Database management system
- 1. DATABASE MANAGEMENT SYSTEM - DBMS Database Management System or DBMS in short refers to the technology of storing and retrieving users’ data with utmost efficiency along with appropriate security measures. Database is a collection of related data and data is a collection of facts and figures that can be processed to produce information. Mostly data represents recordable facts. Data aids in producing information, which is based on facts. For example, if we have data about marks obtained by all students, we can then conclude about toppers and average marks. A database management systemstores data in such a way that it becomes easier to retrieve, manipulate, and produce information. Characteristics A modern DBMS has the following characteristics Real-world entity − A modern DBMS is more realistic and uses real-world entities to design its architecture. It uses the behavior and attributes too. For example, a school database may use students as an entity and their age as an attribute. Relation-based tables − DBMS allows entities and relations among them to form tables. A user can understand the architecture of a database just by looking at the table names. Less redundancy − DBMS follows the rules of normalization, which splits a relation when any of its attributes is having redundancy in values. Consistency − Consistency is a state where every relation in a database remains consistent. There exist methods and techniques, which can detect attempt of leaving database in inconsistent state. A DBMS can provide greater consistency as compared to earlier forms of data storing applications like file-processing systems. Query Language − DBMS is equipped with query language, which makes it more efficient to retrieve andmanipulate data. A user canapply as many and as different filtering options as required to retrieve a set of data. Multiuser and Concurrent Access − DBMS supports multi-user environment and allows them to access and manipulate data at the same time. Though there are restrictions on transactions when users attempt to handle the same data item, but users are always unaware of them. Multiple views − DBMS offers multiple views for different users. A user who is in the Sales department will have a different view of database than a person working in the Production department. This feature enables the users to have a concentrate view of the database according to their requirements.
- 2. Security − Features like multiple views offer security to some extent where users are unable to access dataof other users anddepartments. DBMS offers many different levels of securityfeatures, which enables multiple users to have different views with different features. For example, a user in the Sales department cannot see the data that belongs to the Purchase department. Users A typical DBMS has users with different rights and permissions who use it for different purposes. Some users retrieve data and some back it up. The users of a DBMS can be broadly categorized as follows – Administrators − Administrators maintain the DBMS and are responsible for administrating the database. They are responsible to look after its usage and by whom it should be used. They create access profiles for users and apply limitations to maintain isolation and force security. Administrators also look after DBMS resources like system license, required tools, and other software and hardware related maintenance. Designers − Designers are the group of people who actually work on the designing part of the database. They keep a close watch on what data should be kept and in what format. They identify and design the whole set of entities, relations, constraints, and views. End Users − End users are the users, who use the applications developed. End users need not know about the working, database design, the access mechanism etc. Theyjust usethe system to get their task done. Database Basic Concepts Entity: Object, concept or event Attribute: Characteristic of an entity Row or Record: specific characteristics of an entity Table: Collection of records Database: Collection of tables
- 3. Each attribute has a unique name within an entity All entries in the column are examples of it Each row is unique Ordering or rows and columns is unimportant Each position (tuple) is limited to a single entry Keys in a Table A key of a relation is a subset of attributes with the following characteristics o Unique identification o Non-redundancy Primary Key o It is a unique identifier of records in a table. o Primary key values may be generated manually or automatically Foreign Key o The primary key from another table, this is the only way join relationships can be established