Geography 357 Geographic Information Systems

1

Geography 357

Geographic Information Systems

Realtional Databases

Relational data model

• Composed of a set of tables called relations

• Records (rows) in the table are called tuples

• Fields (columns) in the table are called domains

• We will use the terms tables, records, and fields


• Each record represents a logical entity (e.g. a student) (or a relationship)

• Each field represents an attribute (property) of the logical entity

1 Wood Bob C Geog357

2 Kent Chuck B Geog115

3 Smith Jane A Geog357

4 Boone Dan B Geog357

ID Last First Grade Class

Student

Relational data model• Each table has a primary key, one field (or a

combination of fields) that has a unique value for each and every record in the table

ID is the primary key in this table (two students may share either a last or first name)






Student


• Tables can be related (joined or linked) together based on their keys.






Student

Geog357 48 Jones

Geog115 120 Brower

Geog20 120 Fountain

Class

Name #Stud Instructor







Student

Geog357 48 Jones

Geog115 120 Brower

Geog20 120 Mennis

Class


Primary key Primary keyForeign key







Student

Geog20 120 Brower

Geog115 120 Jones

Geog357 48 Jones

Class


Jones 332

Brower 517

Instructor

Name Office


• Normalization– process of structuring tables and table

relationships in a logical way that minimizes data redundancy

– 3 rules or steps in normalization• first normal form

• second normal form

• third normal form

Functional Dependency• Main concept associated with

normalization.• Functional Dependency

– Describes the relationship between attributes in a relation.

– For example, B is functionally dependent on A (denoted A B), if each value of A in relation R is associated with exactly one value of B in relation R.

• Diagrammatic representation.


• First normal form– only one value per field for each record

1 Wood Bob C, B Geog357, Geog20

2 Kent Chuck B, D Geog115, Geog356

3 Smith Jane A, B Geog357, Geog20

4 Boone Dan B, A Geog357, Geog455

ID Last First Grades Classes

Student

Violates first normal form


• Second normal form– each non-primary key field must be totally

dependent on the entire primary key (and not on only part of the primary key)

2 Wood Bob C sophomore

4 Kent Chuck B senior

3 Smith Jane A junior

3 Boone Dan B junior

Year Last First Grade Status

Student

Violates second normal form because Status is dependent only on Year, not on Year/Last/First

primary key


• To resolve second normal form violation - create separate tables

Wood Bob C 2

Kent Chuck B 4

Smith Jane A 3

Boone Dan B 3

Last First Grade Year

Student

1 freshman

2 sophomore

3 junior

4 senior

Year Status

Wood Bob C

Kent Chuck B

Smith Jane A

Boone Dan B

Last First Grade

Year

primary key primary key


1 Wood Bob C Geog357 Jones

2 Kent Chuck B Geog115 Brower

3 Smith Jane A Geog357 Jones

4 Boone Dan B Geog357 Jones

ID Last First Grade Class Instructor

Student

• Third normal form– every field that is not a primary key must be

totally and directly dependent on the primary key (no transitive dependency)

Violates third normal form because Instructor is dependent on Class, not on the primary key ID


• To resolve third normal form violation - create separate tables






Student

Geog357 48 Jones

Geog115 120 Brower

Geog20 120 Jones

Class


Class is dependent on primary key ID

Instructor is dependent on primary key Name

Why Normalization?






Student

1. If the instructor to a class changed - all students with that class would have to have their instructors changed

2. Every time a student changed a class, the instructor would also have to be changed

Why Normalization?



3 Smith Jane A Geog357 Knight



Student

Logical inconsistency

Logical inconsistency






These update problems may result in logical inconsistencies in the database

Original table

Updated table

Why Normalization?

When the table is in third normal form, these logical inconsistencies cannot take place.

When an instructor is changed, the change is enforced for all students

When a student changes classes, the change is instructor is automatically enforced






Geog357 48 Jones

Geog115 120 Brower

Geog20 120 Jones

Class



• Operations on the relational data model: defined by relational algebra

– intersection– union– difference– join– projection– selection

Each operation takes one or more tables as input and returns one table as output


• Intersection: find records common to two tables given certain criteria (an and operation)

• Intersection: Find all classes that are Geography classes and that are also Gen Ed classes

Geog357 Jones

Geog115 Brower

Geog20 Fountain

Geog435 Karnes

Geog20 Fountain

Geog115 Brower

Meteo110 Stankle

Meteo200 Turlock

Class Instructor Class InstructorGeography Classes Gen Ed Classes

Geog20 Fountain

Geog115 Brower

Class InstructorResult of Intersection



• Union: find records common to either of two tables (an or operation)

• Union: Find all classes that are either Geography classes or that are Gen Ed classes

Geog357 Jones

Geog115 Brower

Geog20 Fountain

Geog435 Karnes

Geog20 Fountain

Geog115 Brower

Meteo110 Stankle

Meteo200 Turlock


Geog357 Jones

Geog20 Fountain

Geog115 Brower

Geog435 Karnes

Meteo110 Stankle

Meteo200 Turlock

Class Instructor


Results of Union


• Difference: Find the records in one table that are not also present in another table (an xor operation)

• Difference: Find all classes that are Geography classes but that are not Gen Ed classes

Geog357 Jones

Geog115 Brower

Geog20 Fountain

Geog435 Karnes

Geog20 Fountain

Geog115 Brower

Meteo110 Stankle

Meteo200 Turlock


Geog357 Jones

Geog435 Karnes

Class Instructor


Results of Difference


• Join: Match records in both tables based on a common field

Geog357 Jones

Geog115 Brower

Geog20 Fountain

Geog435 Karnes

Class InstructorGeography Classes

Jones 332

Brower 423

Fountain 125

Karnes 312

Instructor Office Instructor

Geog357 Jones 332

Geog115 Brower 423

Geog20 Fountain 125

Geog435 Karnes 312

Class Instructor Office

Result of Join


• Projection: reduces one table in the attribute dimension (a selection of a subset of fields, for all records)

• Projection: List all Geography classes, but not the instructors

Geog357 Jones

Geog115 Brower

Geog20 Fountain

Geog435 Karnes



Geog357

Geog115

Geog20

Geog435

ClassResult of Projection

Relational data model• Selection (restriction): reduces one table in the record dimension (a selection of a subset of

records, for all fields)

• Criteria for selection is called a predicate

• Selection: Find Geography classes taught by ‘Jones’

Geog357 Jones

Geog115 Brower

Geog20 Fountain

Geog435 Karnes



Result of Selection

Geog357 Jones

Class Instructor

Documents

Geography 357 Geographic Information Systems