DATABASE PROGRAMMING Lecture on 16 – 05 – 2005

PREVIOUS LECTURE QUIZ: - Some students were very creative in transforming 2NF to 3NF. Excellent! - Some of the answers were not effective and seemed forcing to decompose a table unnecessarily. - Some students just copied their friends' answers. It's OK for Quiz but not for exam! Remember this, in exam you will get 0.

NEWS 1. All lecture materials and Normalixation quiz marks are available on

DATABASE APPLICATION A database application is a program that is used to manipulate data contained in a database. Application isolates users from the data in the database. Thus, users should not know or care: which data elements are stored in what tables or columns, what data types are used, or how much storage is available. Users should only care about: entering data correctly, or extracting data that is needed.

EVOLUTION OF DATABASE APPLICATION 1. Networks The advent of networks. Exchanging data in a network, lead to 'client-server architecture'. 2. The Internet Exchanging data through some set of networking protocols, such as (SMTP/POP2/IMAP) and FTP. 3. The Web Ability to break database application into modules, so users only know or care about entering data and extracting data that is needed. 4. Intranets Simulates 'mini Internet' in an enterprise. Applying Internet protocols in the intranet.

THREE-TIER MODEL This model divides a database application into three sections or tiers. Each tier receives data and performs a well-defined task upon it. If all goes well, the tier then forwards the data; if an error occurs, it returns an error to the data source. Three-tier model can be described as follows: 1. Bottom Tier: Access to the database (MySQL, Oracle) 2. Middle Tier: Business Logic (JavaBean) 3. Top Tier: User Interface (JSP)

BOTTOM TIER This tier is the 'data-source'. It consist of the database engine, plus drivers and networking software with which your application accesses the engine. For example, MySQL - Connector J - TCP/IP. This tier receives instructions from the tier above it, executes them, generates results (reply to those instructions or error), and return to the tier above it

MIDDLE TIER Sometimes is also called as middleware. This tier is where the application business logic implemented. This tier receives instructions from the tier above it, compares with the rules programmed into it, sends instructions to the bottom tier, waits for reply from the bottom tier, forwards the reply from bottom tier to top tier. Example of rules in this tier: check whether the book is not borrowed, then someone can borrow it.

TOP TIER The top tier holds the user interface, so sometimes also called Presentation Logic as it is responsible for presentation of data. This tier displays instructions and data, waits for user interaction, then forward the instruction to the middle tier.

BENEFITS OF THE THREE- TIER Easier Design It will be easier for human being to think clearly about a complex task by dealing with it one piece at a time. Easier Implementation Each piece can be written and debugged separately. Reusability As it is decomposed into modules, modules that perform the same task should be able to be used repeatedly. Distributability Each module can be distributed over a network.

EXAMPLE OF THE THREE- TIER Bottom Tier: MySQL as database engine. Middle Tier: PHP or JAVABEAN Top Tier: HTML with CSS or Javascript

DRIVERS In our previous discussion, we talk about accessing database directly. However, it is becoming common that we have a driver between our database engine and the application. The most commonly used drivers are built around: Microsoft's Open Database Connectivity (ODBC), and Sun's Java Database Connectivity( JDBC).

ODBC ODBC definition according to Webpodia( Stand for Open DataBase Connectivity, a standard database access method developed by the SQL Access group in The goal of ODBC is to make it possible to access any data from any application, regardless of which database management system (DBMS) is handling the data. ODBC manages this by inserting a middle layer, called a database driver, between an application and the DBMS. The purpose of this layer is to translate the application's data queries into commands that the DBMS understands. For this to work, both the application and the DBMS must be ODBC-compliant -- that is, the application must be capable of issuing ODBC commands and the DBMS must be capable of responding to them.

ODBC(2) Microsoft Definition ( us/odbc/htm/dasdkodbcoverview.asp) : The Microsoft® Open Database Connectivity (ODBC) interface is a C programming language interface that makes it possible for applications to access data from a variety of database management systems (DBMSs). The ODBC interface permits maximum interoperability — an application can access data in diverse DBMSs through a single interface. Furthermore, that application will be independent of any DBMS from which it accesses data. Users of the application can add software components called drivers, which interface between an application and a specific DBMS.

Why ODBC Portable Data Access Code Available in many platforms. Microsoft has made some enhancements to its ODBC. Unix/Linux platform can take the same advantage using UnixODBC Dynamic Data Binding Easy to configure an application to use any ODBC compliant data source. No need to recompile application to change the data source

REFERENCES Michele Petrovsky, Linux Database Bible Chapter 12, Hungry Minds.