![]() The two entities would be the student and the course, and the relationship depicted is the act of enrolling, connecting the two entities in that way. For example, the named student might register for a course. How entities act upon each other or are associated with each other. Foreign key: Identifies the relationship between entities. Primary key: A candidate key chosen by the database designer to uniquely identify the entity set. An entity set may have more than one candidate key. Candidate key: A minimal super key, meaning it has the least possible number of attributes to still be a super key. Super key: A set of attributes (one or more) that together define an entity in an entity set. Entity keys can be super, candidate or primary. An associative entity associates entities (or elements) within an entity set.Įntity keys: Refers to an attribute that uniquely defines an entity in an entity set. A strong entity can be defined solely by its own attributes, while a weak entity cannot. A related term is instance, in which the specific person or car would be an instance of the entity set.Įntity categories: Entities are categorized as strong, weak or associative. Other examples: Customers who purchased last month, cars currently registered in Florida. Other examples: customers, cars or products.Įntity set: Same as an entity type, but defined at a particular point in time, such as students enrolled in a class on the first day.
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