Database Concepts

Frage	Antworten
Database	Collection of interrelated data.
File System	It is a container to store data in a computer.
Difficulty in Access	Files themselves do not provide any mechanism to retrieve data.
Data Redundancy	Redundancy means same data are duplicated in different places
Data Inconsistency	Data inconsistency occurs when same data maintained in different places do not match.
Data Isolation	Data isolation is a property that determines when and how changes made by one operation become visible to other concurrent users and systems.
Data Dependence	Data are stored in a specific format or structure in a file independently.
DBMS	Database Management System
Examples of open source and commercial DBMS	MySQL, Oracle, PostgreSQL, SQL Server, Microsoft Access, MongoDB.
Database Schema	It is the skeleton of the database that represents the structure (table names and their fields/columns), the type of data each column can hold, constraints on the data to be stored (if any), and the relationships among the tables.
Data Constraint	certain restrictions or limitations on the type of data that can be inserted in one or more columns of a table.
Meta-data or Data Dictionary	The database schema along with various constraints on the data is stored by DBMS in a database catalog or dictionary, called meta-data. A meta-data is data about the data.
Database Instance	When we define database structure or schema, state of database is empty i.e. no data entry is there.
Query	A query is a request to a database for obtaining information in a desired way.
Data Manipulation	Modification of database consists of three operations viz. Insertion, Deletion or Update.
Database Engine	Database engine is the underlying component or set of programs used by a DBMS to create database and handle various queries for data retrieval and manipulation.
RDBMS	Relational Database Management System
ATTRIBUTE	Characteristic or parameters for which data are to be stored in a relation.
TUPLE	Each row of data in a relation (table) is called a tuple.
DOMAIN	It is a set of values from which an attribute can take a value in each row.
DEGREE	The number of attributes in a relation is called the Degree of the relation.
CARDINALITY	The number of tuples in a relation is called the Cardinality of the relation.
Candidate Key	A super key with no redundant attribute is known as candidate key.
Primary key	unique identification of tuples.
Foreign key	Primary key of another table
Composite Primary key	If no single attribute in a relation is able to uniquely distinguish the tuples, then more than one attribute are taken together as primary key. Such primary key consisting of more than one attribute is called Composite Primary key.

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