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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
Increased overheads on update : On the drawbacks side, it will need the system to ensure that all replicas of a relation are consistent. This shows that all the replicas of the rel
Explain the term- signal-to-noise ratio A signal-to-noise ratio of 20 dB means that S/N = 100. As log2101 is around 6.658, the Shannon limit is around 19.975 kbps. The Nyquist
What is meant by heuristic optimisation?Discuss the major heuristics that are applied during query optimisation.
What are the benefits of prepared statements and place holders? Parameter binding operations automatically handle escaping of characters Encourage Statement reuse
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You are managing the following database system: • DBMS: Oracle 11g • OS: Sun Solaris • System architecture: Web-based application using ASP.Net • Purpose of Server: HR manage
Explain data independence ? Data independence is the capacity to modify the schema at one stage of a database system without having to change the schema at the further level.
BCNF Boyce-Codd Normal Form A relation schema R is in BCNF if it is in 3NF and accepts an additional constraint that for every FD X A, X has to be a candidate key. If a relati
Consider the relations EMP(ENO,ENAME,AGE,BASIC_SALARY) WORK_IN(ENO,DNO) DEPT(DNO,DNAME,CITY) Express the following queries in SQL (i) Find names of employees who work in a dep
What is the difference among a primary index and a secondary index? Primary Index: A primary index is an ordered file whose records are of fixed length along with two fields.
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