Modeling A database can be modeled as: a collection of entities. relationship among entities. An entity is an object that exists and is distinguishable from other objects. Example:specific person,company,event,plant Entities have attributes Example:people have names and addresses An entity set is a set of entities of the same type that share the same properties. Example:set of all persons,companies,trees,holidays Database System Concepts-5th Edition,Oct 5,2006 6.3 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 5 6.3 ©Silberschatz, Korth and Sudarshan th Edition, Oct 5, 2006 Modeling A database can be modeled as: a collection of entities, relationship among entities. An entity is an object that exists and is distinguishable from other objects. Example: specific person, company, event, plant Entities have attributes Example: people have names and addresses An entity set is a set of entities of the same type that share the same properties. Example: set of all persons, companies, trees, holidays