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Introduction Web Environments
2017, Fall Pusan National University Ki-Joune Li
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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
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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.
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Distributed Systems Example of Distributed Systems
Internet (or Mobile) Games Apps of Smartphones Internet Banking Social Media (Kakaotalk, Tweeter, Facebook, SMS, etc…)
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Distributed Systems A basic question How do they cooperate?
Example: Starcraft
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At Early Stage of Distributed Systems
Client-Server Architecture Request (e.g. a query) Response (e.g. search results)
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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
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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
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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
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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 ftp://example.com/mydata.zip URI – Uniform Resource Identifiers A more general concept than URL Just identifies resources on the internet – Identifier (name)
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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
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With error code + contents
Web Concepts – HTTP HTTP – HyperText Transfer Protocol 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
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Web Concepts – HTTP Example
Read hello.htm from Write the following document at GET /hello.htm HTTP/1.1 User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT) Host: 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: Accept-Language: en-us Connection: Keep-Alive Content-type: text/html Content-Length: 182 <html> <body> <h1>Hello, World! </h1> </body> </html>
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Web Concepts – What Web Browser Does
Requests to Web Server Web Browser (e.g. Chrome) Receives from Web Server, interprets, display.
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Web Concepts – 3-tier in WWW environments
Web Client (Web Browser e.g. Chrome) Web Server
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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.
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