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Database relationship
The document discusses various degrees of relationships in database design, including unary, binary, and ternary relationships, as well as cardinality constraints that dictate how entities can relate. It emphasizes the importance of integrity constraints, such as domain, entity, and referential integrity, in maintaining data consistency. Furthermore, it outlines mapping ER diagrams to relations and the specific rules governing relationships among entities in a relational database.
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This slide introduces the concept of degree of relationship, which refers to the number of entities involved.
Unary relationship is where subjects can serve as prerequisites for other subjects.
Discusses M:N, 1:M, and 1:1 unary relationships with examples involving subjects and employees.
Defines binary relationships as those involving two entities.
Explains ternary relationships involving three entities, providing an example related to university courses.
Describes cardinality limits in relationships. Example: teacher's subjects (0, N) and subjects taught (0, 1).
Introduces relation schemas using an example of Employee Table attributes.
Outlines various integrity constraints including domain, entity integrity, and referential integrity.
Details domain constraints for data types such as Age and Phone_no with value ranges.
States that every relation must have a primary key, which is non-null and unique.
Discusses entity integrity issues when primary keys are not unique.
Clarifies that null values are not allowed in primary keys to maintain integrity.
Describes referential integrity, requiring foreign keys to match primary keys, ensuring consistency.
Discusses allowance for repeated foreign keys and null values in the EMPLOYEE table.
Highlights issues with referential integrity when foreign keys don't match primary keys.
Outlines the rules for maintaining referential integrity in database management.
Explains cascading delete where deleting a primary key also deletes associated foreign keys.
Explains the prohibitive delete rule before removing a primary key from the database.
Describes how to handle foreign keys by inserting NULL when primary keys are deleted.
Discusses the transformation of conceptual models into relational models, highlighting entity types.
Further details on mapping regular entity types into relational schemas.
Explains how to handle composite entity types during the mapping process.
Describes the mapping of multi-valued entity types in ER diagrams.
Defines weak entities and their dependence on strong entities for existence.
Explains how to map 1-1 binary relationships with foreign keys.
Details the mapping process for 1-N binary relationships.
Explains the mapping of M-N relationships highlighting multiple associations.
Describes how to map unary relations like supervisory roles in relationships.
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- 1. CHAPTER 3 Degree ofrelationship Degree of relationship refers to the number of participating entities in a relationship. Dr.Girija Narasimhan 1
- 2. Unary Relationship Subjects maybe prerequisites for other subjects. Dr.Girija Narasimhan 2
- 3. M:N unary relationship:A Subject may have many other Subjects as prerequisites and each Subject may be a prerequisite to many other Subjects 1:M unary relationship: An Employee may manage many Employees, but an Employee is managed by only one Employee 1:1 unary relationship: A Person may be married to only one Person. Dr.Girija Narasimhan 3
- 4. Binary Relationship If thereare two entities involved in relationship then it is referred to as binary relationship. Dr.Girija Narasimhan 4
- 5. Ternary Relationship If thereare three entities involved then it is called as ternary relationship and so on. The University might need to record which teachers taught which subjects in which courses. Dr.Girija Narasimhan 5
- 6. The cardinality ofa relationship is the number of instances of entity B that can be associated with entity A. There is a minimum cardinality and a maximum cardinality for each relationship, with an unspecified maximum cardinality being shown as N. Cardinality limits are usually derived from the organizations policies or external constraints. At the University, each Teacher can teach an unspecified maximum number of subjects as long as his/her weekly hours do not exceed 24 (this is an external constraint set by an industrial award). Teachers may teach 0 subjects if they are involved in non teaching projects. Therefore, the cardinality limits for TEACHER are (O,N). Dr.Girija Narasimhan The University's policies state that each Subject is taught by only one teacher, but it is possible to have Subjects that have not yet been assigned a teacher. Therefore, the cardinality limits for SUBJECT are (0,1). 6
- 7. Relation Relation schema Employee Table Relation(R ) Attributes (A1,A2…An) Employee (Emp_id,ename,Salary) Foreign key Primary key or identifier Employee (Emp_id,ename,Salary) Employee (Emp_id,ename,Salary,dept_name) Foreign key Composite key Department(dept_name,ename,Salary) Over_time (emp_id, dept_name,No_of_hour) Composite key Dr.Girija Narasimhan 7
- 8. INTEGRITY CONSTRAINTS DOMAIN CONSTRAINTS ENTITY Integrity CONSTRAINTS Dr.GirijaNarasimhan Referential Integrity CONSTRAINTS 8
- 9. DOMAIN CONSTRAINTS Domain_name Meaning Data type Age Yearsof the person Phone_no Conduct number Mark size number 3 number Scored by Student in Exam number Dr.Girija Narasimhan 8 3 Allowable value or range <=110 Must be 8 digit and <99999999 and >90000000 >=0 and <=100 9
- 10. ENTITY Integrity CONSTRAINTS Everyrelation must have primary key Every primary key attribute is non- null and unique Unique means, value of the primary key must be different not be same. Null is a value, suppose no other value not assign or apply. Null is not zero (0) or blank (“ “) Dr.Girija Narasimhan 10
- 11. ENTITY Integrity CONSTRAINTS NotUnique Department Entity integrity not enforced Not Unique Same value Dr.Girija Narasimhan 11
- 12. ENTITY Integrity CONSTRAINTS Nullis a value, suppose no other value not assign or apply. Null is not zero (0) or blank (“ “) Not Null Entity integrity not enforced No null value allowed in the primary key Dr.Girija Narasimhan 12
- 13. Referential Integrity CONSTRAINTS • Twotables have relationship or association then use foreign key Why Referential Integrity constraints? To maintain Consistency among rows of two relationship. Rule: Rule 1: Foreign key must match with primary key of the other relation. Rule 2: Otherwise, If it is not matching then Foreign key value must be “NULL” Dr.Girija Narasimhan 13
- 14. Referential Integrity CONSTRAINTS EMPLOYEE Foreignkey Department EMPLOYEE Repetition in the foreign key - allowed Null value allowed in the foreign key Dr.Girija Narasimhan 14
- 15. EMPLOYEE Referential Integrity CONSTRAINTS Department Notmatching any dept_name in department table. So Referential integrity not enforced Dr.Girija Narasimhan 15
- 16. Referential Integrity CONSTRAINTS Rule1: Foreign key must match with primary key of the other relation. CASCADING DELETE PROHIBIT DELETE Dr.Girija Narasimhan 16
- 17. Referential Integrity CONSTRAINTS Dr.GirijaNarasimhan 17
- 18. CASCADING DELETE If deletethe Primary key table record, automatically the foreign key referencing table record information also deleted. For example: Suppose if I delete deptno 20 in DEPT table (master /parent), automatically in the EMP table empno 6666 and Empno 7329 also deleted because both are referencing deptno 20. Dr.Girija Narasimhan 18
- 19. PROHIBIT DELETE Before deletingprimary key record, first delete all the foreign key associated records in referencing table or child table. For example: First delete EMP table empno 6666 and Empno 7329 and then delete DEPT table deptno 20 Dr.Girija Narasimhan 19
- 20. Rule 2: Otherwise,If it is not matching then Foreign key value must be “NULL” Place a null value in the Foreign key. When? Suppose I want to remove deptno 20 from DEPT TABLE, but I want to retain or keep the employee 6666 and 7329 in the EMP table , then in the foreign key attribute DEPTNO column in EMP table instead of 20 I will put “Null” in both the record 6666 and 7329. Dr.Girija Narasimhan 20
- 21. Mapping ER diagramsto Relations Why? Transform Conceptual model to Relational model Entity type Regular Week entity type Create a new relation Composite Binary Relations Unary Relation 1-1 relation type 1-N relation type M-N relation type Multivalued Dr.Girija Narasimhan 21
- 22. Mapping ER diagramsto Relations Entity type Regular Dr.Girija Narasimhan 22
- 23. Mapping ER diagramsto Relations Entity type Dr.Girija Narasimhan Composite 23
- 24. Mapping ER diagramsto Relations Entity type Dr.Girija Narasimhan Multi valued 24
- 25. Mapping Weak Entities weakentity type does not have an independent existence, but exists only through an identifying relationship with another entity type called the owner or strong entity. Dr.Girija Narasimhan 25
- 26. Mapping 1-1 BinaryRelationship Type Employee must assign by only one Employee may manage one or may department. not manage any department One and only One (Mandatory One) Zero or One (Optional One) Using foreign key Dr.Girija Narasimhan 26
- 27. Mapping 1-N BinaryRelationship Type Department have one or more employee One or More (Mandatory One) Employee must work only one department. One and only One (Mandatory One) Dr.Girija Narasimhan 27
- 28. Mapping M-N BinaryRelationship Type Employee join one or more project Project has one more employee One or More (Mandatory One) One or More (Mandatory One) Dr.Girija Narasimhan 28
- 29. Mapping Unary RelationType one employee appointed as supervisor Dr.Girija Narasimhan 29