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Created with Fabric.js 1.4.5 Number of participating entity types in a relationship is called the DEGREE of the relationship - A relationship of degree two is called BINARY relationship. - A degree of three is called a TERNARY relationship - A degree of greater then 3 is called a N-ART relationship. - A degree of one is called a UNARY/RECURSIVE relationship. your artboard start from scratch[clears the canvas] Database Design Week 3 Conceptual database design stage - Represent data requirements gathered in 'requirement analysis' unambiguously - Represents concepts graphically - This course will use UML to draw diagrams Entity-Relationship (ER) Model - Semantic data model Popularly used at the UML - Unified Modeling Language Entity type or Entity: - Group of objects with the same properties.- Independent existence MembermemberNoNameAddresstelNo Name of Entity E.g. Fruit Entity occurrence is described by its attribuesEach attribute has an ATTRIBUTE DOMAIN - A set of possible values the attribute can have Attributes Single-valued attribute - Holds a single value for each occurance e.g. memberNo has a single value for each member Multi-valued attribute - Holds multiple values for each occurrence e.g. telNo possibly multiple numbers for each member Derived attribute - may be derived from other attributes. e.g. age is deriviable from birthdate & current date Candidate key - Minimal number of attributes that uniquely identifies each occurance of an entity set. Primary Key - A candidate key is selected and designated as primary key. Used to uniquely identify an entity occurence Member memberNo {PK]namedateOfBirthaddress no city state ziptelNo [1..3]/age Primary Key Derived Attribute Multi-valued attribute Composite attribute Relationship - Association among two or more entities Relationship Occurance -A uniquely identifiable association that includes one occurance from each participating entity type Relationship Type - Collection of similar relationships M1M2M3 R1R2R3 T1T2 Member entity(memberNo) BelongTorelationship MemberType entity(typeNo) BelongTo MemberType Member Member belongs to Member Type' Registers Students Course Semester Relationships with a degree of man than 2 is represented using a diamond
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