1. Data Modeling 1 Yong Choi School of Business CSUB

2. Part # 2 2 Study Objectives Understand concepts of data modeling and its purpose Learn how relationships between entities are defined and refined, and how such relationships are incorporated into the database design process Learn how ERD components affect database design and implementation Learn how to interpret the modeling symbols

3. Part # 2 Data Modeling Model: an abstraction of a real-world object or event Useful in understanding complexities of the real-world environment Data model Relatively simple representations of complex real-world data structures Data modeling is iterative and progressive process So, “complete” and “100% error free” model is not possible! Only “Optimized” model is possible…..

4. Part # 2 4 The data modeling revolves around discovering and analyzing organizational and users data requirements based on business rules. Identify what data is important Identify what data should be maintained The major activity of this phase is identifying entities, attributes, and their relationships to construct model using the Entity Relationship Diagram. Data Modeling (con’t)

5. Part # 2 The Importance of Data Model Blue print: documentation Facilitate interaction among the managers, the designers, and the end users Effective Communication Tool User involvement Independence from a particular DBMS

6. Part # 2 What is an Entity Relationship Diagram (ERD)? ERD is a data modeling technique used in software engineering to produce a conceptual data model of a information system. So, ERDs illustrate the logical structure of databases. Video clip for basics of ERD development 6

7. Part # 2 Data Model by Access 7

8. Part # 2 8 Data Model by PowerDesigner

9. Part # 2 Data Model by Peter Chen’ Notation (first - original)

10. Part # 2 10 ERD Notation (most popular)

11. Part # 2 Data Model Notation 1-to-1 relationship 1-to-M relationship M-to-N relationship

12. Part # 2 Data Model Notation

13. Part # 2 Data Model Basic Building Blocks

14. Part # 2 Data Model Basic Building Blocks

15. Part # 2 Data Model Basic Building Blocks

16. Part # 2 Data Model Basic Building Blocks

17. Part # 2 Business Rules Let’s see the real world example on the class website Descriptions of policies, procedures, or principles within a specific organization Use for discovering and analyzing organizational and user’s data requirements for the data model Allow designer team to develop appropriate relationship participation rules and constraints

18. Part # 2 Discovering Business Rules Sources of business rules: Direct interviews with stakeholders (i.e., users, senior managers) Documents Procedures, Forms, Operations manuals, Budget report, etc.. Rules must be bi-directional.

19. Part # 2 Business Rules Example 1 A professor can advise many students (professor to student) and each student is advised by one professor (student to professor). A professor can teach many classes and each class is taught by one professor. 19

20. Part # 2 Business Rules Example 2 Each sales representative writes many invoices and each invoice is written by one sales representative. Each sales representative is assigned to many department and each department has one at most one sales representative. Each customer can generate many invoices and each invoice is generated by one customer. 20

21. Part # 2 21 Entity Instance Entity instance: a single occurrence of an entity. 6 instances Student ID Last Name First Name 2144ArnoldBetty 3122TaylorJohn 3843SimmonsLisa 9844MacyBill 2837LeathHeather 2293WrenchTim Entity: student instance

22. Part # 2 22 Entity Instance (con’t)

23. Part # 2 Entity Type and Entity Instances 23

24. Part # 2 24 “Describe detail information about an entity ” Entity: Employee Attributes: Employee-Name Address (composite) Phone Extension Date-Of-Hire Job-Skill-Code Salary Attributes

25. Part # 2 25 Classes of attributes Simple attribute Composite attribute Derived attributes Single-valued attribute Multi-valued attribute

26. Part # 2 26 A simple attribute cannot be subdivided. Examples: Age, Gender, and Marital status A composite attribute can be further subdivided to yield additional attributes. Examples: ADDRESS --  Street, City, State, Zip PHONE NUMBER --  Area code, Exchange number Simple/Composite attribute

27. Part # 2 27 is not physically stored within the database instead, it is derived by using an algorithm. Example 1: Late Charge of 2% MS Access: InvoiceAmt * 0.02 Example 2: AGE can be derived from the date of birth and the current date. MS Access: int(Date() – Emp_Dob)/365) Derived attribute

28. Part # 2 28 can have only a single (atomic) value. Examples: A person can have only one social security number. A manufactured part can have only one serial number. A single-valued attribute is not necessarily a simple attribute. Part No: CA-08-02-189935 Location: CA, Factory#:08, shift#: 02, part#: 189935 Single-valued attribute

29. Part # 2 29 can have many values. Examples: A person may have several college degrees. A household may have several phones with different numbers A car color Multi-valued attributes

30. Part # 2 30 Example - “Movie Database” Entity: Movie Star Attributes: SS#: “123-45-6789” (single-valued) Cell Phone: “(661)123-4567, (661)234-5678” (multi-valued) Name: “Harrison Ford” (composite) Address: “123 Main Str., LA, CA” (composite) Gender: “Female” (simple) Age: 24 (derived)

31. Part # 2 31 How to find entities? Entity: people, places, objects, and events that information will be stored Tangible: customer, product Intangible: order, invoice look for singular nouns (beginner) BUT a proper noun is not a good candidate….

32. Part # 2 32 How to find attributes? Attribute: property of an entity A descriptor whose values are associated with individual entities of a specific entity type

33. Part # 2 33 “ attributes that uniquely identify entity instances” Uniquely identify every instance of the entity One or more of the entity’s attributes Composite identifiers are identifiers that consist of two or more attributes Identifiers are represented by underlying the name of the attribute(s) Employee (Employee_ID), student (Student_ID ) (unique) Identifier