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Although, the essential features of E-R diagrams are enough to design many database situations. Though, with more difficult relations and advanced database applications, it is need to move to enhanced features of E-R models. The three such features are:
In this part, we have described them with the help of an example. More detail on them are available in the further readings and MCS-043.
Example: A bank has an account entity set. The accounts of the bank can be of two parts:
The statement as above shows a specialisation/generalisation hierarchy. It can be shown as
Figure: Generalisation and Specialisation hierarchy
List any two significant differences between a file processing system and a DBMS. File Processing System vs. DBMS Data Independence - Data independence is the capacity t
a brief definition
Data Manipulation Language Data manipulation language (DML) describes a set of commands that are used to query and change data within existing schema objects. In this case comm
Question: (a) Can a set of data requirements be correctly modelled by two or more different ER diagrams? Explain your answer. You may use a small example, if you think it will
What are the various symbols used to draw an E-R diagram? Explain with the help of an example how weak entity sets are represented in an E-R diagram. Various symbols used to d
Question: This form represents one of a number used for each sailing of a range of boats. A passenger may go on many sailings and will have the same passenger number for each.
What is E-R model? This data model is based on real world that having of basic objects called entities and of relationship between these objects. Entities are explained in a da
Adding Redundant Associations for Efficient Access Redundant associations do not add any type of information, therefore during design we should actually examine structure of o
Define the concept of aggregation. Give two examples where this concept is useful. Ans: Aggregation transforms a relationship among the objects into a higher-level object. A
What are the objectives of query processing? Ans: The objectives of query processing is to transform a query written in a high level language into a accurate and efficien
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