1 Chapter 29 Web Technology and DBMSs Transparencies.

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Chapter 29

Web Technology and DBMSs

Transparencies

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Chapter 28 - Objectives

• Basics of Internet, Web, HTTP, HTML, URLs.• Difference between two-tier and three-tier

client-server architecture.• Advantages and disadvantages of Web as a

database platform.• Approaches for integrating databases into

Web:– Scripting Languages– Common Gateway Interface (CGI)– HTTP Cookies

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Chapter 28 - Objectives

– Extending the Web Server– Java and JDBC, SQLJ, Servlets, and JSP– Microsoft Web Solution Platform: ASP and

ADO– Oracle Internet Platform.

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Introduction

• Web: the most popular and powerful networked information system to date.

• As architecture of Web was designed to be platform-independent, can significantly lower deployment and training costs.

• Organizations using Web as strategic platform for innovative business solutions, in effect becoming Web-centric.

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Introduction

• Many Web sites today are file-based where each Web document is stored in separate file.

• For large sites, this can lead to significant management problems.

• 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.

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InternetWorldwide collection of interconnected networks.

• Began in late ‘60s in ARPANET, a US DOD project, investigating how to build networks that could withstand partial outages.

• Starting with a few nodes, Internet estimated to have over 100 million users in 1997, and over 390 million users in over 100 countries in 2001.

• May be 640 million users of Web by year 2003. • About 2.5 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 organization.

• Extranet - An intranet that is partially accessible to authorized outsiders.

• Whereas intranet resides behind firewall and is accessible only to people who are members of same organization, extranet provides various levels of accessibility to outsiders.

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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 transactions may reach $1.3 trillion by 2003.

• eCommerce may account for $3.2 trillion in worldwide corporate revenue by 2003 and could represent 5% of sales in the global economy.

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The Web

Hypermedia-based system that provides a simple ‘point and click’ means of browsing information on the Internet using hyperlinks.

• Information presented on Web pages, which can contain text, graphics, pictures, sound, and video.

• Can also contain hyperlinks to other Web pages, which allow users to navigate in a non-sequential way through information.

• Web documents written using HTML.

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The Web

• Web consists of network of computers that can act in two roles: – as servers, providing information; – as clients (browsers), requesting information.

• Protocol that governs exchange of information between Web server and browser is HTTP and locations within 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

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HyperText Transfer Protocol (HTTP)

Protocol used to transfer Web pages through Internet.

• Based on request-response paradigm:

• Connection - Client establishes connection with Web server.

Request - Client sends request to Web server.

Response - Web server sends response (HTML document) to client.

Close - Connection closed by Web server.

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HyperText Transfer Protocol (HTTP)

• HTTP/1.0 is stateless protocol - each connection is closed once server provides response.

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

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HyperText Markup Language (HTML)

Document formatting language used to design most Web pages.

• A simple, yet powerful, platform-independent document language.

• HTML is an 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)

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HyperText Markup Language (HTML)

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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 services.

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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.

http://www.w3.org/Markup/MarkUp.html

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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 servers. • Need scripts that perform conversions from

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

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Requirements for Web-DBMS Integration

• Ability to access valuable 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 server.

• Connectivity solution that takes advantage 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 variety of systems and technologies. For example: – different Web servers; – Microsoft's (Distributed) Common Object Model

(DCOM/COM);– CORBA/IIOP (Internet Inter-ORB protocol);– Java/Remote Method Invocation (RMI).

• Cost-effective solution that allows for scalability, growth, and changes in strategic directions, and helps reduce applications development costs.

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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-level productivity tools to allow

applications to be developed, maintained, and deployed with relative ease and speed.

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Two-Tier Client-Server Architecture

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Three-Tier Client-Server Architecture

• Client side presented two problems preventing true scalability:– ‘Fat’ client, requiring considerable resources on

client’s computer to run effectively.– Significant client side administration overhead.

• By 1995, three layers proposed, each potentially running on a different platform.

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Three-Tier Client-Server Architecture

• Advantages: – ‘Thin’ client, requiring less expensive hardware.– Application maintenance centralized. – Easier to modify or replace one tier without

affecting others. – Separating business logic from database

functions makes it easier to implement load balancing.

– Maps quite naturally to Web environment.

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Three-Tier Client-Server Architecture

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Advantages of Web-DBMS Approach

• DBMS advantages• Simplicity• Platform independence• Graphical User Interface• Standardization• Cross-platform support• Transparent network access• Scalable deployment• Innovation

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Disadvantages of Web-DBMS Approach

• Reliability• Security• Cost• Scalability• Limited functionality of HTML• Statelessness• Bandwidth• Performance• Immaturity of development tools

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Approaches to Integrating Web and DBMSs

• Scripting Languages. • Common Gateway Interface (CGI).• HTTP Cookies.• Extending the Web Server.• Java, JDBC, SQLJ, Servlets, and JSP.• Microsoft Web Solution Platform: ASP and

ADO.• Oracle Internet Platform.

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Scripting Languages (JavaScript and VBScript)

• Scripting languages can be used to extend browser and Web server with database functionality.

• As script code is embedded in HTML, it is downloaded every time page is accessed.

• Updating browser is simply a matter of changing Web document on server.

• Some popular scripting languages are: JavaScript, 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 between a Web server and a CGI program.

• Server only intelligent enough to send documents and to tell browser what kind of document it is.

• But server also knows how to launch other programs.

• When server sees that URL points to a program (script), it executes script and sends back script’s output to browser as if it were a file.

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CGI - Environment

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CGI - Passing Parameters on Command Line

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CGI - Advantages

• CGI is the de facto standard for interfacing Web servers with external applications.

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

• Advantages:– simplicity, – language independence, – Web server independence, – wide acceptance.

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CGI - Disadvantages

• Communication between client and database server must always go through Web server.

• Lack of efficiency and transaction support, and difficulty validating user input inherited from statelessness of HTTP protocol.

• HTTP never intended for long exchanges or interactivity.

• Server 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 server send it

to client’s browser 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 virtual shopping cart).

• However, not all browsers support cookies.

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Server-Side JavaScript for Database Access

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Java

• Proprietary language developed by Sun.

• Originally intended to support environment of networked 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 (servlets).

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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 every Web browser vendor has already licensed Java and implemented an embedded JVM, Java applications can currently be deployed on most end-user platforms.

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import java.sql.*;import java.io.*;import java.util.*;public class Total1 {

public static void main (String[] arg) { try { Class.forName ("oracle.jdbc.driver.OracleDriver"); } catch (Exception e) { System.out.println("Could not load driver"); }

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// Connect to the database try { Connection conn=DriverManager.getConnection("jdbc:oracle:thin:@orion.towson.edu:1521:cosc", “user_name",“password"); Statement stmt = conn.createStatement (); ResultSet rset=null; try { rset= stmt.executeQuery("SELECT * from department"); ResultSetMetaData rsmd=rset.getMetaData(); while (rset.next()) { System.out.println(" " + rset.getString(1) + " " + rset.getString(2) + " " + rset.getString(3) +" "); } }

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catch (SQLException e){ System.out.println("writetolog: error in SQL "+e+"<br>"); } } catch (SQLException e) { System.out.println("Something wrong " + e.toString());

}}}

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Java

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Java 2 Platform

• In mid-1999, Sun announced it would pursue a distinct and integrated Java enterprise platform:– J2ME: aimed at embedded and consumer-electronics

platforms.– J2SE: aimed at typical desktop and workstation

environments. Essentially equivalent to JDK 1.2.– J2EE: aimed at robust, scalable, multiuser, and secure

enterprise applications.

• J2EE was designed to simplify complex problems with development, deployment, and management of multitier enterprise applications.

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Java 2 Platform• Cornerstone of J2EE is Enterprise JavaBeans

(EJB), a standard for building server-side components in Java.

• Two types of EJB components:– EJB Session Beans, components implementing

business logic, business rules, and workflow. – EJB Entity Beans, components encapsulating

some data contained by the enterprise. Entity Beans are persistent.

• From database perspective, interested in two J2EE components: JDBC and JSP.

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Java 2 Platform

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JDBC• Modeled after ODBC, JDBC API supports

basic SQL functionality. • With JDBC, Java can be used as host

language for writing database applications. • On top of JDBC, higher-level APIs can be

built. • Currently, two types of higher-level APIs:

– An embedded SQL for Java (e.g. SQLJ). – A direct mapping of relational database tables to Java

classes (e.g. Java Blend from Sun).

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JDBC - Advantages/Disadvantages• Advantage of using ODBC drivers is

that they are a de facto standard for PC database access, and are available for many DBMSs, for very low price.

• Disadvantages with this approach:– Non-pure JDBC driver will not necessarily work

with a Web browser.– Currently downloaded applet can connect only

to database located on host machine.– Deployment costs increase.

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Java Servlets

• Servlets are programs that run on Java-enabled Web server and build Web pages, analogous to CGI.

• Have a number of advantages over CGI:– improved performance;

– portability;

– extensibility;

– simpler session management;

– improved security and reliability.

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Java Server Pages (JSP)

• JSP is a Java-based server-side scripting language that allows static HTML to be mixed with dynamically-generated HTML.

• Behind scenes, JSP is compiled into Java servlet and processed by a Java-enabled Web server (JSP works with most Web servers).

• Since servlet is compiled, performance is improved.

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Microsoft Web Solution Platform

• Microsoft Web Solution Platform, a precursor to .NET, has been created for building and deploying interoperable Web solutions.

• Contains various tools, services, and technologies, such as:– Windows 2000, – Exchange Server, – Visual Studio, – HTML/XML, – scripting languages, – components (Java, ActiveX).

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Object Linking and Embedding for DataBases (OLE DB)

• Microsoft has defined set of data objects, collectively known as OLE DB.

• Allows OLE-oriented applications to share and manipulate sets of data as objects.

• OLE DB is an object-oriented specification based on C++ API.

• Components can be treated as data consumers and data providers. Consumers take data from OLE DB interfaces and providers expose OLE DB interfaces.

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OLE DB Architecture

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Active Server Pages (ASP)• ASP is programming model that allows dynamic,

interactive Web pages to be created on server. • ASP provides flexibility of CGI, without

performance overhead discussed previously. • ASP runs in-process with the server, and is

optimized to handle large volume of users. • When an ‘.asp’ file is requested, Web server calls

ASP, which reads requested file, executes any commands, and sends generated HTML page back to browser.

• http://triton.towson.edu/~cscfr/htmlPage/

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Active Server Pages (ASP)

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Comparison of ASP and JSP

• Both designed to enable developers to separate page design from programming logic through use of callable components.

• Differences:– JSP is essentially platform and server independent

whereas ASP primarily restricted to MS Windows-based platforms.

– JSP perhaps more extensible as JSP developers can extend the JSP tags available.

– JSP components are reusable across platforms.– JSP benefits from in-built Java security model.

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Oracle Internet Platform

• Comprises Oracle Internet Application Server (iAS) and Oracle DBMS.

• It is n-tier architecture based on industry standards such as:– HTTP and HTML/XML for Web enablement.

– OMG’s CORBA technology.

– IIOP for object interoperability and RMI.

– Java, EJB, JDBC, and SQLJ for database connectivity, Java servlets, and JSP.

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Oracle Internet Platform