IM LEC QUIZ ADVANCED DATA MODELLING

• Extended Entity Relationship Model is the result of adding semantic constructs to the original entity relationship model
• Entity Supertype is the generic entity type related to one or more entity subtype
• Entity Subtype contains unique characteristics of each of the entity subtype.
• Inheritance enables the entity subtype to inherit the attributes and relationships from the entity supertype.
• Specialization identifies more specific entity subtypes. It uses the top-down process and is based on grouping unique characteristics and relationships.
• Generalization identifies more common entity supertypes. It uses the bottom-down process and is based on grouping common characteristics and relationships.
• Completeness Constraint specifies whether an occurrence of a supertype must be a member of at least one subtype.
• Total Completeness is a constraint where every occurrence of the supertype must be a member of at least one subtype
• Partial Completeness is a constraint where some supertype occurrences are not members of any subtype
• Disjointness Constraint specifies whether an instance of the supertype may be a member of at least two or more entity subtypes.
• Disjoint Rule is a constraint where an instance of the supertype can be a member of only one subtype.
• Overlap Rule is a constraint wherein an instance of the supertype can be a member of two or more subtypes.
• A Subtype Discriminator is an attribute in the supertype entity. It is used to determine which entity subtypes are related to the supertype.
• Disjoint Subtype is a subtype that contains a unique subset of the supertype entity set.
• Overlap Subtypes is a subtype that contains non unique subsets of the supertype entity set.
• Primary Key is the most important characteristic of an entity as it guarantees entity integrity.
• Primary Key Characteristics:

  1. Unique values
  2. Non intelligent
  3. No change over time
  4. Preferably single attribute
  5. Preferably numeric
  6. Security compliant
• A natural key is a real world identifier used to identify real world objects