How the World Wide Web works Barend Kbben

How the World Wide Web works Barend Köbben International Institute for Geo-information Science and Earth Observation (ITC) Department of Geo-information Processing

History of the Web (1969) start of ARPAnet (1983) ARPAnet, USEnet en EUnet adopt TCP/IP communication: birth of the Internet many protocols run “on top of” TCP/IP (telnet, ftp, smpt) because of IP-adressing all networks can be seen as one big network (1991) definition of the WWW-protocols: HTTP: Hyper. Text Transfer Protocol HTML: Hyper. Text Markup Language Department of Geo-information Processing

IP-adressing & DNS (domain name servers) INTERNET DNS aliasing www. kartografie. nl Department of Geo-information Processing SURFNET admin nl-domain: xx. nl ITC router admin ITCdomain: xx. itc. nl NVK server 192. 92. 70 = kartoweb. itc. nl

HTTP communication Client-server architecture Client Browser Can I have that file? Webserver (IIS, Netscape, HTTPd) (Explorer, Netscape, Opera) Here it is. . . Department of Geo-information Processing Server

HTML code <P>Hello<B>World</B><HR>How are<I>you</I>? <P><A HREF= ”otherfile. html”>Click here</a> to go. Looks like: Hello World How are you? Click here to go. Department of Geo-information Processing

Standard configuration GET file. html PUT file. html file. gif GET file. gif <img src = “file. gif”> <i>STATIC </i> MAP Department of Geo-information Processing http: // www. itc. nl /file. html STATIC MAP

Constraints Standard configuration offers: HTTP communication-protocol HTML–, GIF– en JPEG–formats Static maps only No interactivity (except “clickable maps”) Overcoming the constraints: Only possible by adding data-formats and protocols Possible loss of platform independency Department of Geo-information Processing

Plugins (client-side) PDF-READER file. pdf <img src = “file. pdf”> <i> interactive </i> map Department of Geo-information Processing interactive map

Java applets (client-side) Java Virtual Machine map. class Javaapplet code Department of Geo-information Processing <applet src = “map. class”> map applet

Java. Script (client-side) Java Virtual Machine <script > <!-Document. write(“map ”); } //--> </script> Department of Geo-information Processing map

CGI–applications (server-side) www. kartografie. nl /CGI? makemap &title=“itc” CGIAPPLICATION Department of Geo-information Processing itc

Active Server Pages (server-side) handles Java. Script or VBscript Microsoft IIS HTML in memory server-plugin (asp. dll) <img src = map. gif> database stuff <img src = <% foundrecords. image %> database stuff Department of Geo-information Processing

Java servlets (server-side) Java Virtual Machine map. class Javaapplet code Department of Geo-information Processing <%applet src = “map. class”% > map applet

Arc. View-IMS: a mixed solution server-plugin (esrimap. dll) Java Virtual Machine mapcafe. class Javaapplet code Department of Geo-information Processing arcview map

Internal server (itcnt 07 student sites) administrator (blenke@itc. nl) IIS server itcnt 07. itc. nl Only available within ITC (within “firewall”) special dir “www” on personal drive M: windows network http Anonymous access (Web) Web-browsers Department of Geo-information Processing authors

External Web server (eg. Kartoweb) administrator (kartoweb@itc. nl) Kartoweb server ftp http Anonymous access (Web) Web-browsers Department of Geo-information Processing username/password privileges authors