Three-Tier and n-Tier Architectures
for Web Applications

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

Two-Tier Client/Server Architectures for DBMSs

The user interface programs and application programs can run on the client side. When DBMS access is required, the program establishes a connection to the DBMS (which is on the server side); once the connection is created, the client program can communicate with the DBMS. A standard called Open Database Connectivity (ODBC) provides an application … Read more

Basic Client/Server Architectures in DBMS

The client/server architecture was developed to deal with computing environments in which a large number of PCs, workstations, file servers, printers, database servers, Web servers, e-mail servers, and other software and equipment are connected via a network. The idea is to define specialized servers with specific functionalities. For example, it is possible to connect a … Read more

Centralized DBMSs Architecture in DBMS

Architectures for DBMSs have followed trends similar to those for general computer system architectures. Older architectures used mainframe computers to provide the main processing for all system functions, including user application programs and user interface programs, as well as all the DBMS functionality. The reason was that in older systems, most users accessed the DBMS … Read more

Tools, Application Environments, and Communications Facilities in DBMS

Tools in DBMS Tools are often available to database designers, users, and the DBMS. CASE tools12 are used in the design phase of database systems. Another tool that can be quite useful in large organizations is an expanded data dictionary (or data repository) system. In addition to storing catalog information about schemas and constraints, the … Read more

Database System Utilities

In addition to possessing the software modules just described, most DBMSs have database utilities that help the DBA manage the database system. Common utilities have the following types of functions: Loading. A loading utility is used to load existing data files—such as text files or sequential files—into the database. Usually, the current (source) format of … Read more

DBMS Interfaces

User-friendly interfaces provided by a DBMS may include the following: Menu-based Interfaces for Web Clients or Browsing These interfaces present the user with lists of options (called menus) that lead the user through the formulation of a request. Menus do away with the need to memorize the specific commands and syntax of a query language; … Read more

DBMS Languages

Once the design of a database is completed and a DBMS is chosen to implement the database, the first step is to specify conceptual and internal schemas for the database and any mappings between the two. In many DBMSs where no strict separation of levels is maintained, one language, called the data definition language (DDL), … Read more

Data Independence in DBMS

The three-schema architecture can be used to further explain the concept of data independence, which can be defined as the capacity to change the schema at one level of a database system without having to change the schema at the next higher level. We can define two types of data independence: Logical data independence Logical … Read more