1. CSC450 Software Engineering
Devon M. Simmonds
University of North Carolina, Wilmington
Architectural Design
Some slides adapted from various sources

2. Requirements Analysis
Outline
Requirements Analysis
Software Design
Implementation
Testing
Deployment
Evolution
Systems Engineering
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

3. Requirements Analysis
Outline
Requirements Analysis
Software Design
Implementation
Testing
Deployment
Evolution
Systems Engineering
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

4. 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.

5. Moving from problem to Architecture
Requirements Spec
Design Spec
System attributes, anticipated
changes, design constraints
Design goals
Use Cases
Contracts
Architecture
subsystem structure
subsystem interfaces
etc.
Class Diagrams
Other models

6. The Place of Architecture in Design Phases
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

7. UML Diagram Types for Architectural Design
Package diagrams
Component diagrams
Deployment diagrams

8. 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

9. Architecting a dog house
Can be built by one person
Requires
Minimal modeling
Simple process
Simple tools

10. Architecting a house Built most efficiently and timely by a team
Requires
Modeling
Well-defined process
Power tools

11. Architecting a high rise
The more complex the problem the greater the need for:
Teams of developers
Modeling
Well-defined processes
Significant tool support

12. Computer Architecture is not Software Architecture
The assembly of logical elements into a computing device.
Specifying the relations between parts of a computer system.

13. 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). M B C A P K

14. What are the goals of Software Architecture?
The goal of architectural design is to meet present and future demands on the architecture. M B C A P K 14

15. Software Architecture in UML
In UML, the architecture of a software may be described using:
Package diagrams
Component diagrams
Deployment diagrama 15

16. Requirements Analysis
Outline
Requirements Analysis
Software Design
Implementation
Testing
Deployment
Evolution
Systems Engineering
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

17. How do we go about creating an architecture for a system?
Exploring architectural Styles

18. Architectural styles 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
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
Each architectural style defines a class of architectures.
Component N
Component N-1
Component 2
Component 1 18

19. Components & Connectors
What is an architectural component/subsystem?
A modular unit with well defined provided and required interfaces that is replaceable.
What is an architectural connector?
A mechanism that mediates communication, coordination or cooperation among components.
e.g. remote procedure calls, message passing
Component N
Component N-1
Component 2
Component 1

20. Popular architecture styles
Layered
Client-server
Peer-to-peer
Model-view controller
Pipe and Filter
Shared Repository

21. A Layered Architectural Style
Layered Architectures, cont.
A Layered Architectural Style
Figure 2-1. Tanenbaum et al. 21

22. 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
. . . 22

23. Classical Three-Tiered Architecture
Layered Architectures, cont.
Classical Three-Tiered Architecture
Figure 2-4 (Tanenbaum). The simplified organization of an Internet search engine into three different layers. 23

24. Benefits of layered Architectures
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. 24

25. Popular architecture styles
Layered
Shared Repository
Client-Server
Peer-to-peer
Model-view controller
Pipe and Filter 25

26. Shared repository architecturesK A T
Multiple sub-systems share a common database.

27. 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.

28. Popular architecture styles
Layered
Shared Repository
Client-Server
Peer-to-peer
Model-view controller
Pipe and Filter 28

29. Client-server (“two-tier”) architectures
A network architecture in which each computer or process on the network is either a client or a server. 29

30. The client/Server Model
Architectural Styles
The client/Server Model
Fig. 2.2 Coulouris et al.: Clients invoke individual servers

31. A service provided by multiple servers
Coulouris etal.Distributed Systems: Concepts and Design Edn. 3 © Addison-Wesley Publishers 2000
Client/Server Model, cont.
A service provided by multiple servers
Fig. 2.3 Coulouris et al.

32. Web proxy servers and caches
Coulouris etal.Distributed Systems: Concepts and Design Edn. 3 © Addison-Wesley Publishers 2000
Client/Server Model, cont.
Web proxy servers and caches
Fig. 2.4 Coulouris et al.: Web proxy servers

33. Peer-to-peer (P2P) architectures
Each network node has equivalent responsibilities – is both a client and a server. B A C 33

34. Client-server characteristics
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. 34

35. Popular architecture styles
Layered
Shared Repository
Client-Server
Peer-to-peer
Model-view controller
Pipe and Filter 35

36. The Model-view-controller architecture
Data
Functionality
Model
change
Controller
notifies
query
change
View
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).

37. Popular architecture styles
Layered
Shared Repository
Client-Server
Peer-to-peer
Model-view controller
Pipe and Filter 37

38. Pipe and Filter architecturesK 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

39. 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.

40. 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.

41. Architectural Design Process
Identify potential subsystems
Select architectural styles
Arrange subsystems to fit architectural styles
Identify subsystem dependencies

42. Lets do an example!

43. Architectural Design Exercise
Draw layered, client-server, shared repository and pipe-and-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.

44. Requirements Analysis
Outline
Requirements Analysis
Software Design
Implementation
Testing
Deployment
Evolution
Systems Engineering
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

45. Architecture as a process
Mary Shaw, CMU
Grady Booch,
Philippe Kruchten,
Rich Reitman
Kurt Bittner, Rational
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.

46. Requirements Analysis
Outline
Requirements Analysis
Software Design
Implementation
Testing
Deployment
Evolution
Systems Engineering
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

47. Many stakeholders, many views
Architecture is many things to many different interested parties
customer
project manager
architect
developer
maintainer
etc.
Multiple stakeholders  many views

48. 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.

49. Models, Views, and Diagrams
A model is a complete description of a system from a particular perspective
Models, Views, and Diagrams
Use Case
Diagrams
State
Diagrams
Class
State
Diagrams
Object
Use Case
Diagrams
Sequence
Scenario
Diagrams
Collaboration
State
Diagrams
Component
Models
Scenario
Diagrams
Statechart
Component
Diagrams
Deployment
Activity
Diagrams

50. Diagrams A diagram is a view into a model UML diagrams
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

51. The 4 + 1 View Model – Philippe Kruchten(95)
Logical view
Development view
Programmers
Software management
End-user Functionality
Use case view
Process view
System integrators:
Performance, Scalability, Throughput
Physical view
System topology, Delivery, installation
Contrast logical & development view
Development: directories, names
Logical: source code analysis.
Conceptual
Physical

52. Example Logical Architecture
System Static Structural Diagram
Customer Care
Order Processing
Domain
Accounts Receivables
invoice
query order
customer update
order update
bill order

53. Deployment Diagram
Captures the topology of a system’s hardware

54. Requirements Analysis
Outline
Requirements Analysis
Software Design
Implementation
Testing
Deployment
Evolution
Systems Engineering
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

55. 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.

56. Architecting system characteristics
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.

57. Requirements Analysis
Outline
Requirements Analysis
Software Design
Implementation
Testing
Deployment
Evolution
Systems Engineering
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

58. Architectural design decisions
Summary
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?

59. Summary
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.

60. The End Qu es ti ons? ______________________ Devon M. Simmonds
Computer Science Department
University of North Carolina Wilmington
_____________________________________________________________

61. Architectural Design Exercise
Draw layered, client-server, shared repository and pipe-and-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.