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Relationships

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Umair Shakir
Umair Shakir

The document defines key concepts related to relationships in databases including: binary and ternary relationships which involve two or three entities, respectively. It describes the cardinality (minimum and maximum number of instances) of relationships as either one-to-one, one-to-many, or many-to-many depending on whether the maximum is one or many on each side. Examples of relationships given include students reading for a degree or employees being employed by a company.

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Muhammad Umair Oracle Database 11g Developer Track
A mathematical definition: if A, B are sets, then a relation R is a subset of A x B A={1,2,3}, B={a,b,c,d}, R = {(1,a), (1,c), (3,b)} - makes is a subset of Product x Company: 1 2 3 a b c d A= B= makes Company Product
Relationship Relationship is defined as a meaningful association among instance of one or more entities. E.g. Students reads for degree, Students passes course, Teacher serve department. Degree of Relationship Number of entities involved in a relationship Types of Relationship Unary Relationship A relationship among instance of single entities
Binary Relationship A relationship among instance of two entities Ternary Relationship A relationship among instance of three entities. Maximum Cardinality If and b are two associated entities then maximum cardinality of A will be the maximum number of instance of A that can be associated with a single instance of B. Maximum cardinality can be either one or many
Minimum Cardinality If and b are two associated entities then minimum cardinality of A will be the minimum number of instance of A that can be associated with a single instance of B. minimum cardinality can be either zero or one Types of Relationship on the basis of Maximum Cardinality One-to-One Relationship A relationship having cardinality one on both sides One-to-Many Relationship A relationship having cardinality one on one side and many on other side Many-to-Many Relationship A relationship having cardinality many on both sides
one-one: many-one many-many 1 2 3 a b c d 1 2 3 a b c d 1 2 3 a b c d
address name ssn Person buys makes employs Company Product name category stockprice name price

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Relationships

  • 1. Muhammad Umair Oracle Database 11g Developer Track
  • 2. A mathematical definition: if A, B are sets, then a relation R is a subset of A x B A={1,2,3}, B={a,b,c,d}, R = {(1,a), (1,c), (3,b)} - makes is a subset of Product x Company: 1 2 3 a b c d A= B= makes Company Product
  • 3. Relationship Relationship is defined as a meaningful association among instance of one or more entities. E.g. Students reads for degree, Students passes course, Teacher serve department. Degree of Relationship Number of entities involved in a relationship Types of Relationship Unary Relationship A relationship among instance of single entities
  • 4. Binary Relationship A relationship among instance of two entities Ternary Relationship A relationship among instance of three entities. Maximum Cardinality If and b are two associated entities then maximum cardinality of A will be the maximum number of instance of A that can be associated with a single instance of B. Maximum cardinality can be either one or many
  • 5. Minimum Cardinality If and b are two associated entities then minimum cardinality of A will be the minimum number of instance of A that can be associated with a single instance of B. minimum cardinality can be either zero or one Types of Relationship on the basis of Maximum Cardinality One-to-One Relationship A relationship having cardinality one on both sides One-to-Many Relationship A relationship having cardinality one on one side and many on other side Many-to-Many Relationship A relationship having cardinality many on both sides
  • 6. one-one: many-one many-many 1 2 3 a b c d 1 2 3 a b c d 1 2 3 a b c d