Objectives • What is logical architecture? • What is the presentation layer? • What is the business logic layer? • What is the data layer?
Logical vs. Physical Architecture • Logical Architecture • Attempts to define the system in terms of its software components and the desired functionality of those components • Physical Architecture • Defines the hardware needed to host and maintain a website
Logical Architecture Four main logical models have evolved over the years: • Mainframe: systems are built around a single, monolithic computer that is shared by all users on the system • Client/Server: a central server is used to store information that is accessed and acted upon by any number of client machines connected to the server through a network
Logical Architecture (cont’d) • N-Tier: compartmentalizes different functions of a system into modules that interact with one another • Distributed: is a system of servers, loosely coupled across a dispersed network, that work together to deliver a website
N-Tier Architecture PCs with Web Browsers Presentation Layer Business Logic Layer Data Layer
Distributed Architecture External Payment Processing PCs with Web Browsers External Link Three-Tier System Internal Link Internal Inventory System
Three-Tier Architecture Presentation Browsers Payment User/Admin Content Business Logic Web Server Data Database
The Data Layer • The main function of the data layer is to provide fast, reliable access to data needed to run a system • Additionally, the data layer is responsible for maintaining information about the relationships between data
Types of Databases • Flat-File: are simple computer files that store all of the information for a system • Relational: data are stored in a series of tables, each table stores a discrete piece of data for the system • Object Oriented: encapsulates all data into different types of objects
The Business-Logic Layer • The business-logic layer is responsible for implementing the basic rules of the system according to the operating rules of the business • This layer is often divided into a number of submodules, each handling different aspects of the system
The Presentation Layer • The presentation layer is responsible for all communications with the user’s computer • The most common ways to present data to site users are: • HTML • ASP • JSP
Exercises • What is the difference between logical and physical architecture? • What is a distributed architecture? • What are the three layers of a three-tier architecture?
Summary • What is site logical architecture? • What is the presentation layer? • What is the business logic layer? • What is the data layer?