DATA BASE MANAGE SYS
DATA BASE MANAGE SYS COP 5725
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Hans Farrell PhD
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This 5 page Class Notes was uploaded by Hans Farrell PhD on Friday September 18, 2015. The Class Notes belongs to COP 5725 at University of Florida taught by Markus Schneider in Fall. Since its upload, it has received 20 views. For similar materials see /class/206689/cop-5725-university-of-florida in Computer Programming at University of Florida.
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Date Created: 09/18/15
What you should have learned after this lecture El further concepts of the EntityRelationship Model like weak entity sets total par ticipation and min maxnotation Example conceptual university schema isprecondi tionof predecessor m n n lectures e ma 1 ma grade m 1 SUCCESSOF 6 Extensions CI 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 l identifying relationship set a weak entity set E1 must be associated with an identifying entity set E2 by an identifying relationship set if the key of E1 comprises the key of E2 and if it con tains one or more additional attributes of E1 relationship from the weak entity set to the superior entity set has usually an m 1 cardinality and more seldom a 11cardinality graphical notation ltgtgt El example El total participation of an entity set in a relationship all entities of an entity set E1 are associated with another entity set E2 by a rela tionship set R this holds in particular for weak entity sets example lt department El more precise characterization of cardinalities of relationship sets min max notation for each entity set participating in a relationship set min expresses that each entity of this set is in relationship at least min times max expresses that each entity of this set is in relationship at most max times special cases min 0 an entity does not have to be in relationship optional max an entity may be in relationship arbitrarily many times example conceptual university schema with min maXnotations isprecondi tionof predecessor SUCCESSOF 0 3 0 m a 11 w an m e c D 13 or 1 11 0 l d b