Several criteria can be used to classify DBMSs. The first is the data model on which the DBMS is based. The main data model used in many current commercial DBMSs is the relational data model, and the systems based on this model are known as SQL systems. The object data model has been implemented in … Read more
Many Web applications use an architecture called the three-tier architecture, which adds an intermediate layer between the client and the database server This intermediate layer or middle tier is called the application server or the Web server, depending on the application. This server plays an intermediary role by running application programs and storing business rules … Read more
Data abstraction Data abstraction generally refers to the suppression of details of data organization and storage, and the highlighting of the essential features for an improved understanding of data Data model A data model a collection of concepts that can be used to describe the structure of a database provides the necessary means to achieve … Read more
In traditional file processing, the structure of data files is embedded in the application programs, so any changes to the structure of a file may require changing all programs that access that file. By contrast, DBMS access programs do not require such changes in most cases. The structure of data files is stored in the … Read more
A number of characteristics distinguish the database approach from the much older approach of writing customized programs to access data stored in files. In traditional file processing, each user defines and implements the files needed for a specific software application as part of programming the application. For example, one user, the grade reporting office, may … Read more
In 1985, Dr. E. F. Codd published a list of 12 rules to define a relational database system.2 The reason Dr. Codd published the list was his concern that many vendors were marketing products as “relational” even though those products did not meet minimum relational standards Dr. Codd’s 12 Relational Database Rules 1: Information All … Read more
The introduction of a database system over the file system provides a framework in which strict procedures and standards can be enforced. Consequently, the role of the human component changes from an emphasis on programming (in the file system) to a focus on the broader aspects of managing the organization’s data resources and on the … Read more
A DBMS performs several important functions that guarantee the integrity and consistency of the data in the database. Most of those functions are transparent to end users, and most can be achieved only through the use of a DBMS. They include data dictionary management, data storage management, data transformation and presentation, security management, multiuser access … Read more
A DBMS can support many different types of databases. Databases can be classified according to the number of users, the database location(s), and the expected type and extent of use. single-user database A single-user database supports only one user at a time. In other words, if user A is using the database, users B and … Read more
The DBMS serves as the intermediary between the user and the database. The database structure itself is stored as a collection of files, and the only way to access the data in those files is through the DBMS The DBMS receives all application requests and translates them into the complex operations required to fulfill those … Read more