Mapping rules
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The document outlines 7 steps for mapping entity-relationship diagrams to relational database tables: 1) Map regular entity types to tables with primary keys. 2) Map weak entity types to tables with foreign keys to their owner entities. 3) Add foreign keys for 1:1 relationships. 4) Add foreign keys to the table on the N side for 1:N relationships. 5) Create join tables for M:N relationships. 6) Create tables for multi-valued attributes with foreign keys. 7) Create tables for ternary relationships with foreign keys to the 3 entities. The number of tables equals the number of entities, M:N relationships, multi-valued attributes, and ternary relationships.
Mapping rules
- 1. Eng.Samir Sabry IT Instructor Mapping Rules Step 1: regular entity types Create a new relation that includes Simple attributes For a composite attribute include only the simple component attributes Leave out multivalued attributes (to step 6) Pick a PK Step 2: weak entity types Note: Weak entity type has no key - Related to an identifying or owner entity type. Has total participation constraint with identifying entity. Create a new relation with simple attributes Include an FK to the owner entity's relation Step 3: 1:1 relationship types Add to one of the participating relations an FK to the other relation: It is better to add to a relation that has total participation in the relationship Include any relationship attributes Step 4: 1: N relationship types Add to the relation on the N-side an FK to the other relation. Include any relation attributes Step 5: M: N relationship types Create a New relation containing as FK of the primary keys of both entity types participating relations Include any relation attributes Step 6: multi-valued attribute Create new relation containing FK of the PK from the Entity Step 7: ternary relationship types Create new relation containing a FK referencing each of the 3 entities involved Include any relation attributes Notes: How many relations? 1. Entity (both regular and weak) 2. M:N relationship 3. Multi-valued attribute 4. Ternary relationship