Levels of Abstraction
(Views of Data )
• 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 : integer;
end;
• View level: application programs hide details of data types.
Views can also hide information (such as an employee’s salary)
for security purposes.
View of Data
An architecture for a database system
DATA MODELING AND ITS
COMPONENTS
Data Modeling
• In computer science, data modeling is the process of
structuring and organizing data.
• These data structures are then typically implemented in
a database management system.
• In addition to defining and organizing the data,
• data modeling may also impose constraints or limitations
on the data placed within the structure
• Managing large quantities of structured and
unstructured data is a primary function of
information systems.
• Data models describe structured data for
storage in data management systems such as
relational databases.
• They typically do not describe unstructured
data, such as word processing, documents,
email messages, pictures, digital audio, and
video.
Data model
• Data model fall into three different groups.
1.Object based logical model.
2.Record based logical model.
3.Physical model
Object based logical model
• object based logical model are used in describing data at
the logical and view level.
• They are characterized by the fact that they provide
fairly flexible structuring capabilities and allow data
constrains to a specified explicity.
Record Based Logical Model
•
•
•
Record based logical model used in describing data at the
logical and view level.
In contrast to object based data models they are used both to
specify the overall logical structures of the data base and to
provide a higher level description of the implementation.
Record based models are so named because the database is
structured in fixed format records of several types. Each
record type defines a fixed number of fields, or attributes,
and each field is usually fixed length
The three most widely accepted record based data models are
1.
2.
3.
Relational Model
Network Model
Hierarchical Model.
RELATIONAL MODEL
• Relational model uses a
collection of tables to
represent both data and
the relationship among
those data. Each table
has multiple columns and
each column has a
unique name.
Table Name: Student
Student code
name
k101
raja
s102
geeta
Table Name: Course
Course code
Course name
C21
agronomy
C32
maths
C33
economics
C50
extension
C81
horti
C86
pathology
NETWORK MODEL
• Data in the network model are represented by collection
of records and relation ship among data are represented
by links, which can be viewed as pointers.
• The records in the database are organized as collection
of arbitary graphs.
K101
Rajat
Kataria
96
56
S102
69
88
92
c math
3 s
C34
c AG
2 R C33
AEX
Geet
a
Subr
ama
nian
76
89
82
92
C81
C50 ENT
AEC
96
C86
PAT
HOR
HIERARCHICAL MODEL.
• Hierarchical model is similar to the network model in the
sense that data and relationship among data are
represented by records and links, respectively.
• It differs from Network model in the records are
organized as collection of trees rather then arbitrary
graphs.
• Student code stu.name
k101
raja
Course code , cou.name, marks
C21
c32
agro
88
maths
96
c33 nom economics
69
c34
extension
y
c50
entomology
56
76