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 DataAn architecture for a database system

DATA MODELING AND ITS DATA MODELING AND ITS COMPONENTSCOMPONENTS

Data Modeling Data Modeling

• In computer science, In computer science, data modelingdata modeling is the process of is the process of structuring and organizing data.structuring and organizing data.

• These data structures are then typically implemented in These data structures are then typically implemented in a database management system.a database management system.

• In addition to defining and organizing the data, In addition to defining and organizing the data, • data modeling may also impose constraints or limitations data modeling may also impose constraints or limitations

on the data placed within the structure on the data placed within the structure

• Managing large quantities of structured and Managing large quantities of structured and unstructured data is a primary function of unstructured data is a primary function of information systems.information systems.

• Data models describe structured data for Data models describe structured data for storage in data management systems such as storage in data management systems such as relational databases.relational databases.

• They typically do not describe unstructured They typically do not describe unstructured data, such as word processing, documents, data, such as word processing, documents, email messages, pictures, digital audio, and email messages, pictures, digital audio, and video. video.

Data modelData model• Data model fall into three different groups.Data model fall into three different groups.

1.Object based logical model.1.Object based logical model.

2.Record based logical model.2.Record based logical model.

3.Physical model3.Physical model

Object based logical modelObject based logical model• object based logical model are used in describing data at the object based logical model are used in describing data at the

logical and view level.logical and view level.• They are characterized by the fact that they provide fairly They are characterized by the fact that they provide fairly

flexible structuring capabilities and allow data constrains to a flexible structuring capabilities and allow data constrains to a specified explicity.specified explicity.

Record Based Logical ModelRecord Based Logical Model

• Record based logical model used in describing data at the Record based logical model used in describing data at the logical and view level. logical and view level.

• In contrast to object based data models they are used both to In contrast to object based data models they are used both to specify the overall logical structures of the data base and to specify the overall logical structures of the data base and to provide a higher level description of the implementation.provide a higher level description of the implementation.

• Record based models are so named because the database is Record based models are so named because the database is structured in fixed format records of several types. Each structured in fixed format records of several types. Each record type defines a fixed number of fields, or attributes, record type defines a fixed number of fields, or attributes, and each field is usually fixed lengthand each field is usually fixed length

The three most widely accepted record based data models are The three most widely accepted record based data models are

1.1. Relational Model Relational Model 2.2. Network Model Network Model 3.3. Hierarchical Model.Hierarchical Model.

RELATIONAL MODELRELATIONAL MODEL

• RelationalRelational model uses a model uses a collection of tables to collection of tables to represent both data and represent both data and the relationship among the relationship among those data. Each table those data. Each table has multiple columns and has multiple columns and each column has a each column has a unique name.unique name.

Student codeStudent code namename

k101k101 rajaraja

s102s102 geetageeta

Table Name: Student

Course codeCourse code Course nameCourse name

C21C21 agronomyagronomy

C32C32 mathsmaths

C33C33 economicseconomics

C50C50 extensionextension

C81C81 hortihorti

C86C86 pathologypathology

Table Name: CourseTable Name: Course

NETWORK MODELNETWORK MODEL

• Data in the network model are represented by collection Data in the network model are represented by collection of records and relation ship among data are represented of records and relation ship among data are represented by links, which can be viewed as pointers.by links, which can be viewed as pointers.

• The records in the database are organized as collection The records in the database are organized as collection of arbitary graphs.of arbitary graphs.

K101Rajat

Kataria

c32

maths

C34 AEX

c21

AGR C50 ENT

S102 Geeta Subramanian

C33 AEC

C81 HOR

C86 PAT

96 56 88 69 76

92 89 82 92 96

HIERARCHICAL MODEL.HIERARCHICAL MODEL.

• Hierarchical model is similar to the network model in the sense Hierarchical model is similar to the network model in the sense that data and relationship among data are represented by that data and relationship among data are represented by records and links, respectively. records and links, respectively.

• It differs from Network model in the records are organized as It differs from Network model in the records are organized as collection of trees rather then arbitrary graphs. collection of trees rather then arbitrary graphs.

• Student code stu.nameStudent code stu.name

Course code , cou.name, marksCourse code , cou.name, marks

k101 raja

C21 agronomy

88

c32 maths 96

c33 economics 69

c34 extension 56

c50 entomology 76