Transcript Document

ITEC 3010 “Systems Analysis and Design, I”
LECTURE 8-2:
Elements of Systems Design
[Prof. Peter Khaiter]
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Topics
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Elements of Design
Inputs for System Design
Design and Integrate the Network
Design the Application Architecture
Design the User Interfaces
Design the System Interfaces
Prototype for Design Details
Deployment Environment
Software Application Functions
Internet and Web-Based Application
Architecture
Middleware
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Elements of Design
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Design is process of describing, organizing,
and structuring system components at
architectural design level and detailed
design level
Focused on preparing for construction
Like developing blueprints
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Three questions
What components require systems design?
What are inputs to and outputs of design
process?
How is systems design done?
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Components Requiring Systems
Design
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Inputs for System Design
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Design
Converts functional models from analysis into models
that represent the solution
Focused on technical issues
Requires less user involvement than analysis
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Design may use structured or OO approaches
Database can be relational, OO, or hybrid
User interface issues
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Analysis versus Design
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Traditional
Structured
and ObjectOriented
Models
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SDLC Phases with Design Phase
Activities
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Design Phase Activities and Key
Questions
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Design and Integrate the Network
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Network specialists establish network based on
strategic plan
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Project team typically integrates system into
existing network
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Technical requirements have to do with
communication via networks
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Technical issues handled by network specialists
Reliability, security, throughput, synchronization
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Design the Application Architecture
and Software
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Specify how system use cases are carried
out
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Described during system analysis as logical
models of system activities
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After design alternative is selected, detailed
computer processing is designed as
physical models
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Approach varies depending on development
and deployment environments
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Design the User Interfaces
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User interface quality is critical aspect of system
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Design of user interface defines how user interacts
with system
GUI – windows, dialog boxes, mouse interaction
Sound, video, voice commands
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To user of system, user interface is the system
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User interface specialists – interface designers,
usability consultants, human factors engineers
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Design the System Interfaces
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System interfaces enable systems to share
and exchange information
Internal organization systems
Interfaces with systems outside organization
New system interfaces with package application
that organization has purchased and installed
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System interfaces can be complex
Organization needs very specialized
technical skills to work on these interfaces
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Design and Integrate the Database
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System analysis data model used to create
physical database model
Collection of traditional computer files, relational
databases, and/or object-oriented databases
Technical requirements, such as response times,
determine database performance needs
Design work might involve
Performance tuning
Integration between new and existing databases
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Prototype for Design Details
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Continue to create and evaluate
prototypes during design phase
Prototypes confirm design choices
Database
Network architecture
Controls
Programming environment
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Rapid application development (RAD)
design prototypes evolve into finished
system
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Design and Integrate the System
Controls
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Final design activity to ensure system has
adequate safeguards (system controls) to
protect organizational assets
Controls are needed for all other design
activities
User interface – limit access to authorized users
System interface – protect from other systems
Application architecture – record transactions
Database – protect from software/hardware
failure
Network design – protect communications
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Network Design
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Integrate network needs of new system
into existing network infrastructure
Describe processing activity and network
connectivity at each system location
Describe communications protocols and
middleware that connects layers
Ensure that network capacity is sufficient
Data size per access type and average
Peak number of access per minute or hour
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Computer Networks
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Set of transmission lines, specialized
hardware, and communication protocols
Enables communication among different
users and computer systems
Local area network (LAN) less than one
kilometer long – connects computers
within single building
Wide area network (WAN) over one
kilometer long – implies much greater,
global, distances
Router – directs information within
network
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A Possible Network Configuration
for RMO
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The Internet, Intranets, and
Extranets
Internet – global collection of
networks that use TCP/IP networking
protocols
 Intranets
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Private networks using same TCP/IP
protocols as the Internet
Limited to internal users
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Extranets
Intranets that have been extended
outside the organization
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Network Diagram for RMO
Customer Support System
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Deployment Environment
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Deployment environment definition
bridges analysis and design
Hardware
System software
Networking
Common deployment environments
in which system will operate
 Related design patterns and
architectures for application software22
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Application Architecture
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Complex hardware/networks require more
complex software architectures
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There are commonly used approaches
(patterns) for application architecture
Client/server architecture
Three-layer client/server architecture
Web services architecture
Internet and Web-based application
architecture
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Software Application Functions
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Presentation logic (i.e. HCI)
Application logic (i.e. the processing of business
rules processing)
Data access logic (i.e. the processing required
to access data – database queries in SQL)
Data storage (i.e. data files)
There are several alternatives for the processing
environment:
Centralized systems
Distributed computing
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Centralized systems
• Prior to the early 1970’s there was only one technological environment –
the mainframe computer system at a central location
• The only options focused around kinds of input/output (e.g., keypunch,
key-to-tape, or interactive input using video display terminal) and
whether input/output devices would be placed in remote locations
• Although they are no longer the preferred platform for deploying ISs,
they are still widely used as a subsystem of a larger, sometimes
distributed information system or for large-scale batch processing
applications (e.g., banking, insurance, government, etc.) where:
– Some input transactions don’t need to be processed in real time
– On-line data-entry personnel can be centrally located
– Large numbers of periodic outputs are produced by the system
There are three types of centralized systems: single, clustered and
multicomputer architectures
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Single Computer Architecture
• Places all information system resources on a single computer system
and its directly attached peripheral devices
• Users interact with the system via simple input/output devices directly
connected to the computer
• Requires all users be located near the computer
• All 4 software application functions are realized on a mainframe
computer (server host) – server-based architecture
Advantage:
• Simplicity of maintenance: relatively easy to design, build and operate
Disadvantage:
• The capacity limits make single computer impractical or unusable for
large ISs: cannot provide all the required processing, data storage, and
data retrieval tasks. However, many systems require more computing
power than one single machine can provide (a clustered or
multicomputer architecture is required)
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Single-Computer, Clustered, and
Multicomputer Architectures
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Server-based Architecture
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Clustered Architecture
• Clustered architecture is a group (or cluster) of computers
of the same type that have the same operating environment
and share resources
• Computers from the same manufacturer and model family are
networked together
• Application programs may be executed on any machine in the
cluster without modification due to similar hardware and
operating systems
• Cluster acts like a single large computer system (program
movement and access to resources on other machines occur
quickly and efficiently due to rapid and direct communication
at the operating system level)
• Often one computer may act as entry point and the others
function as slave computers
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Multicomputer Architecture
• Multicomputer architecture is a group of dissimilar computers that
are linked together but the hardware and operating systems are not
required to be a similar as in the clustered architecture
• Hardware and software differences do not allow movement of
application programs between computers (instead, resources are
exclusively assigned to each computer system)
• System still functions like one single large computer
• Can have central computer and slave computers
–Main computer may execute programs and hold database
–The front-end computer may handle all communication lines with
other computers or simple terminals
Notes on Centralized Systems
• Clustered architectures may be cost efficient and provide greater total
capacity if similar operating system and hardware are used
• Multicomputer architectures are good when the centralized system
can be decomposed into relatively independent subsystems (each
possibly with its own operating system and/or hardware platform) 30
Distributed Architecture
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Distributes system across several
computers and locations – distributed
computing
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Relies on communication networks for
geographic connectivity
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Client/server architecture dominant
model for distributed computing
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Client/Server Architecture
The dominant architectural model for distributing information
resources
• Two-tire architecture divides the information system
processes into two classes:
– Server: manages system resources and provides access
to those resources and services to other computers on the
network
– Client computer: uses communication interface to
requests services from other computers on the network
• Computer software that implements communication protocols
on the network is called middleware
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Advantage – deployment flexibility
Location, scalability, maintainability
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Disadvantage – complexity
Performance, security, and reliability
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Interaction Among Multiple
Clients and a Single Server
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Client/Server Architecture: shared
printer
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“Fat” Client Architecture
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“Fat” Server Architecture
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Three-Layer Client/Server
Architecture
• The data layer is a layer on a client-server configuration that
manages stored data implemented as one or more databases
• The business logic layer contains the programs that
implement the rules and procedures of business processing
(or program logic of the application)
• The view layer contains the user interface and other
components to access the system (accepts user input, and
formats and displays processing results)
• This approach is called tree-layer architecture
 The IS divided into three layer is relatively easy to distribute
and replicate across a network (interactions among the layers
are always have a form of either request or response)
 It makes the layer relatively independent of one another, thus
they can be placed on different computer systems with
network connections and middleware serving
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Three-Layer Architecture
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Three-Layer Architecture Software
Application Functions
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N-Layer Client/Server Architecture
• When processing requirements or data resources are complex, threelayer architecture can be expanded into a larger number of layers (nlayer or n-tiered architecture)
Next slide shows an example in which the data layer is split into two
separate layers: the combined database server and servers that control
the individual databases (marketing, production, accounting).
The business logic layer interacts with a combined database server that
provides a unified view of the data stored in several different
databases.
The responses from the individual database servers are then combined
to create a single response to send to the business logic layer.
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N-Layer Architecture
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Four-Tier Architecture
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Internet and Web-Based
Application Architecture
Web is complex example of
client/server architecture
 Can use Web protocols and browsers
as application interfaces
 Benefits
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Accessibility
Low-cost communication
Widely implemented standards
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Negative Aspects of
Internet Application Delivery
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Breaches of security
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Fluctuating reliability of network
throughput
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Throughput can be limited
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Volatile, changing standards
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Web Services Architecture
A client/server architecture
 Packages software functionality into
server processes (“services”)
 Makes services available to
applications via Web protocols
 Web services are available to internal
and external applications
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Developers can assemble an application
using existing Web services
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Web Services Architecture
(continued)
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Middleware
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Aspect of distributed computing
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Connects parts of an application and enables
requests and data to pass between them
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Transaction process monitors, object request
brokers (ORBs), Web services directories
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Designers reply on standard frameworks and
protocols incorporated into middleware
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Readings
Today’s lecture: Chapter 9 – “Elements
of Systems Design”
For next lecture: Chapter 11 – “ObjectOriented Design”
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