1. Architectural Design Copyright © 2016 – Curt Hill
Chapter 6 of Sommerville 10th
Copyright © 2016 – Curt Hill

2. Introduction
This is a brief review of something that you should have seen in an earlier class
This is the design of programs and systems
It is intended to get us into design patterns
Copyright © 2016 – Curt Hill

3. What is this about?
Organizing and designing the structure of a program or system of programs
Link between requirements and design
This is where we structure the components
The result is a model of the future product
Model consists of communicating components
Copyright © 2016 – Curt Hill

4. Large and Small Sommerville has two coverages of this large and small
Large is chapter 17 and 18
Small is chapter 6
The communicating components are:
In the large programs and systems of programs
In the small classes and functions
This presentation is mostly about small
Copyright © 2016 – Curt Hill

5. Timing The architecture needs to be established early
The design and implementation of components depends on the architecture
Any changes to the architecture tends to nullify the results of component design and implementation
Copyright © 2016 – Curt Hill

6. Why? Allows team to communicate with stakeholders
In a way that is helpful to the non-technical
Enables the team to determine if the system can meet its non-functional requirements
Provides the possibility of reusing components
The architecture may give rise to several resulting implementations – a product line rather than just a product
Copyright © 2016 – Curt Hill

7. Design Decisions Design is not a science with fixed rules
Rather it is a creative process
Each project is different
The text provides a number of questions to ask
The answer drive the process
Copyright © 2016 – Curt Hill

8. Questions Does a common architecture work for this system?
What patterns will work?
What is the fundamental approach used to design the system?
How will the operation of the components be controlled?
How will the system be spread across hardware?
What form of documentation will be used?
How will the components be subdivided into subcomponents?
What structures will work for the constraints on the system?
Copyright © 2016 – Curt Hill

9. Lines Projects in the same domain often have similar architectures
A product line might use the same architecture with variations in the components
These facts enable component reuse
Copyright © 2016 – Curt Hill

10. Architectural Modifiers
Performance
Minimize communication
Larger rather than smaller components
Maintainability
Components should be small to ease replacement
Safety
Localize features in few components
Security
Critical assets should be in inner layers of a layered architecture
Upper layers provide authentication
Availability
Redundant components
Fault tolerance
Copyright © 2016 – Curt Hill

11. Perspectives
There are many different point of views in considering an architecture
Corresponding to these different perspectives are representations of the architecture
Sommerville promotes the 4+1 model
Copyright © 2016 – Curt Hill

12. 4 + 1
Copyright © 2016 – Curt Hill

13. 4 + 1 Pieces Logical – how the system interfaces with the end users
Development – programmer view
Process – communication of the various processes of the system
Physical – considers machines and communication lines
Scenarios – a series of use cases that show how the pieces interact
Copyright © 2016 – Curt Hill

14. Representation
There is a large variance of opinion on how formal (and permanent) architectural representations should be
The informal extreme are box and line diagrams
ERDs, UMLs and DFDs are in somewhere in the middle
How many of these are familiar to you?
The formal extreme has substantial semantics
Copyright © 2016 – Curt Hill

15. Box and Lines Two components: These do not show:
A rectangle indicates a component
A single or double headed arrow indicates communication flow
These do not show:
Component properties
How the pieces relate
Very understandable at a very abstract level
Makes them helpful for non-technical stakeholders
Copyright © 2016 – Curt Hill

16. Example (Sommerville)
Vision System
Object Identification System
Arm Controller
Gripper Controller
Packaging Selection System
Conveyor Controller
Packing System
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17. UML
The original paper was written by Kruchten, who was working at Rational Software
They are known proponents of UML
Not surprisingly there are one or more UML type diagrams for each of the four views
Somerville is unenthusiastic
UML encompasses many different types of diagrams
Not yet the next two
Copyright © 2016 – Curt Hill

18. Entity Relationship Diagrams
A favorite of DBers
Rectangle is an entity
Diamond is a relationship
Lines connect these and show arity
Either this was seen or will be seen in the database class or a separate presentation is forthcoming
Copyright © 2016 – Curt Hill

19. DFD Data Flow Diagrams Show how the data flows though a system
Arrows show the flow
An open box is a database or file
A rounded rectangle is process that transforms the data
Like ERDs this will receive another presentation if needed
Copyright © 2016 – Curt Hill

20. DFD Example
Copyright © 2016 – Curt Hill

21. Finally
Finally we need to focus on designing the objects of a program using design patterns
First we must consider a survey of numerous design patterns
In the next presentation
Copyright © 2016 – Curt Hill