abordagem er - dca.ufrn.branderson/ftp/dca0120/aula2.pdf · técnica de modelagem de dados mais...
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Abordagem ER
Capítulo 2
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Abordagem Entidade-Relacionamento
� Técnica para construir modelos conceituais de bases de dados
� Técnica de modelagem de dados mais difundida e utilizada
� Criada em 1976, por Peter Chen
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Abordagem Entidade-Relacionamento
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Abordagem Entidade-Relacionamento
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Entidade
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Entidade e instância - terminologia
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ExercícioIdentificar entidades
Sistema de vendasDeseja-se construir um banco de dados para um sistema de vendas. Em cada venda são vendidos vários produtos e um determinado produto pode aparecer em diferentes vendas. Cada venda é efetuada por um vendedor para um determinado cliente. Um produto está armazenado um uma prateleira.
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Exercício 3.5Identificar entidades
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Exercício 3.5Entidades identificadas
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Relacionamento e instância
� Relacionamento é um conjunto de associações entre instâncias de entidades� Uma instância (ocorrência) é uma associação
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Papel de relacionamento
� Função que uma ocorrência de uma entidade cumpre em uma ocorrência de um relacionamento� Relacionamento de casamento
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ExercícioIdentificar relacionamentos
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Cardinalidade de relacionamentos
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Cardinalidade máxima no DER
D > E < F G >= 7 9 < : E < 8 7 H E > 7 8 9 : 7 ; < = >
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Cardinalidade máxima - DER
D > E < F G >= 7 9 < : E < 8 7 H E > 7 8 9 : 7 ; < = >
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Cardinalidade máxima no DER
& ' ( ) & * * + , - & + - . + / 0 / ) ) 1 2 0 3 + 4 &
5 6 7 8 9 : 8 ; 6 < : = > & 2 ? 3 4 + 4 & + / @ + 4 /
/ ( / * ? / 4 + + 2 / ? + A B / C ( / 4 & . & * ? + )
+ * * / 0 3 + 4 + * . - 3 ? + * > D 2 E C / 0 / ) ) 1 2 0 3 + * 4 &
6 ; 7 9 6 F 8 5 =
G = : 8 H I =5 6 7 8 9 : 8 ; 6 < : = 6 ; 7 9 6 F 8 5 =
JK
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Cardinalidade máxima - valores
� Para projeto de BD relacional
� � � � � � � � � � � � � � � � � � � � � � � � � � � � � �
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� Dois valores de cardinalidades máximas são usados
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Classificação de relacionamentos
� Cardinalidade máxima pode ser usada para classificar relacionamentos binários� Relacionamento binário
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� Relacionamentos binários
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Relacionamentos 1:1
7 6 � � = 8
� 8 � 8 ; 6 < : =
� � � �
6 ; 7 9 6 F 8 5 =
8 G = � 8 H I =
; 6 � 8
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Relacionamentos 1:n
8 G � < = � < � � 9 � H I = � � 9 � =
�2
6 ; 7 9 6 F 8 5 = 5 6 7 6 < 5 6 < : 6
� 2
6 ; 7 9 6 F 8 5 =
� � 7 6 9 � � � I =
� 2
* - ( & ) � 3 * / ) * - ( & ) � 3 * 3 / 2 + 4 /
� � � � �� � �� � � �
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Relacionamentos n:n
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! " # $ " % & ' ( "
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$ $
ExercícioIdentificar cardinalidades
Deseja-se construir um banco de dados para um sistema de vendas. Em cada venda são vendidos vários produtos e um determinado produto pode aparecer em diferentes vendas. Cada venda é efetuada por um vendedor para um determinado cliente. Um produto está armazenado um uma prateleira.
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Exercício 3.6Identificar relacionamentos
� � � � � � � � � � � � � � � � � � �
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! " � � � � � � � � � � � � � � � � � � � � � � � � � " # " $ � �%
& � � � � � � � ' � � � � � � � � # � � � � � � � � � � � � � � � � � � � � � � � � � " � � � " � � �
� � # " � � � � � � � ( � � � � � ) � � *
+ � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � ( � � � � � � � , � � " � � � � � � �
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+ - � � � " � � � � � � � � � � � � � � � � � $ � � , � � , � � � � � � � � � " � � � " � � � �
, � � � � � �%
& � � , � � � � � , � � � , � � � " � � � � ' � � � � � " � � � � � � �%
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Exercício 3.6Identificar relacionamentos
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Relacionamento ternário
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Cardinalidade em relacionamento ternário
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ExercícioRelacionamento ternário
Identifique as entidades, os relacionamentos e as respectivas cardinalidades para o seguinte problema:Em uma empresa de desenvolvimento de sistemas informatizados, pessoas são alocadas a tarefas. No momento da alocação da pessoa a tarefa, também lhe é alocado um equipamento para resolver a tarefa.
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Exercício 2.7Mostre como o modelo ER da ao lado pode ser representado sem uso de relacionamentos ternários, apenas usando relacionamentos binários
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Exercício 2.7(solução)
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Exercício 2.7(solução incorreta)
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Cardinalidade mínima
� Número mínimo de ocorrências de entidade que são associadas a uma ocorrência de uma entidade através de um relacionamento� Para fins de projeto de BD, consideram-se apenas
duas cardinalidades mínimas
& ' ( ) * + ( , + * ( * - . / + . ( 0
& ' ( ) * + ( , + * ( * - . / + . ( 1
� Denominação alternativa:
& ' ( ) * + ( , + * ( * - . / + . ( 1 2 3 ( 4 4 & ' + ( 5 6 & & 7 ) + 8 ( 9 : ) + ( ;
& ' ( ) * + ( , + * ( * - . / + . ( 0 2 3 ( 4 4 & ' + ( 5 6 & & < ' + & ( , ;
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Cardinalidade mínima - DER
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Exemplo - entidades e relacionamentos
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Exercício 2.15
� Modifique as cardinalidades mínimas de forma a especificar o seguinte:
& � . ' � ) 4 & 6 & < & * - - 4 9 ( ) � ( � + &�
+ 4 9 & ��
* - � - < & 4 4 � + )
( & . - & 4 � . ( * + 4 ' + < , + ( - . 4 - � ' � ) ) / ' � , &
& � . ( , � &�
. - 4 . & � � - 6 & + 4 ' ) + 9 & - . - � � .
' � ) 4 &�
* - � - < - ) . ( - ' - ) < & ) ( , 8 � . 9 - . < & & 7 ( ' &
* - * ( * & 4
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Atributo
Dado ou informação que é associado a cada ocorrência de uma entidade ou de um relacionamento
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ExercícioIdentificar atributos
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Atributos com cardinalidade
� Cardinalidade mínima
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� Cardinalidade máxima
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Exercício 2.16
Sem usar
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- .
& ( 9 ) + 7 � 9 & 4 . � , 9 + � ( , & ) ( * & 4
construa um DER que contenha as mesmas informações do modelo anterior
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Atributo em relacionamento
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Atributo em relacionamento 1:n
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ExercícioAtributos
Altere o modelo ER do sistema de vendas para incorporar as seguintes informações:Tanto clientes, quanto vendedores podem ter vários telefones.Um produto pode ter vários preços, cada um com uma data de início e de fim de validade.Para cada produto vendido em uma venda, é necessário conhecer o número de unidades vendidas e o preço de venda.
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Identificador de entidade
� Cada entidade deve possuir um identificador
Identificador de entidade=
conjunto propriedades de uma entidade (atributos e relacionamentos) cujos valores servem para
distinguir uma ocorrência da entidade das demais ocorrências da mesma entidade
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Atributo identificador
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Relacionamento identificador (recursão)
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Identificador de relacionamento
� Uma ocorrência de relacionamento diferencia-se das demais do mesmo relacionamento pelas ocorrências de entidades que dela participam.
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ExercícioIdentificador de entidade
Determine quais os identificadores das entidades do sistema de vendas
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Exercício 2.11
Construa um DER que modela a mesma realidade que a mostrada no DER abaixo, usando apenas relacionamentos 1:n.
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Exercício 2.11(solução)
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