Yong Choi School of Business CSUB MIS 340: Data Modeling 1 Yong Choi School of Business CSUB

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

Why Data Modeling? Represent “reality” of the actual database Blue print: documentation Effective Communication Tool User involvement Represent abstraction of requirements Identify the business rules to be stored in the database Independence from a particular DBMS

Conceptual data modeling The conceptual data modeling revolves around discovering and analyzing organizational and users data requirements (see the supplement). What data is important 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 methodology. 7

Entity Relationship diagram (ERD) Data modeling methodology Developed by Peter Chen (1976). See his original ERD article on the class website ERD is commonly used to: Translate different views of data among managers, users, and programmers to fit into a common framework. Define data processing and constraint requirements to help us meet the different views. Help implement the database. 16

Basic ERD Elements Entity : a collection of people, places, objects, events, concepts of interest (a table) Entity instance – a member of the Entity : a person, a place, an object … (a row in a table) Attribute - property or characteristic of interest of an entity (a field in a table) Relationship – association between entities (corresponds to primary key-foreign key equivalencies in related tables) 2

ERD using Chen’ Notation (first - original)

Chen’s Notation Entities Attributes Relationships rectangle containing the entity’s name. Attributes oval containing the attribute’s name. Relationships diamond containing the relationship’s name. 17

Steps for creating an ERD Identify entities Identify attributes Identify relationships

Entity “A fundamental THING of relevance to the enterprise about which data may be kept” What should be an Entity: both tangible & intangible An object that will have many instances in the database An object that will be composed of multiple attributes An object that we are trying to model What should NOT be an Entity: A user of the database system An output of the database system (e.g. a report)

ERD using IE Notation (most popular)

Entity Instance Student ID Last Name First Name 2144 Arnold Betty 3122 Entity instance: a single occurrence of an entity. 6 instances Student ID Last Name First Name 2144 Arnold Betty 3122 Taylor John 3843 Simmons Lisa 9844 Macy Bill 2837 Leath Heather 2293 Wrench Tim Entity: student instance

Entity Instance (con’t)

Attributes “describe property or characteristic of an entity ” Entity: Employee Attributes: Employee-Name Address (composite) Phone Extension Date-Of-Hire Job-Skill-Code Salary 18

Classes of attributes Simple attribute Composite attribute Derived attributes Single-valued attribute Multi-valued attribute 5

Simple/Composite attribute 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 22

Derived attribute is not physically stored within the database instead, it is derived by using an algorithm. Example: AGE can be derived from the date of birth and the current date. MS Access: int(Date() – Emp_Dob)/365) 22

Single-valued attribute 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 23

Multi-valued attributes can have many values. Examples: A person may have several college degrees. A household may have several phones with different numbers A car color 23

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) Birthdate: “1-1-50” (simple) Age: 50 (derived)

How to find entities? Entity: A fundamental THING of relevance to the enterprise about which data may be kept: things acted on by business activities people, places, objects, events…. Tangible: customer, product intangible (active/conceptual): equipment breakdown look for nouns (beginner) BUT a proper noun is not a good candidate….

How to find attributes? Attribute: property or characteristic of an entity A descriptor whose values are associated with individual entities of a specific entity type look for descriptions, characteristics, and properties of entity (beginner)

(unique) Identifier “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) 18