Update anomalies

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  • For each weak entity type W in the ER schema with owner entity type E, create a relation R and include all simple attributes (or simple components of composite attributes) of W as attributes of R. In addition, include as foreign key attributes of R the primary key attribute(s) of the relation(s) that correspond to the owner entity type(s). The primary key of R is the combination of the primary key(s) of the owner(s) and the partial key of the weak entity type W, if any.

    ppt32p thienthanoze 12-11-2012 29 2   Download

  • GUIDELINE 3: Relations should be designed such that their tuples will have as few NULL values as possible  Attributes that are NULL frequently could be placed in separate relations (with the primary key)  Reasons for nulls: attribute not applicable or invalid attribute value unknown (may exist) value known to exist, but unavailable

    ppt60p thienthanoze 12-11-2012 23 2   Download

  • Database System: Chapter 7 - Functional Dependencies includes Informal Design Guidelines for Relational Databases (Semantics of the Relation Attributes, Redundant Information in Tuples and Update Anomalies, Null Values in Tuples, Spurious Tuples), Functional Dependencies (FDs).

    ppt33p cocacola_17 10-12-2015 8 1   Download

  • Chapter 7: Functional Dependencies presents about Informal Design Guidelines for Relational Databases (Semantics of the Relation Attributes, Redundant Information in Tuples and Update Anomalies, Null Values in Tuples, Spurious Tuples), Functional Dependencies (FDs).

    pdf110p cocacola_17 10-12-2015 11 1   Download

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