An Introduction to WWW TechnologyPresentation OverviewPresentation Overview (cont'd)The InternetIntranetsIntranets (cont’d)Client/Server ArchitectureTypical Client: Web BrowserTypical Server: Web ServerWorld Wide WebHTMLHTML TagsPhysical Markup TagsLogical Markup TagsDocument StructureExampleLinking WWW PagesLinking WWW Pages (cont’d)URLsURLs (cont’d)URIsHTTPHTTP CookiesHTTP Cookies (cont’d)The Common Gateway Interface : CGICGI (cont’d)Downloaded codeMobile CodeScripting Languages: JavaScriptScripting Languages: VBScriptScripting Languages: VBScript (cont'd)Scripting languages and JavaJavaJava (cont'd)Java Virtual Machine (JVM)JVM (cont'd)Java for WWWJava appletsJava ServletsJava Servlets vs CGIThe Microsoft Active PlatformThe Microsoft Active Platform (cont’d)OLECOMCOM (cont’d)DCOMWindows DNAActive Desktop and Active ServerActive Server PagesJava Server PagesThin ClientThin Client (cont'd)Application ServersTypical Application Server: ColdFusionColdFusion (cont'd)Extensible Markup Language (XML)1An Introduction to WWW TechnologyYelena YeshaOlga Streltchenko2Presentation OverviewThe InternetClient/Server ArchitectureWorld Wide WebHTML, URLs, HTTPDownloaded and Mobile CodeCGIScripting languages (JavaScript/JScript, VBScript)3Presentation Overview (cont'd)JavaJava AppletsJava ServletsMicrosoft Active Platform (ASP, ActiveX)Java Server PagesThin ClientsApplication ServersXML4The Internet The Internet is a vast interconnected collection of computer networks of many different types.Large distributed system;Enables user to employ services like World Wide Web, Email, ftp, etc.;The set of services can be extended.ISPProvides connection to individual users and organizations enabling them to access services via the Internet;Provides local services, like Web hosting.5Intranets •A portion of the Internet that is separately administered and has a boundary that can be configured to enforce local security policies;•Connected to the rest of the Internet via a router;•Employ firewalls to prevent unauthorized access from outside;Go beyond password protection by disabling an entire class of services (ftp, telnet) for all but specified IP address. Passwords are still required.6Intranets (cont’d)Linked together by backbones.BackboneA network link with a high transmission capacity, employing fibre optics and other high-bandwidth circuits.7Client/Server ArchitectureThe terms “Client” and “Server” can be applied to both computer programs and to machines. Server provides services like receiving and executing instructions, sending results. processes, objects Server runs continuously, waiting for clients’ requests. processes, objects8Typical Client: Web BrowserDisplays files for readingDownloads as neededSends requests (filenames) and processes responses (file contents)9Typical Server: Web ServerListens for and fulfils requests from Web browsersBasic activities: receive simple URL specifying an HTML file; locate the file locally; return to requesting browser.10World Wide WebWWW is an application of the Internet.Evolving system for publishing and accessing resources and services across the Internet.Open system: can be extended and implemented in new ways without disturbing its existing functionality;Moved beyond simple data resources to encompass services, like electronic purchasing of goods.11HTMLHyperText Markup Language.Used to specify the text and images that make up the contents of a web page, and to specify how they are formatted for presentation to the user.The set of markups (tags) is fixed.12HTML TagsTags come either singly or in pairs:<HR><TAG>Some text here</TAG> (Tags are case insensitive)13Physical Markup TagsThey change the physical appearance of the text directly -- the WWW browser has no influence over the typeface used,Section titles/headers; use H1 through H6 tags:<H1>Big and Bold Header</H1><H2>Slightly Smaller Header</H2>Also, H3, H4, H5 and H6Font styles<B> Bold </B> <I> Italics </I> <U> Underlined </U> <TT> are in Typewriter font </TT>14Logical Markup TagsThey give a specific reason for changing the appearance of text -- it is up to the browser to decide in what fashion to change the appearance. <EM> Emphasized </EM> : Emphasized <STRONG> Strong </STRONG> : Strong <CODE> some code </CODE> : some code <CITE> citation </CITE> : This is a citation15Document StructureDocument Structure<HTML> This surrounds the entire document and lets the browser know what language is being used (<SGML> might also be used)<HEAD> This surrounds the header portion of the document. Title is within the head as well. <TITLE> The title of the document as shown in the title bar of the WWW browser. <BODY> The main body of the document16Example <HTML> <HEAD> <TITLE> Title of Page </TITLE> The Header of the document. </HEAD> <BODY> The Main body of the document </BODY> </HTML>17Linking WWW PagesHTML pages on the Web are linked to one another.The basic tag for hypertext is called the AnchorAnchors can bethe starting point for a link: a name proceeded by a #;the destination (path) of a link.A URL is placed in the HREF portion of the Anchor tagThe HREF can be either a Relative: <A HREF = "http://www.cs.umbc.edu/~streltch/myfile.html> This is a relative reference </A> or Absolute reference: <IMG SRC=“picture.gif" ALIGN=LEFT>right, middle, top, bottom18Linking WWW Pages (cont’d)Good design practice is to use absolute referencing.This enables portability of the entire site.19URLs Uniform Resource Locator.Identifies a resource in such a way as to enable the browser to locate the resource on the Internet.Has two top-level components: scheme:scheme-specific-locationScheme declares which type of URL it is:mailto, ftp, http, nntp, telnet.Only schemes sanctioned by W3C.20URLs (cont’d) HTTP URLs: http://servername[:port][/pathNameOnServer][/arguments]Domain Name Service (DNS) name;Optional path name of the server resource;Arguments, like query to a search engine.Pathname conventions:~streltch refers to subdirectory public_html of user streltch’s home directory;A pathname that end in a directory name rather than a simple file refers to a file index.html in
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