7/28/20091SIT103 SIT103 -Introduction to Database DesignWeek 3 – lecture 1Entity-Relationship ModelingGeelongThe Entity Relationship (ER) model•Entity Relationship Diagrams (ERDs) represent the conceptual database as viewed by the end user•ERDs depict the ER model’s three main ERDs depict the ER model s three main components: •Entities•Attributes•Relationships28 July 20092T2-2009Entities•An entity is represented by a rectangle containing the entity’s name•It is usually written in capital letters, and is a noun•Corresponds to a table and not to a row in the relational environment28 July 20093T2-2009
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7/28/20092Attributes•Composite attribute –canbe further subdivided•Simple attribute–cannotbe further subdivided•Single-valued attribute –can onlyhave a single value•Multi-valued attributes –can have manyvalues•A single-valued attributeis not necessarily a simple attribute28 July 20094T2-2009Attributes (cont.)A Composite Attribute –STU_NAME can be subdivided into these three simple attributesSingle-Value AttributeSimple Attribute ?Entity5Domains•Attributes have a domain:•set of possible values •Attributes may share a domain28 July 20096T2-2009