slide cơ sở dữ liệu tiếng anh chương (29) web technology and dbmss transparencies

The Web ◆ Web consists of netw ork of computers that can act in two roles: – as serv ers, providing information; – as clients brow sers, requesting information.. ◆ Protocol that gov e

Chapter 29

Web Technology and DBMSs

Transparencies

Chapter 29 - Objectives

◆ Basics of Internet, Web, HTTP, HTML, URLs.

◆ Advantages and disadv antages of Web as a

Chapter 29 - Objectives

– Extending the Web Server

– Java, J2EE, JDBC, SQLJ, CMP, JDO, Servlets,

and JSP

– Microsoft Web Platform: NET, ASP, and ADO

– Oracle Internet Platform.

◆ Organizations using Web as strategic platform for innovative business solutions, in effect becoming

W eb-centric

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◆ Also many Web sites now contain more dynamic

information, such as product and pricing data

◆ Maintaining such data in both a database and in

separate HTML files is problematic

◆ Accessing database directly from Web would be a better approach.

Internet

Worldw ide collection of interconnected networks.

◆ Began in late ‘60s in ARPANET, a US DOD project, investigating how to build networks that could w ithstand partial outages

◆ Starting with a few nodes, Internet estimated to have ov er 945 million users by end of 20 04

◆ 2 billion users projected by 20 10

◆ About 3.5 billion documents on Internet (550 billion if intranets/extranets included).

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Intranet and Extranet

◆ Intranet - Web site or group of sites belonging to an organization, accessible only by members of that

eCommerce and eBusiness

◆ eCommerce - Customers can place and pay for orders via the business’s Web site.

◆ eBusiness - Complete integration of Internet technology into economic infrastructure of the business.

◆ Business-to-business transac tions may reach $2.1 trillion in Europe and $7 trillion in US by 2006.

◆ eCommerce may account for $12.8 trillion in worldwide corporate revenue by 2006 and could represent 18% of sales in the global economy.

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The Web

Hypermedia-based system that prov ides a simple

‘point and click’ means of brow sing information on the Internet using hyperlinks.

◆ Information presented on Web pages, which can contain text, graphics, pictures, sound, and v ideo

◆ Can also contain hy perlinks to other Web pages,

w hich allow users to navigate in a non-sequential

w ay through information

◆ Web documents written using HTML.

The Web

◆ Web consists of netw ork of computers that can act

in two roles:

– as serv ers, providing information;

– as clients (brow sers), requesting information

◆ Protocol that gov erns exchange of information

betw een Web serv er and brow ser is HTTP and

locations w ithin documents identified as a URL.

◆ Much of Web’s success is due to its simplicity and platform-independence

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Basic Components of Web Environment

HyperText Transfer Protocol (HTTP)

Protocol used to transfer Web pages through Internet.

◆ Based on request-response paradigm:

Connection - Cl ient establ ishes connection w ith Web server Request - Cl ient sends request to Web server.

Response - Web server sends response (HTML document)

to cl ient.

Cl ose - Connection cl osed by Web server.

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HyperText Transfer Protocol (HTTP)

◆ HTTP/1.0 is stateless protocol - each connection is closed once serv er prov ides response

◆ This makes it difficult to support concept of a session that is essential to basic DBMS transactions

HyperText Markup Language (HTML)

Document formatting language used to design most Web pages.

◆ A simple, yet pow erful, platform-independent document language

◆ HTML is application of Standardized Generalized Markup Language (SGML), a system for defining structured document types and markup languages to represent instances of those document types.

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HyperText Markup Language (HTML)

Uniform Resource Locators (URLs)

String of alphanumeric characters that represents location or address of a resource on Internet and how that resource should be accessed.

◆ Defines uniquely where documents (resources) can

be found

◆ Uniform Resource Identifiers (URIs) - generic set

of all Internet resource names/addresses

◆ Uniform Resource Names (URNs) - persistent, location-independent name Relies on name lookup serv ices.

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Uniform Resource Locators (URLs)

◆ URL consists of three basic parts:

– protocol used for the connection,

– host name,

– path name on host where resource stored

◆ Can optionally specify:

– port through which connection to host should be

made,

– query string.

Static and Dynamic Web Pages

◆ HTML document stored in file is static Web page.

◆ Content of dynamic Web page is generated each time it is accessed

◆ Thus, dynamic Web page can:

– respond to user input from browser;

– be customized by and for each user

◆ Requires hypertext to be generated by serv ers

◆ Need scripts that perform conv ersions from

different data formats into HTML ‘ on-the-fly ’

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◆ Based on open standards and focus on communication and collaboration among people and applications

◆ Unlike other Web-based applications, Web serv ices have no user interface and are not targeted for brow sers Instead, consist of reusable software components designed to be consumed by other applications

Web Services – Technologies & Standards

◆ eXtensible Markup Language (XML).

◆ SOAP (Simple Object Access Protocol) protocol, based on XML, used for communication over

Internet.

◆ WSDL (Web Services Description Language)

protocol, again based on XML, used to describe the Web service

◆ UDDI (Universal Discovery, Description and

Integration) protocol used to register the Web

service for prospective users

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Web Services

◆ Common example is stock quote facility, which receiv es a request for current price of a specified stock and responds w ith requested price

◆ Second example is Microsoft MapPoint Web service that allows high quality maps, driving directions, and other location information to be integrated into a user application, business process,

or Web site.

Requirements for Web-DBMS Integration

◆ Ability to access v aluable corporate data in a

secure manner.

◆ Data- and vendor-independent connectivity to

allow freedom of choice in DBMS selection.

◆ Ability to interface to database independent of any proprietary browser or Web serv er.

◆ Connectivity solution that takes adv antage of all

the features of an organization’s DBMS.

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Requirements for Web-DBMS Integration

◆ Open architecture to allow interoperability with a

varie ty of sy stems and te chnologie s For example :

– different Web servers;

– Microsoft's (Distributed) Common Object Model

(DCOM/COM);

– CORBA/IIOP (Internet Inter-ORB protocol);

– Java/Remote Method Invocation (RMI);

– XML;

– Web services (SOAP, WSDL, UDDI).

Requirements for Web-DBMS Integration

◆ Support for transactions that span multiple HTTP requests.

◆ Support for session- and application-based

authentication.

◆ Acceptable performance.

◆ Minimal administration overhead.

◆ Set of high-lev el productivity tools to allow

applications to be developed, maintained, and

deployed with relativ e ease and speed.

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Advantages of Web-DBMS Approach

◆ Immaturity of development tools

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Approaches to Integrating Web and DBMSs

◆ Scripting Languages

◆ Common Gatew ay Interface (CGI).

◆ HTTP Cookies.

◆ Extending the Web Serv er.

◆ Java, J2EE, JDBC, SQLJ, JDO, Serv lets, and JSP.

◆ Microsoft Web Solution Platform: NET, ASP, and ADO.

◆ Oracle Internet Platform.

Scripting Languages (JavaScript and VBScript)

◆ Scripting languages can be used to extend browser and Web server w ith database functionality

◆ As script code is embedded in HTML, it is downloaded ev ery time page is accessed

◆ Updating browser is simply a matter of changing Web document on serv er

◆ Some popular scripting languages are: Jav aScript, VBScript, Perl, and PHP

◆ They are interpreted languages, not compiled, making it easy to create small applications.

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Common Gateway Interface (CGI)

Specification for transferring information betw een a Web server and a CGI program.

◆ Server only intelligent enough to send documents and to tell brow ser what kind of document it is

◆ But serv er also knows how to launch other programs

◆ When serv er sees that URL points to a program (script), it executes script and sends back script’s output to browser as if it w ere a file.

CGI - Environment

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◆ Before serv er launches script, prepares number

of env ironment v ariables representing current state of the server, who is requesting the information, and so on

◆ Script picks this up and reads STDIN

CGI

◆ Then performs necessary processing and writes its output to STDOUT

◆ Script responsible for sending MIME header,

w hich allows browser to differentiate between components

◆ CGI scripts can be written in almost any language, prov ided it supports reading and writing of an operating system’s environment v ariables

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◆ Four primary methods for passing information from brow ser to a CGI script:

– Passing parameters on the command line.

– Passing environment variables to CGI programs – Passing data to CGI programs via standard

input.

– Using extra path information.

CGI - Passing Parameters on Command Line

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CGI - Advantages

◆ CGI is the de facto standard for interfacing Web

serv ers with external applications.

◆ Possibly most commonly used method for interfacing Web applications to data sources

◆ HTTP nev er intended for long exchanges or interactivity

◆ Serv er has to generate a new process or thread for each CGI script

◆ Security.

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HTTP Cookies

◆ Cookies can make CGI scripts more interactive

◆ Cookies are small text files stored on Web client

◆ CGI script creates cookie and has Web serv er send it to client’s brow ser to store on hard disk

◆ Later, when client revisits Web site and uses a CGI script that requests this cookie, client’s browser sends information stored in the cookie

◆ Cookies can be used to store registration information or preferences (e.g for v irtual shopping cart).

Extending the Web Server

◆ To overcome limitations of CGI, many servers prov ide an API that adds functionality to server

◆ Two of main APIs are Netscape’s NSAPI and Microsoft’s ISAPI

◆ Scripts are loaded in as part of the serv er, giv ing back-end applications full access to all the I/O functions of server

◆ One copy of application is loaded and shared between multiple requests to server

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Extending the Web Server

◆ Approach more complex than CGI, possibly requiring specialized programmers

◆ Can provide v ery flexible and powerful solution

◆ API extensions can prov ide same functionality as

a CGI program, but as API runs as part of the serv er, API approach can perform significantly better than CGI

◆ Extending Web serv er is potentially dangerous, since server executable is being changed

Comparison of CGI and API

◆ CGI and API both extend capabilities of serv er

◆ CGI scripts run in environment created by Web serv er program.

◆ Scripts only execute once Web serv er interprets request from browser, then returns results back

to the serv er

◆ API approach not nearly so limited in its ability

Java

◆ Proprietary language dev eloped by Sun

◆ Originally intended to support env ironment of netw orked machines and embedded systems.

◆ Now, Java is rapidly becoming de facto language

for Web computing

◆ Interesting because of its potential for building

Web applications ( applets) and server applications (serv lets)

Java

‘A simple, object-oriented, distributed, interpreted, robust, secure, architecture neutral, portable, high-performance, multi-threaded and dynamic language’

◆ Has a machine-independent target architecture, the Java Virtual Machine (JVM)

◆ Since almost ev ery Web browser vendor has already licensed Jav a and implemented an embedded JVM, Java applications can currently

be deployed on most end-user platforms.

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Java

◆ Class file can be loaded from local hard driv e or downloaded from network

◆ Finally, bytecodes must be verified to ensure that they are v alid and do not v iolate Java’s security restrictions

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◆ Loosely speaking, Jav a is a ‘safe’ C++

◆ Safety features include strong static type checking, automatic garbage collection, and absence of machine pointers at language lev el

◆ Safety is central design goal: ability to safely transmit Java code across Internet

◆ Security is also integral part of Jav a’s design - sandbox ensures untrusted application cannot gain access to system resources

– J2SE: aimed at typical desktop and workstation

env ironments Serves as foundation for J2EE and Web services.

– J2EE: aimed at robust, scalable, multiuser, and

secure enterprise applications.

◆ J2EE was designed to simplify complex problems with dev elopment, deployment, and management

of multi-tier enterprise applications

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Java 2 Platform

Java 2 Platform

◆ Cornerstone of J2EE is Enterprise JavaBeans (EJB), a standard for building server-side components in Java.

◆ Three types of EJB components:

– EJB Session Beans, components implementing

business logic, business rules, and workflow

– EJB Message-Driv en Beans (MDBs), which

process messages sent by clients, EJBs, or other J2EE components.

– EJB Entity Beans, components encapsulating

some data contained by the enterprise Entity Beans are persistent.

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Java 2 Platform

◆ Two types of entity beans:

– Bean-Managed Persistence (BMP), which

requires developer to w rite code top make bean persist using an API such as JDBC or SQLJ

– Container-Managed Persistence (CMP) , where

persistence is prov ided automatically by container.

◆ Discuss 5 ways to access a database: JDBC, SQLJ, CMP, JDO, and JSP.