Intro Flashcards
What is a DBMS
Stands for database management system
It is a system that creates, controls access to and manages queries for DB
What is a Hierarchical database model
Hierarchical: parent-child relationship to store data
What is a Network database model
Network: extension of hierarchical with the same structure, but there is no limit on the number of parents a child can have
What is a relational database model
A database that supports relationships in the form of predefined tables - which is also referred to as ‘relations’.
What is a Object-relational database model
It is similar to relational, but it also supports concepts like class, object, and inheritance.
What is the overall description of the DB called?
The DB schema
When data is retrieved from the database, what do the user see?
The data as it really is or something else?
A representation; an instance.
In RDBMS (relational) What are the three kinds of languages provided to write in
- Data Definition Language (DDL)
- Data Manipulation Language (DML)
- Data Control Language (DCL)
What is DDL?
Data Definition Language:
Used to Defines / modify a schema
CREATE : to create objects in database
ALTER : alters the structure of database
DROP : delete objects from database
RENAME : rename an objects
What is DML?
Data Manipulation Language: used by users to insert, update, delete and retrieve data
What is DCL?
Data Control Language: used by the administrator to control the access to the DB-
What is the external schema
A schema that shows only relevant info for users.
For example, a user from the sales department will see only sales related data.
What is the conceptual schema?
Describes all the entities, their attributes and their relationships with integrity constraints
What is the internal schema?
The internal schema contains the definitions of the stored records, methods, data fields and indexes.
Name the thing that describes how the database looks (relations and attributes and so on)
database schema
