Jan. 2013Dr. Yangjun Chen1 Chapter 21 (2nd. Edition) Advanced Data Modeling Subclasses Superclasses Specialization Attribute inheritance Generalization Discriminator Lattice Category EER-to-Relational Mapping Aggregation Association Hierarchy Classification Instantiation Identification Constraints

Jan. 2013Dr. Yangjun Chen2 FUsed where more complex relationships need to be represented Fis becoming more common, more mainstream, more accepted FExamples –Computer Aided Design (CAD) & Computer Aided Manufacturing (CAM) –databases –Image and graphic databases –multimedia databases –geographic databases Chapter 21

Jan. 2013Dr. Yangjun Chen3 FSubclasses FSuperclasses FSpecialization FGeneralization FAttribute Inheritance FCategory FEnhanced-ERD FEERD - Relational MappingConcepts

Jan. 2013Dr. Yangjun Chen4Subclass/Superclass FExample: Employee entity Fhave subgroupings that need to be represented separately –Example: Engineer, secretary, manager, technician etc. Fsubgroupings are called subclasses of employee FEmployee entity is called a superclass FA superclass is sometimes referred to as just a class FClass/subclass relationship is also called an is-a relationship

Jan. 2013Dr. Yangjun Chen5Constraints employee technicianmanager superclass/class subclasses It is not necessary for an entity in a superclass to belong to a subclass An entity cannot be a member of a subclass without being a member of the superclass

Jan. 2013Dr. Yangjun Chen6 Subclass Concept FCertain attributes may apply to some entities but not all –Example: Entityunique attributes Engineer type secretary typing speed technician tgrade managerbusiness unit managed

Jan. 2013Dr. Yangjun Chen7 FSubclasses may participate in different relationships –Example: Technician might be a member of a trade union Manager manages a business unit employee technicianmanager Trade union Department manages member of Subclass Concept

Jan. 2013Dr. Yangjun Chen8 FEntities in a subclass inherit all the attributes of a superclass –Example: Employee (id, name, bdate) Engineer, Secretary and Technician all inherit id,name, bdate attributes from employee Engineer (id, name, bdate, Eng_type) Attribute Inheritance

Jan. 2013Dr. Yangjun Chen9 FEntities in a subclass also inherit relationships of its superclass employee technicianmanager Trade union Department manages member of works in Every employee (technicians and managers) works in a department Relationship Inheritance

Jan. 2013Dr. Yangjun Chen10 FWhy is this distinction important? –to better represent the real world –to express semantics (meaning) more precisely –to save storage space(?)Inheritance