IMS 4212: Introduction to Data Modeling 1 Dr. Lawrence West, Management Dept., University of Central Florida [email protected] Introduction to Data Modeling—Topics

IMS 4212: Introduction to Data Modeling

1Dr. Lawrence West, Management Dept., University of Central [email protected]

Introduction to Data Modeling—Topics

• Introduction to Data Modeling

• Information elements

• Introduction to Entities, Attributes, and Relationships

• Basic notation

– Chen

– Alternative

• More on attributes



What is Data Modeling?

• Data modeling is a step in the process that begins with the planning phase of Information Engineering and ends with construction of the physical database

InformationSystemsPlanning

InformationElements

EntitiesAttributesRelation-

shipsRules

PhysicalDatabase

Data Modeling



What is Data Modeling (cont.)

• Data Modeling is a process of requirements identification, documentation, and revision that results in a finished DB design

– Process begins with gross identification of basic DB components

– Design is refined according to rules for storage and retrieval efficiency

• Finished DB design is converted to the physical DB

– Some DB design tools make the conversion automatically



Information Elements

• IS Design involves interviews with clients

– Clients don’t understand our terminology or DB concepts (or they wouldn’t need us!)

– We probably don’t understand much of theirs

– Examine forms and reports

• Interviews will result in a collection of "Information Elements" (my term)

– Lists of items of concern to the client

– Items that crop up in interviews

– Items you recognize from your experience

Exercise



Information Elements (cont.)

• Task is to determine which part of a data model the different information elements fit– Entity– Attribute– Relationship– Business rule– System input or output– None of the above (irrelevant)

• Our determinations generate the base data model• Further analysis modifies and extends the data model

to its final form



Entities

• "A person, place, object, thing, event, or concept about which the organization wishes to maintain data"

• Examples from the university's database might be STUDENT, CLASS, and PROFESSOR

• Each entity in the final data model will become a table in the physical database

• It is important to distinguish between entities and attributes of an entity

– Distinction may change with perspective

• We will also create new entities as we refine our data model



Occurrences

• "Occurrences" of an entity are individual instances of the entity

– You are an occurrence of the STUDENT entity

– I am an occurrence of the FACULTY entity

• Occurrences correspond to records in the database

• Take care not to confuse occurrences with entities

– Some authors use the term “Entity Set” to imply that the Entity is a collection of occurrences



Defining Entities

• It is amazingly important to explicitly define what is meant by each entity

• What is contained in the following entities?

– Customer − Order

– Sale − Employee

• Entity descriptions become part of the DB documentation (description property in SQL Server)

• You cannot assume that developers using the DB will have the save vision for the meaning of an entity that you do



Defining Entities (cont.)

• (One occurrence of this entity represents…) “A person or organization that has purchased products from the company or who has inquired about purchasing products” (Customer)

• … “A person that has signed an employment agreement with the company including former employees. Excludes applicants, contractors, and contractor employees” (Employee)

• Try very hard to avoid using the entity name as part of the definition.



Attributes

• "A property or characteristic of an entity that is of interest to the organization"

• E.g., what characteristics of a STUDENT are of interest to the University?

– SSN, First Name, Last Name, Major, DOB, …

• What characteristics are not of interest?

• What about Professors and Classes?

• What about your project?

• Attributes become fields in a record in the physical database



Describing Attributes

• Attributes must be described just like entities

• What do these mean for a Product entity?

– Price − Weight

– Supplier − ProductID

• “Street address excluding apartment number or P.O. Box where employee receives mail”

• “Shipping weight of one unit of product including packaging in decimal fractions of a pound”

• “Current retail price that will be charged to a customer purchasing this product”

• Use Attribute description in SQL table definitions



Entities and Attributes

• There can be ambiguity—depending on perspective—in determining what should be an entity and what should be an attribute

– UCF may have an attribute of STUDENT that contains the high school each student graduated from

– The State of Florida Dept. of Education may consider high schools to be an entity with its own attributes

• Refinement of the database may require that some attributes be turned into new entities—watch for this as we continue in the course



Naming Entities and Attributes

• Balance brevity with completeness

• No Spaces

– Order Detail → OrderDetail or Order_Detail

• No SQL Reserved Words

– Order → CustomerOrder

– Date → OrderDate, HireDate, BirthDate

– Time, Table, Insert, …

• My preference is for “Pascal Case”

– CustomerOrder

– LastInventoryDate

Documents

IMS 4212: Introduction to Data Modeling 1 Dr. Lawrence West, Management Dept., University of Central Florida [email protected] Introduction to Data Modeling—Topics