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DBMS-ER2, Study notes of Database Management Systems (DBMS)

Christ UniversityDatabase Management Systems (DBMS)

The slides are explained with an example on DBMS. What are entities, attributes and relationship in DBMS and explains it further with an ER diagram.

Typology: Study notes

2010/2011

Uploaded on 08/31/2011

aditi
aditi 🇮🇳

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PROBLEM GIVEN
• Still Water Antiques company buys and sells
antiques of all kinds.
• Still Water works with many different individual
called Clients
• Clients sell, buy and both sell and buy items from
still water.
• Owner wants to record commission paid, actual
selling price, sales tax and date sold while selling
an item to a client.
• Owner wants to record purchase cost, date
purchased and condition at the time of purchase.
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PROBLEM GIVEN

• Still Water Antiques company buys and sells

antiques of all kinds.

• Still Water works with many different individual

called Clients

• Clients sell, buy and both sell and buy items from

still water.

• Owner wants to record commission paid, actual

selling price, sales tax and date sold while selling

an item to a client.

• Owner wants to record purchase cost, date

purchased and condition at the time of purchase.

PROBLEM and ANALYSIS

Still Water Company Still Water is a company that

which

Includes items eg. Furniture, jewelry, chinaware, etc.

Each item is uniquely identified by , so it is a KEY

ATTRIBUTE or a

IDENTIFIER of each item. Each item is also characterized by description

which is a COMPOSITE ATTRIBUTE and consists of price, condition and

open ended comment. Thus description is a fundamental attribute and its

components are price, condition and open ended comment. Since

comments can have more than one values so it is a MULTIVALUED

ATTRIBUTE.

Antiques

Item_no.. Description Price

Condition Comment

Includes

Owner of the company wants to record ,

and when he buys any item from the clients .Since these

attributes are related to relationship type ,therefore these are

ATTRIBUTES ON RELATIONSHIP.

Similarly owner wants to record , , and

when he sells any item to the clients. Since these attributes are

related to relationship type ,therefore these are also ATTRIBUTES

ON RELATIONSHIP.

Condition_at_purchase Purchase_cost date_of_ purchase Buys Selling_price sells Sales_tax Date_sold Comm_paid

ENTITIES

An entity is a person, place, object, event or concept in the user environment about which organization wishes to maintain data. Entities are represented by a rectangular box Here Entities types are:

Still Water Company

Antiques

Clients

A COMPOSITE ATTRIBUTE A composite attribute is an attribute that can be broken down into component parts. Description Price (^) Condition

Comment

Client_add City Street add State Client_name Mid_name last_name first_name

Multivalued attribute A multivalued attribute can have more than one value. It is represented by an ellipse with double lines. Here multivalued attribute is:

CommentComment

ATTRIBUTES ON RELATIONSHIPS Attributes which are associated with the relationships. They are connected to the relationship symbol. Here attributes on relationship are: Condn_at_pur date_of_ purchase Pur_cost Buys Sales_tax Selling_price Date_sold Comm_paid sells

Still Water Company

Sales_tax Comm_paid Date_sold Buys

Includes Antiques

Description Price (^) Condition

Clients

Client_add Client_name Client_no. Item_No date_of_ purchase Pur_cost Selling_price

Comment

sells City Street add State Condn_at_pur first_name Mid_name last_name E R Diagram