Information Management Module 3: Enhanced ER Model PDF

INFORMATION MANAGEMENT MODULE 3: Enhanced ER Model  MODULE 3 SUBTOPIC 3 THE ENHANCED E-R MODEL  MODULE 3 OBJECTIVES At the end of the chapter, the learner should be able to: Define terms Understand use of supertype/subtype relationships U...

INFORMATION MANAGEMENT MODULE 3: Enhanced ER Model  MODULE 3 SUBTOPIC 3 THE ENHANCED E-R MODEL  MODULE 3 OBJECTIVES At the end of the chapter, the learner should be able to: Define terms Understand use of supertype/subtype relationships Understand use of specialization and generalization techniques Specify completeness and disjointness constraints Develop supertype/subtype hierarchies for realistic business situations Develop entity clusters  Enhanced ER model: extends original ER model with new modeling constructs Subtype: A subgrouping of the entities in an entity type that has attributes distinct from those in other subgroupings Supertype: A generic entity type that has a relationship with one or more subtypes Attribute Inheritance: Subtype entities inherit values of all attributes of the supertype An instance of a subtype is also an instance of the supertype a) EER notation  b) Microsoft Visio Notation Different modeling tools may have different notation for the same modeling constructs.  Relationships at the supertype level indicate that all subtypes will participate in the relationship The instances of a subtype may participate in a relationship unique to that subtype. In this situation, the relationship is shown at the subtype level All employee subtypes will have employee number, name, address, and date hired Each employee subtype will also have its own attributes  Generalization: The process of defining a more general entity type from a set of more specialized entity types. BOTTOM-UP Specialization: The process of defining one or more subtypes of the supertype and forming supertype/subtype relationships. TOP- DOWN  Figure 3-4 Example of generalization a) Three entity types: CAR, TRUCK, and MOTORCYCLE All these types of vehicles have common attributes  Figure 3-4 Example of generalization (cont.) b) Generalization to VEHICLE supertype So we put the shared attributes in a supertype Note: no subtype for motorcycle, since it has no unique attributes Figure 3-5 Example of specialization a) Entity type PART Only applies to manufactured parts Applies only to purchased parts  Figure 3-5 Example of specialization (cont.) b) Specialization to MANUFACTURED PART and PURCHASED PART Created 2 subtypes Note: multivalued composite attribute was replaced by an associative entity relationship to another entity Completeness Constraints: Whether an instance of a supertype must also be a member of at least one subtype Total Specialization Rule: Yes (double line) - A rule that specifies that each entity instance of a supertype must be a member of some subtype in the relationship. Partial Specialization Rule: No (single line) - A rule that specifies that an entity instance of a supertype is allowed not to belong to any subtype. Figure 3-6 Examples of completeness constraints a) Total specialization rule Figure 3-6 Examples of completeness constraints (cont.) b) Partial specialization rule  Disjointness Constraints: Whether an instance of a supertype may simultaneously be a member of two (or more) subtypes – Disjoint Rule: An instance of the supertype can be only ONE of the subtypes – Overlap Rule: An instance of the supertype could be more than one of the subtypes Figure 3-7 Examples of disjointness constraints a) Disjoint rule Figure 3-7 Examples of disjointness constraints (cont.) b) Overlap rule Subtype Discriminator: An attribute of the supertype whose values determine the target subtype(s) Disjoint – a simple attribute with alternative values to indicate the possible subtypes Overlapping – a composite attribute whose subparts pertain to different subtypes. Each subpart contains a Boolean value to indicate whether or not the instance belongs to the associated subtype Figure 3-8 Introducing a subtype discriminator (disjoint rule) Figure 3-9 Subtype discriminator (overlap rule) When a new instance is added to PART, these components are coded as follows: Figure 3-10 Example of supertype/subtype hierarchy  EER diagrams are difficult to read when there are too many entities and relationships. Solution: Group entities and relationships into entity clusters. Entity cluster: Set of one or more entity types and associated relationships grouped into a single abstract entity type Figure 3-13a Possible entity clusters for Pine Valley Furniture in Microsoft Visio Related groups of entities could become clusters Figure 3-13b EER diagram of PVF entity clusters More readable, isn’t it? Figure 3-14 Manufacturing entity cluster Detail for a single cluster In this lesson, you should have learned the following: Use of supertype/subtype relationships Use of specialization and generalization techniques Specify completeness and disjointness constraints Develop supertype/subtype hierarchies for realistic business situations Develop entity clusters  Taylor, A. G. (2019). SQL for dummies (9th ed.). Hoboken, NJ: For Dummies. Harrington, J. (2016). Relational Database Design and Implementation (4th Edition). Morgan Kaufmann Juric, N., Vrbsky, S., Nestorov, S. (2016). Database Systems: Introduction to Databases and Data Warehouses. Prospect Press Kroenke, D. M., & Auer, D. J. (2016). Database Concepts. Pearson. Sullivan, D. (2015). NoSQL for Mere Mortals (1st ed.). Boston: Addison-Wesley. Hoffer, J., Ramesh, V., Topi, H. (2013). Modern Database Management 11th Edition, Prentice Hall. ASK ANY QUESTION RELATED TO OUR TOPIC FOR TODAY.