Software Architectural StylesAndrew Midwinter, Mark Mullen, Kevin Wong, Matt Jones

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What is Software Architecture?• Provides a very high level view of the

parts of the system and how they are related to form the whole system.

• More specifically, architecture partitions the system in logical parts such that each part can be comprehended independently and then describes the system in terms of these parts and their relationships.

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Some Examples…• Client-Server• Event-Driven• Peer-to-peer• Pipes and Filters• Three-Tier• Service-Oriented• Monolithic

• Blackboard• Implicit Invocation• Plug-in• Search-Oriented• Distributed Computing• Cloud Computing• Front end and Back end

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What Software Architecture is not

• Design patterns• Low-level design• Implementation• Computer Architecture

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Design vs. Software Architecture

• Architecture deals with “what” and “where” whereas design deals with the “how”

• Design patterns are to design as architectural styles are to architecture

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Event-Driven Architecture• Very common architecture• Three main components:• The Event• The Event Bus• The Listener

Figure 1: Block Diagrams for Event Driven Applications(Li, 2005)

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The Event• Something that happens, either inside or outside the system,

that causes some kind of action in the system.• Most of the time it is an external input, such as input from a

keyboard or controller, or sensors.• Can also be other processes.

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The Event Bus• The connector between events and listeners.• Performs event-stream-analysis, which includes data cleansing

and normalization.• Propagates events to the listeners connected to them.• Also handles listener registration.

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The Listener

• An object that executes some function when a specific event occurs.

• Registers its interest in certain events through the event bus.

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Pros and Cons• Pros:• Analysis of events and actions related to them are done quickly. • Very good for systems that need to be able to respond to external

events.• Cons:• More complex programs: can be difficult to follow the flow of a

system.

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Uses• Graphical User Interfaces• Swing

• Financial Trading systems• Pipeline monitoring systems• Sensor networks• Heart Rate Monitors

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Client-Server Architecture• Very common type of

architecture• Used in computer networking• Some example protocols : DNS,

FTP, SMTP, HTTP• Three main Components:• The Client• The Server• A Network

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The Client• Usually a personal computer• Connects to a server, makes a request• Receives a reply, makes more requests, etc.

• Often accesses the server through an application• There are several different kinds of clients

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The Server• A computer program running to serve the requests of other

programs• Often performs computational tasks for the clients• There are several different types

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Pros and Cons• Pros:• Performance• Simplicity (for clients)• Accessibility• Scalability

• Cons:• Cost• Overloading

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3-Tier• Was developed by John J. Donovan in Open Environment

Corporation (OEC)• User interface, process logic, computer data storage and data

access are developed and maintained as independent modules, often on separate platforms

• Eg) a change of an OS may want only to change the presentation layer would only affect the UI code (Windows 8?)

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3-Tier

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Example: Siri?

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Peer-to-Peer• P2P is a network architecture in which each computer has

equivalent capabilities and responsibilities. (Miller, 2001)

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A better definition• 5 Characteristics:• Computers connect to each other in real-time• Peers are both clients and servers• Primary content is provided by peers• Peers are autonomous and control their own activities• Peers are not necessarily permanent and many connect and

disconnect at will

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Three forms• Pure• Centralized• Hybrid

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Pros and Cons• Pros• Speed• Reliability• Availability• Privacy• Scalability

• Cons• Security• No mediator• Unavailability

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Monolithic• A somewhat older style of

architecture, not used as often now

• Everything is compiled and linked into a single application

• Many programs we deal with day-to-day use it (sort of):• Word processors• Powerpoint• Older mainframes• Development Environments• Older accounting software• Some Games

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Monolith – In Programming• Usually written in a single

programming language• Can operate in both batch

mode or GUI mode• Can have concurrency:• Multi-threading• Multi-Processing

• But only one executable!

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Pros and Cons• Pros• Performance• Simplicity

• Cons• Problems with shared access• Quantity of Data

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Summary• Architectural styles are used in

most applications today• They implement standards that

can be reused• These standards make it easier to

make early design decisions

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Questions?

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