Outline

• / architecture • Web basics Client / Server Networking • Browser / Server architecture

James Vorbach, Ph.D.

Client / Server architecture Client / Server architecture

• In a network, the difference between • A server stores a resource shared by two ‘client’ and ‘server’ computers is primarily or more clients the role played in executing applications • Typically, servers are more powerful • A client computer , or simply client, makes computers with greatgreaterer storage capacity requests which are satisfied by a server than clients in order to provide sufficient computer, or simply server capacity, process network transactions efficiently, and provide effective security

Server Types Two-tier architecture

• Application server – stores shared • Traditional two-tier client/server consists of programs a client-side application and a relational • Server –stores a particular database on the server proprietary database such as MS SQL , – Client – processes user input and formulates Oracle, DB2, Informix, and Sybase a query which is sent to the server • – stores web pages and web- – Server – executes the query and returns the results to the client related applications

1 n-tier architecture (n > 2) Motivation

• 3 or more levels in the network exist • Client / Server networking increases • Client – typically a thin client, which consists of productivity and reduces costs by minimal application-specific software – Sharing resources across the organization • – one or more levels consisting of – Application and database development and application servers maintenance costs are reduced, since only • Backend – database servers the servers store the resources • Example – Security is improved through control at the – Web-based applications such as eCommerce server-level applications

Web Basics Web Basics

• The World-Wide Web • Web browser – a collection of documents linked together via – a WWW program to view Web pages and the Internet interact with web servers – The documents include text, graphics, video, • Internet Explorer (IE) , Safari , Firefox and sound; a hypermedia collection – Hyperlinks embedded in documents allow you to jump from one document to another. – The world-wide web is also referred to as WWW or the Web

WWW standards and protocols WWW standards and protocols

• Uniform Resource Locator (URL) • HyperText Transfer Protocol (HTTP) – standard format for specifying an address on – a protocol for transferring Web documents the Internet • File Transfer Protocol (FTP) • Form – a protocol for transfer files over the internet; protocol://server-name/path… •Examples used for updating pages on web sites http://www.stjohns.edu • HyperText Markup Language (HTML) ftp://www.porres.org – a non-proprietary language for creating Web pages which is interpreted by a browser

2 WWW standards and protocols Browser / Server architecture

• Search Engine • Two–tier – Browser (client) sends a URL to a web server – a WWW program used in connection with a browser – Web server responds with a written in to search for information on the Web based on HTML keywords and/or categories. •N–tier • Google, Yahoo – Browser sends data from a user form to the server – Web server passes the data to the appropriate server-side application which constructs a query – Database server executes the query and returns the results – The server-side app packages the results in HTML to be returned by the web server to the client browser

Browser / Server Communication Embedded Applications

• Browsers communicate with web servers – Web pages may contain applications written via hypertext transfer protocol (HTTP) in languages other than HTML; such application are embedded within a page using • HTTP is stateless, i.e. no memory special tags – When a we b server rece ives a URL from a • VBscript, JavaScript, and Java are interpreted by browser, it responds with the corresponding browsers web page then ‘goes to sleep’ until the next – The user is transparent to the running of request embedded applications in a browser

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