DATA MODELING AND DATABASE DESIGN DATA MODELING AND DATABASE DESIGN Part 1

Objectives Learn the stages of system development. Define basic types of data relationships. Recognize the optionality and degree of a relationship Read an entity relationship diagram. Translate an entity relationship diagram into set of table instance charts. Complete translation from logical to physical database design.

Development Stages Creating CONCEPTUAL database model Making LOGICAL database design Performing PHYSICAL database design

Business Narrative Interview notes Existing documentation Current System Specs Course # Code * Name o Start Date o Duration Instructor # id * last name o first name * phone taught by leads a

Benefits of Entity Relationship Diagrams Quickly present concepts in people's minds Provide an easily understood graphical map of the system May be easily refined and upgraded Separate the information required by a business from the activities performed by the business

Entity Relationship Modeling Terms Entity –A thing of significance about which information needs to be known –Examples: department, employee, order Attribute –Something that describes or qualifies an entity –Examples: dept_id, address, customer_id Relationship –An association between two entities –Examples: region and department, customer and order

Entity Relationship Model Create an entity relationship diagram from business specifications or narratives. Scenario (from Department’s side) – "... Assign one or more employees to a certain department..." – "... Some departments do not yet have assigned employees..." DEPARTMENT #* id *name oregion_id EMPLOYEE #* id *last name ousername Contains Belongs to

CUSTOMER #* id *name ophone EMPLOYEE #* id *last name ofirst name (#)* username assigned to the sales rep to the sales rep to Entity Relationship Modeling Conventions ENTITY Soft box Singular, unique name Uppercase ENTITY Soft box Singular, unique name Uppercase attribute Singular name Lowercase Mandatory marked with "*" Optional marked with "o" attribute Singular name Lowercase Mandatory marked with "*" Optional marked with "o" Unique Identifier (UID) Primary marked with "#" Secondary marked with "(#)" Unique Identifier (UID) Primary marked with "#" Secondary marked with "(#)"

Entity Relationship Syntax Syntax –Each source entity {may be | must be} relationship name {one and only | one or more} destination entity. Example –Each ORDER must be for one and only one CUSTOMER. –Each CUSTOMER may be the client for one or more ORDERs. ORDER #* id * ord_date o ship_date CUSTOMER #* id *name ophone for the client for the client for Degree - One or more Optionality - May be Mandatory - Must be Degree - One and only one

Relationships Solid line represents a mandatory relationship often called a MUST BE relation. Dashed Line represents an optional relationship often called a MAY BE relation. OPTIONALITY DEGREE One and only One --- ONE-TO-ONE One or More (Many) --- ONE-TO-MANY

Degree Types One-to-one –Have a degree of one and only one in both directions. –Are rare. –Example: Computer and Motherboard One-to-many –Have a degree of one or more in one direction and a degree of one and only one in the other direction. –Are very common. –Example: Customer and Order. Many-to-many –Have a degree of one or more in both directions. –Are resolved with an intersection entity. –Example: Reader and Magazine

UID Bar: Example ITEM #* id *price oquantity ORDER #* id *ord_date oship_date in made up of made up of EMPLOYEE #* id *last name ofirst name taken by the sales rep for the sales rep for UID bar - relationship is part of the entity’s unique identifier.

UID Bars A Unique Identifier bar indicates that the relationship participates in an entities UID. In other words the UID of one entity becomes part of the composite UID of the other entity as well as a foreign key.

Rules: 1) The UID Bar is always at the many end of a one to many relationship. 2) The entity at the many end always receives the UID of the other entity. UID Bars

COURSE # code * duration o fee INSTRUCTOR # id # last name # first name o hire date PROGRAM # code # start date is taught by is the teacher of included in includes Reading ERD’s