•Redundancy
•Multiple value problems - many supplier of ordered item
•Update anomalies- change ph#
•Insertion anomalies - new supplier
•Deletion anomalies - delete supplier
•Two or more tables that are linked together through common fields
•Each table in can be joined with more than one table
•Each row called a tuple
•Each column has an allowable set of values called a domain
Entity Relationship modeling
•A database is a collection of entities
•Entities contain properties called attributes - example - “title” for books
•Relationship relate entity classes
▫ Book is writtenBy an Author
Purpose of Attributes
•Describe important properties of entity
•Help uniquely identify individual entities
▫ this is the primary key
▫ publisher id number, customer id number
•Describe relationship between entities in different entity classes
Entity models to Relational Databases
•We implement the abstract ER model to create a concrete database
▫ entity classes transform to relations
▫ attributes transform to fields
▫ entity sets transform to rows or tuples in relations
▫ one-to-many relationships modeled with foreign keys
▫ many-to-many relationships modeled with new table schemes
Many to many relationships
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