, the distribution and the architectural
styles to be used.
• Different architectural models such as a structural model, a
control model and a decomposition model may be developed.
• System organisational models include repository models,
client-server models and pipe-and-filter models.
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The End
Qu es
ti ons?
______________________
Devon M. Simmonds
Computer Science Department
University of North Carolina Wilmington
_____________________________________________________________
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Architectural Design Exercise
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• Draw layered, client-server, shared repository and pipeand-filter architectures using this description
– The Exotic Sunshine Corporation needs software to aid the management of its
business. The corporation is made up of several different companies each having at
least three divisions. The corporation classifies divisions as either production, sales or
marketing. The sales and marketing divisions are given jurisdiction for a specific
geographic region. This region must include the company that owns the division.
Regions have managers, however, an employee may only manage two or more regions if
he/she has in excess of ten years experience with the company, or ten years in a
comparable position. Managers with more than ten years service and managers in the
head office are allowed thirty days of paid vacation per year. In addition, they may
have up to three company vehicles assigned and one of the vehicles may be a luxury
vehicle. Other managers are not allowed luxury vehicles and cannot be allocated in
excess of one vehicle. The corporation manufactures and sells boats, electronic
equipment, fruit juices and paper.
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