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Questions and Answers of Databases

Describe how LDAP can be used to provide multiple hierarchical views of data, without replicating the base level data.
For each of the three partitioning techniques, namely round-robin, hash partitioning, and range partitioning, give an example of a query for which that partitioning technique would provide the
In a range selection on a range-partitioned attribute, it is possible that only one disk may need to be accessed. Describe the benefits and drawbacks of this property.
What factors could result in skew when a relation is partitioned on one of its attributes by:a. Hash partitioningb. Range partitioningIn each case, what can be done to reduce the skew?
What form of parallelism (interquery, interoperation, or intraoperation) is likely to be the most important for each of the following tasks?a. Increasing the throughput of a system with many small
With pipelined parallelism, it is often a good idea to perform several operations in a pipeline on a single processor, even when many processors are available.a. Explain why.b. Would the arguments
Give an example of a join that is not a simple equi-join for which partitioned parallelism can be used.What attributes should be used for partitioning?
Consider join processing using symmetric fragment and replicate with range partitioning how can you optimize the evaluation if the join condition is of the form | r.A − s.B| ≤ k, where k is a
Describe a good way to parallelize each of the following.a. The difference operationb. Aggregation by the count operationc. Aggregation by the count distinct operationd. Aggregation by the avg
Recall that histograms are used for constructing load-balanced range partitions.a. Suppose you have a histogram where values are between 1 and 100, and are partitioned into 10 ranges, 1–10,
Describe the benefits and drawbacks of pipelined parallelism.
Some parallel database systems store an extra copy of each data item on disks attached to a different processor, to avoid loss of data if one of the processors fails.a. Why is it a good idea to
What is the main reason why servlets give better performance than programs that use the common gateway interface (CGI), even though Java programs generally run slower than C or C++ programs?
List some benefits and drawbacks of connectionless protocols over protocols that maintain connections
List three ways in which caching can be used to speed up Web server performance.
a. What are the three broad levels at which a database system can be tuned to improve performance?b. Give two examples of how tuning can be done, for each of the levels.
What is the motivation for splitting a long transaction into a series of small ones? What problems could arise as a result, and how can these problems be averted?
Suppose a system runs three types of transactions. Transactions of type A run at the rate of 50 per second, transactions of type B run at 100 per second, and transactions of type C run at 200 per
Suppose the price of memory falls by half, and the speed of disk access (number of accesses per second) doubles, while all other factors remain the same. What would be the effect of this change on
List some of the features of the TPC benchmarks that help make them realistic and dependable measures.
Why the TPCD benchmark was replaced by the TPCH and TPCR benchmarks?
List some benefits and drawbacks of an anticipatory standard compared to a reactionary standard.
Suppose someone impersonates a company and gets a certificate from a certificate issuing authority. What is the effect on things (such as purchase orders or programs) certified by the impersonated
For each of the SQL aggregate functions sum, count, min and max, show how to compute the aggregate value on a multiset S1 ∪ S2, given the aggregate values on multisets S1 and S2.Based on the above,
Show how to express group by cube (a, b, c, d) using rollup; your answer should have only one group by clause.
Give an example of a pair of groupings that cannot be expressed by using a single group by clause with cube and rollup.
Given a relation S (student, subject, marks), write a query to find the top n students by total marks, by using ranking.
Given relation r (a, b, d, d), Show how to use the extended SQL features to generate a histogram of d versus a, dividing a into 20 equal-sized partitions (thatis, where each partition contains 5
Write a query to find cumulative balances, equivalent to that shown in Section 22.2.5, but without using the extended SQL windowing constructs.
Consider the balance attribute of the account relation. Write an SQL query to compute a histogram of balance values, dividing the range 0 to the maximum account balance present, into three equal
Consider the sales relation from Section 22.2. Write an SQL query to compute the cube operation on the relation, giving the relation in as shown below. Do not use the with cube construct.
Suppose there are two classification rules, one that says that peoplewith salaries between $10,000 and $20,000 have a credit rating of good, and another that says that people with salaries between
Suppose half of all the transactions in a clothes shop purchase jeans, and one third of all transactions in the shop purchase T-shirts. Suppose also that half of the transactions that purchase jeans
Consider the problem of finding large itemsets.a. Describe how to find the support for a given collection of itemsets by using a single scan of the data. Assume that the itemsets and associated
Describe benefits and drawbacks of a source-driven architecture for gathering of data at a data-warehouse, as compared to a destination-driven architecture.
Consider the schema depicted in as shown below. Give an SQL: 1999 query to summarize sales numbers and price by store and date, along with the hierarchies on store and date.
Compute the relevance (using appropriate definitions of term frequency and inverse document frequency) of each of the questions in this chapter to the query “SQL relation.”
What is the difference between a false positive and a false drop? If it is essential that no relevant information be missed by an information retrieval query, is it acceptable to have either false
Suppose you want to find documents that contain at least k of a given set of n keywords. Suppose also you have a keyword index that gives you a (sorted) list of identifiers of documents that contain
What are the two types of time, and how are they different? Why does it make sense to have both types of time associated with a tuple?
Will functional dependencies be preserved if a relation is converted to a temporal relation by adding a time attribute? How is the problem handled in a temporal database?
Suppose you have a relation containing the x, y coordinates and names of restaurants. Suppose also that the only queries that will be asked are of the following form: The query specifies a point, and
Consider two-dimensional vector data where the data items do not overlap. Is it possible to convert such vector data to raster data? If so, what are the drawbacks of storing raster data obtained by
Suppose you have a spatial database that supports region queries (with circular regions) but not nearest neighbor queries. Describe an algorithm to find the nearest neighbor by making use of multiple
Suppose you want to store line segments in an R-tree. If a line segment is not parallel to the axes, the bounding box for it can be large, containing a large empty area.• Describe the effect on
Give a recursive procedure to efficiently compute the spatial join of two relations with R-tree indices.
What problems can occur in a continuous-media system if data is delivered either too slowly or too fast?
Describe how the ideas behind the RAID organization (Section 11.3) can be used in a broadcast-data environment, where there may occasionally be noise that prevents reception of part of the data being
List three main features of mobile computing over wireless networks that are distinct from traditional distributed systems.
List three factors that need to be considered in query optimization for mobile computing that are not considered in traditional query optimizers.
Define a model of repeatedly broadcast data in which the broadcastmedium is modeled as a virtual disk. Describe how access time and data-transfer rate for this virtual disk differ from the
Consider a database of documents in which all documents are kept in a central database. Copies of some documents are kept on mobile computers. Suppose that mobile computer A updates a copy of
Give an example to show that the version-vector scheme does not ensure serializability?
Explain how a TP monitor manages memory and processor resources more effectively than a typical operating system.
Like database systems, workflow systems also require concurrency and recovery management. List three reasons why we cannot simply apply a relational database system using 2PL, physical undo logging,
If the entire database fits in main memory, do we still need a database system to manage the data? Explain your answer.
Consider a main-memory database system recovering from a system crash. Explain the relative merits of• Loading the entire database back into main memory before resuming transaction processing•
In the group-commit technique, how many transactions should be part of a group? Explain your answer.
Is a high-performance transaction system necessarily a real-time system? Why or why not?
In a database system using write-ahead logging, what is the worst-case number of disk accesses required to read a data item? Explain why this presents a problem to designers of real-time database
Explain why it may be impractical to require serializability for long-duration transactions.
Consider amultithreaded process that deliversmessages froma durable queue of persistent messages. Different threads may run concurrently, attempting to deliver different messages. In case of a
Discuss the modifications that need to bemade in each of the recovery schemes covered in Chapter 17 if we allow nested transactions. Also, explain any differences that result if we allow multilevel
What is the purpose of compensating transactions? Present two examples of their use.
Consider a multidatabase system in which it is guaranteed that at most one global transaction is active at any time, and every local site ensures local serializability.a. Suggest ways in which the
Consider a multidatabase system in which every local site ensures local serializability, and all global transactions are read only.a. Show by example that nonserializable executions may result in
Discuss each of the following terms:a. Datab. Fieldc. Recordd. File
What is data redundancy, and which characteristics of the file system can lead to it?
What is data independence, and why is it lacking in file systems?
What is a DBMS, and what are its functions?
Explain the difference between data and information.
What is the role of a DBMS, and what are its advantages? What are its disadvantages?
List and describe the different types of databases.
What are metadata?
Explain why database design is important.
What are the potential costs of implementing a database system?
Use examples to compare and contrast unstructured and structured data. Which type is more prevalent in a typical business environment?
What common problems do a collection of spreadsheets created by end users share with the typical file system?
Explain the significance of the loss of direct, hands-on access to business data that users experienced with the advent of computerized data repositories.
What is structural independence, and why is it important?
What are the main components of a database system?
What are some basic database functions that a spreadsheet cannot perform.
Explain why the cost of ownership may be lower with a cloud database than with a traditional, company database.
How many records does the file contain? How many fields are there perrecord?
What problem would you encounter if you wanted to produce a listing by city? How would you solve this problem by altering the filestructure?
If you wanted to produce a listing of the file contents by last name, area code, city, state, or zip code, how would you alter the filestructure?
What data redundancies do you detect? How could those redundancies lead toanomalies?
Identify and discuss the serious data redundancy problems exhibited by the file structure shown inFigure.
Looking at the EMP_NAME and EMP_PHONE contents in Figure, what change(s) would yourecommend?
Identify the various data sources in the file you examined in Problem5.
Given your answer to Problem 7, what new files should you create to help eliminate the data redundancies found in the file shown inFigure?
Identify and discuss the serious data redundancy problems exhibited by the file structure shown in Figure. (The file is meant to be used as a teacher class assignment schedule. One of the many
Given the file structure shown in Figure, what problem(s) might you encounter if building KOM weredeleted?
Discuss the importance of data modeling.
What is a business rule, and what is its purpose in data modeling?
Describe the basic features of the relational data model and discuss their importance to the end user and the designer.
Explain how the entity relationship (ER) model helped produce a more structured relational database design environment.
What is the difference between an object and a class in the object oriented data model (OODM)?
What is an ERDM, and what role does it play in the modern (production) database environment?
What is a table, and what role does it play in the relational model?

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