1. E-R Model (1) IS 240 – Database Management Lecture #5 – 2004-01-29 Prof. M. E. Kabay, PhD, CISSP Norwich University mkabay@norwich.edu

2. 2 Copyright © 2004 M. E. Kabay. All rights reserved. Topics Entities Attributes Identifiers Relationships Diagrams

3. 3 Copyright © 2004 M. E. Kabay. All rights reserved. Entities What you or the user cares about Entity instance = one particular case Entity class = collection of all cases Examples – discuss instances and classes in University academics Hospital Manufacturing Corner store

4. 4 Copyright © 2004 M. E. Kabay. All rights reserved. Attributes Characteristics, properties Names in text shown with uppercase and lowercase letters FirstName LastName ProductID SourceCode All instances of an entity class have the same attributes

5. 5 Copyright © 2004 M. E. Kabay. All rights reserved. Attributes – contd Give examples of attributes for Students at Norwich Students in Vermont Buildings at Norwich University Buildings in Northfield Composite attribute Several different attributes E.g., [StudentName,StudentID] Usually broken into entities Multi-valued attribute Non-unique E.g., StudentName

6. 6 Copyright © 2004 M. E. Kabay. All rights reserved. Identifiers Attributes that identity entity instances Context-dependent E.g., StudentID, EmployeeNumber, ProductNumber... May be several identifiers possible Unique identifiers – a single instance; e.g., ChemicalFormula Nonunique identifiers – set of instances; e.g., CommercialChemicalName

7. 7 Copyright © 2004 M. E. Kabay. All rights reserved. Relationships Associations among Entity classes; and Entity instances E.g., discuss relationships that may be found among the entity classes of University academics Hospital Bank

8. 8 Copyright © 2004 M. E. Kabay. All rights reserved. Degree of Relationship How many entity classes are bound together? E.g., how many in Sales system for traveling salespeople? Sales system for consulting firm where teams of employees sell to customers? Genealogy charts?

9. 9 Copyright © 2004 M. E. Kabay. All rights reserved. Binary Relationships Two entity classes Very common; e.g., Mother-to-child Employer-to-employee Textbook-to-course Student-to-classroom Three types 1:1 (read one to one) 1:N N:M

10. 10 Copyright © 2004 M. E. Kabay. All rights reserved. Binary Relationships – contd Give examples of 3 types in Drug store Library Social networks Medical diagnosis Exact numbers of entity instances possible are the maximum cardinality of the entity relationship Give the maximum cardinality of Mother:Child PossibleFather:Child

11. 11 Copyright © 2004 M. E. Kabay. All rights reserved. E-R Diagrams Several styles possible Discussed in detail in text pp. 54-56 More in part (2) of lecture series

12. 12 Copyright © 2004 M. E. Kabay. All rights reserved. Homework Using the full SQ3R techniques, study all of Chapter 3 in preparation for next class For 10 points, complete questions 3.1-3.10 and hand in the typewritten (printed) answers by Thu 5 Feb 2004 Continue working on projects in Ferrett et al.

13. 13 Copyright © 2004 M. E. Kabay. All rights reserved. DISCUSSION