Intr to Database Systems
Intr to Database Systems CS 4400
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This 0 page Class Notes was uploaded by Alayna Veum on Monday November 2, 2015. The Class Notes belongs to CS 4400 at Georgia Institute of Technology - Main Campus taught by Leo Mark in Fall. Since its upload, it has received 15 views. For similar materials see /class/234021/cs-4400-georgia-institute-of-technology-main-campus in ComputerScienence at Georgia Institute of Technology - Main Campus.
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Date Created: 11/02/15
MAPPING ENTITY RELATIONSHIP SCHEMAS INTO THE RELATIONAL MODEL Steps of the Algorithm Chapter 9 pages 290295 STEP 1 Map Entity Types STEP 2 Map Weak Entity Types draw identifier from parent entity type into weak entity type Map Relationship Types STEPS 3 to 5 11 options for setting up one two or three relations 1N the many side provides a key to the one side MN need to set up a separate relation for the relationship STEP 6 Map multivalued attributes set up a new relation Step 7 Map higher order relationships ternary 4 way etc they become separate relations STEP 8 Mapping of generalization hierarchies and set subset relationships possibility of collapsing into one relation vs as many as the distinct classes MAPPING Extended Entity Relationship EER SCHEMAS INTO THE RELATIONAL MODEL Section 92 Pages 295299 Attrs R attributes of relation R PK R Primary Key of relation R Assume there is a specialization of class C into subclasses 1 Sz 3 Sm That is there are m subclsses ofa superclass C STEP 8 in the mapping mentions the following options Option 8A 1 One relation for C with all attributes and primary key 2 m additional relations One relation per subclass S with its own attributes Attrs 8 plus the PK C The primary key of each subclass relation is the same as PK C Option 8B NO Relation corresponding to the superclass M subclass relations one per subclass Each relation for subclass Si includes PK C Attrs C and the Attrs Si The primary key of each subclass relation is the same as PK C Option 8C Create a single FAT relation containing all attributes from C the key PK C the union of all attributes from all subclasses and one type attribute t that determines to which one or more subclasses an entity belongs This works well for disjoint subclasses However the type attribute can be so designed that it can represent all possible valid combinations of subclasses that might exist Option 8D Create a single FAT relation containing all attributes from C the key PK C the union of all attributes from all 39 39 and mboolean tvpe attributes t1 t2 t3 tm The attributes to which an entity belongs are set to one This can work for Disjoint as well as overlapping subclasses