Subject: Computer Science
The term database system refers to the components of an organization that defines and regulate the collection, storage, management and use of data within a database environment. From a general management point of view, the database system is composed of the five major parts:
Fig: Database System Environment
A database system gives us a way of gathering together specific pieces of relevant information. It also provides a way to store and maintain that information in a central place. A database system consists of two parts:
The DBMS on which the database system is based, can be classified according to the number of users, the database site locations and the expected type and extent of use.
The numbers of users determine whether the DBMS is classified as a single user or multi-user. A single-user DBMS supports only one user at a time. In other words, if user A is using the database, user B and C must wait until user A has completed his/her database work. If a single user database runs on a personal computer, it is also called a desktop database.
A multiuser DBMS supports multiple users at the same time. If the multiuser database supports a relatively small number of users (less than fifty) or a specific department within an organization, it is called workgroup database. If the database is used by the entire organization and supports many users across many departments, the database is known as an enterprise database.
The database site location might also be used to classify DBMS. For example, DBMS that supports a database located at a single site is called a centralized DBMS. A DBMS that supports a database distributed across several different sites is called distributed DBMS.
The type of computer systems that database can run can be broken down into four broad categories or platforms: Centralized, PC, Client/Server and Distributed.
The different database systems are:
1. Centralized Database Processing System
In a centralized system, all programs run on the main host computer, including the DBMS, the application that accesses the database and the communication facilities that send and receive data from the user’s terminals. The users access the database through either locally connected or dial-up (remote) terminals. The terminals are generally dumb, having little or no processing power of their own and consists of only a screen, keyboard and hardware to communicate with the host.
Fig: Centralized Database Processing System
2. Personal Computer Systems
When a DBMS is run on a PC, the PC acts as both the host computer and the terminal unlike the larger systems. The DBMS functions and the database application functions are combined into one application. Database applications on a PC handle the user input, screen output and access to the data on the disk. Combining these different functions into one unit gives the DBMS a great deal of power, flexibility and speed, usually at the cost of decreased data security and integrity.
Fig: Personal Database Computer System
However, in recent years many have been connected to a Local Area Networks (LANs). In a LAN, the data and usually, the user applications reside on the File Server, a PC running a special Network Operating System (NOS) such as Novell’s NetWare or Microsoft’s LAN Manager or Windows NT. The file server manages the LAN access to other shared resources.
3. Client/Server Database Systems
In a generalized concept, client PC is the computer from where the user requests for data and information and the server provides the requested information. The database application on the client PC referred to as the “front end system” that handles all the screen and user input/output processing.
Fig: Client-Server Database Computer System
The “back end system” on the database server handles data processing and disk access. For example, a user on the front end creates a query for data from the database server and the front-end application sends the request across the network to the server. The database server performs the actual search and sends back only the data that answers the user’s query.
4. Distributed Processing Systems
A simple form of distributed processing has existed for several years. In this limited form, data is shared among various host system via updates sent either through direct connections on the same network or through remote connections via phone or dedicated data lines.
Fig: Distributed Database Processing System
An application which runs one or more of the hosts, extracts the portion of data that has been changed during a programmer-defined period and then transmits the data to either a centralized host or other hosts in the distributed circuit. The other databases are then updated so that all the systems are in sync with each other.
This type of distributed processing usually occurs between departmental computers or LAN's and host systems; the data goes to a large central minicomputer or mainframe host after the close of the business day. The below figure illustrates one form of distributed processing system.
Data security is one of the challenging jobs of Database Administrators (DA). The secured data can be transferred from one server to another server at great distances. For the prevention of data piracy and data mining, proper securities are necessary to be implemented in the system. The two common methods of data security are using the username and password. The username authentication and password verification can allow for data access. So, data security is a preventive measures that aDatabase Administrator (DA) must take for the protection of data from the unauthorized access, theft, corruption, etc.
Fig: Data Security
Khanal, R.C. Khanal, R.C. Computer Concept for XII. Pashupatigriha Marga, Thapathali, Kathmandu, Nepal: Ekta Books Distributors Pvt. Ltd., 2010. 47-50.
Adhikari, Deepak Kumar.,et.al., Computer Science XII,Asia Publication Pvt.Ltd
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