chapter 13 databases and the internet
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Chapter 13 Databases and the Internet. Spring 2014. Uses for Web-based DB Applications. e-commerce has pushed organizations to develop Web-based database applications To create world-wide markets To deliver information To provide better customer service To communicate with their suppliers - PowerPoint PPT PresentationTRANSCRIPT
Chapter 13Databases and the Internet
Spring 2014
Uses for Web-based DB Applications
• e-commerce has pushed organizations to develop Web-based database applications– To create world-wide markets– To deliver information– To provide better customer service– To communicate with their suppliers– To provide training for employees– To expand the workplace– …Many other innovative activities
Databases and the WWW
• WWW is a loosely organized information resource• Some websites use static linked HTML files
– can become inconsistent and outdated
• Many organizations provide dynamic access to databases directly from the Web– introduces new problems for designers and DBAs – combination of communications technology, information retrieval
technology and database technology– XML a standard for document storage, exchange, and retrieval.
Origins of The Internet
• Developed from Arpanet, communications network created in the 1960s by DARPA, US agency, for linking government and academic research institutions
• Used a common protocol, TCP/IP• US National Science Foundation took over
management of the network, then referred to as the Internet
• Navigating and using the Internet required considerable sophistication
World Wide Web
• Tim Berners-Lee proposed a method of simplifying access to Internet resources in 1989
• Led to the development of the World Wide Web
• included notions of URL, HTTP, HTML, hypertext, graphical browsers with links
• Automated finding, downloading, and displaying files on the Internet
Browsers and URLs
• Browser-– software for searching, retrieving, presenting, and
traversing resources on the WWW– Ex. Microsoft Internet Explorer, Mozilla Firefox, Google
Chrome, Apple Safari and others
• URL –Uniform Resource Locator– Specific type of Uniform Resource Identifier (URI)– String giving the location of any type of resource on the
Internet-Web pages, mailboxes, downloadable files, etc. – Gives protocol, server name, path name to resource
HTTP
• Communications protocol– Standard for structure of messages– HTTP request usually has a few lines of text
• HTTP method field (GET or POST), URI of resource, HTTP version• host header, with host name and HTTP port• user agent line, shows the type of the client (optional)• types of files the client will accept (optional)
• HTTP is a stateless protocol– No facility for remembering previous interactions– Creates a problem for e-commerce, which requires a
continuous session with the user
HTML
• Data format used for presenting content on the Internet
• A markup language because HTML documents contain tags that provide formatting information for the text
– Ex <HEAD> ,<BODY> , <B> ,<U> ,<I>, <H1> <UL> <LI> and their ending tags
• HTML document can contain applets, audio files, images, video files, other content
XML
• Extensible Markup Language - standard for document storage, exchange, and retrieval
• Created in 1996 by the World Wide Web Consortium (W3) XML Special Interest Group
• Users can define their own markup language, with their own tags for data items in documents, including databases
• Can define the structure of heterogeneous databases• supports translation of data between different
databases
Components of XML Documents• Element-the basic component • Contains one or more XML elements
– each with a start tag showing the name of the element, some character data, and an end tag
• Can have sub-elements-must be properly nested• Can have attributes-names and values shown inside the
element’s start tag• Attributes occur only once within each element, while sub-
elements can occur any number of times• Comments can occur anywhere <!-- -->,• can contain entity references-refer to external files, common
text, Unicode characters, or reserved symbols
Well-Formed XML Document
• Obey rules of XML– Starts with XML declaration– Root element contains all other elements– All elements properly nested
DTD and XML Schema
• Users can define their own markup language by writing either– A Document Type Declaration (DTD)
• A specification for a set of rules for the elements, attributes, and entities of a document
• A document that obeys the rules of its associated DTD is type-valid
– An XML Schema • New, more powerful way to describe the structure of documents • A document that conforms to an XML schema is schema-valid
DTD Rules• DTD is enclosed in <!DOCTYPE
name[DTDdeclaration]>• each element is declared using a type declaration
with structure <!ELEMENT (content type)> • In an element declaration, the name of any sub-
element can be followed by one of the symbols *, + or ?, to indicate the number of times the sub-element occurs
• Attribute list declarations for elements are declared outside the element
• DTD can be external or internal (embedded in instance document)
XML Schema• Permits more complex structure than DTD• Additional fundamental datatypes, UDTs• User-created domain vocabulary • Supports uniqueness and foreign key constraints• Schema lists elements and attributes
– Elements may be complex, which means they have sub-elements, or simple elements can occur multiple times
– Attributes or elements can be used to store data values– Attributes used for simple values that are not repeated
• Can validate schema at several websites
Three-tier Architecture
• Three major functions for an Internet environment: presentation, application logic, data management
• Placement of functions depends on architecture of system • Three tier architectures completely separate application logic
from data management– Client handles user interface, the presentation layer- first tier– Application server executes application logic -the middle tier– Database server forms the third tier
• Communications network connects each tier to the next
Advantages of 3-tier Architecture
• Allows support for thin clients that only handle the presentation layer
• Independence of tiers; may use different platforms
• Easier application maintenance on the application server
• Integrated transparent data access to heterogeneous data sources
• Scalability
Presentation Layer
• HTML forms often used at the presentation layer
• Scripting languages such as Perl, JavaScript, JScript, VBScript, may be embedded in HTML to provide some client-side processing
• Style sheets specify how data is presented on specific devices-CSS, XSL
Application Server• Middle tier - responsible for executing applications
– Determines the flow of control– Acquires input data from presentation layer– Makes data requests to database server– Accepts query results from database layer– Uses them to assemble dynamically generated HTML pages
• Server-side processing can use different technologies such as Java Servlets, Java Server pages, etc.
• CGI, Common Gateway Interface, can be used to connect HTML forms with application programs
• To maintain state during a session, servers may use cookies, hidden fields in HTML forms, and URI extensions. – Cookies generated at the middle tier using Java’s Cookie class, sent to
the client, where they are stored in the browser cache
Data Layer
• Third layer is standard database or other data source
• Ideally on separate server
Oracle Web Programming
• PL/SQL Web Toolkit– Handles all three layers using PL/SQL
• PL/SQL Server Pages (PSP)– embed PL/SQL code in HTML pages
• JDBC– Application Programming Interface (API) standard
for relational database access from Java
• And several other methods
PL/SQL Web Toolkit• Allows user to access Oracle from a webpage
– Using a browser, user sends request to a Web server, passing input values
– Server sends a message to the database server, invoking a PL/SQL stored procedure in the Oracle database, passing parameters as needed.
– Stored procedure invokes subprograms in the PL/SQL Web Toolkit, generating a Web page dynamically
– Generated page is passed to the Web server– Web server displays the page in the client’s browser
See Figure 13.8
Web Toolkit htp Package
• Enter from SQL*Plus in usual wayCREATE OR REPLACE PROCEDURE pagename IS BEGIN
• Functions generate HTML tagsHTP.HTMLOPEN; HTP.HEADOPEN; HTP.TITLE(‘ ‘); HTP.HEADCLOSE; HTP.BODYOPEN;
HTP.HEADER(n,‘ ‘ ); HTP.PARA; HTP.PRINT(' '); HTP.BODYCLOSE; HTP.HTMLCLOSE
• Inside the body, htp.formOpen (parameter list ) creates a form
• Form elements created using procedureshtp.formText, htp.formCheckbox, htp.formRadio, htp.formTextarea, and others
PL/SQL Server Pages (PSP)• provide the dynamic database content • embed PL/SQL statements in HTML pages• Write standard HTML scripts, using the delimiters <% and
%> to identify PL/SQL statements• Can have Web Toolkit calls in the same application• handled by the Oracle PL/SQL Web gateway (mod_plsql)• reside on the server side• PSP page is loaded into Oracle database space using utility
program loadpsp
• See Figure 13.12
Figure 13.12<%@ page language=”PL/SQL”%><%@ page contentType=”text/html”%><%@ plsql procedure=”StudentList”%><% /** This example displays the last name and first name of every student in the Student table.**/ %><%CURSOR stu_cursor ISSELECT lastName, firstNameFROM StudentORDER BY lastName;%><html><head><meta http-equiv=”Content-Type”content=”text/html”><title>Student List</title></head><body TEXT=”#000000”BGCOLOR=”#FFFF00”><h1>Student List</h1>
<table width=”50%”border=”1”><tr><th align=”left”>Last Name</th><th align=”left”>First Name</th></tr><% FOR stu IN stu_cursor LOOP %><tr><td> <%= stu.lastName %> </td><td> <%= stu.firstName %> </td></tr><% END LOOP;%></table></body></html>
JDBC
• API-standard for relational database access from Java
• Includes a set of Java classes and interfaces• Oracle and other vendors have extended
functionality• Applications are platform independent• Can run on a variety of servers and DBMSs.
JDBC Application Steps• At the start of the application, import the Java classes
import java.sql.*;• For Oracle database add
import oracle.jdbc;• Load the JDBC drivers. For Oracle,write
Class.forName(“oracle.jdbc.driver.OracleDriver”);• Connect to the database using the DriverManager class -GetConnection method creates a connection object, which is used for all
communicationconn = DriverManager.getConnection("jdbc:oracle:oci8:url”,”yourId”,”yourpassword”); • Use SQL to interact with the database and Java for the logic in the
application program• Close the connection object to disconnect from the database conn.close();• See Figure 13.13
Figure 13.13import java.sql.*;import java.io.*;class Test{public static void main(String args[]) {try {Class.forName(“oracle.jdbc.driver.OracleDriver”);} catch (ClassNotFoundException e) {System.out.println(“Cannot load OracleDriver”);}Connection conn = null;Statement stmt = null;ResultSet rset = null;try {conn = DriverManager.getConnection(“jdbc:oracle:oci8”, ”Jones”, ”sesame”);
stmt = conn.createStatement();rset = stmt.executeQuery(“select stuId, lastName, firstName from Student”);while (rset.next())System.out.println(rset.getString(1)+” “ + rset.getString(2)+” “ +rset.getString(3));rset.close();stmt.close();conn.close();} catch (SQLException e) {System.out.println(“SQL error:“ + e.getMessage());} }}
The Connection Object• Has 3 JDBC classes for communicating with database
– Statement -for SQL statements with no parameters
– PreparedStatement precompiled SQL statement – to be executed many times
– CallableStatement -for executing stored procedures
• Has 3 methods to create instances of these classes– createStatement returns a new Statement object
– prepareStatement takes an SQL statement, precompiles it, and stores it in a PreparedStatement object
– prepareCall for call to a stored procedure; has methods for handling input and output parameters and executing the procedure;returns a CallableStatement
• Statement object is used for executing SQL statements– Methods executeUpdate, executeQuery. etc.
– executeQuery method executes an SQL statement and returns a ResultSet object
– ResultSet class has many useful methods; includes a cursor to present one row at a time
– Within a row, columns can be retrieved using a get method
XML and the Semi-structured Data Model• Semi-structured data model uses a tree structure• Nodes represent complex objects or atomic values • An edge represents either relationship between an object and
its sub-object, or between an object and its value• Leaf nodes, with no sub-objects, represent values • Nodes of the graph for a structured XML document are ordered
using pre-order traversal, depth-first, left-to-right order• There is no separate schema, since the graph is self-describing• See Figure 13.14
XML Parsers
• Read in the XML document as a string• parsing technique can use
– event-driven model - a single pass through document– tree-based model- parsing tree built in memory
• DOM parsing- Document Object Model)– W3C standard for the tree-based model– Has methods to create nodes, modify nodes, and delete nodes of tree– Allows the programmer to navigate the tree structure as needed and supports
dynamic data updating
• SAX parsing (Simple API for XML)– Reads document, recognizes each fragment of XML syntax– Streams a series of events – document handlers and error handlers– Events sent to event handlers for processing the elements
XML Data Manipulation
• XQuery is W3C standard query language for XML data– Uses the abstract logical structure of a document as it is
encoded in XML Schema or DTD– Queries use a path expression, which comes from an
earlier language, XPath – Consists of the document name and specification of the
elements to be retrieved, using a path relationship– Can add conditions to any nodes in a path expression– Evaluated by reading forward in the document until a
node of the specified type and condition is encountered
FLWOR Expressions• XQuery uses a FLWOR expression::FOR, LET, WHERE, ORDER BY, and
RETURN clauses• Ex
FOR $C IN doc(“CustomerList.xml”)//Customer)WHERE $C/Type=”Individual”ORDER BY NameRETURN <Result> $N/Name, $N/Status </Result>
• Allows for binding of variables to results• Allows for iterating through the nodes of a document• Allows joins to be performed• Allows data to be restructured• XQuery provides many predefined functions, including count, avg,
max, min, and sum, which can be used in FLWOR expressions.
XML and Relational Databases
• Relational DBMSs extended their native datatypes to allow storage of XML documents
• Also possible to use SQL with XPath expressions to retrieve values from the database
• Existing heterogeneous databases can be queried using standard languages such as SQL, and query results can be placed into an XML instance document
• Query language has to have facilities that can tag and structure relational data into XML format
XML-Database Conversion
• Ultimate goal is Round-Tripping– accept data in XML form– transform it into a relational database– query and update and the database using SQL– transform the output back into XML format
• All without loss of content
Oracle XML DB
• standard feature of Oracle• User can create databases in which the XMLType
is used as a native datatype• actually an object type, can be used as a type for
a column or for an object table, or for parameters and PL/SQL variables
• provides methods for accessing and querying XML content, using XML and SQL syntax
• Follows W3C recommendations for XML
Oracle XML Developer’s Kits• (XDKs) for PL/SQL, Java, C and C++• Include libraries and utilities for using XML with those host
languages• Allows documents to be parsed
– The PL/SQL XDK supports DOM parsing only– Java, C, and C++ parsers provide both DOM and SAX parsing
• XML SQL Utility (XSU) allows two-way mapping between XML and SQL– Can extract data from XML documents and insert it into database tables or
views, using a standard canonical mapping– Update or delete data in the database tables or views using SQL– Extract data from object-relational tables or views and transform the Results
Set into XML