WWW World Wide Web. Aka The Internet

Transcription

1 WWW World Wide Web Aka The Internet

2 WWW history (1) 1968 Doug Engelbart Earlier than ARPANET or UNIX Inventor of the mouse... and of hypermedia... and of videoconferencing

3 1989 Tim Berners Lee WWW history (2) 20 years after Engelbart First Information management proposal at CERN 1990 WorldWideWeb browser (later Nexus) developed by Berners Lee on NEXTSTEP World Wide Web (with spaces) is the abstract information space

4 WWW history (3) More browsers 1992 Line mode browser 1.1 ViolaWWW browser for X Windows 1993 Mosaic for X Windows (Marc Andreessen)

5 WWW history (4) 1994 Mozilla (Netscape) W3C founded (MIT, INRIA, Keio) 1995 Microsoft Internet Explorer

6 WWW history (5) Standards based browsers Mozilla, Firefox (Gecko engine) Safari, Konquerer (KHTML engine) Opera (commercial; proprietary engine)

7 Forms of communication (0) Direct push Indirect push Pull 1 1????????? 1 N????????? N 1????????? N N?????????

8 Forms of communication (1) Direct push Indirect push Pull 1 1 IM?????? 1 N????????? N 1????????? N N?????????

9 Forms of communication (2) Direct push Indirect push Pull 1 1 IM ??? 1 N????????? N 1????????? N N?????????

10 Forms of communication (3) Direct push Indirect push Pull 1 1 IM DNS/LDAP 1 N????????? N 1????????? N N?????????

11 Forms of communication (4) Direct push Indirect push Pull 1 1 IM DNS/LDAP 1 N wall?????? N 1????????? N N?????????

12 Forms of communication (5) Direct push Indirect push Pull 1 1 IM DNS/LDAP 1 N wall Mailing list??? N 1????????? N N?????????

13 Forms of communication (6) Direct push Indirect push Pull 1 1 IM DNS/LDAP 1 N wall Mailing list WWW N 1????????? N N?????????

14 Forms of communication (7) Direct push Indirect push Pull 1 1 IM DNS/LDAP 1 N wall Mailing list WWW N 1 IDS?????? N N?????????

15 Forms of communication (8) Direct push Indirect push Pull 1 1 IM DNS/LDAP 1 N wall Mailing list WWW N 1 IDS Voting/Poll??? N N?????????

16 Forms of communication (9) Direct push Indirect push Pull 1 1 IM DNS/LDAP 1 N wall Mailing list WWW N 1 IDS Voting/Poll Search engine N N?????????

17 Forms of communication (10) Direct push Indirect push Pull 1 1 IM DNS/LDAP 1 N wall Mailing list WWW N 1 IDS Voting/Poll Search engine N N Videoconf??????

18 Forms of communication (11) Direct push Indirect push Pull 1 1 IM DNS/LDAP 1 N wall Mailing list WWW N 1 IDS Voting/Poll Search engine N N Videoconf Chat???

19 Forms of communication (12) Direct push Indirect push Pull 1 1 IM DNS/LDAP 1 N wall Mailing list WWW N 1 IDS Voting/Poll Search engine N N Videoconf Chat Usenet

20 WWW concepts Browser and Webserver 3-tier model Dynamic web pages URLs and HTTP HTML and other markup

21 Browser Client making requests for web pages Interface for the user Graphical User Interface IE, Netscape, Mozilla, Safari,... Terminal based lynx, links, w3m

22 Web server Server responding to requests Apache, IIS, SunONE (iplanet), NCSA See < Looks up information in or via files, databases, scripts locally or remote

23 Netcraft survey Figure 22.1 Web server software

24 3-tier model Presentation layer (user tier) Communicates with (client) browser Business Logic layer (business tier) Applies business rules Data layer (data tier) Interacts with data store (database)

25 LAMP model (L)inux as underlying OS (A)pache as presentation layer (M)ySQL as data layer (P)HP as business logic layer

26 Dynamic pages (1) Client side: DHTML (Dynamic HTML) Works with Document Object Model (DOM) Executes ECMAscript (standard) programs JavaScript (Netscape), JScript (Microsoft) Ajax (Asynchronous Javascript and XML) May execute Applets (JVM) or ActiveX

27 Dynamic pages (2) Server side dynamic web pages CGI (Common Gateway Interface) server-side scripting PHP, JSP, ASP servlets: server-side java applications ASP.NET

28 Document Object Model (1) An ongoing W3C activity for standardizing Dynamic HTML Level 0: proprietary API for HTML (XML) documents Level 1: standardized API for HTML (XML) documents

29 Document Object Model (2) Level 2: modularized with support for events and styles Level 3: support for loading and saving and for keyboard events

30 Uniform Resource Identifiers URI has two forms URL (Uniform Resource Locator) URN (Uniform Resource Name) urn:<nid>:<nid-specific> urn:ietf:rfc:2648 urn:isbn:

31 Uniform Resource Locators <scheme>:<scheme-specific> <scheme> is often some Internet protocol http, ftp, telnet, rtsp <scheme-specific> often starts with // to indicate Internet addresses follow Other forms: mailto, news

32 HTTP URLs <authority> <host> : <port> /<path>?<query> #<fragment> (in URI-reference)

33 HTTP Uses <CR><LF> end of line convention HTTP request (response) request (response) line request (response) headers empty line optional body

34 HTTP request <method> <path> <HTTP-version> GET (get web page), HEAD (get headers only) PUT (store web page) POST (input to server side scripts) DELETE (delete web page) OPTIONS (query web server options)

35 HTTP response <HTTP-version> <status-code> <comment> HTTP/ OK HTTP/ Moved Permanently HTTP/ Bad Request HTTP/ Not Found HTTP/ Method Not Implemented

36 Request headers User-Agent: <client identification> Host: <(virtual) server name> Cookie: <stored user tracking information> Date: <date/time message sent> Authorization: <credentials>...many more...

37 Response headers Content-Type: <MIME type> Content-Length: <page length in bytes> Last-Modified: <date of last page change> Set-Cookie: <string to keep state> Location: <redirection information>...many more...

38 Markup SGML XML HTML XHTML Table 37.1 Markup

39 SGML Standard Generalized Markup Language <!DOCTYPE...> <!ELEMENT...> <!ATTLIST...> <!ENTITY...> DTD: Document Type Definition

40 HTML Instantiation of SGML <!DOCTYPE HTML PUBLIC -/W3C/DTD HTML 4.01//EN > All else is bogus: <BLINK>,...

41 XML Simpler reformulation of SGML Some differences Every start tag must have a close tag Attribute values must always be quoted <?xml...> processing instructions reserved

42 XHTML XML specification of HTML Still needs a DTD strict.dtd Will be replaced by some XML Schema

43 W3C activities See < CSS, XSL RDF, Semantic Web XML Schema SOAP, Web Services Accessibility, Internationalization (I18N)

44 CSS, XSL Cascading Style Sheets (CSS1, CSS2) Extensible Stylesheet Language (XSL) XSL Transformations (XSLT) XSL Formatting Objects (XSL-FO) XML Path Language (XPath)

45 RDF (1) Resource Description Framework Metadata Semantic Web Knowledge Machine readable information

46 RDF (2) Example from UvA/SNE research NDL (Network Description Language) <

47 XML Schema Transforming an SGML DTD into an XML Schema Is written itself in XML syntax Has support for built-in datatypes