IMS 6217: Introduction to Data Modeling 1 Dr. Lawrence West, MIS Department, University of Central Florida Introduction to Data Modeling—Topics Introduction to Data Modeling Information elements Introduction to Entities, Attributes, and Relationships Basic notation –Chen –Alternative More on attributes

IMS 6217: Introduction to Data Modeling 2 Dr. Lawrence West, MIS Department, University of Central Florida 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 Information Systems Planning Information Elements Entities Attributes Relation- ships Rules Physical Database Data Modeling

IMS 6217: Introduction to Data Modeling 3 Dr. Lawrence West, MIS Department, University of Central Florida 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

IMS 6217: Introduction to Data Modeling 4 Dr. Lawrence West, MIS Department, University of Central Florida 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, reports & filing cabinets Interviews & research will result in a collection of "Information Elements" (my term) –Lists of items of concern to the client –Items that crop up in interviews & research –Items you recognize from your experience

IMS 6217: Introduction to Data Modeling 5 Dr. Lawrence West, MIS Department, University of Central Florida 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)

IMS 6217: Introduction to Data Modeling 6 Dr. Lawrence West, MIS Department, University of Central Florida Information Elements (cont.) Our determinations generate the base data model Further analysis modifies and extends the data model to its final form –Add new entities as review of the business model reveals overlooked items –Add many new entities as part of the normalization process

IMS 6217: Introduction to Data Modeling 7 Dr. Lawrence West, MIS Department, University of Central Florida 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

IMS 6217: Introduction to Data Modeling 8 Dr. Lawrence West, MIS Department, University of Central Florida 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

IMS 6217: Introduction to Data Modeling 9 Dr. Lawrence West, MIS Department, University of Central Florida 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

IMS 6217: Introduction to Data Modeling 10 Dr. Lawrence West, MIS Department, University of Central Florida 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. See lesson on Course Lessons Page

IMS 6217: Introduction to Data Modeling 11 Dr. Lawrence West, MIS Department, University of Central Florida 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

IMS 6217: Introduction to Data Modeling 12 Dr. Lawrence West, MIS Department, University of Central Florida 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

IMS 6217: Introduction to Data Modeling 13 Dr. Lawrence West, MIS Department, University of Central Florida 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 My preference is for “Pascal Case” –CustomerOrder –LastInventoryDate Some organizations include data type indicator as an attribute prefix (e.g. smnySalesPrice )

IMS 6217: Introduction to Data Modeling 14 Dr. Lawrence West, MIS Department, University of Central Florida Identifier Attributes (Primary Keys) Identifier Attribute: An attribute whose value uniquely identifies each occurrence of an entity –SSN for student or faculty –VIN for an automobile –SKU for a retail product Composite Identifiers: More than one attribute is needed to uniquely identify an entity occurrence –Dept Code & Number for a course –Building Code & Room Number for a classroom Review Alternate Keys

IMS 6217: Introduction to Data Modeling 15 Dr. Lawrence West, MIS Department, University of Central Florida Identifier Attributes (cont.) Identifier attributes define the entity as well as identifying occurrences –What entity does VIN identify? –What entity does State + TagNumber identify? –SKU, SaleID, SKU + SaleID? –SKU + StartDate? –EmployeeID + SkillID? –EmployeeID + PositionID + StartDate? Always check to ensure that the primary key is consistent with the entity name and the entity description

IMS 6217: Introduction to Data Modeling 16 Dr. Lawrence West, MIS Department, University of Central Florida Documenting Identifier Attributes (cont.) Identifier attributes are underlined in an ER diagram (sometimes bold faced)

IMS 6217: Introduction to Data Modeling 17 Dr. Lawrence West, MIS Department, University of Central Florida Relationships "A meaningful association between (or among) entities" What in the world does this mean? Relationships indicate how entities interact from the organization's perspective Relationships will end up defining paths through the database along which data will be retrieved –The paths usually mirror real world associations between entities

IMS 6217: Introduction to Data Modeling 18 Dr. Lawrence West, MIS Department, University of Central Florida Relationships (cont.) Relationships are verbs –Buys, teaches, sells, owns, … –Is a –Has Relationship verb describes how two entities interact with each other If two entities do not interact (from the organization’s official viewpoint) then there is no relationship between them –Professor ?? Football_Play ‘Direction’ of verb is not very important Important special cases

IMS 6217: Introduction to Data Modeling 19 Dr. Lawrence West, MIS Department, University of Central Florida Two Notation Schemes (Chen LDM) Entities are indicated by a box with the entity name inside Attributes are listed in ovals attached to entities Relationships are indicated by diamonds Relationships are connected to entities by notation to indicate the cardinality of the relationship

IMS 6217: Introduction to Data Modeling 20 Dr. Lawrence West, MIS Department, University of Central Florida Two Notation Schemes (Alternative LDM) Entities shown as boxes Entity name Attributes Relationship shown without the diamond

IMS 6217: Introduction to Data Modeling 21 Dr. Lawrence West, MIS Department, University of Central Florida Multivalued Attributes Multivalued Attributes are those that may have more than one value for the same entity occurrence –EMPLOYEE Skill –STUDENT Major Chen recommends illustrating with a double ellipse around the attribute We will see that multivalued attributes must be eliminated from the ER diagram –I recommend dealing with this immediately (to be covered later) –Don't model multivalued attributes

IMS 6217: Introduction to Data Modeling 22 Dr. Lawrence West, MIS Department, University of Central Florida Derived Attributes A derived attribute is one that can be calculated from other information in the database (data model) –EMPLOYEE.Birthdate and Date give EMPLOYEE.Age –Sum of all CUSTOMER.Purchases minus sum of all CUSTOMER.Payments gives CUSTOMER.Balance Derived attributes are shown with a dashed ellipse or the notation in my modeling technique Later we will cover the decision on whether to implement derived attributes in the database

IMS 6217: Introduction to Data Modeling 23 Dr. Lawrence West, MIS Department, University of Central Florida What's Next? More on relationships –Attributes of relationships –Degree of a relationship –Cardinality of relationships