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Questions and Answers
What is the first step in the ER-to-Relational Mapping Algorithm?
What is the first step in the ER-to-Relational Mapping Algorithm?
What is the purpose of Step 1 in the ER-to-Relational Mapping Algorithm?
What is the purpose of Step 1 in the ER-to-Relational Mapping Algorithm?
What is chosen as the primary key for the relation R in Step 1?
What is chosen as the primary key for the relation R in Step 1?
What happens if the chosen key of E is composite in Step 1?
What happens if the chosen key of E is composite in Step 1?
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What is created in Step 2 for each weak entity type W?
What is created in Step 2 for each weak entity type W?
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What are included as foreign key attributes of the relation R in Step 2?
What are included as foreign key attributes of the relation R in Step 2?
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What is the purpose of Steps 8 and 9 in the ER-to-Relational Mapping Algorithm?
What is the purpose of Steps 8 and 9 in the ER-to-Relational Mapping Algorithm?
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What is the result of mapping the COMPANY ER schema into a relational schema?
What is the result of mapping the COMPANY ER schema into a relational schema?
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What is the primary key of the DEPENDENT relation?
What is the primary key of the DEPENDENT relation?
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Which approach is used to map a binary 1:1 relationship type?
Which approach is used to map a binary 1:1 relationship type?
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What is the purpose of Step 2 in mapping ER schema to relational schema?
What is the purpose of Step 2 in mapping ER schema to relational schema?
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What is the primary key of the relation DEPENDENT renamed to?
What is the primary key of the relation DEPENDENT renamed to?
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Which entity type is chosen to serve in the role of S in a 1:1 relationship type?
Which entity type is chosen to serve in the role of S in a 1:1 relationship type?
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In a binary 1:N relationship type, where is the foreign key included?
In a binary 1:N relationship type, where is the foreign key included?
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What is included as attributes of S in a 1:N relationship type?
What is included as attributes of S in a 1:N relationship type?
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What is the result of mapping the COMPANY ER schema?
What is the result of mapping the COMPANY ER schema?
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What is the primary key of R in the given ER model?
What is the primary key of R in the given ER model?
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What is created to represent an n-ary relationship type R, where n>2?
What is created to represent an n-ary relationship type R, where n>2?
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What is included as attributes of S in the mapping of an n-ary relationship type?
What is included as attributes of S in the mapping of an n-ary relationship type?
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What is the primary key of the relation SUPPLY in the relational schema?
What is the primary key of the relation SUPPLY in the relational schema?
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What corresponds to a 'Relationship' relation in the relational model?
What corresponds to a 'Relationship' relation in the relational model?
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What is mapped to a set of simple component attributes in the relational model?
What is mapped to a set of simple component attributes in the relational model?
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What is the mapping for a multivalued attribute in the relational model?
What is the mapping for a multivalued attribute in the relational model?
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What is the next step after mapping an n-ary relationship type?
What is the next step after mapping an n-ary relationship type?
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What is the primary key of the WORKS_ON relation in the relational database schema?
What is the primary key of the WORKS_ON relation in the relational database schema?
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What is the purpose of including the primary key DNUMBER of the DEPARTMENT relation as a foreign key in the EMPLOYEE relation?
What is the purpose of including the primary key DNUMBER of the DEPARTMENT relation as a foreign key in the EMPLOYEE relation?
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What is included in the relation S to represent the M:N relationship type R?
What is included in the relation S to represent the M:N relationship type R?
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What is the primary key of the relation R created to map a multivalued attribute A?
What is the primary key of the relation R created to map a multivalued attribute A?
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Why is the attribute DLOCATION included in the relation DEPT_LOCATIONS?
Why is the attribute DLOCATION included in the relation DEPT_LOCATIONS?
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What is the purpose of creating a new relation S to represent a binary M:N relationship type R?
What is the purpose of creating a new relation S to represent a binary M:N relationship type R?
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What is the primary key of the DEPT_LOCATIONS relation?
What is the primary key of the DEPT_LOCATIONS relation?
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What is the main difference between Options 8A and 8B?
What is the main difference between Options 8A and 8B?
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What is the purpose of creating a relation L in Option 8A?
What is the purpose of creating a relation L in Option 8A?
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What is common in the attributes of relations Li in Options 8A and 8B?
What is common in the attributes of relations Li in Options 8A and 8B?
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What is the limitation of using Option 8B?
What is the limitation of using Option 8B?
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What is the advantage of using Option 8C?
What is the advantage of using Option 8C?
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What is the purpose of the attribute t in Option 8C?
What is the purpose of the attribute t in Option 8C?
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Which option is suitable for mapping partial specialization?
Which option is suitable for mapping partial specialization?
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What is the primary key of the relation L in Option 8C?
What is the primary key of the relation L in Option 8C?
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Study Notes
ER-to-Relational Mapping Algorithm
- The algorithm consists of 9 steps to map ER diagrams to relational schemas
- Steps 1-7 map ER model constructs to relations
- Steps 8-9 map EER model constructs to relations
Step 1: Mapping of Regular Entity Types
- For each regular entity type E, create a relation R with all simple attributes of E
- Choose a key attribute of E as the primary key for R
- If the chosen key is composite, the set of simple attributes that form it will together form the primary key of R
Step 2: Mapping of Weak Entity Types
- For each weak entity type W, create a relation R with all simple attributes of W
- Include the primary key attribute(s) of the owner entity type(s) as foreign key attributes of R
- The primary key of R is the combination of the primary key(s) of the owner(s) and the partial key of W, if any
Step 3: Mapping of Binary 1:1 Relation Types
- For each binary 1:1 relationship type R, identify the relations S and T that correspond to the entity types participating in R
- Choose one of the relations, say S, and include a foreign key in S, the primary key of T
- It is better to choose an entity type with total participation in R
Step 4: Mapping of Binary 1:N Relationship Types
- For each regular binary 1:N relationship type R, identify the relation S that represents the participating entity type at the N-side of the relationship type
- Include as foreign key in S the primary key of the relation T that represents the other entity type participating in R
- Include any simple attributes of the 1:N relation type as attributes of S
Step 5: Mapping of Binary M:N Relationship Types
- For each regular binary M:N relationship type R, create a new relation S to represent R
- Include as foreign key attributes in S the primary keys of the relations that represent the participating entity types
- Also, include any simple attributes of the M:N relationship type as attributes of S
Step 6: Mapping of Multivalued Attributes
- For each multivalued attribute A, create a new relation R
- R includes an attribute corresponding to A, plus the primary key attribute K as a foreign key in R
- The primary key of R is the combination of A and K
Step 7: Mapping of N-ary Relationship Types
- For each n-ary relationship type R, create a new relation S to represent R
- Include as foreign key attributes in S the primary keys of the relations that represent the participating entity types
- Also, include any simple attributes of the n-ary relationship type as attributes of S
Mapping EER Model Constructs to Relations
- Step 8: Options for mapping specialization or generalization
- Step 9: Mapping of union types (categories)
Step 8: Options for Mapping Specialization or Generalization
- Option 8A: Multiple relations - superclasses and subclasses
- Option 8B: Multiple relations - subclass relations only
- Option 8C: Single relation with one type attribute
- Option 8D: Single relation with multiple type attributes
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Description
This quiz is about mapping n-ary relationship types to new relationships in database design. Learn about the primary keys and foreign key attributes involved in this process.