database objects

7/29/2019 Database Objects

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DATABASE OBJECTS


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Primary keys and Foreign key

attributes

Primary keys

First column

Most designers follow this convention

Unique for each row

Principle: A row is unique if any one of its columns is

unique.


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Primary keys and Foreign key

attributes

Foreign Key

An attribute in one table that matches a primary key of

another table

Many database designers use the same field name forrelated primary key and foreign key columns to

indicate the two columns tie together two tables.

Join

Connecting to or more related tables based on their

matching primary/foreign keys


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Schema of a Relation

Formal term: Relation

Less formal term: Table

Data processing term: File

Schemaoutline

The schema of a relation for a table is the relations

name and its attributes

Customer(CustomerID, CompanyName, Contact, Address, City, State)


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Data dictionary

A collection of tables containing the definition,

characteristics, structure and description of all data

maintained by the RDBMS.

Accessed by the database administrator or theobjects owner

Other information stored:

View definitionsObject owner names

Database login names and password


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Data dictionary

Fields in the data dictionary are automatically

changed whenever an objects structure is changed

Rename operation

Delete operation


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Normalization

Past: data is stored on flat files

Normalization

The process of determining the correct location for each

attribute

Unnormalized databases can lead to redundant,

inconsistent, and anomalous information being stored in

tables

Normal form

A particular subset of ways that attributes can be organized

into tables


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Normal forms

First normal form

Remove repeating data groups

Second normal form

Remove functional dependencies

Third normal form

Remove transitive dependencies

Boyce/Codd normal form

Fourth normal form

Fifth normal form

Domain/Key normal form

Goal:

Start with a collection of tables (relations)

Apply normalization

Arrive at an equivalent collection of tables in a higher normal form


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Table Relationships

One-to-one

Indicate unnecessary tables

Exceptions to the rule

One-to-many Databases often contain tables with one to may

relationships

Many-to-many

Difficult to represent Most database designers create a new table to represent

many-to-many relationship into one-to-many relationship

Intermediate relationship


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General rules on relationships

1. Primary keys cannot be null.

2. Create a foreign key from the primary key on the oneside if the one-to-many relationship

3. Many-to-many relationships are handled by creatingan additional table that consists entirely of theparents tables primary keys.

4. One-to-one relationships indicate unnecessary tables

in the database. Normally, you should merge the twotables.

Exceptions: if there are too many columns in one table


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Fundamental Relational Database

Operations

SELECT

PROJECT

JOIN


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SELECT


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PROJECTION


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JOIN


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Database Design

A well-designed database models an enterprisesoperations

What happen if the business has a bad databasedesign?

Modeling

An important aspect of database design

Carefully choosing rows and columns

Methods Draw information from existing business documents

Entity-relationship modeling


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Creating user views and relations

Listing potential attributes from an existing

document

Identify functional dependencies

Selecting which attributes belongs to which table

Revision (apply normalization)


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Developing Entity-Relationship Models

Introduced by P.P. Chen in 1976 (Chen Notation)

Entities

Attributes

Relationships

Crows Foot Notation

database objects

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