Download Intro to Web Databases-Database System Concepts-Lecture 18 Slides-Computer Science and more Slides Database Management Systems (DBMS) in PDF only on Docsity!
Computing & Information Sciences CIS 560: Database System Concepts Wednesday, 11 Oct 2006 Kansas State University
Lecture 20 of 42
Wednesday, 11 October 2006
William H. Hsu Department of Computing and Information Sciences, KSU
KSOL course page: http://snipurl.com/va Course web site: http://www.kddresearch.org/Courses/Fall-2006/CIS Instructor home page: http://www.cis.ksu.edu/~bhsu
Reading for Next Class: Second half of Chapter 8, Silberschatz et al. , 5 th^ edition
Intro to Web Databases
Discussion: Online DBs
Computing & Information Sciences CIS 560: Database System Concepts Wednesday, 11 Oct 2006 Kansas State University
Chapter 8: Application Design and DevelopmentChapter 8: Application Design and Development
z User Interfaces and Tools z Web Interfaces to Databases z Web Fundamentals z Servlets and JSP z Building Large Web Applications z Triggers z Authorization in SQL z Application Security
Computing & Information Sciences CIS 560: Database System Concepts Wednesday, 11 Oct 2006 Kansas State University
User Interfaces and Tools User Interfaces and Tools
z Most database users do not use a query language like SQL. Forms Graphical user interfaces Report generators Data analysis tools (see Chapter 18) z Many interfaces are Web-based z Back-end (Web server) uses such technologies as Java servlets Java Server Pages (JSP) Active Server Pages (ASP)
Computing & Information Sciences CIS 560: Database System Concepts Wednesday, 11 Oct 2006 Kansas State University
The World Wide WebThe World Wide Web
z The Web is a distributed information system based on hypertext. z Most Web documents are hypertext documents formatted via the HyperText Markup Language (HTML) z HTML documents contain text along with font specifications, and other formatting instructions hypertext links to other documents, which can be associated with regions of the text. forms, enabling users to enter data which can then be sent back to the Web server
Computing & Information Sciences CIS 560: Database System Concepts Wednesday, 11 Oct 2006 Kansas State University
Web Interfaces to Database (Cont.) Web Interfaces to Database (Cont.)
- Dynamic generation of documents Limitations of static HTML documents Ö Cannot customize fixed Web documents for individual users. Ö Problematic to update Web documents, especially if multiple Web documents replicate data. Solution: Generate Web documents dynamically from data stored in a database. Ö Can tailor the display based on user information stored in the database. E.g. tailored ads, tailored weather and local news, … Ö Displayed information is up-to-date, unlike the static Web pages E.g. stock market information, ..
Computing & Information Sciences CIS 560: Database System Concepts Wednesday, 11 Oct 2006 Kansas State University
Uniform Resources Locators Uniform Resources Locators
z In the Web, functionality of pointers is provided by Uniform Resource Locators (URLs). z URL example: http://www.bell-labs.com/topics/book/db-book The first part indicates how the document is to be accessed Ö “http” indicates that the document is to be accessed using the Hyper Text Transfer Protocol. The second part gives the unique name of a machine on the Internet. The rest of the URL identifies the document within the machine. z The local identification can be: Ö The path name of a file on the machine, or Ö An identifier (path name) of a program, plus arguments to be passed to the program E.g. http://www.google.com/search?q=silberschatz
Computing & Information Sciences CIS 560: Database System Concepts Wednesday, 11 Oct 2006 Kansas State University
HTML and HTTP HTML and HTTP
z HTML provides formatting, hypertext link, and image display features. z HTML also provides input features Ö Select from a set of options Pop-up menus, radio buttons, check lists Ö Enter values Text boxes Filled in input sent back to the server, to be acted upon by an executable at the server z HyperText Transfer Protocol (HTTP) used for communication with the Web server
Computing & Information Sciences CIS 560: Database System Concepts Wednesday, 11 Oct 2006 Kansas State University
Sample HTML Source Text Sample HTML Source Text
A-101 Downtown 500
…
The account relation
Select account/loan and enter number
Computing & Information Sciences CIS 560: Database System Concepts Wednesday, 11 Oct 2006 Kansas State University
Client Side Scripting and SecurityClient Side Scripting and Security
z Security mechanisms needed to ensure that malicious scripts do not cause damage to the client machine Easy for limited capability scripting languages, harder for general purpose programming languages like Java z E.g. Java’s security system ensures that the Java applet code does not make any system calls directly Disallows dangerous actions such as file writes Notifies the user about potentially dangerous actions, and allows the option to abort the program or to continue execution.
Computing & Information Sciences CIS 560: Database System Concepts Wednesday, 11 Oct 2006 Kansas State University
Web ServersWeb Servers
z A Web server can easily serve as a front end to a variety of information services. z The document name in a URL may identify an executable program, that, when run, generates a HTML document. When a HTTP server receives a request for such a document, it executes the program, and sends back the HTML document that is generated. The Web client can pass extra arguments with the name of the document. z To install a new service on the Web, one simply needs to create and install an executable that provides that service. The Web browser provides a graphical user interface to the information service. z Common Gateway Interface (CGI): a standard interface between web and application server
Computing & Information Sciences CIS 560: Database System Concepts Wednesday, 11 Oct 2006 Kansas State University
Three-Tier Web ArchitectureThree-Tier Web Architecture
Computing & Information Sciences CIS 560: Database System Concepts Wednesday, 11 Oct 2006 Kansas State University
Two-Tier Web Architecture Two-Tier Web Architecture
Multiple levels of indirection have overheads
- Alternative: two-tier architecture
Computing & Information Sciences CIS 560: Database System Concepts Wednesday, 11 Oct 2006 Kansas State University
ServletsServlets
z Java Servlet specification defines an API for communication between the Web server and application program E.g. methods to get parameter values and to send HTML text back to client z Application program (also called a servlet) is loaded into the Web server Two-tier model Each request spawns a new thread in the Web server Ö thread is closed once the request is serviced z Servlet API provides a getSession() method Sets a cookie on first interaction with browser, and uses it to identify session on further interactions Provides methods to store and look-up per-session information Ö E.g. user name, preferences, ..
Computing & Information Sciences CIS 560: Database System Concepts Wednesday, 11 Oct 2006 Kansas State University
Example Servlet CodeExample Servlet Code
Public class BankQuery(Servlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse result) throws ServletException, IOException { String type = request.getParameter(“type”); String number = request.getParameter(“number”); …code to find the loan amount/account balance … …using JDBC to communicate with the database.. …we assume the value is stored in the variable balance result.setContentType(“text/html”); PrintWriter out = result.getWriter( ); out.println(“Query Result”); out.println(“”); out.println(“Balance on “ + type + number + “=“ + balance); out.println(“”); out.close ( ); } }
Computing & Information Sciences CIS 560: Database System Concepts Wednesday, 11 Oct 2006 Kansas State University
Server-Side Scripting Server-Side Scripting
z Server-side scripting simplifies the task of connecting a database to the Web Define a HTML document with embedded executable code/SQL queries. Input values from HTML forms can be used directly in the embedded code/SQL queries. When the document is requested, the Web server executes the embedded code/SQL queries to generate the actual HTML document. z Numerous server-side scripting languages JSP, Server-side Javascript, ColdFusion Markup Language (cfml), PHP, Jscript General purpose scripting languages: VBScript, Perl, Python
Computing & Information Sciences CIS 560: Database System Concepts Wednesday, 11 Oct 2006 Kansas State University
Improving Web Server Performance Improving Web Server Performance
z Performance is an issue for popular Web sites May be accessed by millions of users every day, thousands of requests per second at peak time z Caching techniques used to reduce cost of serving pages by exploiting commonalities between requests At the server site: Ö Caching of JDBC connections between servlet requests Ö Caching results of database queries Cached results must be updated if underlying database changes Ö Caching of generated HTML At the client’s network Ö Caching of pages by Web proxy
Computing & Information Sciences CIS 560: Database System Concepts Wednesday, 11 Oct 2006 Kansas State University
Trigger Example in SQL:1999Trigger Example in SQL:
create trigger overdraft-trigger after update on account referencing new row as nrow for each row when nrow.balance < 0 begin atomic insert into borrower (select customer-name, account-number from depositor where nrow.account-number = depositor.account-number ); insert into loan values (n .row.account-number, nrow.branch-name,
- nrow.balance ); update account set balance = 0 where account.account-number = nrow.account-number end
