2. UNIT -1
Topics
Section : 1
Introduction to database Systems
File System Versus DBMS
View Of data- Data abstraction,View levels,Data models,Instances & Schemas
Data Independence,Database languages,Database architecture,Database
users
3. Introduction to database Systems
Database: Database is a collection of inter-related data which helps in efficient
retrieval, insertion and deletion of data from database and organizes the data in the
form of tables, views, schemas, reports etc.
Database management system (DBMS) refers to the technology for creating and
managing databases. DBMS is a software tool to organize (create, retrieve, update, and
manage) data in a database.
4. The main aim of a DBMS is to supply a way to store up and retrieve database information
that is both convenient and efficient.
Peoples usually used DBMS (softwares) such as DBASE IV or V, Microsoft ACCESS, or
EXCEL ( store data in the form of a database)
A datum is a unit of data. Meaningful data combined to form information. MS. ACCESS
is one of the most common examples of database management software.
5. File System Versus DBMS
File System
File Management System, better known as File System is the most ancient and still the
most popular way to keep your data files organized on your drives.
It is an easy way to store data in general files like images, text, videos, audios etc., but
security is less because only options available to these files are the options given by the
operating system such as locks, hidden files and sharing. These files are hard to
maintain when it comes to frequent changes to these files.
6. File System Versus DBMS
DBMS
DBMS stores data in the form of interrelated tables and files. These are generally consist of
database management system providers that are used to store and manipulate databases
Database Management System is great way to manage data as,
Data redundancy (Repetitions) is minimized due to interrelation of data entities.
Data integration. It also provide a procedure for data integration due to centralization of
data in the database.
Security of data is also maximized using password protection, encryption/decryption, granting
authorized access and others.
7. View Of data
Date :16-06-2020
Data abstraction
Database systems are made-up of complex data structures.
To ease the user interaction with database, the developers hide internal irrelevant details
from users. This process of hiding irrelevant details from user is called data abstraction.
8. Three levels of abstraction:
Physical level: This is the lowest level of data abstraction. It describes how data is actually stored in
database. You can get the complex data structure details at this level.
Logical level: This is the middle level of 3-level data abstraction architecture. It describes what data is
stored in database.
View level: Highest level of data abstraction. This level describes the user interaction with database
system
Refer : Note 1
10. Data models
Date-17-06-2020
A Database model defines the logical design and structure of a database and defines how data will be
stored, accessed and updated in a database management system.
Data models define how data is connected to each other and how they are processed and stored inside the
system.
The very first data model could be flat data-models, where all the data used are to be kept in the same
plane.
Relational Model is the most widely used database model, there are other models too:
11. Relational Model is the most widely used database model, there are other models too:
Hierarchical Model
Network Model
Entity-relationship Model
Relational Model
12. Hierarchical Model
This database model organises data into a tree-like-structure, with a single root, to which all the other data is linked.
The hierarchy starts from the Root data, and expands like a tree, adding child nodes to the parent nodes.
Network Model
This is an extension of the Hierarchical model. In this model data is organised more like a graph, and are allowed to
have more than one parent node.
13. Date :18-06-2020
Entity-relationship Model ( E –R Diagram)
In this database model, relationships are created by dividing object of interest into entity and its characteristics into
attributes.
Different entities are related using relationships
Relational Model
In this model, data is organised in two-dimensional tables and the relationship is maintained by storing a common
field.
Refer: Notes
14. DBMS Schema & Instance
Schema Instance
Design of a database is called the schema. • The data stored in database at a particular
moment of time is called instance of database
Database schema defines the variable
declarations in tables that belong to a particular
database
• The value of these variables at a moment of
time is called the instance of that database
15. we have a schema that shows the relationship between
three tables:
• Course
• Student
• Section.
The diagram only shows the design of the database, it
doesn’t show the data present in those tables.
Schema is only a structural view(design) of a
database as shown in the diagram
16. Levels of Database
Date : 19-06-2020
The database has 3 levels
Physical/Internal
Conceptual
External
18. Data Independence of DBMS
Data Independence is defined as a property of DBMS that helps you to change the Database schema at
one level of a database system without requiring to change the schema at the next higher level.
Data independence helps you to keep data separated from all programs that make use of it
In DBMS there are two types of of data independence
Physical data independence
Logical data independence
19. Physical Data Independence
Type of Schemas & their Implementation
External Schema
View 1: Course info(cid:int,cname:string)
View 2: studentinfo(id:int. name:string)
Conceptual Shema
Students(id: int, name: string, login: string, age: integer)
Courses(id: int, cname.string, credits:integer)
Enrolled(id: int, grade:string)
Physical Schema
Relations stored as unordered files.
Index on the first column of Students.
