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Differentiate between various levels of data abstraction?
Data Abstraction - Abstraction is the procedure to hide the irrelevant things from the users and represent the relevant things to the user. Database systems are frequent used through non-computer professionals so in which the complexity must be hidden from database system users. This is done through defining levels of abstract as that the database may be viewed; there is logical view or external view, conceptual view and internal view or physical view.
1. External View - This is the highest level of abstraction as seen through a user. It describes only the part of whole database, that is relevant to a particular user.
2. Conceptual View - This is the next higher stages of abstraction that is the sum total of Database Management System user's views. It elaborates what data are in fact stored in the database. It contains information about whole database in terms of a small number of associatively easy structure.
3. Internal View - This is the lowest level of abstraction. It elaborates how the data are physically stored
A Relation Schema represented by R(A1, A2, ..., An) is made up of the relation name the list of attributes and R Ai that it contains. A relation is described as a set of tuples
When is a transaction rolled back? Any changes that the aborted transaction made to the database must be uncompleted. While the changes caused by an aborted transaction have be
Draw the precedence graph of the following schedule and determine whether the schedule is serializable. (Note that all instructions, except lock and unlock, are omitted. We assume
Winfield is a small city with a population of 22,000 with buses serves three routes in Winfield and neighboring areas. As the city’s IT director, you have been asked to set up an i
A domain is a set of permissible values that can be given to an attribute. So each attribute in a table has a definite domain. Values to these attributes cannot be assigned outside
What are the object-oriented approaches Software systems which are designed with structured design methodology never support some of desired quality attributes for example reus
Create Student DB and perform delete operation? STUDENT (name, student#, class, major) COURSE (course name, course#, credit hours, department) SECTION (section identifier, co
explain the level architectures of the database management system
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we need example of 2phase locking
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