BUS 362 Lecture Notes - Lecture 1: Developed Market, Storage Area Network, Activex

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Chapter 8: Architecture Design
Architecture Design – plans for how the system will be distributed across multiple computers and what
hardware, operating system software, and application software will be used for each computer.
Non-functional requirements developed early in the analysis phase play a key role in architecture design
Hardware and software specification
oDefine what hardware and software are needed for the new system
Elements of an Architecture Design
The objective of architecture design is to determine how the software components of the information system
will be assigned to the hardware devices of the system.
Architectural Components
oMajor architectural components of any system are software and hardware
oAll software systems can be divided into four basic functions:
Data storage: information systems need to store and retrieve data e.g., data entities
documented in ERDS
Data access logic: the processing required to access data stored e.g. database entities in SQL
Application logic: the logic documented in the DFDs, use cases, and functional requirements
Presentation logic: the display of information to the user and the acceptance of the user’s
commands (user-interface)
oThe three primary hardware components:
Client computers: input-output devices employed by users (e.g., PCs. Laptops, handheld devices,
and smart phones)
Servers: larger multi-user computers used to store software and data
Network: connects the computers
Client-Server Architecture
oClient-server architectures balance the processing between client devices and one or more server
devices
oThe client is responsible for the presentation logic, whereas the server is responsible for the data
access logic and data storage
oApplication logic could reside on the client, the server, or split between both
oThick/fat client - contains all or most of the application logic
oThin client - contains a small portion of the application logic.
Thin clients are preferred – lower overhead and easier maintenance e.g. web-based systems
(web browser) performs presentation logic and minimum application logic. The server side has
most of the application logic and all of the data access logic and data storage
oClient-server architectures have four important benefits:
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Scalable – easy to increase and decrease storage capabilities of servers e.g. in case of an
overload simply add a server (separate server for each logic) and cost of upgrade is gradual.
Can support different types of clients and servers through middleware.
Connect different computers that use different OS so that you are not locked to one
vendor
Middleware is a software used to translate between different vendor software (installed
on both client computer and server computer)
Presentation logic, application logic, and data processing logic can be separated to be
independent.
It is possible to change the application logic without affecting or changing the
presentation logic or data, which are stored in databases and accessed by SQL
commands.
If a server fails, only the applications requiring the server are affected – the failed served can be
replaced
oThe major limitation is their complexity – they have software on the client side and on the computer and
writing this software is more complicated than writing the traditional all-in-one server software used in
server-based architectures.
oUpdating the software is complicated too – must update all clients and all servers
Client-Server Tiers
oThere are many ways in which the application logic can be partitioned between client and server
oTwo-tiered architecture
Server is responsible for the data and client is responsible for the application and the
presentation.
Uses only two sets of computers – clients and servers
oThree-tiered architecture
The software on the client computer is responsible for presentation logic, an application server
is responsible for the application logic and a separate database server (relational DBMS) is
responsible for data access logic and data storage
oN-tiered
Distributes work of the application (the middle tier) among multiple layers of more specialized
server computers
Common in today’s web-based e-commerce systems
Elements of business logic or detailed processing are stored on the application server and are
accessible to any application.
Can be used by multiple independent applications that need a particular business logic
The database servers manage the data components of the system.
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