01 - Fundamentals.pdf

IT135-8: Web Systems and Technologies 2 Fundamentals Learning Objectives After completing this chapter, you will be able to: Introduction to the Internet Define Internet Explain how the internet works Describe and explain AJAX, XML,...

IT135-8: Web Systems and Technologies 2 Fundamentals Learning Objectives After completing this chapter, you will be able to: Introduction to the Internet Define Internet Explain how the internet works Describe and explain AJAX, XML, and JSON  A Brief ARPANet Introduction Network constructed by the US Department of Defense’s to the Advanced Research Project Agency that connected a Internet dozen ARPA-funded research laboratories and (1 of 3) universities. Used packet switching to allow multiple computers to communicate on a single network. The first node of the network was established at UCLA in 1969. Primary early use was simple text-based communications through electronic mail.  A Brief BITNET Introduction Acronym for Because It’s Time Network that began in City to the University of New York Internet Initially built to provide electronic mail and file transfers (2 of 3) CSNET Acronym for Computer Science Network Connected the University of Delaware, Purdue University, the University of Wisconsin, the RAND Corporation, and Bolt, Beranek, and Newman (Massachusetts-based research company) Initial purpose was to provide electronic mail  A Brief NSFNet Introduction New national network created in 1986 sponsored by the to the National Science Foundation Internet Initially connected the NSF-funded supercomputer (3 of 3) centers that were at five universities By 1990, replaced ARPANet for most nonmilitary uses By 1992, connected more than one million computers globally In 1995, a small part of NSFNet returned to being a research network, the rest became known as the Internet  What is the The Internet is a huge collection of computers connected in a communications network. These computers are of Internet? every imaginable size, configuration, and manufacturer. Transmission Control Protocol/Internet Protocol (TCP/IP) allows diverse devices to communicate with each other. It became the standard for computer network communications in 1982. All devices connected to the Internet must be uniquely identifiable.  Internet Protocol The Internet Protocol (IP) address of a machine connected to the Internet is a unique 32-bit number. Addresses IP addresses are usually written as four 8-bit numbers, separated by periods. The four parts are separately used by Internet-routing computers to decide where a message must go next to get to its destination. Organizations are assigned blocks of Ips, which in turn assign to their machines that need Internet access. In late 1998, a new IP standard IPv6, was approved which expanded the address size from 32 bits to 128 bits. Domain Due to the difficulty remembering numbers, machines on the internet also have textual names. Names These names begin with the name of the host machine, followed by progressively larger enclosing collections of machines called domains The first domain name is the domain to which the host is a part The second domain name gives the domain of which the first domain is a part The last domain identifies the type of organization in which the host resides Fully qualified domain name example: movies.marxbros.comedy.com Domain Name System Domain name conversion  Different telnet – protocol developed in 1969 to allow user on one Protocols computer on the Internet to log onto and use another computer on the Internet File Transfer Protocol (ftp) – developed to transfer files among computers on the Internet Usenet – developed to serve as an electronic bulletin board mailto – developed to allow messages to be sent from the user of one computer to other users of the computer on the Internet This variety of protocols, each having their own interface and useful only for which it was designed, restricted the growth of the Internet. The World Wide Web In 1989, Tim Berners-Lee proposed a new protocol for the Internet, which suggested a way to let all users, but particularly scientists, browse each other’s papers on the Internet. He developed HTML, URLs, and HTTP. Basic Web Architecture The web is a two-tiered architecture. A web browser displays information content, A web server that transfers information to the client.  Web Browser A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. The primary purpose of a web browser is to bring information resources to the user. The major web browsers are Windows Internet Explorer, Mozilla Firefox, Apple Safari, Google Chrome, and Opera.  Web Server The term web server or webserver can mean one of two things: A computer program that accepts HTTP requests and return HTTP responses with optional data content. A computer that runs a computer program as described above. HTML Document layout language (not a programming language) Defines structure and appearance of Web pages Many HTML documents are the result of manual authoring or word processing HTML converters. HTML files are viewed using a web browser. Universal Resource Identifier(URI) URIs are used for two different purposes: To name a resource (Uniform Resource Names) To provide a path to, or location, of a resource (Uniform Resource Locators) Universal Resource Identifier (URI) URLs are location dependent It contains four distinct parts: the protocol type, the machine name, the directory path and the file name. There are several kinds of URLs: file URLs, FTP URLs, and HTTP URLs. HTTP HTTP is an application-level protocol for distributed, collaborative, hypermedia information systems. HTTP is a request/response standard of a client and a server. Typically, an HTTP client initiates a request. Resources to be accessed by HTTP are identified using Uniform Resource Identifiers (URIs). Request Message The request message consists of the following: Request line Headers (Accept-Language, Accept, ….) An empty line An optional message body Request HTTP defines methods (sometimes referred to as "verbs") Methods indicating the desired action to be performed on the identified (1 of 2) resource. HEAD - The HEAD method asks for a response identical to that of a GET request, but without the response body. GET - The GET method requests a representation of the specified resource. Requests using GET should only retrieve data. POST - The POST method is used to submit an entity to the specified resource, often causing a change in state or side effects on the server. PUT - The PUT method replaces all current representations of the target resource with the request payload. Request HTTP defines methods (sometimes referred to as "verbs") Methods indicating the desired action to be performed on the identified (2 of 2) resource. DELETE - The DELETE method deletes the specified resource. TRACE - The TRACE method performs a message loop-back test along the path to the target resource. OPTIONS - The OPTIONS method is used to describe the communication options for the target resource. CONNECT - The CONNECT method establishes a tunnel to the server identified by the target resource. PATCH - The PATCH method is used to apply partial modifications to a resource.  Safe Methods HEAD, GET, OPTIONS and TRACE are defined as safe (no side effects). POST, PUT and DELETE are intended for actions which may cause side effects on the server. Status The first line of the HTTP response is called the Lines status line. The way the user agent handles the response primarily depends on the code and secondarily on the response headers. Informational: 1xx Success: 2xx Redirection: 3xx Client-Side Error: 4xx Server-Side Error: 5xx Sample HTTP Request and Response Client request Server response  HTTP is a stateless protocol. HTTP Hosts do not need to retain information about users Session between requests. State Statelessness is a scalability property. For example, when a host needs to customize the content of a website for a user. Solution: Cookies Sessions Hidden variables (when the current page is a form) URL encoded parameters (such as /index.php? session_id=some_unique_session_code) Cookie Cookie is a small piece of text stored on a user's computer by a web browser. A cookie consists of one or more name-value pairs containing bits of information such as user preferences. It is sent as an HTTP header by a web server to a web browser and then sent back unchanged by the browser each time it accesses that server. A cookie can be used for authenticating, session tracking (state maintenance), and remembering specific information about users. Setting a Cookie  Cookie Cookies expire, and are therefore not sent by the Expiration browser to the server, under any of these conditions: At the end of the user session (i.e. when the browser is shut down) if the cookie is not persistent An expiration date has been specified, and has passed The expiration date of the cookie is changed (by the server or the script) to a date in the past The browser deletes the cookie by user request Session A session is a reference to a certain time frame for communication between two devices, two systems or two parts of a system. A user session begins when a user logs in to or accesses a particular computer, network, or software service. It ends when the user logs out of the service, or shuts down the computer. A session can temporarily store information related to the activities of the user while connected.  Session Variables In computer programming, session variables store temporary information, sometimes to use for retrieving and viewing data on multiple web pages. Websites requiring a username and password use session variables to help transfer data between web pages, but only while the user is logged in to the computer. Sample HTTP Request and Response This basic web architecture is fast evolving to serve a wider variety of needs beyond static document access and browsing. CGI extends the architecture to three-tiers by adding a back-end server that provides services to the Web server. Common Gateway Interface CGI is a standard protocol for interfacing external (CGI) application software with a web server. CGI programs are executable programs that run on the Web server. The CGI program typically returns HTML pages that it constructs on the fly. Traditional JavaScript is a scripting language designed for Uses of creating dynamic, interactive Web JavaScript applications that link together objects and resources on both clients and servers. Getting your Web page to respond or react directly to user interaction with form elements and hypertext links Preprocessing data on the client before submission to a server Changing content and styles Database-driven Website Architecture Server-side processing In server-side processing, the Web server: Receives the dynamic Web page request Performs all the processing necessary to create the dynamic Web page Sends the finished Web page to the client for display in the client’s browser Client-side processing In client-side processing: Some processing needs to be “executed” by the browser, either to form the request for the dynamic Web page or to create or display the dynamic Web page. Eg. Javascript code to validate user input Programming Languages Server-side processing Client-side processing PHP CSS ASP HTML ASP.NET JavaScript Perl Adobe Flex J2EE Microsoft Silverlight Python, e.g. Django Ruby, e.g. Ruby on Rails ColdFusion AJAX Asynchronous JavaScript and XML Ajax isn’t a technology. It’s really several technologies, each flourishing in its own right, coming together in powerful new ways. Ajax incorporates: XHTML and CSS Jesse James Document Object Model Garrett, essay in XML and XLST February 18, 2005 XMLHttpRequest Ajax: A New JavaScript Approach to Web Applications AJAX Drawbacks It breaks browser history engine (Back of AJAX button). No bookmark. The same origin policy. Ajax opens up another attack vector for malicious code that web developers might not fully test for. Web Services Web Service is a software system designed to support machine-to- machine interaction over a network. Web services are frequently just Internet Application Programming Interfaces (API) that can be accessed over a network.  Web Web Services are platform-independent and language- Services independent, since they use standard XML languages. Most Web Services use HTTP for transmitting messages (such as the service request and response). Style of Use RPC SOAP REST XML XML is a universally agreed markup meta-language primarily used for information exchange. The two primary building blocks of XML are elements and attributes. Elements are tags and have values. Elements are structured as a tree. Alternatively, elements may have both attributes as well as data Attributes help you to give more meaning and describe your element more efficiently and clearly. XML 1111 Smith John New York 21 2nd Street 10021 NY JSON JSON is a lightweight computer data interchange format. JSON is based on a subset of the JavaScript programming language. It is considered a language- independent data format. It serves as an alternative to the use Douglas Crockford is a of the XML format. senior JavaScript Architect at Yahoo! He is well known for his work in introducing JavaScript Object Notation (JSON).  { JSON "firstName": "John", "lastName": "Smith", "address": { "street": "212nd Street", "city": "New York", "state": "NY", "postalCode": 10021 }, "phoneNumbers":[ "212 555-1234", "646555-4567" ] }  R|R Questions ?