RelationalDatabaseDesignbyER-andEER-to-RelationalMapping.ppt

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RelationalDatabaseDesignbyER-andEER-to-RelationalMapping.ppt

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Chapter 7 Relational Database Design by ER- and EER-to-Relational Mapping Chapter 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). ER-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 as shown. FIGURE 7.1The ER conceptual schema diagram for the COMPANY database. FIGURE 7.2Result of mapping the COMPANY ER schema into a relational schema. ER-to-Relational Mapping Algorithm (cont.) 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 e