Lecture04 - What you should have learned after this lecture what a weak entity set is what total participation means what the(min max-notation is

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Unformatted text preview: What you should have learned after this lecture ... what a weak entity set is what total participation means what the (min, max)-notation is further concepts of the Entity-Relationship Model multi-valued attributes composite attributes generalization aggregation Extensions ¡ existence dependent ( weak ) entity sets − assumption so far: entities exist autonomously and can be uniquely identified within an entity set by their key attributes ( strong entity set) − in reality there are also weak entities that do not have sufficient attributes to form a key. These entities are + dependent in their existence from another, superior entity and + can be uniquely identified only in combination with the key of a superior entity − superior entity set is called identifying or owner entity set − graphical notation: ¡ identifying relationship set − a weak entity set E 1 must be associated with an identifying entity set E 2 by an identifying relationship set , if the key of E 1 comprises the key of E 2 and if it con- tains one or more additional attributes of E 1 − relationship from the weak entity set to the superior entity set has usually an m :1- cardinality and more seldom a 1:1-cardinality − graphical notation: ¡...
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This note was uploaded on 02/14/2012 for the course COP 5725 taught by Professor Staff during the Spring '08 term at University of Florida.

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Lecture04 - What you should have learned after this lecture what a weak entity set is what total participation means what the(min max-notation is

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