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Web Technology and DBMSs

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Title: Web Technology and DBMSs


1
Chapter 28
  • Web Technology and DBMSs
  • Transparencies

2
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

3
Chapter 28 - Objectives
  • Extending the Web Server
  • Java and JDBC, SQLJ, Servlets, and JSP
  • Microsoft Web Solution Platform ASP and ADO
  • Oracle Internet Platform.

4
Introduction
  • Web 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.

5
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.

6
Internet
  • Worldwide 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).

7
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.

8
eCommerce and eBusiness
  • eCommerce - Customers can place and pay for
    orders via the businesss 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.

9
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.

10
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 Webs success is due to its simplicity
    and platform-independence.

11
Basic Components of Web Environment
12
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.

13
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.

14
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.

15
HyperText Markup Language (HTML)
16
HyperText Markup Language (HTML)
17
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.

18
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

19
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.

20
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 organizations DBMS.

21
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.

22
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.

23
Two-Tier Client-Server Architecture
24
Three-Tier Client-Server Architecture
  • Client side presented two problems preventing
    true scalability
  • Fat client, requiring considerable resources on
    clients computer to run effectively.
  • Significant client side administration overhead.
  • By 1995, three layers proposed, each potentially
    running on a different platform.

25
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.

26
Three-Tier Client-Server Architecture
27
Advantages of Web-DBMS Approach
  • DBMS advantages
  • Simplicity
  • Platform independence
  • Graphical User Interface
  • Standardization
  • Cross-platform support
  • Transparent network access
  • Scalable deployment
  • Innovation

28
Disadvantages of Web-DBMS Approach
  • Reliability
  • Security
  • Cost
  • Scalability
  • Limited functionality of HTML
  • Statelessness
  • Bandwidth
  • Performance
  • Immaturity of development tools

29
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.

30
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.

31
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
    scripts output to browser as if it were a file.

32
CGI - Environment
33
CGI
  • CGI defines how scripts communicate with Web
    servers.
  • A CGI script is any script designed to accept and
    return data that conforms to the CGI
    specification.
  • Before server launches script, prepares number of
    environment variables representing current state
    of the server, who is requesting the information,
    and so on.
  • Script picks this up and reads STDIN.

34
CGI
  • Then performs necessary processing and writes its
    output to STDOUT.
  • Script responsible for sending MIME header, which
    allows browser to differentiate between
    components.
  • CGI scripts can be written in almost any
    language, provided it supports reading and
    writing of an operating systems environment
    variables.

35
CGI
  • Four primary methods for passing information from
    browser 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.

36
CGI - Passing Parameters on Command Line
37
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.

38
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.

39
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 clients browser to store on hard disk.
  • Later, when client revisits Web site and uses a
    CGI script that requests this cookie, clients
    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.

40
Extending the Web Server
  • To overcome limitations of CGI, many servers
    provide an API that adds functionality to server.
  • Two of main APIs are Netscapes NSAPI and
    Microsofts ISAPI.
  • Scripts are loaded in as part of the server,
    giving 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.

41
Extending the Web Server
  • Approach more complex than CGI, possibly
    requiring specialized programmers.
  • Can provide very flexible and powerful solution.
  • API extensions can provide same functionality as
    a CGI program, but as API runs as part of the
    server, API approach can perform significantly
    better than CGI.
  • Extending Web server is potentially dangerous,
    since server executable is being changed.

42
Server-Side JavaScript for Database Access
43
Comparison of CGI and API
  • CGI and API both extend capabilities of server.
  • CGI scripts run in environment created by Web
    server program.
  • Scripts only execute once Web server interprets
    request from browser, then returns results back
    to the server.
  • API approach not nearly so limited in its ability
    to communicate.
  • API-based extensions are loaded into same address
    space as Web server.

44
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).

45
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.

46
Java
47
Java
  • Before Java application can be executed, it must
    first be loaded into memory.
  • Done by Class Loader, which takes .class
    file(s) containing bytecodes and transfers it
    into memory.
  • Class file can be loaded from local hard drive or
    downloaded from network.
  • Finally, bytecodes must be verified to ensure
    that they are valid and do not violate Javas
    security restrictions.

48
Java
  • Loosely speaking, Java is a safe C.
  • Safety features include strong static type
    checking, automatic garbage collection, and
    absence of machine pointers at language level.
  • Safety is central design goal ability to safely
    transmit Java code across Internet.
  • Security is also integral part of Javas design -
    sandbox ensures untrusted application cannot gain
    access to system resources.

49
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.

50
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.

51
Java 2 Platform
52
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).

53
JDBC
  • JDBC API consists of two main interfaces an API
    for application writers, and a lower-level driver
    API for driver writers.
  • Applications and applets can access databases
    using
  • ODBC drivers and existing database client
    libraries
  • JDBC API with pure Java JDBC drivers.

54
JDBC
55
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.

56
SQLJ
  • Another JDBC-based approach uses Java with static
    embedded SQL.
  • SQLJ comprises a set of clauses that extend Java
    to include SQL constructs as statements and
    expressions.
  • SQLJ translator transforms SQLJ clauses into
    standard Java code that accesses database through
    a CLI.

57
Comparison of JDBC and SQLJ
  • SQLJ is based on static embedded SQL while JDBC
    is based on dynamic SQL.
  • Thus, SQLJ facilitates static analysis for syntax
    checking, type checking, and schema checking,
    which may help produce more reliable programs at
    loss of some functionality.
  • It also potentially allows DBMS to generate an
    execution strategy for the query, thereby
    improving performance of the query.

58
Comparison of JDBC and SQLJ
  • JDBC is low-level middleware tool with features
    to interface Java application with RDBMS.
  • Developers need to design a relational schema to
    which they will map Java objects, and must write
    code to map Java objects to corresponding rows of
    relations.
  • Problems
  • need to be aware of two different paradigms
    (object and relational)
  • need to design a relational schema to map onto an
    object design
  • need to write mapping code.

59
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.

60
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.

61
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).

62
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.

63
OLE DB Architecture
64
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.

65
Active Server Pages (ASP)
66
ActiveX Data Objects (ADO)
  • Programming extension of ASP supported by
    Microsoft IIS for database connectivity.
  • Supports following key features
  • Independently-created objects.
  • Support for stored procedures.
  • Support for different cursor types.
  • Batch updating.
  • Support for limits on number of returned rows.
  • Support for multiple recordsets.
  • Designed as an easy-to-use interface to OLE DB.

67
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.

68
Microsoft Access and Web Page Generation
  • Microsoft Access provides 3 wizards for
    automatically generating HTML pages
  • Static pages user can export data to HTML
    format.
  • Dynamic pages using ASP user can export data to
    an asp file on Web server.
  • Dynamic pages using data access pages data
    access pages are dynamic HTML Web pages bound
    directly to data in the database. Can be used
    like Access forms, except pages are stored as
    external files.

69
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.
  • OMGs CORBA technology.
  • IIOP for object interoperability and RMI.
  • Java, EJB, JDBC, and SQLJ for database
    connectivity, Java servlets, and JSP.

70
Oracle Internet Platform
71
Oracle Internet Application Server (iAS)
  • A reliable, scalable, secure, middle-tier
    application server designed to support eBusiness.
  • Currently available in three versions
  • Standard Edition lightweight Web server with
    minimal application support
  • Enterprise Edition for Web sites that handle
    high volume of transactions
  • Wireless Edition same as EE but also includes
    Portal-to-Go for delivering content to wireless
    devices.

72
iAS Communication Services
  • Handles all incoming requests received by iAS, of
    which some are processed by the Oracle HTTP
    Server and some requests are routed to other
    areas of iAS.
  • Oracle HTTP Server is extended version of Apache
    Server.
  • Although default Apache HTTP Server supports only
    stateless transactions, it can be configured to
    support stateful transactions using Apache JServ.

73
Oracle HTTP Server Modules (mods)
  • Oracle has enhanced several of the compiled
    Apache mods provided with Apache server, and has
    added Oracle-specific ones e.g.
  • mod_ssl, provides standard S-HTTP
  • mod_plsql, routes PL/SQL requests to Oracle
    PL/SQL service, which then delegates servicing to
    PL/SQL programs
  • mod_perl, forwards Perl application requests to
    the embedded Perl Interpreter
  • mod_jserv, routes all servlet requests to the
    embedded Apache JServ servlet engine.

74
Business Logic Services
  • These services support the application logic
    e.g.
  • Oracle JVM, a server-side Java platform
    supporting EJBs, CORBA, and database stored
    procedures.
  • Oracle PLSQL, a scalable engine for running
    business logic against data in the Oracle Cache
    and the Oracle database.
  • Oracle Forms, enables users to run applications
    based on Oracle Forms technology over Internet or
    intranet to query or modify data in the database.

75
Presentation Services
  • These services deliver dynamic content to client
    browsers, supporting servlets, JSP, Perl/CGI
    scripts, PL/SQL pages, forms, and business
    intelligence e.g.
  • Apache Jserv, a Java servlet engine
  • OracleJSP, an implementation of Suns JSP
  • Oracle PSP (PL/SQL Server Pages), analogous to
    JSP, but uses PL/SQL rather than Java for the
    server-side scripting. In the simplest case, a
    PSP is nothing more than an HTML file or an XML
    file.

76
Oracle Portal Services
  • A portal is a Web-based application that provides
    a common, integrated entry point for accessing
    dissimilar data types on a single Web page.
  • Oracle Portal provides portal services for users
    connecting from a traditional desktop.
  • Oracle Portal-to-Go is a portal service for
    delivering information and applications to mobile
    devices. Portal-to-Go allows portal sites to be
    created that use Web pages, Java applications,
    and XML-based applications.
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