(Databases) Databases & DBMS & ER Model & Relational Databases

Databases 

: an organized collection of data that exists over a long period of time ( Persistent storage )

- collection of data about different kinds of individuals(Entities) and the relationship between individuals.

DBMS ( Database Management System )

: a complex software package developed to store and mange databases

 

- supports convenient, efficient, and secure access and manipulation of large amounts of data.

- (high-level) Programming interface : gives users the ability to create, query, and modify the data

- Persistent stroge : supports the storage of data over a long period of time

- Transaction management and recovery : controls access to shared data from multiple, simultaneous users with properties Atomicity, Consistency, Isolation, Durability (ACID) 

 

In a database application system, the DBMS acts as an "interface" between the database application and the database.

 

* 3 types of inputs to DBMS

: Queries, Transactions(data modification), and Schema Creations/Modification.

: transcation manager: responsible for the consistency of the data

 

* Two Types of Languages provided by DBMS (ex - SQL)

- DDL (Data Definition Language)

: language for defining a database schema

 

- DML (Data Manipulation Language)

: language for accessing and manipulating the data

 

 

==>  Database system = Database + DBMS 

 

ER Model 

: An Entity Relationship shows how different entity sets in the DB relate to each other, and the constraints that my exist. 

 

Relational Databases

: A relational database is a set of relations ( Relations can be viewd as tables of data )

(ex) Oracle, IBM, Microsoft, etc. 

What is Relations?? 

: A relation schema describing its structure includes a set of attributes(ordered columns in a table)

and each attribute has a domain(int, varchar, float,...) which specifies the set of valid values for the attribute 

 

Data Independence

: the ability to modify definition of schema at one level with littel or no affect on the schema at a higher level.