CSC550 Software
Engineering
Devon M. Simmonds
Computer Science Department
University of North Carolina, Wilmington
simmondsd@uncw.edu
Introduction to Software
Architectures
Devon M. Simmonds
Computer Science Department, CSC592
1
Architectural Design
• Lecture Outline
– Architectural styles
•
•
•
•
•
Layered
Client-server
Event-based
Shared repository
Class exercise
– Other topics on Architectures
• Interceptors, adaptive software, failure models, design requirements
– Summary
Devon M. Simmonds
Computer Science Department, CSC592
2
What is Software Architecture?
• A model describing the overall structure of the
software in terms of components/subsystems,
their interrelationships and behaviors.
A
P
K
M
B
Devon M. Simmonds
Computer Science Department, CSC592
C
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General Architecture of
Distributed Systems
A
P
K
M
B
C
• An architectural model defines structure - system
components and their relationships as well as behaviour –
how components interact.
• The goal of architectural design is to meet present and future
demands on the architecture.
• Each architectural style defines a class of architectures.
Devon M. Simmonds
Computer Science Department, CSC592
4
Architectural Styles
Architectural styles
• An architecture style is a specification of
how subsystems in a software may be
structured.
– 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
Devon M. Simmonds
Computer Science Department, CSC592
Component 2
Component 1
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Architectural Styles,
cont.
• 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.
• E.g. remote procedure calls, message passing
Component 2
Component 1
Devon M. Simmonds
Computer Science Department, CSC592
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Architectural Styles,
cont.
Important architectural styles for distributed
systems
• Layered architectures
• Client/Server architectures
• Object-based architectures
• Data-centered architectures
• Event-based architectures
• Model View Controller
Devon M. Simmonds
Computer Science Department, CSC592
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Layered Architectures,
cont.
A Layered Architectural Style
• Figure 2-1. Tanenbaum et al.
Devon M. Simmonds
Computer Science Department, CSC592
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Layered Architectures,
cont.
Classical Three-Tiered Architecture
• Figure 2-4 (Tanenbaum). The simplified organization
of an Internet search engine into three different layers.
Devon M. Simmonds
Computer Science Department, CSC592
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Layered Architectures,
cont.
Characteristics of layered Architectures
• Advantages
– Clear separation of parts/roles/subsystems.
– Easy to plug and play components.
– Relatively simple to implement as either a concurrent or
sequential system.
Devon M. Simmonds
Computer Science Department, CSC592
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Architectural Styles
Important architectural styles for distributed
systems
• Layered architectures
• Client/Server architectures
• Object-based architectures
• Data-centered architectures
• Event-based architectures
• Model View Controller
Devon M. Simmonds
Computer Science Department, CSC592
11
Client-server (“two-tier”)
architectures
• A network architecture in which each
computer or process on the network is either
a client or a server.
Devon M. Simmonds
Computer Science Department, CSC592
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Architectural Styles
•The client/Server Model
Client
invocation
res ult
Server
invocation
Server
res ult
Client
Key:
Process :
Computer:
Fig. 2.2 Coulouris et al.: Clients invoke individual servers
Devon M. Simmonds
Computer Science Department, CSC592
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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.
Devon M. Simmonds
Computer Science Department, CSC592
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Coulouris etal.Distributed Systems: Concepts and Design Edn. 3 © Addison-Wesley Publishers 2000
Architectural Styles,
cont.
Important architectural styles for distributed
systems
• Layered architectures
• Client/Server architectures
• Object-based architectures
• Data-centered architectures
• Event-based architectures
• Model View Controller
Devon M. Simmonds
Computer Science Department, CSC592
15
Object-Based Architectural Style
• Figure 2-1. (b) The object-based architectural style.
Devon M. Simmonds
Computer Science Department, CSC592
16
Coulouris etal.Distributed Systems: Concepts and Design Edn. 3 © Addison-Wesley Publishers 2000
Architectural Styles,
cont.
Important architectural styles for distributed
systems
• Layered architectures
• Client/Server architectures
• Object-based architectures
• Data-centered architectures
• Event-based architectures
• Model View Controller
Devon M. Simmonds
Computer Science Department, CSC592
17
Event-Based Architectural Style
• Figure 2-2. (a) The event-based architectural style
Devon M. Simmonds
Computer Science Department, CSC592
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Coulouris etal.Distributed Systems: Concepts and Design Edn. 3 © Addison-Wesley Publishers 2000
Architectural Styles,
cont.
Important architectural styles for distributed
systems
• Layered architectures
• Client/Server architectures
• Object-based architectures
• Data-centered architectures
• Event-based architectures
• Model View Controller
Devon M. Simmonds
Computer Science Department, CSC592
19
Shared repository Architectural Style
• Figure 2-2. (b) The shared data-space architectural style.
Devon M. Simmonds
Computer Science Department, CSC592
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Shared Repository 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.
Devon M. Simmonds
Computer Science Department, CSC592
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Coulouris etal.Distributed Systems: Concepts and Design Edn. 3 © Addison-Wesley Publishers 2000
Architectural Styles,
cont.
Important architectural styles for distributed
systems
• Layered architectures
• Client/Server architectures
• Object-based architectures
• Data-centered architectures
• Event-based architectures
• Model View Controller
Devon M. Simmonds
Computer Science Department, CSC592
22
The Model-view-controller architecture
Data
Model
change
notifies
Controller
query
View
Functionality
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).
Devon M. Simmonds
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Computer Science Department, CSC592
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Devon M. Simmonds
Computer Science Department, CSC592
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Architectural Design Example
• Draw layered, client-server, and data-centric architectures
using this description.
– A school video library tracking system is to be developed. Videos can be scientific,
religious or general. General videos are classified as miscellaneous, sports or
entertainment. Students and professors can belong to research groups. A research group
must have at least 2 professors. Every student must belong to some research group.
Professors that belong to a research group are called research professors. Research
professors do not teach courses every semester. Each semester, a student must register for
at least one course offered by a professor in his research group. A student cannot
register for courses outside the subject areas of the research groups in his academic
department. A research group can consist of members with various subject area
interests. However, subject areas are only classified as an area of interest for the group
if at least two members have interest in the area. In general, professors can check out
any number of videos, however, visiting professors can check out at most seven videos.
Unlike regular professors, visiting professors can check out videos for the duration of
only two weeks. Students can check out any number of religious videos and at most 2
scientific videos. Students can check out only scientific videos in the subject areas
Devon M. Simmonds
represented
Computer Science Department,
CSC592 in their research groups.
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Summary: What an
architectural model does
• Simplify and abstract the functions of individual
components
• Consider the placement of components across a
network of computers, seeking to define useful
patterns for the distribution of data and workload
• Consider the interrelationships between the
components, i.e., the functional roles and
patterns of communication between them
Devon M. Simmonds
Computer Science Department, CSC592
26
CSC550, Devon M. Simmonds, Computer Science Department, University of North Carolina Wilmington
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Devon M. Simmonds
Computer Science Department, CSC592
The End
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Architectural Design Example
• Draw layered, client-server, and data-centric 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 of the seven 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.
Devon M. Simmonds
Computer Science Department, CSC592
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