1. Introduction to Internet and to the Web

Motto People are using the web to build things they have not built or written or drawn or communicated anywhere else. —Tim Berners-Lee

History: ARPANET Developed in late 1960’s by ARPA – Advanced Research Projects Agency, Dept. of Defense Connected computers in a dozen of universities and institutions – 56KB communications lines Allowed computers to be shared Key benefit: fast communication between researchers – ! Precursor of Internet

Goals of ARPANET Multiple users can simultaneously send and receive data Must withstand nuclear attack – No centralized control – If a piece of the network fails, other portions will still route the packets

Achievements of ARPANET Pioneered packet switching – Data is sent in small "packets" – Packets contain data, address, error-control, sequencing info – Greatly reduced transmission costs Transmission Control Protocol (TCP) – Common protocol – Ensures that messages are properly routed and that they arrive intact Used both for inter- and intra-communication Connected huge variety of hardware and software

Internet: How it Grew Initially only universities and research institutions Military became big user Clinton government opened Internet for commercial purposes – Businesses invested heavily in Internet improvements – Fierce competition among communications carriers and hardware and software suppliers – Massive increase in bandwidth – Plummeting costs

Internet: Standards & Applications Tim Berners-Lee at CERN – Invents Hypertext Transfer Protocol (HTTP) communications protocol for the web – Invents HyperText Markup Language (HTML) describe data and its appearance – Coins the term World Wide Web 1993 First browser: Mosaic – Web becomes usable for the public Netscape Company – Commercial browser – Initiates the explosive Internet of late 1990s

W3C World Wide Web Consortium – – Founded in 1994 by Tim Berners-Lee Goals – Make Internet universally accessible – Standards HyperText Markup Language (HTML— getting obsolete) Extensible HyperText Markup Language (XHTML) Cascading Style Sheets (CSS) Extensible Markup Language (XML) Web 2.0

Web s and early 2000s Big companies fight browser wars – Microsoft vs. Netscape Search engines vie for eyeballs Every web site wants to be THE portal A few companies produce content Users browse “brochure web”

2003+: Web 2.0 New technologies – Storage became abundant – Ajax – Rich Interaction Applications – Software as a Service (SaaS) Make new ways of using the web possible – Users create the content Companies provide the platforms – Wikipedia, eBay, MySpace, Facebook, Flickr, YouTube

Web Services Functionality of existing applications and websites is provided to public Large companies provide services – Amazon Web Services, Google Maps Small businesses create niche web applications – e.g. combine maps web services with classifieds

Future: Web x.0 Semantic Web – Understand the meaning of the data on the web Petabyte statistics – Is it needed to understand the web? – Inferences based on super-huge data amounts work

Web Elements: Markup Languages Define data Platform-independent HTML – HyperText Markup Language – defines web page elements and their layout – fixed, predefined elements and grammar – elements can overlap, not strictly a tree XML – eXtended Markup Language – arbitrary elements – strictly hierarchical – processed using scripting languages XHTML – XML–compliant HTML

Web Elements: Programming Languages Scripting Languages – interpreted slow to execute flexible: direct evaluation of text as code possible – e.g. JavaScript, Perl, ActionScript, PHP, Ruby on Rails Compiled (or Hybrid) Languages – e.g. C, C++, Java, C# extra compilation step fast execution – hybrid: compiled into intermediate code, then interpreted – used on server-side

Scripting vs. Compiled Languages Scripting languages start executing fast, but are much slower during execution – no compilation step – interpreters are slow Scripting languages are easier to port to another platform – It is harder to write a compiler than to write an interpreter Scripting languages are more dynamic – e.g., server-side applications can generate code and send it to the browser where it can then be immediately interpreted

Object-Oriented Programming Vastly superior paradigm Programmers can be more productive – software can be easier to write, understand, debug and modify Reusable software components – Extensive free libraries are available online! Languages for Web programming are object- oriented – take advantages of it – JavaScript, Java, C#, ActionScript

Tasks Read textbook Chapter 1 and Chapter 2