Remarks%20on%20Software%20Design

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Remarks onSoftware Design
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Todays Lecture

• System design and implementation design
• System design

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Informatics 43 View

• Architecture design
• high-level partitioning of a software system into
  separate modules (components)
• focus on the interactions among parts
  (connections)
• focus on structural properties (architecture)
• How does it all fit together?
• Module design
• detailed design of a component
• focus on the internals of a component
• focus on computational properties
• How does it work?

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Informatics 121 View

• System design
• describes what the software system should do
• focus towards addressing Goal and Domain of Use
• How do we fundamentally approach the problem?
• typically represents an intermediate design in
  progress
• architecture design can be part of system design
• Implementation design
• describes what the implementer should do
• focus towards addressing Domain of Materials
• How do we make the approach reality?
• typically represents a final completed design
• module design can be part of implementation design

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Definitions

• A system design captures the essence of the
  solution
• customers
• system designers themselves
• implementation designers
• testers
• An implementation design captures the full
  solution
• system designers
• implementation designers themselves
• programmers
• testers

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Design Diamond
Domain of Materials
Implementation Design
Representation
System Design
Activity
Ideas
concern
manipulates
informs
Goal
captures
enhances
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Design Diamond
Domain of Materials
Representation
System Design
Activity
Ideas
concern
manipulates
informs
Goal
captures
enhances
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Traditional View of System Design
SystemDesign
architecture
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Traditional View of System Design
SystemDesign
architecture
or...
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Traditional View of System Design
SystemDesign
Statecharts
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Traditional View of System Design
SystemDesign
Statecharts
or...
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Traditional View of System Design
UML
SystemDesign
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Traditional View of System Design
UML
SystemDesign
or...
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Traditional View of System Design
SystemDesign
Data Flow Diagrams
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Traditional View of System Design
SystemDesign
Data Flow Diagrams
or...
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Traditional View of System Design
SystemDesign
Data Flow Diagrams
etc., etc., etc.
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Informatics 121 View of System Design
Booch

pi calculus
informal drawing
UML
SystemDesign
pseudo code
architecture
text
code
data flow diagrams
JSD
Statecharts
any and all as needed
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Design Concerns

• A typical design problem consists of many
  different concerns that must all be addressed by
  a design solution
• Some of these concerns are more important and/or
  have more impact than others
• I want my e-commerce site to have a recognizable
  logo versus My e-commerce site must scale to 1
  million hits per minute
• Sometimes, the importance and/or impact of a
  concern is not obvious (the devil is in the
  details)
• I want my payroll software to properly handle
  the exchange rate

As a designer, you need to find the concernsthat
are most important and have most impact
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Design Depth

• Some concerns need to be designed in much greater
  depth than others
• call control sequence of a cell phone versus the
  menu input mechanism of that same cell phone
• This depth relates to
• importance
• impact
• audience
• This depth usually requires a rationale

As a designer, you need to work out each
concernto the appropriate level of depth needed
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Design Depth
Concern 1
Concern 2
Concern 3
Concern 4
Concern 5
Concern 6

System A
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Design Depth
Concern 11
Concern 12
Concern 13
Concern 14
Concern 15
Concern 16

System B
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Design Depth
Concern 21
Concern 22
Concern 23
Concern 24
Concern 25
Concern 26

System C
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The Essence of a Design Solution Where?

• Structure
• Context
• Communication
• User interface
• Persistence
• Algorithms
• Naming
• Interchange

• Internal data structures
• Error handling
• Distribution
• Glue

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The Essence of a Design Solution Where?

• Often, the essence is located in multiple places,
  related or unrelated
• internal data structures and persistence
• communication and protocols
• user interface, persistence, and internal data
  structure
• The essence usually constitutes a nucleus of
  concerns of high importance and high impact
• The essence needs to be detailed at an
  appropriate depth
• The essence needs to be captured in one or more
  appropriate design notations

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Structure

• Why may the essence be found here?
• what if the design concerns a distributed
  application?
• what if the design concerns a highly scalable
  application?
• what if the design concerns a business
  application with highly changeable business
  rules?
• What may be a good design notation?
• software architecture
• UML2 component diagrams
• simple drawings

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Structure Examples
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Architecture Examples
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Context

• Why may the essence be found here?
• what if the design concerns an integrated system
  constituting many existing systems?
• what if the design concerns an application that
  will automate a significant portion of an
  organizations business?
• what if the design concerns an application
  spanning multiple businesses?
• What may be a good design notation?
• context diagrams
• informal drawings of external entities

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Context Examples
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Context Examples
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Communication

• Why may the essence be found here?
• what if the design concerns a sensor network
  consisting of many different sensors emitting
  much different data?
• what if the design concerns network quality of
  service?
• what if the design concerns a broadcasting
  satellite?
• what if the design concerns a document-centric
  system?
• What may be a good design notation?
• labeled transition systems
• UML sequence diagrams
• data flow diagrams
• protocols

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Communication Examples
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Communication Examples
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Communication Examples
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User Interface

• Why may the essence be found here?
• what if the design concerns real-time
  visualization?
• what if the design concerns multiple kinds of
  displays?
• what if the design concerns a drawing program?
• what if the design concerns a new interaction
  mechanism?
• what if the design concerns an e-commerce system?
• What may be a good design notation?
• sketches
• mock-ups
• interaction scenarios
• prototypes

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User Interface Examples
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User Interface Examples
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Persistence

• Why may the essence be found here?
• what if the design concerns a database
  application?
• what if the design concerns a system that must be
  fail safe?
• what if the design concerns an application that
  must span multiple sessions?
• What may be a good design notation?
• entity-relationship diagram
• file format definition
• UML class diagram
• database schema

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Persistence Examples
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Persistence Examples
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Algorithms

• Why may the essence be found here?
• what if the design concerns a search engine?
• what if the design concerns encryption?
• what if the design concerns a scheduling tool?
• what if the design concerns a file converter?
• What may be a good design notation?
• pseudo code
• flow chart
• Petri net

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Algorithms Examples
public boolean moveRobot (Robot aRobot)    
//IF robot has no obstacle in front THEN        
// Call Move robot         // Add the move
command to the command history         // RETURN
true     //ELSE         // RETURN false without
moving the robot     //END IF
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Algorithms Examples
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Algorithms Examples
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Naming

• Why may the essence be found here?
• what if the design concerns a distributed system?
• what if the design concerns replicated data?
• what if the design concerns a complex set of
  interrelated data items?
• What may be a good design notation?
• examples and counterexamples
• regular expressions

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Naming Examples
http//www.clothes.com/mens/shirts/formal.html
http protocol // separators
www.clothes.com/ domain name mens/
subdirectory name shirts/ subdirectory
name formal.html document name (Web page)
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Naming Examples
D/eclipse/edu/uci/isr/palantir/core/PalantirPlugi
n1.2.80c318ce.109c2515402.f96511d31371ce2.0nu
ll artifactID filenameVIDwsIDparentID par
entID artifactID null VID 0-9. wsID
a-b0-9. filename ltltcontinue with regular
expression for pathnamesgtgt
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Interchange

• Why may the essence be found here?
• what if the design concerns a manufacturers
  supply chain management system?
• what if the design concerns a credit report
  system?
• what if the design concerns an airline booking
  system?
• What may be a good design notation?
• ontology
• data declarations
• application programmer interface

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Interchange Examples
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Interchange Examples
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The Essence of a Design Solution Where?

• Structure
• Context
• Communication
• User interface
• Persistence
• Algorithms
• Naming
• Interchange

• Internal data structures
• Error handling
• Distribution
• Glue

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Informatics 121 View of System Design
Booch

pi calculus
informal drawing
UML
SystemDesign
pseudo code
architecture
text
code
data flow diagrams
JSD
Statecharts
any and all as needed
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Pocket Guide to System Design

• Consider your goals and identify key issues
• what is at the heart of the system?
• what do people (including you) need to understand
  about this system?
• Choose design notations that will help you
  explain these issues
• what depth of understanding is needed?
• what does your audience already know?
• Remember to reflect on these representations as
  you progress
• you will not have all the answers up front
  change course as needed