CSUN Information Systems
Systems Analysis & Design
http://www.csun.edu/~dn58412/IS431/IS431_F15.htm
Systems Design &
Application Architecture
IS 431: Lecture 8
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Systems Design &
Application Architecture
 Design Phase in Systems Development Life Cycle
 In-house vs. Commercial-of-the-shelf (COTS)
Application Development.
 Application Architecture: Data, Processes, Interface
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Physical Data Flow Diagrams (DFDs)
Distributed vs. Centralized Systems
Client/Server Architecture
Interface Architecture
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Systems Design in SDLC
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Systems Design
 Information systems design: tasks that focus on
the specification of a detailed computer-based
solution (also called physical design.)
 Systems analysis emphasizes on the business
problem, (WHAT) whereas systems design
emphasizes on the technical or implementation
concerns of the system (HOW).
 BUILD (In-house) vs. BUY (COTS)
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System Design of an
In-House Projects (BUILD)
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Design Tasks of
an In-House Project
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Design Tasks of
an In-House Project …
 Design the Application Architecture
– Defines the technologies to be used and used to build
– Physical Data Flow Diagram
 Design the System Databases
– Database schema (Data Dictionary)
 Design the System Interface
– User Interfaces: Input, output, and dialogue specifications
– Prototypes
 Package Design Specifications
– Specifications to guide programmers
 Update Project Plan
– Modified Budget/Schedule
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System Design for a
COTS Solution (BUY)
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Tasks for COTS Solution
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Tasks for COTS …
 Research Technical Criteria and Options
 Solicit Proposals/Quotes from Vendors
 Validate Vendor Claims and Performances
 Evaluate and Rank Vendor Proposals: Gap
Analysis on the differences between proposed and
desired features. Cost/Benefit Analysis.
 Contract “Winning” Vendor and Debrief “Losing”
Vendors
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Application Architecture
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Application Architecture
An application architecture specifies the
technologies to be used to implement one or more
(and possibly all) information systems in terms of
DATA, PROCESS, and INTERFACE, and how
these components interact across a network. It
serves as an outline or blueprint for detailed design
and implementation.
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Application Architecture …
The blueprint to communicate the following design
decisions:
– The degree to which the information system will be
centralized or distributed.
– The distribution of stored data.
– The implementation technology for software developed
in-house.
– The integration of commercial off-the-shelf software.
– The technology to be used to implement the user
interface.
– The technology to be used to interface with other systems
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DFD Deliverables
for a System
Development Project
 CURRENT SYSTEM (AS-IS)
– Context Diagram
– Logical Level-0 DFD
– Logical Level-1 DFD’s (for multi-task functions)
(No Physical DFD for current system, unless the focus
of the project is security & control)
 PROPOSED SYSTEM (TO-BE)
– Context Diagram
– Logical Level-0 DFD Level-0
– Logical Level-1 DFD’s (for multi-task functions)
– Physical Level-0 DFD Level-0
– Physical Level-1 DFD’s (for multi-task functions)
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Physical Data Flow
Diagrams (DFDs)
Physical data flow diagrams (DFDs) model the
technical and human decisions to be implemented as
part of an information system (HOW, BY WHOM).
Physical DFDs communicate technical choices and
other design decisions to those actually construct and
implement the system.
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A Physical DFD
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Physical Processes
A physical process is either a processor, such as a
computer or person, or a technical implementation of
specific work to be performed, such as a computer
program or manual process.
Logical Process
4.3
Check
Customer
Credit
Sample Physical Process Implementations
4.3
4.3
4.3
4.3
Check
Customer
Credit
Check
Customer
Credit
Check
Customer
Credit
Check
Customer
Credit
Acct Clerk
COBOL/CICS
Visual Basic
Quickbooks
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Computerized Process
Implementation
 A purchased application software package (COTS)
 A system or utility program
 An existing application program with possible
modification
 A program to be written
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Physical Data Flows
A physical data flow represents any of the following:
– The planned implementation of an input to, or output
from a physical process.
– A database command / action such as create, read,
update, or delete.
– The import of data from, or the export of data to another
information system across a network.
– The flow of data between to modules or subroutines
(represented as physical processes) in a program.
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Physical Data Flows …
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Physical Data Flows …
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Physical Data Stores
A physical data store represents the planned
implementation of one of the following:
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–
–
–
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A database
A table in a database
A computer file
A tape or media backup of anything important
A temporary file or batch
Any type of noncomputerized file
(paper file folders, accounting books etc…)
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Physical Data Stores…
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Distributed vs.
Centralized Systems
Distributed system : DATA, PROCESS, and
INTERFACE components of an information system
are distributed to multiple locations in a computer
network. Accordingly, the processing workload is
distributed across the network.
Centralized systems : a central, multi-user computer
hosts all the DATA, PROCESS, and INTERFACE
components of an information system. Users interact
with the system via terminals (or terminal emulators).
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Why Distributed Systems?
 Modern businesses are already decentralized and
distributed.
 Distributed computing moves information and
services closer to the customers and users who need
them.
 Distributed computing consolidates the power of
personal computers across the enterprise.
 Distributed computing solutions are more userfriendly because they utilize the PC as the end user
interface.
 Personal computers and network servers are cheaper
than centralized mainframe computers.
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Distributed Computing
Layers
 Presentation layer—the user interface
INTERFACE
 Presentation layer logic—such as input editing
 Application logic layer—the business rules, policies, and
procedures
PROCESS
 Data manipulation layer—to store and retrieve data to and
from the database
DATA
 Data layer—the actual business data
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Distributed Computing
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File Server Architecture
A local area network (LAN) is a set of client computers (PCs)
connected to one or more server computers either through cable
or wireless connections over relatively short distances.
A file server system is a LAN-based solution in which a server
hosts only the data layers of an information system. All other
layers are implemented on the client computers. Disadvantages
include:
– Frequently excessive network traffic to transport data between
servers and clients.
– Client must be fairly robust (“fat”) because it does most of the work
– Database integrity can be easily compromised.
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Client/Server Architecture:
The Clients
A client/server system is a solution in which the
presentation, presentation logic, application logic, data
manipulation, and data layers are distributed between
client PCs and one or more servers.
• A thin client is a personal computer that does not have very
powerful processor speed and memory because it only presents
the user interface to the user.
• A fat client is a personal computer or workstation that has
typically more powerful processor speed, memory, and storage
capacity. It has software applications to process data at the
client site.
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Client/Server Architecture:
The Servers
 A database server hosts one or more shared databases but
also executes all data manipulation commands.
 A transaction server hosts services that ultimately ensure
that all database updates for a single transaction succeed or
fail as a whole.
 An application server hosts the application or business
logic and services for an information system.
 A messaging or groupware server hosts services for email, calendar, and other work group functionality.
 A web server hosts Internet or intranet web sites and
services, communicating through thin-client interfaces such
as web browsers.
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Client/Server :
Distributed Presentation
A distributed presentation client/server system is a
solution in which the presentation and presentation
logic layers only are shifted from the server to reside
on the client.
The application logic, data manipulation, and data
layers remain on the server (frequently a mainframe).
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Client/Server:
Distributed Data
A distributed data client/server system is a solution
in which
1) the data and data manipulation layers are
placed on the server(s),
2) the application logic, presentation logic, and
presentation layers are placed on the clients.
Also called two-tiered client/server computing.
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Client/Server:
Distributed Data and Application
A distributed data and application client/server
system is a solution in which:
1) the data and data manipulation layers are placed
on their own server(s),
2) the application logic is placed on its own server,
3) the presentation logic and presentation layers
are placed on the clients.
Also called three- or n-tiered client/server computing.
It requires design partitioning to distribute or
duplicate application components (DATA,
PROCESS, and INTERFACE) across the network.
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Internet- and Intranetbased Architectures
A network computing system is a multi-tiered
solution in which the presentation and presentation
logic layers are implemented in client-side Web
browsers using content downloaded from a Web
server. The presentation logic layer then connects to
the application logic layer running on the application
server, which subsequently connects to the database
servers on the backside of the system.
An intranet is a secure network, usually corporate,
that uses Internet technology to integrate desktop,
work group, and enterprise computing into a cohesive
framework.
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Data Architectures
•A relational database stores data in tabular form.
Each file is implemented as a table. Each field is a
column in the table. Related records between two
tables are implemented by intentionally duplicated
columns in the two tables (Primary and Foreign Keys).
•A distributed relational database distributes or
duplicates tables to multiple database servers located
in geographically important locations.
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Data Distribution Options
 Store all data on a single server (Centralization)
 Store specific tables on different servers.
 Store subsets of specific table(s) on different servers
– Subsets of columns (Vertical Partitioning)
– Subsets of rows (Horizontal Partitioning)
 Replicate (duplicate) specific tables or subsets on
different servers for back up (Replication)
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Database Distribution
• Data partitioning truly distributes rows and columns of
tables to specific database servers with little or no duplication
between servers.
– Vertical partitioning assigns different columns to
different servers.
 Sensitive data columns, Transactional data columns
– Horizontal partitioning assigns different rows to
different servers.
 Customers in LA; Customers in SF
• Data replication duplicates some or all tables (or parts of
tables) on more than one database server. Database technology
controls access to, and manages consistency of duplicated data
across the servers.
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Database Distribution
Vertical partitioning
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Database Distribution
Horizontal partitioning
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Database Distribution
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Database Distribution
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Data Partitioning vs.
Data Replication
Logical Data Store
1
2
CUSTOMERS
PRODUCTS
Physical Data Stores
using Partitioning
1P.#
Oracle 7:
REGION 1
CUSTOMERS
1P.#
Oracle 7:
REGION 2
CUSTOMERS
Not applicable. All
branch offices need
access to data for all
products, regardless of
sales region.
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Physical Data Stores
using Replication
Not applicable. Branch
offices do not need
access to data about
customers outside of
their own sales region.
2M
Oracle 8i:
PRODUCTS
(Master)
2R
Oracle 8i:
PRODUCTS
(Replicated Copy)
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Interface Architectures
How to get input and display output of the system:
 Batch inputs and outputs
 On-line inputs and outputs
 Remote batch
 Keyless data entry (and automatic identification)
 Pen input
 Electronic Data Interchange (EDI)
 Middleware (BizTalk)
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Design Units
Design unit – a self-contained collection of processes,
data stores, and data flows that share similar design
characteristics.
– A design unit serves as a subset of the total system whose
inputs, outputs, files and databases, and programs can be
designed, constructed, and tested as a self-contained unit.
– Ultimately, design units must be integrated into a whole
system.
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Application Architecture
Strategies for System
Design
 The Enterprise Application Architecture Strategy
– Enterprise-wide information technology architecture to be followed
in all subsequent development projects.
 Approved network, data, interface, and processing technologies
and development tools.
 Strategy for integrating legacy systems and technologies.
 On-going process for continuously reviewing application
architecture.
 On-going process for researching emerging technologies
 Process for analyzing requests for variances from the above.
 The Tactical Application Architecture Strategy
– Defines architecture for each new system on an application-byapplication basis as needed.
– Requires feasibility analysis for each application.
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