Introduction Web Environments 2017, Fall Pusan National University Ki-Joune Li
Web? WWW (World Wide Web) Web (or World Wide Web) provides An information space where documents and other web resources are identified by URL, interlinked via hyperlinks and accessed via internet from Wikipedia Web (or World Wide Web) provides A type of distributed computing environments A Graphic User Interface (GUI) – Document Presentation An Extension of Operating System
Distributed Systems What is “Distributed Systems”? A distributed system is a model in which components located on networked computers communicate and coordinate their actions by passing messages.
Distributed Systems Example of Distributed Systems Internet (or Mobile) Games Apps of Smartphones Internet Banking Social Media (Kakaotalk, Tweeter, Facebook, SMS, etc…)
Distributed Systems A basic question How do they cooperate? Example: Starcraft
At Early Stage of Distributed Systems Client-Server Architecture Request (e.g. a query) Response (e.g. search results)
Distributed Systems How to implement Client-Server Architecture Example – Data Server (processing queries) What are the problems of client-server architecture? Clients have to know all about the server Message Format Functions and Data Catalog Locations (e.g. IP address) Failure Duplication Binding – Static Binding
Middleware – Resolving Everything Distributed Systems Three Tier Architecture Data Catalog and Functions Heterogeneity, Dynamic Binding, Transparency Client Client Client Middleware – Resolving Everything Server Server Server
Web Concepts – a Distributed Systems Web Environment User User User Internet (TCP/IP) HTTP Web Browser - Chrome Web Browser - Firefox Web Browser - IE Document in HTML/CSS and JavaScript HTTP Protocol Web Server Data Server
Web Concepts – URL and URI URL – Uniform Resource Locators Specifies the location of resources containing documents and server side program Static document: in HTML Dynamic resource: program or functions e.g. looking-up databases Example http://example.com/mypage.html ftp://example.com/mydata.zip URI – Uniform Resource Identifiers A more general concept than URL Just identifies resources on the internet – Identifier (name)
Web Concepts – Internet A world-wide computer networks that use TCP/IP protocol. Most widely used computer networks in the world Standard by IETF (Internet Engineering Task Force) IPv4 or IPv6 IPv4 header
With error code + contents Web Concepts – HTTP HTTP – HyperText Transfer Protocol http://lik.pnu.edu/FP/2017/FP2017Spring.html Overview – CRUD Create (PUT) Read (GET) Update (POST) Delete (DELETE) URL specifies the protocol (access method) Create/Read/ Update/ Delete HTTP Client With error code + contents HTTP Server
Web Concepts – HTTP Example Read hello.htm from www.tutorialspoint.com Write the following document at www.tutorialspoint.com GET /hello.htm HTTP/1.1 User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT) Host: www.tutorialspoint.com Accept-Language: en-us Accept-Encoding: gzip, deflate Connection: Keep-Alive PUT /hello.htm HTTP/1.1 User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT) Host: www.tutorialspoint.com Accept-Language: en-us Connection: Keep-Alive Content-type: text/html Content-Length: 182 <html> <body> <h1>Hello, World! </h1> </body> </html>
Web Concepts – What Web Browser Does Requests to Web Server Web Browser (e.g. Chrome) Receives from Web Server, interprets, display.
Web Concepts – 3-tier in WWW environments Web Client (Web Browser e.g. Chrome) Web Server
Web Concepts - Hyperlink a reference to document or resource that the reader can directly follow either by clicking within hypertext document. Reference is usually given as a URL.