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Class Number – CS 304

Class Number – CS 304. Class Name - DBMS. Instructor – Sanjay Madria. Lesson Title – EER Model –21th June. Figure 3.15 ER diagram for the COMPANY schema, with all role names included and with structural constraints on relationships specified using the alternate notation (min, max).

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Class Number – CS 304

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  1. Class Number – CS 304 Class Name - DBMS Instructor – Sanjay Madria Lesson Title – EER Model –21th June

  2. Figure 3.15 ER diagram for the COMPANY schema, with all role names included and with structural constraints on relationships specified using the alternate notation (min, max).

  3. 5 Relationships of Higher Degree - Relationship types of degree 2 are called binary - Relationship types of degree 3 are called ternary and of degree n are called n-ary - In general, an n-ary relationship is not equivalent to n binary relationships

  4. Figure 3.10 Some relationship instances of a ternary relationship SUPPLY

  5. Figure 3.16 An ER diagram for an airline database.

  6. Figure 3.17 An ER diagram for a BANK database.

  7. Figure 3.18 An ER diagram for a database that keeps track of company and employee phones.

  8. Figure 3.19 An ER diagram for a database that keeps track of textbooks used in courses.

  9. 6 Extended Entity-Relationship (EER)Model

  10. Specialization and Generalization • ER diagrams consider entity types to be primitive objects • EER diagrams allow refinements within the structures of entity types • Specialization: top-down refinement into (super)classes and subclasses

  11. Figure 4.1 EER diagram notation for representing specialization and subclasses.

  12. Figure 4.2 Some instances of the specialization of EMPLOYEE into the {SECRETARY, ENGINEER, TECHNICIAN} set of subclasses.

  13. Generalization groups entity types; bottom up synthesis • Subclasses inherit the attributes and relationships of their superclasses

  14. WHY • Relationship types only partially applicable to the superclass • Attributes only partially applying to superclasses

  15. Figure 4.3 Examples of generalization. (a) Two entity types CAR and TRUCK. (b) Generalizing CAR and TRUCK into VEHICLE.

  16. Disjointness Constraints • Disjoint (d) • The subclasses must have disjoint sets of entities • Overlap (o) • The subclasses may have overlapping sets of entities

  17. Figure 4.4An attribute-defined specialization on the JobType attribute of EMPLOYEE.

  18. Completeness Constraints • Partial • An entity may not belong to any of the subclasses (single-line) • Total • Every entity in the superclass must be a member of some subclass (double-edge)

  19. Membership Constraints • Predicate defined subclasses • The subclass is defined through a predicate on the attributes of the superclass • Attribute defined subclasses • The subclasses in the specialization are all defined by the same attribute of the superclass • User defined subclasses • Membership in the subclasses is determined at the insertion operation level

  20. Figure 4.5 Notation for specialization with overlapping (nondisjoint) subclasses.

  21. Structures in Specialization • Multiple Specializations • Specialization Hierarchy • Each subclass belongs to at most one class • Lattice Specializations • A subclass may belong to more than one class

  22. Figure 4.6 A specialization lattice with the shared subclass ENGINEERING_MANAGER.

  23. Categories • Associate more than one superclass to a subclass. • In categories, different entries of the subclass may inherit attributes from different superclsses • An entity in Category is a member of only one of its superclass • In specializations, all the subclasses inherit all the attributes of the superclass • Category types: Total or Partial

  24. Figure 4.7 A specialization lattice (with multiple inheritance) for a UNIVERSITY database.

  25. Figure 4.8 An illustration of how to represent the UNION of two or more entity types/classes using the category notation. Two categories are shown: OWNER and REGISTERED_VEHICLE.

  26. Class Number – CS 304 Class Name - DBMS Instructor – Sanjay Madria Lesson Title – ER to Relational –26th June

  27. 7 Mapping ER and EER Schemas into the Relational Model Steps of The Algorithm (Chapter 9 – pages 290 to 296, Elmasri/Navathe ed. 3) -  STEP 1: Map Entity Types – Each strong Entity to a table • All simple attributes will become column in the table • Include only simple attributes of the composite attribute in the table as columns • Derived attribute will not become part of the table • Choose key attribute as Primary key of the table -  -

  28. -  STEP 2: Map Weak Entity Types to a table and draw identifier from parent entity type into weak entity type • Key of weak entity will be partial key of weak entity and key attribute of the owner entity on which it depends.

  29. Map Relationship Types (STEP 3): 1:1 - options for setting up one, two or three relations • Include PK of one of the entity T into other, say S, better to choose the PK of the entity type T and include that in the entity S with total participation in the relation. • Include attributes of R in S • No table for R • Or a table for R with PK of both plus its own attributes or all the attributes into one relation

  30. 1:N – the many side of the relationship type T provides a PK to the one side, say S, no new relation - include attributes of R into S M:N – need to set up a separate relation for the relationship - include PKs of T and S , and attributes of R into new table STEP 4: Map multivalued attributes – set up a new relation for each multi-valued attribute and the PK of the corresponding entity type -

  31. STEP 5: Mapping of generalization hierarchies and set-subset relationships – possiblity of collapsing into one relation vs. as many relations as the number of distinct classes. Convert each subclass S and superclass C, where attributes of C are {k, a,b..} and k is PK of C into a relation using following • Create a table L for C with attributes of L are {k, a, b..} and PK(L) = k. Create a table for each subclass S, with attributes of S are {k} U attributes of S, with PK of S as {k} • Create a relation for S , with attributes of S as {k,a, b..} and its own attributes and PK = k.

  32. Mapping Categories • Specify a new key called a surrogate key when creating a relation for category. (Because keys for all participating classes are different) • Include any attribute of its own • Add the surrogate key as foreign key to all other participating relations • If a category’s superclasses share the same key , there is no need for surrogate key

  33. .       Problem statement: Concise but thorough description of the application for which you propose to build a database system, and why the database system is essential. 2  System requirements: Define the scope of the system -- what it does, what it doesn’t do, and how the system will be used. 3  Conceptual database design: Documents the conceptual database design using ER/EER diagrams.

  34. 4. Functional requirements: Describe the various retrieval and update transactions and discuss how they collectively meet the database system requirements. • 5.    Estimate of effort: Discuss the expected effort required (in terms of person-weeks) to complete the design and implementation of the complete system as proposed.

  35. Keep in mind that you have a limited amount of time to complete the project so you need to be aggressive but realistic in your design.

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