Web Technologies

Lecture 1: Introduction Web Technologies Abdenbayeva Aigerim IITU – 2014

Sillabus

WORLD List of websites Google google.com 1 4,533,883 Search Facebook facebook.com 2 8,190,877 Social Networking YouTube youtube.com 3 3,637,788 Video-Sharing Yahoo! yahoo.com 4 1,888,093 Search Baidu baidu.com 5 325,710 Search Wikipedia wikipedia.org 6 2,154,423 Reference Windows Live live.com 7 149,315 Portal Amazon.com amazon.com 8 1,177,136 Commerce Tencent QQ qq.com 9 472,087 Instant Messaging Twitter twitter.com 10 6,183,107 Microblogging Taobao taobao.com 11 185,399 Commerce Blogspot blogspot.com 12 30,878 Blogging Google India google.co.in 13 47,760 Search LinkedIn linkedin.com 14 1,454,0 Social Networking Yahoo! Japan yahoo.co.jp 15 153,463 Search Sina Corp sina.com.cn 16 206,014 News MSN msn.com 17 448,492 News Yandex yandex.ru 18 320,854 Search eBay ebay.com 19 227,785 Commerce Google Japan google.co.jp 20 133,004 Search

KAZNET

Place #10 – 16834 (unique visitors)

Place #9 - 19969

Place #8 - 23913

Place #7 - 25169

Place #6 - 25951

Place #5 - 38832

Place #4 - 64792

Place #3 - 82542

Place #2 - 88061

Place #1 - 103937

3 methods for creating website

What is this lecture about? • Introduction to the basic Web technologies that are used to implement the „Web“ portion of Web Services: Some historical details Core Web Technologies Wide area integration Tunneling, Firewalls, EDIFACT

Some historical details • Start of standard groups • TCP • handles conversion between messages and streams packets • IP • handles addressing of packets across networks • TCP/IP • enables packets to be sent across multiple networks using multiple standards • Telnet • One of the earliest standards for exchanging transmission, directly connect accounts on different systems. • SMTP • specifies another way of direct connection

Some historical details • MIME • Extension to the SMTP Protocol which supports the exchange of richer data files such as audio-, video-, and images data. • FTP • (1973) supports file transfer between Internet sites and allows a system to publish a set of files by hosting an FTP sever innovation  permits anonymous users to transfer files • Archie • Late 1980‘s distributed file system based on FTP • Gopher • First simple system, providing GUI

Core Web Technologies • HTTP(HyperText Transfer Protocol) • generic, stateless protocol • governs the transfer of files across a network • developed at CERN (Central European Research Network), they also came up with the name WWW, later W3C • supports access to SMTP,FTP and other protocols • was designed to support hypertext

Core Web Technologies • Exchanged information, can be static or dynamic • Every resource, accessible over the Web has a URL(Uniform resource locator) • HTTP mechanism is based on client/server model typically using TCP/IP sockets

Core Web Technologies • since Version 1.1 HTTP requires servers to support persistent connections, to minimize overhead associated with opening and closing connections. • Typical methods on the server side are: • OPTIONS • send information about the communication options • GET • retrieve document or document produced by a program • POST • Append or attach information • PUT • Store information • DELETE • Delete the resource indicated in the request

Core Web Technologies • Another limitation HTTP is stateless • Does not provide storing of information between requests • No indication of any relationship between two different requests  cookies, small data structures that a web server requests the HTTP client to store on the local machine, are used to maintain state information e.g. cookies store recently view items on a web shop

REST(Representational State Transfer) • architectural style, defining the principles of distributed network systems. • is the underlying architectural model, guiding the design and development of the current and next generation web architectures

REST • Provides a set of architectural constraints, that emphasizes • Scalability of component interaction • Generality of interfaces • Independent deployment of components • Enforce Security • Etc.

REST vs. Web Services • Rest promotes and recommends generic operations on resources • HTTP methods: PUT GET POST DELETE • SQL: select create drop ect. • Utilizes the caching mechanism • WS does not promote generic operations • First generation only utilizes HTTP POST • Each service defines its own application specific operations • Requires additional means of discrption,discovery mechanisms on top of the web • No caching capabilities

Rest Principles • Web consists of addressable resources  a user, utilizing an application selects a specific address(URL) a specific representation of that resource is returned over the web  places the client application into a specific state. On accessing another URL, the client application gets another representation of the resource and in turn, transferring from the current to the new state.

Core Web Technologies • HTML(HyperText Markup Language) • Defines a standard set of special textual indicators(markups) specifying how a Web pages words and images should be displayed by the web browser

Technologies for Supporting Remote Clients • Original intent of core Web Technologies  enable linking and sharing documents • It was quickly realized, that by wrapping local information systems to expose their presentation layer by using HTML documents, one could leverage the core Web technologies to have clients that are distributed across the internet.

B2C (Business to consumer) • Conventional 3-tier architectures are designed to operate within a single company  data exchanges occur within the safe boundaries of the company • in principle there are no reasons why the system could not be opened to other users if the need arises • ATM(automatic teller machines are an excellent example of the advantages if doing so

B2C • ATM(automatic teller machines are an excellent example of the advantages if doing so • client/server system • a PC with a network connection to the information services of the bank • gives customers easier access to their accounts without the bank incurring • a significant part of manual work disappears • more efficient interactions with the customer  great service, but there are limitations

B2C • Limitations • Customers must travel to the nearest ATM, would not be necessary, access to their bank accounts any time, helps extend its functionality. This architecture is called B2C, indicating that the business allows consumers to access their information services directly

Problem • Users wanting to take advantage of this opportunity would need to have specialized clients for every company they want to interact with • Complexity would grow enormous -> administration

Solution • One of the biggest contributions of the Web  providing a universal client for such extensions • Nowadays such architectures are implemented by letting the remote computer use a Web Browser as a client • since Web Browsers are standard tools, no application specific client has to be installed

Web Browsers • One of the first problems  web Browsers were originally intended only to display static documents, returned by HTTP calls • Difficult to build sophisticated application specific clients for web browsers

Applets • One answer to this problem  Applets • Java programs, can be embedded in an HTML document • When the document is downloaded, the program is executed by the JVM, presented in the browser, turning the browser into a client by sending the client code as an applet • Limitations  download the code • Advantage  complexity

CGI(Common Gateway Interface) • Web servers must be able to server up content from dynamic sources • How can a Web server respond to a request by invoking an application that will automatically generate a document to be returned • One of the first approaches to solve this problem, was CGI, a standard mechanism that enables HTTP servers, to interface with external applications, which can serve as „gateways“ to the local information system

CGI • How does CGI work • it assigns programs to URLs, so that when the URL is invoked, the program is executed • CGI programs often serve as an interface between a database and a Web server, allowing users to submit complex queries over the DB through predefined URLs • When the Web server receives request for the URL, it will run a program, that will act as a client of the database and submit the query  executing and packs the result into a HTML document  returned to remote browser

Servlets • Performance  CGI programs involve a certain overhead • Separate process for each instance  takes time, requires a context switch in the operating system • Multiple request results – multiple process • To avoid this overhead, Jave servlets can be used instead • The idea is exactly the same as in CGI programs, but the implementation differs.

Servlets • How do they work? • Execution and result is the same, but servlets are invoked directly by embedding servlet-specific information within an HTTP request  run as threads of the Java server process, moreover they run as a part of the Web server  eliminates overhead

Application Servers – short overview • Equivalent to middleware platforms • Main difference  intercorporation of the Web as a key access channel to the services implemented using the middleware  several important implications • The presentation layer acquires a much more relevant role • Direct consequence of how HTTP and the Web work

Application servers – short overview • Realized by merging the presentation layer related to the Web with the application layer of the middleware platform Reason  to allow the efficient delivery of content trough the Web as well as to simplify the management of Web applications

J2EE • There are two competing frameworks for Web-based middleware • Suns J2EE • Microsoft's .NET • very similar

J2EE • A significant aspect of application servers is the bundling of more and more functionality within the middleware platform • Providing integrated support for many different middleware abstractions • Therefore blurring the borders between application servers and other middleware

Application server - Application Layer • At the application layer, application servers conceptually resemble conventional middleware, provided functionality similar to CORBA, TP monitors and message brokers • Goal of application server vendors • providing a unique environment for hosting all kinds of application logic, whether Web-based or otherwise,

J2EE - EJB • EJB (Enterprise JavaBeans) specification is at the heart of J2EE  there the bulk of the application logic resides • An EJB is a server-side component, that delivers application-specific funktionality(responding to a request for a quote…)

J2EE - EJB • The EJB specification defines 3 different types of beans, based on how they interact with other components and how they manage state and persistence • Session beans • Entity beans • Message-driven beans

J2EE –EJB container • Provides the environment in which the beans run  all interactions go through the container • Provides a number of services • Supports transactions  freeing a developer from having to define transaction boundaries and implement the related code

J2EE - JNDI • Defines an interface for directory services, without mandating any implementation • Clients can bind to servers based on the object name (EJB  binding to a server involves binding to an object that provides the interface for interacting with a server)

J2EE - JDBC • is an API that enables developers to access almost any tabular data source by executing SQL commands from a java program • methods can be called from an EJB or directly from a servlet

Application Server • Offer services that simplify administration and management of the application • Caching frequently needed objects • Checking that an application is running and restarting • Object administration and security, defining user has access to which application and enforcing access restrictions

Web Technologies