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UT Dallas CS 6360 - Ch09

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Chapter 9Chapter OutlineThe ER conceptual schema diagram for the COMPANY database.Result of mapping the COMPANY ER schema into a relational schema.ER-to-Relational Mapping AlgorithmIllustration of mapping stepsER-to-Relational Mapping Algorithm (contd.)Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Ternary relationship types. (a) The SUPPLY relationship.Mapping the n-ary relationship type SUPPLYSummary of Mapping constructs and constraintsMapping EER Model Constructs to RelationsSlide 26EER diagram notation for an attribute-defined specialization on JobType.PowerPoint PresentationGeneralization. (b) Generalizing CAR and TRUCK into the superclass VEHICLE.Slide 30Mapping EER Model Constructs to Relations (contd.)Slide 32Slide 33FIGURE 4.5 EER diagram notation for an overlapping (non-disjoint) specialization.Slide 35Slide 36A specialization lattice with multiple inheritance for a UNIVERSITY database.Mapping the EER specialization lattice using multiple options.Slide 39Two categories (union types): OWNER and REGISTERED_VEHICLE.Mapping the EER categories (union types) to relations.Chapter SummaryRelational Database Design by ER- and EER-to-Relational MappingChapter 9Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe 2Chapter OutlineER-to-Relational Mapping Algorithm Step 1: Mapping of Regular Entity TypesStep 2: Mapping of Weak Entity TypesStep 3: Mapping of Binary 1:1 Relation TypesStep 4: Mapping of Binary 1:N Relationship Types.Step 5: Mapping of Binary M:N Relationship Types.Step 6: Mapping of Multivalued attributes.Step 7: Mapping of N-ary Relationship Types.Mapping EER Model Constructs to Relations Step 8: Options for Mapping Specialization or Generalization.Step 9: Mapping of Union Types (Categories).Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe 3The ER conceptual schema diagram for the COMPANY database.Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe 4Result of mapping the COMPANY ER schema into a relational schema.Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe 5ER-to-Relational Mapping AlgorithmStep 1: Mapping of Regular Entity Types.For each regular (strong) entity type E in the ER schema, create a relation R that includes all the simple attributes of E.Choose one of the key attributes of E as the primary key for R.If the chosen key of E is composite, the set of simple attributes that form it will together form the primary key of R.Example: We create the relations EMPLOYEE, DEPARTMENT, and PROJECT in the relational schema corresponding to the regular entities in the ER diagram.SSN, DNUMBER, and PNUMBER are the primary keys for the relations EMPLOYEE, DEPARTMENT, and PROJECT.Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe 6Illustration of mapping stepsCopyright © 2007 Ramez Elmasri and Shamkant B. Navathe 7ER-to-Relational Mapping Algorithm (contd.)Step 2: Mapping of Weak Entity TypesFor each weak entity type W in the ER schema with owner entity type E, create a relation R & include all simple attributes (or simple components of composite attributes) of W as attributes of R.Also, 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.Example: Create the relation DEPENDENT in this step to correspond to the weak entity type DEPENDENT.Include the primary key SSN of the EMPLOYEE relation as a foreign key attribute of DEPENDENT (renamed to ESSN). The primary key of the DEPENDENT relation is the combination {ESSN, DEPENDENT_NAME} because DEPENDENT_NAME is the partial key of DEPENDENT.Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe 8Illustration of mapping stepsCopyright © 2007 Ramez Elmasri and Shamkant B. Navathe 9ER-to-Relational Mapping Algorithm (contd.)Step 3: Mapping of Binary 1:1 Relation TypesFor each binary 1:1 relationship type R in the ER schema, identify the relations S and T that correspond to the entity types participating in R.There are three possible approaches:1. Foreign Key approach: 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 in the role of S. Example: 1:1 relation MANAGES is mapped by choosing the participating entity type DEPARTMENT to serve in the role of S, because its participation in the MANAGES relationship type is total.2. Merged relation option: An alternate mapping of a 1:1 relationship type is possible by merging the two entity types and the relationship into a single relation. This may be appropriate when both participations are total.3. Cross-reference or relationship relation option: The third alternative is to set up a third relation R for the purpose of cross-referencing the primary keys of the two relations S and T representing the entity types.Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe 10The ER conceptual schema diagram for the COMPANY database.Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe 11Illustration of mapping stepsCopyright © 2007 Ramez Elmasri and Shamkant B. Navathe 12ER-to-Relational Mapping Algorithm (contd.)Step 4: Mapping of Binary 1:N Relationship Types.For each regular binary 1:N relationship type R, identify the relation S that represent 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. Example: 1:N relationship types WORKS_FOR, CONTROLS, and SUPERVISION in the figure.For WORKS_FOR we include the primary key DNUMBER of the DEPARTMENT relation as foreign key in the EMPLOYEE relation and call it DNO.Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe 13The ER conceptual schema diagram for the COMPANY database.Copyright © 2007 Ramez Elmasri and Shamkant B. Navathe 14Illustration of mapping stepsCopyright © 2007 Ramez Elmasri and Shamkant B. Navathe 15ER-to-Relational Mapping Algorithm (contd.)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


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