13. Databases on the Web

Transcription

1 13. Databases on the Web

2 Requirements for Web-DBMS Integration The ability to access valuable corporate data in a secure manner Support for session and application-based authentication The ability to interface to the database independent of any proprietary Web browser or Web server An open architecture Acceptable performance Support for transactions that span multiple HTTP requests Minimal administration overhead A connectivity solution that takes advantage of all the features of an organization's DBMS A set of high-level application development tools 189

3 Web-DBMS Architecture Three-tier architecture First Tier (Client) a Web browser acting as a 'thin' client Second Tier (Application Server) a Web server Third Tier (Database Server) 190

4 Advantages of the Web-DBMS Approach DBMS advantages Simplicity Platform independence Graphical user interface Standardization Cross-platform support Transparent network access Scalable deployment Innovation 191

5 Disadvantages of the Web-DBMS Approach Reliability Security Cost Scalability Limited functionality of HTML Statelessness Bandwidth Performance Immaturity of development tools 192

6 Approaches to the Web-DBMS Integration Common Gateway Interface (CGI) Server-Side Includes HTTP cookies Extension to the Web server Java and JDBC, JSQL, JRB Scripting languages such as JavaScript and VBScript Microsoft's Active Platform Oracle's Network Computing Architecture (NCA) 193

7 Common Gateway Interface (CGI) CGI is a specification to allow a program (the CGI program) to control the information passed between a Web browser and a Web server during a connection session The CGI program executes at the Web server The output from the CGI program is passed back by the Web server to the Web Browser Information from the browser is passed to the CGI program via environment variables or read from standard input A URL can point to a CGI program Form s data is passed to the CGI program specified in the Action parameter 194

8 Extending the Web Server Server API called non-cgi gateways Netscape Server API (NSAPI) Microsoft's Internet Information Server API (ISAPI) Interface between the server and back-end applications using DLL or shared objects More powerful and complex than CGI Reliability and non-portability problems 195

9 JAVA, JDBC, JSQL A proprietary language developed by Sun A simple, object-oriented, distributed, interpreted, robust, secure, architecture neutral, high-performance, multi-threaded and dynamic language The de facto standard language for Web programming Web applications (applets) and server applications (servlets) Java bytecodes (class) can be interpreted by JVM, or translated to native methods JDBC define a databases access API JSQL is a specification for Java with static embedded SQL 196

10 Scripting Languages The script code is embedded in the HTML an interpreted by the client JavaScript Netscape's Web scripting language The JavaScript language resembles Java Server-side JavaScript for database access VBScript Microsoft proprietary interpreted scripting language Syntax like Visual Basic ActiveX controls 197

11 Active Server Pages (ASP) Microsoft ASP is a programming model that allows dynamic, interactive Web pages to be created on the Server VBScript is the default scripting language for ASP ASP files can contain: text, HTML tags, Script command When a browser request and '.asp' file, the Web server calls ASP, which reads the file and executes any commands, and sends the generated HTML page to the browser 198

12 ... Active Server Pages (ASP) With ASP we can Generate dynamic Web pages Process content of HTML forms Create database-driven Web pages Track user sessions Create searchable Web pages Detect the capabilities of different browsers Send and retrieve Integrate custom components into Web site Internet resources aspsite.com, activeserverpages.com, 15seconds.com serverobjects.com, asphole.com msdn.microsoft.com/workshop/server/default.asp microsoft.com/ntserver/web/ 199

13 How ASP Works IIS Static HTML pages.asp dynamic pages ASP.dll A server-side scripting environment ASP editor Script delimiters <% and %> Script language IIS Default ASP language Language=JScript %> <script language= JScript runat= server > 200

14 ASP Example <body> This is a <% for i=1 to 10 %> very, <% next %> very long sentence. <% If Time >= #12:00:00 AM# And Time < #12:00:00 PM# Then %> Good Morning! <% Else %> Hello! <% End If %> 201

15 Internet Security Proxy Servers Improve performance Filter requests Firewalls A system designed to prevent unauthorized access to or from a private network Encryption Secure Sockets Layer (SSL) Secure HTTP (S-HTTP) Kerberos A server of secured user names and passwords 202