System Architecture Design
Chapter 10
Key Definitions
The system architecture design consists
of plans for the hardware, software,
communications, security , and global
support for the new application
The designers must decide if processing
will occur in the server (server-based), at
the personal computer (client-based), or
in some combination of these (clientserver based).
Key Definitions
The network model shows major
components of the system, where
they are located and how they will
be connected to one another.
The hardware and software
specifications describe these
components in detail and aid those
responsible for purchase and
acquisition of these products.
COMPUTING
ARCHITECTURES
Functions of the
Application System
Data storage
Data access logic
Application logic
Presentation logic
Architectures
Server based
Client based
Client-server based
Alternative Servers
In server based architectures,
the servers do the work and
present the results
Mainframe
Minicomputer
Microcomputer (personal
computer)
Server-Based Computing
Alternative Clients
In client based architectures, clients
do most of the work (except data
storage) and present the results
Terminals
Microcomputer (personal computer)
Special purpose terminals
(ATMs, kiosks, Palm Pilots,
and many others)
Client-Based Computing
Client-Server-Based
Computing (2 Tiers)
Client-Server Attributes
Typical Pros
Compatible with
web-based system
design
Scaleable
Work with multiple
vendors/products
No central point of
failure
Typical
Cons/Limits
Complexity
New programming
languages and
techniques (stress
for personnel)
More complex to
update
Client-Server -- Three
Tiers
Client-Server -- Four Tiers
N-Tiered Client-Server
Attributes
Typical Pros
Separates
processing to
better balance
load
More scaleable
Typical
Cons/Limits
Greater load on
the network
More difficult to
program and
test
Distributed Objects
Computing
Middleware between clients and
servers
Update middleware when changing
client code
May reduce efficiency of the
application
CORBA
DCOM
Realities of Infrastructure
Design
Most often the infrastructure
will be in place
Coordination of infrastructure
components is very complex
The application developer will
need to coordinate with
infrastructure specialists
Selecting a Computing
Architecture
Server-Based
Client-based
Client-server
Cost of infrastructure
Very high
Medium
Low
Cost of development
Medium
Low
High
Ease of development
Low
High
Low-medium
Interface capabilities
Low
High
High
Control and security
High
Low
Medium
Scalability
Low
Medium
High
INFRASTUCTURE
DESIGN
The Network Model
No standard format
Conveys complexity of the system
and how components fit together
Components are
Clients
Equipment
Connection to external systems or
networks
Top-Level Network Model
Hardware and Software
Specification
Used if new hardware or
software must be purchased
Actual acquisition of hardware
and software usually left to a
purchasing department -especially in larger firms
Steps in Hardware and
Software Specification
Note hardware in low-level network
model to create list of needed hardware
Describe equipment in as much detail as
possible
Consider whether increased processing
and traffic will absorb unused hardware
capacity
Note all software running on each
hardware component
GLOBAL ISSUES
Global Requirements
Multilingual requirements
Concurrent multilingual systems
Discrete multilingual systems
Local versus centralized control
Unstated norms (e.g. dates,
currency)
24-7 Support
Communications infrastructure
SECURITY
Identifying Threats to the
System
A threat is any potential adverse
occurrence that can do harm to the
application or its data
Threats come from internal as well
as external sources
Categories of threats
Disruptions, destruction and disaster
Unauthorized access
Most Common Threats
Assessing the Risk of Each
Threat
Creating Controls
A control is something that
mitigates or stops a threat
Controls include
redundancy
fault tolerant servers
disaster recovery plans
anti-virus software
Additional Controls
Include
A security policy
Passwords and encryption
Firewalls
Summary
The three fundamental computing
architectures are server-based, client-based,
and client-server based.
The network model shows technical
components of the system and their
geographic location throughout the
organization.
Hardware and software must be specified for
acquisition in the project
The systems analyst needs to also account
for global issues and security measures.