1. Software Architecture
CS 4311

2. Architecture Design at the highest level Example: bridge architectures
Cable-stayed
Beam
Suspension

3. Why do civil engineers talk about bridge architectures?
Design at the highest level
Example: bridge architectures
Arch
Cable-stayed
Beam
Suspension

4. What is architecture? Dictionary definitions:
archangel, archenemy, archduke, archbishop
matriarch, patriarch, monarch
Arch as prefix or suffix:
main, chief, principal, most important, highest, fundamental, basic, extreme or most characteristic, ruler, leader

5. Architecture The art and science of designing and erecting buildings
Fundamental underlying design of buildings
Style and method of design and construction of buildings
Buildings and other structures

6. What is software architecture?
Framework
Mechanism
Way
Shape
Form
Means
Organization
Arrangement
The Big Picture !

7. Software Architecture
the structure or structures of the system
software components
externally visible properties of those components
the relationships between them
the set of principle design decisions made about a software system.

8. What design decision? System structure Functional behavior Interaction
Nonfunctional properties
Implementation
System goals, Stakeholders, Nontechnical considerations

9. Independent Components
Broadcasts
Client-server
Event driven
Components register for an event. System invokes all registered components when event happens.
Example: Java AWT
Dynamic, responsibility with event handler, not event generator.
Can be hard to test/debug.

10. Virtual Machines Interpreters: Examples: Program to be executed
Interpreter: simulate instructions in program
State: State of program, state of interpreter
Examples:
JVM
Command language processors

11. Repositories Central Data store + operations {store, retrieve, update}
Traditional: transactions trigger processing
Blackboard: Central store controls processing
Processes write to central store (knowledge sources)
Processes respond to changes in the store

12. Layered Architecture Layers are hierarchical
Each layer provides services to the outer layer which is a client to the inner layer
Layers can have access to adjacent layers (direct access only)
The design includes how each pair of layers interact (protocols)
Layered architectures are often used for interactive information services

13. Example Layered security architecture Cryptography File interface
Key management
User

14. Advantages and Drawbacks
+ Each layer can be seen as a higher level of abstraction + A change on one layer affects only layers interacting with the changed layer + Clearly favors reuse - Layers are not always obvious when looking at the requirements - Performance may suffer from the extra coordination among the layers

15. Layered Architectures in Interactive Information Systems
Browsers
Presentation
Web Server
Application
Control and
Coordination
App Server
Domain
Services and
Information
Db Server
Legacy
Database
Services

16. Characteristic Object Roles
Windows and Widgets
Presentation
Interfacers
Events
Coordinators, and (application) controllers
Results
Application
Services
Messages
Results
Information holders, service providers,
Structures, coordinators, and domain controllers
Domain
Services
Messages
Results
Technical
Services
Interfacers

17. Locating Objects in Layers
Once we have agreed on a layered architecture, we need to identify objects (classes) in layers
One approach is to use Class-Responsibility-Collaboration
-objects collaborates mostly within their layers
-client objects will tend to be in an outer layer (requests go inside)
-information goes outside

18. Process Control Process maintains setpoint Control based on Examples:
input variables (feedforward)
Output variables (feedback)
Examples:
Thermostat controlled heater
“smart” stock trader

19. Architecture Elements
Components
Connectors
Configuration Topologies
Models

20. Components
Elements that encapsulate processing and data in a system’s architecture are referred to as software components.
An architectural entity that
encapsulates a subset of the system’s functionality and/or data,
restricts access to that subset via an explicitly defined interface, and
had explicitly defined dependencies on its required execution context.

21. Connector
Elements that are tasked with effecting and regulating interactions among components.
Application independent.

22. Configuration Topology
A set of specific associations between the components and connectors of a software system’s architecture.

23. Models
An artifact that captures some or all of the design decisions that comprise a system’s architecture.
Architectural modeling is the reification and documentation of those design decisions.
Different models:
structural vs. behavioral
static vs. dynamic
scope

24. Architectural Styles
A named collection of architectural design decisions that:
are applicable in a given development context,
constrain architectural design decisions that are specific to a particular system with that context, and
elicit beneficial qualities in each resulting system.
Not about: specific systems, components, interaction mechanisms, or configurations.

25. An Architectural Style Example
Physically separate the software components used to request services from the components that provide the services, to allow for proper distribution and scaling up, both in the number of service providers and service requesters.
Make the service providers unaware of the requesters’ identity to allow the providers to service transparently many, possibly changing requestors.
Insulate the requesters from one another to allow for their independent addition, removal, and modification. Make the requesters dependent only on the service providers.
Allow for multiple service providers to emerge dynamically to off-load the existing providers should the demand for services increase above a given threshold.

27. Architectural Styles Remarks:
Each style has its own advantages and drawbacks
An application may require several architectural views
Choosing the right views is a key factor in
having a good design

28. Advantages of Architectural Styles
Each combination of styles emphasizes one or more of the quality attributes below:
Usability
Availability
Security
Performance
Maintainability
Flexibility
Portability

29. Example Software Architectures
Batch Sequential
Blackboard
Client Server
Database-centric
Distributed Computing
Event driven
Interpreter
Monolithic application
Peer-to-peer
Pipe and Filter
Plug-in
Service-oriented
Search-oriented
Space-based
Shared nothing
Three-tier model
Rule evaluation

30. Assignment: Base Groups
Each teams has until next class to prepare a 3 minute description of the provided architecture
You will present next class
What is it
What problem does it solve
How does it solve the problem
Who are the actors
How do they relate to each other
You will need to be efficient to cover the architecture in 3 minutes
Send Aditi 2 or 3 powerpoint slides by 5pm Wednesday
INCLUDE YOUR SOURCES

31. Example Software Architectures
Team 1 Blackboard
Team 2 Interpreter
Team 3 Plug-in
Team 4 Search-oriented
Team 5 Space-based
Team 6 Shared nothing
Team 7 Publisher-subscriber
Team 8 Rule evaluation

32. Batch Sequential Architecture
A series of dedicated and independent components that transforms data in a sequential manner (Each component needs to finish its task before the next one can start).

33. Batch Sequential Architecture
Solve complex task
Divide complex tasks into several easier tasks.
Modifiability/Maintainability
Easy to change/fix the behavior of a component.
Reusability
By only changing the components that interact with the environment the system can work on different structures.
Flexibility
Additional components are easy to integrate.

34. Batch Sequential Architecture
Actors
The actors consist of the independent components (programs) that run in sequence to achieve the ultimate desired output of the system.
Each components is responsible for a particular task and supplies the next component with the intermediate data once it has completed its task.
How do they relate to each other?
They are related to each other by the data that they each transform.

35. Batch Sequential Architecture
*Example: Compiler
*Software Design Methodology, By Hong Zhu © 2005

36. Client-Server Architecture
Application context:
Clients request services from a server
Centralization of computation and data at the server
Separation of user interface tasks from computation and data management and storage
For examples:
Websites, etc.

37. Client Server Architecture
Example:

38. Database-Centric Architecture
Critical databases applications always need a global transaction monitor.
can significantly reduce performance and scalability.
Architecture solves data management and processing of it.
Computes all the data to a single place, in this case the database.

39. Actors and their roles Benefits:
DBMS
SERVER 1
SERVER 2
Client 1
Client 3
Client 4
Client 6
Client 2
Client 5
Benefits:
Reduces amount of code, development time, network traffic, complexity of applications.

40. Distributed Computing Architecture
Also known as grid computing.
Makes use of the hardware on several computers.
Primarily used to solve those problems that require exceptionally heavy computation.
was the first project that demonstrated the feasibility of distributed computing to solve these problems.
Indeed, this was one of the primary goals of
The specific problem is used for is to detect intelligent life outside of Earth.

41. Distributed Computing Architecture
The software written for requires 2 components:
Central server software manages the distribution of data across personal computers and the collection of analyzed data.
Personal computer software performs analysis and monitors processor usage, ensuring that analysis is done only when the processor is not otherwise needed.

42. Event Driven Architecture
Components in the system react to certain events.
For example
State changes
I/O events
Creates responsiveness in a changing environment
Actors
Agents: components in a system that generate events
Sinks: event consumers
Responsibility of applying action as soon as event is present
May act as a filter to another component
May provide an action based the given event

43. Event Driven Architecture
Characteristics
Facilitates responsiveness
Works great in un-normalized unpredictable environments
Event flow
Sensing of fact
Technical representation in the form of an event
Reaction(s) to set event
Example
application displays a message stating that a new has been received

44. Event Driven Architecture
Agent
Sink 1
Sink 2
Sink 3
Sink n-1
Sink n
event
action
transformation

45. Monolithic Architecture
Single-Tier Architecture
Concept of having user interface and application of data access in one single program.
Only application is accountable for computations
Simplest software configuration
No modularity
Not a typical Software Engineering Concept 45

46. Why Monolithic Architecture?
Low Cost
Less Complex
No need to develop external computational or processing modules
Simple and Quick design
Single independent application
No need for future expansion of software
Not easily maintained

47. Peer-to-Peer Architecture
A type of architecture in which each class has equivalent capabilities and responsibilities
A class can collaborate with any other class and vice versa
Every class has access to the resources needed
Every class gives access to all its resources
No Super-classes
Every class has access to the resources needed to fulfill its responsibilities
and at the same time gives access to all of its resources to all other classes 47

48. Peer-to-Peer Architecture
Advantages:
Decentralized computing with flow of control and resources distributed among peers
Highly robust in the face of failure
Scalable in terms of access to resources and computing power
Cautions:
When information retrieval is time critical
Security

49. Pipe and Filter This is an architecture composed of filters and pipes:
A filter is a program that reads a stream and writes a stream
A pipe is middle where that directs the output stream of one program to the input stream of another
Transformed
Data
Transformed
Data
Input
Data
Filter
Filter
Filter

50. Pipe and Filter This is an architecture composed of filters and pipes:
A filter is a program that reads a stream and writes a stream
A pipe is middle where that directs the output stream of one program to the input stream of another
Useful when you have common stream processing programs that can be reused
The cost is that a lot of I/O processing is duplicated (e.g., parsing the data)

51. Example Pipe and Filter
Example: Unix shell scripts
ccl1 fred.txt | ccp0 | ccp1 | ccp2 > fred.o
| is the pipe operator
Read from the standard output of program to left
Write to standard input of program to right

52. Pipe and Filter Components are isolated
Easy to understand and reuse filters
Evolution is easy: replace filter
Allows concurrent execution
May be easy to analyze (analyze each filter for throughput, accuracy)
Batch or stream, not interactive
Replication of effort (reading, writing, parsing)

53. Service-Oriented Architecture (SOA)
Problem
Client needs access to multiple features however the client shouldn’t know how those features are implemented
SOA:
Provides access to multiple components or functions
Client doesn‘t know what components or how functionality is implemented

54. SOA Solve the Problem Actors
Provides an interface that hides the components and gives the client a single access point.
Actors
Client
Components

55. Three-Tier Architecture
client-server architecture
Three different tier
Presentation
Input/ output
Business
Data processing
Data Access
Read/Write

56. Three-Tier Advantages
Highly cohesive and lowly coupled
Allows change in modules with out effect on the other tiers
Encapsulates tasks