Ringkasan Materi #3 - The Enhanced E-R Model

 Chapter 3:The Enhanced E-R Model

• 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.
  

Generalization and Specialization

• 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

Constraints in Supertype/SUBTYPE RELATIONSHIPS

• Completeness Constraints: Whether an instance of a supertype must also be a member of at least one subtype
  
• Total Specialization Rule: Yes (double line), setiao entitas di dalam superclass harus merupakan anggota dari salah satu subclass.
  
• Partial Specialization Rule: No (single line), setiap entitas di dalam superclass dapat merupakan anggota dari subclass-subclass yang didefinisikan (bias A atau B atau bukan keduanya). 
• Disjointness Constraints:  Whether an instance of a supertype may simultaneously be a member of two (or more) subtypes 
• Disjoint Rule: entitas merupakan anggota salah satu subclass (hanya satu).
  
• Overlap Rule: entitas mungkin lebih dari satu subclass. 
• Subtype Discriminator: An attribute of the supertype whose values determine the target subtype(s) 

Disjoint – setiap instance entitas dari supertype hanya dapat muncul di salah satu subtype

Overlapping – setiap instance entitas dari supertype dapat muncul di lebih dari satu subtype (ada ya atau tidaknya?).

Sumber: PPT Dosen Pengampu Mata Kuliah Teknik Basis Data 2019/2020