'Attribute'에 해당되는 글 1

  1. 2011.02.23 Business database building

Business database building

Education | 2011.02.23 10:26 | Posted by 스마트 안전보건
What is wrong with flat files?


Multiple value problems - many supplier of ordered item

Update anomalies- change ph#

Insertion anomalies - new supplier

Deletion anomalies - delete supplier

Relational Database

Two or more tables that are linked together through common fields

Each table in can be joined with more than one table

Each row called a tuple

Each column has an allowable set of values called a domain



Entity Relationship modeling

A database is a collection of entities

Entities contain properties called attributes - example - “title” for books

Relationship relate entity classes

▫ Book is writtenBy an Author


Purpose of Attributes

Describe important properties of entity

Help uniquely identify individual entities

▫ this is the primary key

▫ publisher id number, customer id number

Describe relationship between entities in different entity classes

Entity models to Relational Databases

We implement the abstract ER model to create a concrete database

▫ entity classes transform to relations

▫ attributes transform to fields

▫ entity sets transform to rows or tuples in relations

▫ one-to-many relationships modeled with foreign keys

▫ many-to-many relationships modeled with new table schemes



Design Phase I: Create ER Diagram
Identify the entity 
Identify the A++ attribute - the primary key 
Identify relationships 
Identify cordinality
1 to many
many to many

e.g., Runner and Race
Runners participate races (many to many relationship)
A runner receives prizes (one to many relationship)


Design Phase II: Create table structure
Entities - tables
Attributes - columns
1 to many relationships

Many to many relationships


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