Architecture 2 J2EEOverview.pdf

Computer Systems Architecture Adapted from material provided by Sang Shin at www.javapassion.com 1 Objectives     To introduce computer system architecture concepts. To discuss logical and physical tiers To look at a typical layered architecture for a single tier. To present a typical N-Ti...

Computer Systems Architecture Adapted from material provided by Sang Shin at www.javapassion.com 1 Objectives     To introduce computer system architecture concepts. To discuss logical and physical tiers To look at a typical layered architecture for a single tier. To present a typical N-Tier architecture that uses Java technology. 2 Introduction to Computer Systems Architecture 1   The structural arrangement of the major components of both the hardware and software from which a computer system is composed defines the architecture of a system. Since networking is often a key aspect of most modern computer systems the functionality provided is often distributed across multiple computer systems. 3 Introduction to Computer Systems Architecture 2    The layers of software present on a specific system to provide services to software components are often referred to as a tier. Complicated computer systems often employ multiple logically separated and/or physically separated tiers. Lower level layers in a tier provide services to the higher level layers in a tier. 4 Terminology  Presentation Logic   Business Logic   Functionality which deals with the display of information. Functionality which deals with the processing of information, the execution of commands and the coordination of application execution Data Access Logic  Functionality that makes it easy to access the data held in a data store such as a database. 5 Single Tier (Mainframe-based)‫‏‬    Dumb terminals are directly connected to a mainframe A centralized model as opposed to a distributed model.‫‏‬ Presentation logic, business logic, and data access logic are intertwined in one monolithic mainframe application 6 Single Tier (Workstation Based)‫‏‬    The user employs a single workstation e.g. PC, Mac and a single application e.g. Microsoft Word, Photoshop. Not a distributed architecture since the application does not employ network connectivity.‫‏‬ Presentation logic, business logic, and data access logic are intertwined in a single‫„‏‬Fat‫‏‬Client‟‫‏‬application. 7 Single-Tier: Pros & Cons  Pros:   Data consistency is easy to achieve Cons:   Functionality (presentation logic, business logic , data access logic) intertwined Difficult to apply updates 8 Two-Tier SQL request Database SQL response  Fat client software applications talking to a database server   SQL queries sent, raw data returned Presentation Logic ,Business logic and Data Access Logic intertwined in the fat client applications 9 Two-Tier: Pros and cons  Pros:   Shared Database between clients‫‏‬ Cons:     Presentation logic, business logic and data access logic are intertwined (at client side), difficult for updates to be applied Data‫‏‬Model‫‏‬is‫“‏‬tightly‫‏‬coupled”‫‏‬to‫‏‬every‫‏‬client:‫‏‬If‫‏‬the‫‏‬ Database Schema changes, all clients break Database connection for every client, thus difficult to scale (Database connections use a lot of system resources) Raw data transferred to client for processing causes high network traffic 10 Three-Tier   Many different technologies can be used in a three tier computer system Three Tier examples include:   Three tier: Remote Object based Three tier: Web/Application server based 11 Three-Tier (Remote Object based)‫‏‬ Object request Object response   SQL request SQL response Database Business logic and data access logic are encapsulated in objects hosted on a middle tier server. OMG CORBA, Sun Microsystems RMI and Microsoft .Net remoting are the typical technologies used 12 Three-tier (Remote Object based): Pros & Cons  Pro:   Middle Tier server code can be shared between clients Cons:  Complexity can be a problem in the middletier 13 Three-Tier (Web/Application Server)‫‏‬ HTML request HTML response    WEB Server SQL request SQL response Database Browser (A Thin Client) only handles presentation of web pages provided by a server. The browser may also execute some presentation logic code embedded in the pages it presents. HTTP protocol used for browser/ server interaction Business logic and data access logic are handled by “dynamic‫‏‬content‫‏‬generation”‫‏‬technologies‫(‏‬CGI,‫‏‬ Servlet/JSP, ASP.NET)‫‏‬ 14 Three-tier (Web/Application Server based): Pros & Cons  Pros:    Ubiquitous client types Zero client management Supports various client hardware platforms   cell-phones and other hand held devices. Cons:  Complexity can be a problem in the middletier since it hosts the presentation logic, business logic and data access logic. Moving to n-tier can overcome this. 15 Trends  The industry is moving from:    Single-tier and two-tier to multi-tier architecture Procedure based application development to Object-Oriented application development using software components Fat client applications to thin client applications that use HTML to present their user interface. 16 Single Tier / Multi Tier Comparison Single tier   No separation between presentation logic, business logic and database access logic Hard to maintain Multi-tier   Separation between presentation logic, business logic and database access logic More flexible when making changes, i.e. presentation logic can change without affecting the other tiers 17 Monolithic / Object-based Software Comparision Monolithic Object-based    1 Binary file Recompiled, relinked and redeployed every time there is a change     Pluggable Components Reusable Components Promotes better design Easier to update Implementation can be separated from interface, only the interface is published 18 Layers    A common approach to software architecture involves arranging software into a set of layers. Lower level layers in a layer stack provide services and functionality to higher level layers. Examples of the services that might be provided by a layer are the rendering of graphics objects on a display and the passing of information, without any corruption, between the software tiers present on different computer systems. 19 Layering Examples    The seven layer International Standards Organisation (ISO) Open Systems Interconnect (OSI) model. The TCP/IP five layer model often called the Internet reference model. The Direct X and OpenGL computer graphics programming interfaces. 20 TCP/IP 5-Layer Reference Model  Also‫‏‬called‫„‏‬Internet‫‏‬Reference‫‏‬Model‟ Application Layer : contains functionality used by users of the system or which hosts or contains components that provide functionality e.g Web Browser, email client , FAT client in two tier system Transport Layer : Contains the functionality to allow data to be transferred reliably between tiers Internet Layer : Contains the functionality to allow data to be routed between tiers Network Access Layer : Provides the functionality to allow a tier to pass information over its physical network hardware. Physical Layer : allows the data bits and bytes to be passed across the physical connections between tiers. 21 Example N-tier Architecture (Using Java Technology) Web Tier EJB Tier 22