Database concepts

DATABASE CONCEPTS

DBMS(DATABASE MANAGEMENT SYSTEM)

DBMS contains information about a particular enterprise
Collection of interrelated data
Set of programs to access the data
An environment that is both convenient and efficient to use
Database Applications:
Banking: all transactions
Airlines: reservations, schedules
Universities: registration, grades
Sales: customers, products, purchases
Online retailers: order tracking, customized recommendations
Manufacturing: production, inventory, orders, supply chain
Human resources: employee records, salaries, tax deductions
Databases touch all aspects of our lives

Purpose of Database Systems
In the early days, database applications were built directly on top of file systems
Drawbacks of using file systems to store data:
Data redundancy and inconsistency
Multiple file formats, duplication of information in different files
Difficulty in accessing data
Need to write a new program to carry out each new task
Data isolation multiple files and formats
Integrity problems
Integrity constraints (e.g. account balance > 0) become buried in program code rather than being stated explicitly
Hard to add new constraints or change existing ones

Drawbacks of using file system
Atomicity of updates
Failures may leave database in an inconsistent state with partial updates carried out
Example: Transfer of funds from one account to another should either complete or not happen at all
Concurrent access by multiple users Concurrent accessed needed for performance
Uncontrolled concurrent accesses can lead to inconsistencies
Example: Two people reading a balance and updating it at the same time
Security problems
Hard to provide user access to some, but not all, data
Database systems offer solutions to all the above problems

Levels of Abstraction

Physical level: describes how a record (e.g., customer) is stored.

Logical level: describes data stored in database, and the relationships among the data.
type customer = record
customer_id : string; customer_name : string; customer_street : string; customer_city : string;
end; View level: application programs hide details of data types.
Views can also hide information (such as an employees salary) for security purposes.
DBMS(DATABASE MANAGEMENT SYSTEM)

An architecture for a database system