Database Exam 2 Quizzes

Entity supertypes and subtypes are organized in a specialization hierarchy. Select the statement that IS NOT correct regarding supertypes and subtypes.

• Every subtype has one supertype to which it is directly related.

• A subtype exists within the context of a supertype.

• Every subtype has one or more supertypes to which it is directly and indirectly related.

• A supertype can have many subtypes.

Select the statement that IS NOT correct with respect to "specialization hierarchy".

• It supports attribute inheritance.

  
  

• It describes relationships in terms of "has-a" relationships.

  
  

• It defines a special supertype attribute known as the subtype discriminator.

  
  

• It defines disjoint or overlapping constraints and complete or partial constraints.

  
  

Select the statement that IS NOT correct.

• An entity subtype contains unique characteristics which differentiate its instances from other instances of the supertype.

  
  

• The selection of supertypes and and subtypes is independent of their attributes.

  
  

• An entity supertype is a generic entity type related to one or more entity subtypes.

  
  

• EER diagrams (EERDs) use the EER model.

  
  

Select what IS NOT correct regarding surrogate primary keys.

• It is used to simplify the identification of entity instances.

  
  

• It is helpful if selected candidate key has embedded semantic contents or is too long.

  
  

• It is useful when there is no natural key.

  
  

• It is flexible allowing multiple NULL values.

  
  

Select what IS NOT correct regarding disjoint subtypes.

• They contain a unique subset of the supertype entity set.

  
  

• Its Implementation is based on the value of the subtype discriminator attribute in the supertype.

  
  

• They are known as nonoverlapping subtypes.

  
  

• They share few instances that guarantee the relationship among them.

  
  

Select the best definition of partial completeness.

• Not every subtype occurrence is a member of a supertype.

  
  

• Not every supertype occurrence is a member of a subtype.

  
  

• Every supertype occurrence is a member of a subtype.

  
  

• Every subtype occurrence is a member of a supertype.

  
  

Select the best definition of overlapping subtypes.

• They contain nonunique subsets of the supertype entity set.

  
  

• Its implementation is based on the value of the subtype discriminator attribute in the supertype.

  
  

• Its implementation does not require discriminator attribute.

  
  

• They contain the same number of instances.

  
  

Select the statement that IS NOT correct.

• Specialization identifies lower-level, more specific entity subtypes from a higher-level entity supertype.

  
  

• Specialization is a top-down process.

  
  

• Specialization is based on grouping unique characteristics and relationships of the subtypes.

  
  

• Specialization is based on grouping common characteristics and relationships of the subtypes.

  
  

Select best definition of generalization.

• It identifies clusters of entities based on a given subtype.

  
  

• It identifies a higher-level, more generic entity supertype from lower-level entity subtypes.

  
  

• It is a top-down process.

  
  

• It is the process that finds entity subtypes that are disjoint sets.

  
  

Select the best definition of total completeness.

• Every subtype occurrence must be a member of at least two supertypes.

  
  

• Not every subtype occurrence is a member of a supertype.

  
  

• Not every supertype occurrence is a member of a subtype.

  
  

• Every supertype occurrence must be a member of at least one subtype.