unit4 database

Wang,X., ENGO351

Unit 5: Data Management


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Data management: Outline

Definition of a database

Database management systems

Conceptual data modelling

The entity-relationship model

Logical data modelling

The relational database model

The standard query language (SQL)

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Database

A database is a logical, structured collection of data about

things, their attributes and their relationships to each other

A database is a collection of related data.

Within a GIS, these things and relationships have a

spatial component

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Spatial Data Examples

Examples of non-spatial data

Names, UCID, grades of a student

Examples of Spatial data

Census Data

NASA satellites imagery - terabytes of data per day

Weather and Climate Data

Rivers, Farms

Medical Imaging

Exercise: Identify spatial and non-spatial data items in

A phone book

A cookbook with recipes

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Why use database?

Data Redundancy and Inconsistency - The same piece of information may be duplicated in several different files.

Difficulty in Accessing Data: Conventional file processing environments do not allow data to be retrieved in a convenient and efficient manner.

Data Isolation: Data is scattered in a number of different files. Linking these data to provide new information may require a substantial amount of programming to answer each specific query.

Concurrent Access Problems: Multiple users attempting to access the same file may lead to problems.

Security Problems: Certain users should not be allowed to access certain data-sets and not be permitted to edit certain data that they do not own.

Integrity Problems: Some data values should satisfy certain consistency constraints.

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Database management system

A database management system (DBMS) is a collection

of software programs that facilitates the processes of

defining, construction, and manipulating the database for

various applications

A DBMS provides tools for data input, search, retrieval,

manipulation, and output

Most commercial GIS include database management

tools for local databases

ArcGIS uses Microsoft Access

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Data model

A data model is a description or view of the real world and

data modeling is the process that formalizes the description

or view at different levels of data abstraction

The real-world is made up of complex spatial objects and

phenomena

A data model tends to be tailored to a specific application or

problem context

Different users may have different data models

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Data models and levels of abstraction

Data modeling involves three steps corresponding to

increasing levels of abstraction:

conceptual modeling

logical modeling

physical modeling

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A conceptual model represents the users perception of the real world Data abstraction

is strictly limited to the description of the information content of the users view of the real world, without any concern for computer implementation

(Brown, 1997)

Conceptual model (1)

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The function of a conceptual data model is to provide the necessary language to describe how we naturally conceptualize data organization Although conceptual data modeling is part of the database

design process, conceptual models are database-independent

A conceptual model provides a basic reference for users who need to understand the structure of the data in the system

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A conceptual data model provides a way to communicate between users, designers and computers

(Worboys, 2004)

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The entity-relationship model

The entity-relationship (E-R) data model is one of the most commonly-used conceptual data models for GIS data modelling

It is based on the concepts of:

entities

attributes

relationships

to represent real-world features, their properties and their relationships

KimHighlight

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The entity-relationship diagram

An entity-relationship diagram (E-R diagram) can be used to express the features and properties of an E-R model

(Lo and Yeung, 2007)

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Entity

An entity is a thing or object in the real world that is distinguishable from all other objects

each person in a classroom is an entity

An entity has an independent existence

physical existence: a person, a car, a forest

conceptual existence: a company, a job, an agenda

Entities can be thought of as nouns.

Examples: a computer, an employee, a song, a mathematical theorem

Entities are represented as rectangles.

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Relationships between entities

A relationship captures how two or more entities are related to one another. i.e. the relationship performs between the entity artist and song

Relationships can be thought of as verbs, linking two or more nouns

Relationships are represented as diamonds, connected by lines to each of the entities in the relationship.

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Attributes

Entity and relations can have attributes. i.e. an employee entity might have an SIN attribute

i.e. entity City has attribute types name, population, density

The attributes are associated to each occurrence of the entity type

Attributes are represented as ellipses connected to their

owning entity sets by a line.

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Relationship types (1)

Relationship types are subdivided into three categories: one-to-one (1:1)

many-to-one (N:1)

many-to-many (M:N)

Participation constraint: entity occurrence may only exist if it participates in a relationship. One can have total and partial participation constraints

i.e. one director is the manager of at most one cinema (double lines means mandatory)

(Worboys, 2004)

A BDouble line m e ans B ca nnot exist

without A. A c an exist without B.

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In a many-to-one relationship, many occurrences of one entity type may have a relationship with at most one occurrence of another entity type i.e. many cinemas are located in a town

(Worboys, 2004)

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In a many-to-many relationship, many occurrences of one entity type may have a relationship with many occurrences of another entity type i.e. many roads connect

many cities

(Worboys, 2004, p. 58)

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Process of creating E-R model

1. Start with textual description

2. Identify entities (nouns)

3. Tabulate entities

4. Determine relationships

5. Determine cardinality ratio/participation constraints

6. Determine attributes & key attributes

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An Example: World Database

Conceptual Model 3 Entities: Country, City, River

2 Relationships: capital-of, originates-in

Attributes listed in the figure

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Logical model (1)

A logical data model represents the real world by means of diagrams, lists, and tables designed to reflect the recording of the data in terms of some formal language

Logical models are software dependent; they must be expressed in terms of the language of a specific database management system (i.e. relational model)

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Logical model (2)

This figure illustrates the logical model that was created from the conceptual model previously shown

(Brown, 1997)

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The relational database model (1)

The relational database model,

developed by Codd in the early 1970s, is

the most widely used logical database

model in the computer industry

It represents the database as a collection

of tables (simple files) called relations.

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(Aronoff, 1993)

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Each table in the

database

represents an entity

type identified in

the data modeling

process

(Brown, 1997)

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Column and tuple

In a particular table,

each column represents an attribute

each row, called a tuple (or record), represents a collection of

data values associated to the occurrence of an entity

(Lo a

nd Y

eung,

2007)

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Relation

A relation can be simply thought of as a table of data

A relation is made up of a set of tuples

There can be any number of tuples in a relation

Within a relation, the logical order of the tuples is not

important

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Domain

A domain is a set of attribute values associated to each

column of a relation

A domain is identified by an attribute name

There are occasions when the values of some attributes

within a particular tuple are unknown or missing

a special value, called null (which is not zero), is assigned

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Primary and foreign keys (1)

Tables, in a relational database, are connected to each

other using keys

A primary key represents one or more attributes (columns

in the table) whose values can uniquely identify a record in

a table

Its counterpart in another table for the purpose of linkage

is called a foreign key

http://www.datagovernance.com/

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Thus, a key

common to two

tables are used to

establish

connections

between

corresponding

records in the

tables

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Keys are a simple

way to connect

tables within a

relational database

Collector

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Primary key

Attribute values of the primary key allow users to identify

individual tuples uniquely

e.g. SIN, an identification number

The primary key must not contain null values (Why?)

What if cannot use of a certain attribute alone in a relation

to identify the unique identification of a tuple?

use one or more additional attributes to form a compound key

create an additional attribute to hold a unique identifier for each

occurrence of an entity

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Foreign key

A foreign key is an attribute in a relation that is a primary

key in another relation

The identical values of the primary and the foreign keys

make it possible to logically link different tuples in different

relations

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Join and Relate

Two common operations for linking tables in a relational

database are join and relate.

A join operation brings together two tables by using a

key that is common to both tables.

A relate operation temporarily connects two tables but

keeps the tables physically separate.

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Figure 8.10 (Chang, 2012)

Primary key and foreign key provide the linkage to join the table on the

right to the feature attribute table on the left.

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This example of a many-to-one relationship in the SSURGO database

relates three tree species in cotreestomng to the same soil component

in component.

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This example of a one-to-many relationship in the SSURGO database

relates one soil map unit in mapunit to two soil components in

component.

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Normalisation

Normalising is the splitting of the database into multiple tables.

Two main reasons for normalising a database: prevents unnecessary duplication of data, thus conserving time

and disk space, and in some cases, preventing errors.

makes it easier to extract exactly the information from the database.

Each normal form is built on the normal form before it. e.g. if a table is in 3-NF it is in 2_NF

KimHighlight

KimHighlight

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Normal Forms

1-NF: attributes are atomic or single valued.

2-NF: All non-primary attributes are fully dependent on the primary key; no non-primary attributes are

functionally determined by a subset of the key

3-NF: No non-prime attributes are functionally determined by another non-prime attribute; all non-

primary attributes are directly dependent on the primary

key.

Example: A company runs many projects. Employees work on particular tasks on different projects. How do we invoice the time

each employee allocates to their different tasks on each project?

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Guidelines for relational database design

1. Create E-R model

2. Produce table for each entity

3. For 1:1 relationships,

add foreign key to either participating entities

For 1:M relationships,

add foreign key to entity on "Many" side of relationship

4. For N:M relationships, create a new table

5. Check design is "normalised"

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Advantages of the relational model

A relational database is simple and flexible

Each table in the database can be prepared, maintained,

and edited separately from other tables

The tables can remain separate until a query or an

analysis requires that attribute data from different tables be

linked together

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Physical model

A physical data model describes the physical storage of the data in the computer by record formats and access paths

It is hardware dependent and is concerned primarily with the implementation details of a database

It is intended for the system programmer and database manager, not the general user


KimHighlight

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SQL

SQL (Structured Query Language) is a data query

language designed for relational databases

SQL has been developed by IBM in the 1970s and many

commercial database management systems such as

Oracle, DB2, Access, and Microsoft SQL Server have since

adopted the query language

This is an English-like language that consists of a set of

powerful and flexible commands for the manipulation of the

data in the relational tables

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Relational algebra

The SQL language is made with a set of relational

operators and commands that can be combined to query a

database. These operators and commands form what is

called relational algebra

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Relational operators (1)

With SQL, six logical operators can be used:

equal to

not equal to

smaller than

greater than

smaller or equal to

greater or equal to

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Relational operators (2)

With SQL, three boolean

operators can be used:

NOT

AND

OR

(Chang,

2006)

The shaded area represents:

the complement of A (NOT)

the union of A and B (OR)

the intersection of A and B (AND)

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SQL commands (1)

SQL is used to create and query the database using a set

of SQL commands. e.g.

the create command creates databases and tables

the select command selects rows that have been inserted into the

tables

By using SQL commands, the user needs only to specify

the tables, columns, and row qualifiers to retrieve any data

item in the entire database

the users do not need to know the technical details of how the data are stored

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SQL commands (2)

SQL commands are used to perform two main functions:

to define the database structure (data definition)

e.g., CREATE

to insert, modify, and retrieve data from the database (data

manipulation)

e.g. SELECT

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CREATE command

To create a database:

CREATE DATABASE database_name

To create a table in a database:

CREATE TABLE table_name (column_name1 data_type,

column_name2 data_type, ....... )

CREATE TABLE ADDRESS_BOOK (

NAME CHAR (30)

COMPANY CHAR (20)

E-MAIL CHAR (25)

)

NAME COMPANY E-MAIL

ADDRESS_BOOK

KimSticky Note;

KimSticky Note;

KimSticky Note;

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INSERT and DELETE

To insert new rows into a table:

INSERT INTO table_name VALUES (value1, value2,....)

INSERT INTO River (Name, Origin, Length) VALUES (Mississippi, USA, 6000)

To delete rows in a table:

DELETE FROM table_name WHERE column_name =

some_value

DELETE FROM City

WHERE Country = Canada;

NAME COMPANY E-MAIL

John Smith Travelcity [email protected]

INSERT INTO ADDRESS_BOOK (NAME, COMPANY, E-MAIL)

VALUES (John Smith, Travelcity, [email protected]) DELETE FROM ADDRESS_BOOK WHERE COMPANY =

Travelcity;

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SELECT command

The select command extracts data items in specified

rows of a table. It returns a new table that has a subset of

tuples of the original.

SELECT * FROM table_name

SELECT column_name(s) FROM table_name

SELECT column_name(s) FROM table_name(s) WHERE conditions

GROUP BY column_name

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World database data tables

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SELECT Example 1.

Simplest Query has SELECT and FROM clauses

Query: List all the cities and the country they belong to.

SELECT Name, Country

FROM CITY

Result

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SELECT Example 2.

Commonly 3 clauses (SELECT, FROM, WHERE) are used

Query: List the names of the capital cities in the CITY table.

SELECT Name

FROM CITY

WHERE CAPITAL=Y

SELECT *

FROM CITY

WHERE CAPITAL=Y

Result

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SELECT Example 3

Query: List the attributes of countries in the Country

relation where the life-expectancy is less than seventy

years.

SELECT Co.Name,Co.Life-Exp

FROM Country Co

WHERE Co.Life-Exp

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Multi-table Query Examples

Query: List the capital cities and populations of

countries whose GDP exceeds one trillion dollars.

Note:Tables City and Country are joined by matching City.Country = Country.Name.

SELECT Ci.Name,Co.Pop

FROM City Ci,Country Co

WHERE Ci.Country =Co.Name

AND Co.GDP >1000.0

AND Ci.Capital=Y

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Multi-table Query Example

Query: What is the name and population of the capital city

in the country where the St. Lawrence River originates?

SELECT Ci.Name, Ci.Pop

FROM City Ci, Country Co, River R

WHERE R.Origin =Co.Name

AND Co.Name =Ci.Country

AND R.Name =St.Lawrence AND Ci.Capital=Y

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