Java offers several benefits to the developer creating a front -end application for a database server. Java is ‘Write Once Run Everywhere’ language. This means that Java programs may be deployed without recompilation on any computer architectures and operating systems that possesses a Java Virtual Machine.
In addition there is a cost associated with deployment and maintenance of the hardware and software of any system (client) the corporation owns Systems such as Windows PC, Macintosh and Unix desktop centric clients (fat clients) can cost corporations between $10,000 to $15,000 per installation seat. Java technology has made it possible for any company to use smaller system footprint. These systems are based on Java chip set and run any and all Java programs from built -in Java operating system.
Java based clients (thin clients) that operate with minimum of hardware resources, yet run the complete Java environment are expected to cost around $70 per seat. According to studies, saving for the corporations moving 10,000 fat clients to thin clients systems could be much as $100 million annually. There are many industrial-strength DBMS available in the market. These include Oracle DB2, Sybase and many other popular brands. The challenge to Sun Microsystems faced in the late 1990s was to develop a way for Java developer to write a high level code that accesses all popular DBMSs.
The Sun Microsystems met the challenge in 1996 with the creation of JDBC driver for JDBC API. Both were created out of necessity, because until then Java wasn’t industrial strength programming language since Java was unable to access the DBMS.
The JDBC driver developed by Sun wasn’t driver at all. It was specification that described the detail functionality of JDBC driver. DBMS manufacturers and third-party vendors encouraged to build JDBC drivers that confirmed to Sun’s specifications. Those firm that built JDBS drivers for their product could tap into growing Java applications market. The specifications required a JDBC driver to be a translator that converted low-level proprietary DBMS messages to low-level messages understood by JDBC API and vice-versa.
This meant that Java programmer could use highlevel Java data -objects defined in the JDBC API to write a routine that interacted with the DBMS. Java data objects convert the routine into low-level message that conform to the JDBC driver specification and send them to the JDBC driver. The JDBC driver translates the routine into low-level messages that understood and processed by DBMS.
Database client-server methodology
Relational databases are the most common DBMS. A main characteristic of a relational database is the absolute separation between physical and logical data. Data is accessed through the associated logical model to avoid supplying physical storage locations and to reduce the limitations imposed by using physical information.
Database client/server architecture
Relational databases allow the definition of relations and integrity rules between data sets. E.F. Codd developed this model at the IBM San Jose Research Lab in the 1970s. A language to handle, define, and control data was also developed at the IBM lab: SQL. SQL stands for Structured Query Language.
SQL is a query language that interacts with a DBMS. It allows data access without supplying physical access plans, data retrieval as sets of records, and the performing of complex computations on the data.
The first generation of client-server architectures is called two-tiered. It contains two active components: the client, which requests data, and the server, which delivers data. Basically, the application’s processing is done separately for database queries and updates, and for user interface presentations. Usually the network binds the back end to the front end, although both tiers could be present on the same hardware. For example, hundreds or thousands of airline seat reservation applications can connect to a central DBMS to request, insert, or modify data.
While the clients process the graphics and data entry validation, the DBMS does all the data processing. Actually, it is inadvisable to overload the database engine with data processing that is irrelevant to the server, thus some processing usually also happens on the clients. The typical client-server architecture is shown in Figure below:
Two-tier client server architecture
The two tiers are often called as Application layer includes JDBC drivers, business logic and user interfaces whereas second layer i.e. Database layer consists of RDBMS server.
Although the two-tiered architecture is common, another design is starting to appear more frequently. To avoid embedding the application’s logic at both the database side and the client side, a third software tier may be inserted. In three -tiered architectures, most of the business logic is frozen in the middle tier. In this architecture, when the business activity or business rules change, only the middleware must be modified. Figure below illustrates the three-tier architecture.
Three-tier client/server architecture
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