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The ER Model Revisited

UniversityMumbai University
CourseInformation Technology
ModuleThe ER Model Revisited
Total Lecture : 8 Remark :Important from point view of exam...
Module Brief Module 4: The ER Model Revisited
Abstract Data types (ADT) in ER models provide means to explicitly define a structural type within the larger context of the database structure. It is a series of attribute names paired with system data types plus optional methods to manipulate those properties. There are several reasons why ADT's are useful within an object database:
i. Encapsulation - Because each user-defined data type exists as a complete entity, including the data definitions, default values, and value constraints, this entity insures uniformity and consistency. Once defined, a user-defined data type may participate in many other user-defined data types, such that the same logical data type always has the same definition, default values and value constraints, regardless of where it appears in the database.
ii. Reusability - As hierarchies of common data structures are assembled, these can be re-used within many definitions, saving coding time and insuring uniformity.
iii. Flexibility - The ability to create real-world data representations of data allows the database object designer to model the real world as it exists.
The other concepts included here are Inheritance, Specialization and Generalization. Inheritance refers to continuing the implementation of certain properties or functions in sub-classes from super-classes. Specialization refers to decomposing a particular entity into its types while generalization implies giving a common entity to various types of that entity.
Expert Remark Subtopic: Specialization and Generalization
Subclasses, Super classes, Inheritance
Relationship Types of Degree Higher Than Two.
Google Best Link 1.http://en.wikipedia.org/wiki/E ntity-relationship_model
2.http://db.grussell.org/section 004.html
3.http://dbmsbasics.blogspot.com /2008/03/entity-relationship-m odel.html
4.http://www.eazynotes.com/pages /database-management-system/en tity-relationship-diagram.html
5.http://www.kimballgroup.com/ht ml/articles_search/articles199 7/9708d15.html
6.http://cse.csusb.edu/dick/cs37 2/d3.html
TagsER Model Revisited,Abstract,Data-Types,ER-Diagram,Encapsulation,Reuseability,Flexibility

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