Database Management Systems

History of Database Technology

•        Hierarchical and Network Models were introduced in 60s.
•          Still we can see the use of these database models.

 NEED

Database Management Systems are basically used to dealing with
huge amount of Data.

 What is Data ?

Data is any source that can be recorded or saved.

Ex- text, numbers, images, videos, speech

 What is Database ?

Database is a collection of related Data.

Evolution of database Storage

1. Final Oriented Systems
2. Database Management Systems.

Problems with File Oriented Systems

1. Data Redundancy - Each application has its own files which leads
                     to input data several times and update all the
                     occurrences. Valuable storage space is wasted to
                     data duplication.

2. Inconsistent data - Several versions of the same data may exist.

3. Security Problems

Advantages of database Approach

1. Minimal data Redundancy
2.Consistency of data
3.sharing of data
4.data control
5.Security

Disadvantages of databases

1. Complexity
2. Large size
3. High Cost
4. Additional money must be spent for Hardware Cost


Main Components of database Management Systems.

1. Hardware - Set of physical devices

ex - computers, printers, connecting cables

2. DBMS Software - used to define, create, maintain and provide
                   access to the database.

ex - MS Access, Oracle, SQL Server, MYSQL and etc....

3. Liveware - People who need information from the database and
              People responsible for the database maintain.

4. DATA - Database must contain correct and valid data

Relational Model Based Systems     

•              Introduced in 1970

Object-Oriented Based Systems (OODBMSs)

·         

•         Introduced in late 80s.

Data Model

A set of concepts to describe the structure of a database.

Categories of Data Models

1. Conceptual data models:

2. Physical data models:

3. Implementation data models:

4. Self-Describing Models

Database Schema

                A description of a database structure. This may be includes descriptions of the structure, data types, and the constraints on the database.

2. Schema Diagram

                An illustration of database schema

3. Schema Construct

                An Object within the Schema

                Ex: Employee, Company

Database Statement

                All the data in the database at a particular time. 

Three-Schema Architecture

•  Used to explain database system organization
•  There are mainly three common levels
•  Internal Schema – Explains the Physical storage structures and accessible paths.
•  Conceptual Schema – Describes the structure and Constraints for the whole database.
•  External Schemas – To explain various user views.

Data Independence

Logical Data Independence - Ability to change the Conceptual schema without having to change the                external schemas and their associated applications.

Physical Data Independence – Capability to change the internal schema without having to change the conceptual schema.

Database Management Systems Languages

1.       Data Definition Language (DDL)

2.       Data Manipulation Language (DML)

Centralized DBMS

Combines DBMS Software, Hardware, Application programs and user interface processing software.

2-Tier (Client-Server) Architecture

Clients can access the specialized servers as needed.

Three Tier (Client-Server) Architecture

Used in Web applications

Intermediate Layer can be defined as Application Server or Web Server

This Architecture can enhance the Security of the system compared to the 2-Tier architecture

1.       Database server only accessible through the middle tier

DBMSs classification as to the data model used

1.       Legacy: Network, Hierarchical.

2.       Currently Used : Relational, Object-oriented, Object-relational

3.       Recent : Key-value storage systems,

NoSQL systems: document based, column based, graph based and key-value based

Native XML DBMSs.

    

Also there some other terms that can be classify DBMSs, Some of them are….

1.       . Single user vs. Multiple user
2.       . Centralized vs. Distributed

Entity-Relationship model

Entities

·       

1.             Displayed in a rectangular box.
2.          Entities are specific object that are represented are represented in the database.

Ex: Student, Faculty, Course

Weak Entity type

An Entity that does not have a key attribute (Primary key) and dependent on another entity type.

Attributes

·        

1.        Displayed in ovals.
2.             Key value attribute is underlined.

Ex: Student entity may have the attributes Name, student_id, Address, sex, BirthDate.

Type of Attributes

1.          Simple

Entity has a single atomic value for the attribute

Ex: Birthday, Gender

1. 2   Composite

·         Attribute may be built on set of other several components

·         Sub components of a composite attributes are connected to the oval representing the composite attribute.

Ex: Name (FirstName, MiddleName, LastName)

3.       Multi valued

·         An Entity may have multiple values for that attribute.

·         Multivalued attributes displayed in double ovals

Value

Each entity has a value for each of its attributes.

 Ex: Student entity

                               Name=’Harry Oliver’

                                Student_id=’123456’

                                Address= ‘33/13 New Street’

                                Sex=’Male’

                                BirthDate=’25-05-1996’

Relationships

·       

           A relationship relates two or more entities with a specific meaning.

·         Represents by a Diamond shaped box in ER diagrams.

To be Continued...