Physical Architecture Layer Design
Chapter 13
1
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 (client-server based).
2
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.
3
COMPUTING ARCHITECTURES
4
Functions of the Application System
Data storage
Data access logic
Application logic
Presentation logic
5
Architectures
Server based
Client based
Client-server based
6
Alternative Servers
In server based architectures, the servers do the
work and present the results
Mainframe
Minicomputer
Microcomputer (personal computer)
7
Server-Based Computing
8
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)
9
Client-Based Computing
10
Client-Server-Based Computing (2 Tiers)
11
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
12
Client-Server -- Three Tiers
13
Client-Server -- Four Tiers
14
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
15
Distributed Objects Computing
Middleware between clients and servers
Update middleware when changing client code
May reduce efficiency of the application
CORBA
DCOM
16
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
17
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
18
INFRASTUCTURE DESIGN
19
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
20
Top-Level Network Model
21
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
22
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
23
GLOBAL ISSUES
24
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
25
SECURITY
26
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
27
Most Common Threats
28
Assessing the Risk of Each Threat
29
Creating Controls
A control is something that mitigates or stops a
threat
Controls include
redundancy
fault tolerant servers
disaster recovery plans
anti-virus software
30
Additional Controls Include
A security policy
Passwords and encryption
Firewalls
31
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.
32