Friday, September 22, 2017

CBSE Class 12 - Computer Science/ Informatics Practices - Database Concepts - Important Terms (#cbseNotes)

Basic Database concepts - Important Terms

CBSE Class 12 - Computer Science/ Informatics Practices - Database Concepts - Important Terms (#cbseNotes)

Data:
Raw facts and figures which are useful to an organization. We cannot take decisions on the basis of data.


Information:
Well processed data is called information. We can take decisions on the basis of information.


Field:
Set of characters that represents specific data element.


Record:
Collection of fields is called a record. A record can have fields of different data types.


File:
Collection of similar types of records is called a file.


Data Model:
Data models capture the nature of and relationships among data and are used at different levels of abstraction as a database is conceptualized and designed.




Entity:
A person, a place, an object, an event, or a concept in the user environment about which the organization wishes to maintain data.


Table:
Collection of rows and columns that contains useful data/information is called a table. A table generally refers to the passive entity which is kept in secondary storage device.


Relation:
Relation (collection of rows and columns) generally refers to an active entity on which we can perform various operations.


Database:
Collection of logically related data along with its description is termed as database.


DBMS:
Software used to manage databases is called Data Base Management System (DBMS).


RDBMS:
A DBMS used to manage Relational Databases is called an RDBMS (Relational Data Base Management System). Some popular RDBMS software available are: Oracle, MySQL, SQL-Server.


Tuple:
A row in a relation is called a tuple.


Attribute:
A column in a relation is called an attribute. It is also termed as field or data item.


Degree:
Number of attributes in a relation is called degree of a relation.


Cardinality:
Number of tuples in a relation is called cardinality of a relation.


Primary Key:
Primary key is a key that can uniquely identifies the records/tuples in a relation. This key can never be duplicated and NULL.


Foreign Key:
Non key attribute of a table acting as primary key in some other table is known as Foreign Key in its current table. This key is used to enforce referential integrity in RDBMS.


Candidate Key:
Attributes of a table which can serve as a primary key are called candidate key. Alternate Key: All the candidate keys other than the primary keys of a relation are alternate keys for a relation.


Conceptual Schema:
A detailed, technology-independent specification of the overall structure of organizational data.


DBA:
Data Base Administrator is a person (manager) that is responsible for defining the data base schema, setting security features in database, ensuring proper functioning of the data bases etc.


SQL:
It stands for Structured Query Language. SQL is a non procedural language that is used to create, manipulate and process the databases(relations).


Select Operation:
The select operation selects tuples from a relation which satisfy a given condition. It is denoted by lowercase Greek Letter σ (sigma).


Project Operation:
The project operation selects columns from a relation which satisfy a given condition. It is denoted by lowercase Greek Letter π (pi). It can be thought of as picking a sub set of all available columns.


Union Operation:
The union (denoted as ∪) of a collection of relations is the set of all distinct tuples in the collection. It is a binary operation that needs two relations.


Set Difference Operation:
This is denoted by – (minus) and is a binary operation. It results in a set of tuples that are in one relation but not in another.


Constraints:
Constraints are the conditions that can be enforced on the attributes of a relation. The constraints come in play whenever we are trying to insert, delete or update a record in a relation.


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