Web for Database Management Systems BCA 4th Sem

8/2/2019 Web for Database Management Systems BCA 4th Sem

1/7

Web Answers for Database Management

System (BCA)

Chapter 1: Introduction

Q1.What is difference between DBMS and RDBMS?

Answer:

RDBMS is DBMS plus Referential Integrity. DBMS is mainly a storage area and it does not employ

any tables for storing the data or does not use any special function keys or foreign keys for the

retrieval of the data. RDBMS has the major difference of solving the queries easily as they are stored

in table format and use many functional keys in solving the queries. DBMS Doesnt follow the

normalization while RDBMS follows the normalization. This is the major difference between them.

They follow the 12 Codd's rules. DBMS does not support client/server Architecture but RDBMS

supports client/server Architecture. Only one user can access the database at a time in DBMS. But

RDBMS allows simultaneous access of users to the database.


2/7

Chapter 2: Entity Relationship Model

Q1. State the rules for naming an entity.

Answer:

1. "Create a name that accurately, clearly and unambiguously identifies the subject of a table.2. Use the minimum number of words necessary to convey the subject of the table.3. Do not use words that convey physical characteristics of the database. Avoid using words

such as 'File', 'Record,' and 'Table.'

4. Do not use acronyms and abbreviations.5. Do not use proper names or other words that will unduly restrict the data that can be entered

into the table.

6.

Do not use a name that implicitly or explicitly identifies more than one concept (e.g. facilityor branch entity).

7. Do not use the plural form of the name."


3/7

Chapter 4: SQL & Integrity Constraints

Q1. What to connect to an oracle database from java program?

Answer:

A: There are six things that need to know to connect to an oracle database from a Java program:

1. DRIVER2. IP ADDRESS3. PORT NUMBER: The well-known port for oracle is 15214. ORACLE INSTANCE: The default at Pace is ORA15. USERNAME as given by DBA6. PASSWORD as given by DBA

Q2. What is a Stored Procedure?Answer:

A stored procedure is a set of SQL commands that has been compiled and stored on the database

server. Once the it is "stored", client applications can execute the stored procedure repeatedly without

sending it to the database server again and without compiling it again. Stored procedures improve

performance by reducing network traffic and CPU load.


4/7

Chapter 5: Relational Database Design

Answer to Review Question No 7

Banker-schema is not in BCNF since banker-name is not a superkey.

If we apply BCNF decomposition algorithm, we obtain the following BCNF decomposition.

banker-branch-schema = (banker-name, branch-name)

customer-banker-schema = (customer-name, banker-name)

The decomposed schemas preserve only banker-name branch-name (and trivial dependencies) but

the closure of {banker-name branch-name} does not include customer-name branch-name

banker-name. The violation of this dependency cannot be detected unless a join is computed.

To see why the decomposition of Banker-schema into the schemas Banker-branch-schema and

customer-banke-schema is not dependency preserving, we apply the algorithm of testing for

dependency preservation, we find that the restrictions F1 and F2 of F to each schema are as follows: -

F1 = {banker-name, branch-name}

F2 = (only trivial dependencies hold on customer-banker-schema)

Thus, a canonical cover for the set F is F1.

It is easy to see that dependency Customer-name branch-name banker-name is not in F+

even

though it is in F+. Therefore, F

+F

+, and the decomposition is not dependency preservation.

Answer to Review Question No 13

There are relation schemas that are in BCNF that do not seem to be sufficiently normalized, in the

sense that they still suffer from the problem of repetition of information. Consider banking example.

Let us assume that, in an alternative design for the bank database schemas, we have the schema

BC-schema = (loan-number, customer-name, customer-street, customer-city)

The astute reader will recognize this schema as a non-BCNF schema because of the functional

dependency

Customer-name customer-street customer-city that we asserted and because customer-name is not

a key for BC-schema. However, let us assume that out bank is attracting wealthy customers who have

several addresses (say, a winter home and a summer home). Then, we no longer wish to enforce the

functional dependency customer-name customer-street customer-city. If we remove this functional

dependency, we find BC-schema to be in BCNF with respect to our modified set of functional

dependencies. Yet, even though BC-schema is now in BCNF, we still have the problem of repetition

of information.

To deal with this problem, we must define a new form of constraint, called a multivalued dependency.

(We use multivalued dependencies to define a normal form for relation schemas. This normal form,

called fourth normal form (4 NF), is more restrictive than BCNF).


5/7

Chapter 6: Internal Structure of RDBMS

Q1. What is a Transactional Database?

Answer:

A transactional database is a DBMS where write operations on the database are able to be rolled back

if they are not completed properly. If a transactional database system loses electrical power half-way

through a transaction, the partially completed transaction will be rolled back and the database will be

restored to the state it was in before the transaction started.

Assume that a front-end application is sending a customer order to a database system. The front-end

application sends the request to product to the customer and subtracts the product from inventory. The

front-end application is about to send the request to create an invoice for the customer and suddenly

the front-end application crashes. A transactional database can then roll back the partially completed

transaction. An alternative to using a transactional database is to use atomic operations.

Q2. What is Database Replication? List the advantages of Replication.

Answer:

Database replication is the creation and maintenance of multiple copies of the same database. In most

implementations of database replication, one database server maintains the master copy of the

database and additional database servers maintain slave copies of the database. Database writes are

sent to the master database server and are then replicated by the slave database servers. Database

reads are divided among all of the database servers, which results in a large performance advantage by

load sharing. Database replication can also improve availability because the slave database servers can

be configured to take over the master role if the master database server becomes unavailable.

Advantages of Replication:

Availability: Failure of site containing relation r does not result in unavailability of r as its replicas

exist.

Parallelism: Queries on r may be processed by several nodes in parallel.

Reduced data transfer: Relation r is available locally at each site containing a replica of r.

Q3. What is fragmentation?

Answer:

A fragment is a distribution unit that is a subset of a relation (or object in a more general sense) that

can be obtained by an expression on the data model language. Common expressions used for

fragmentation of relations include: selections, projections and semi-joins.

In addition to reduce network transfer cost, fragmentation also maximizes concurrency by allowing

concurrent transactions that access disjoint sets of a relation to proceed independently one of the

other. In addition, a single query can also benefit from fragmentation by accessing in parallel different

fragments.


6/7

Chapter 7: File Organization & Index Structures

Q1. What is a BLOB?

Answer:

A BLOB (Binary Large Object) is a large chunk of data which is stored in a database. A BLOB

differs from regular database data. It is not forced into a certain schema. A normal database field

might be structured to be 14 characters long and accept lowercase letters only. A BLOB field is not

usually restricted in content type. A content can be several gigabytes in size. Normal database fields

have space allocated for them whether they are utilized or not. BLOB fields are only allocated space

when they are utilized. BLOB fields are normally used to store graphics, audio, video, or documents.

BLOB fields can be added, changed, and deleted. However, they cannot be searched and manipulated

with standard database commands.

Q2. What is a DSN?

Answer:

A DSN (Data Source Name) is an identifier which defines a data source for an ODBC driver. A DSN

consists of information such as:

Database name

Directory

Database driver

User ID

Password

Under Unix, DSN configuration is usually stored in /etc/odbc.ini. In Microsoft Windows, DSN

configuration is normally stored in the registry, although it may also be stored in configuration files

with a .dsn extension

Q3. What is B-TREE-P?

Answer:

B-TREE-P is software that allows data to be instantly located and output, without having to wait for

lengthy file sorts or searches. B-TREE-P is a software product from Semaphore Corporation that

enhances the Pick operating system and makes it easier to use.

Q4. How much disk space do B-trees require?

Answer:

Each B-tree is only a list of item identifiers, along with a few extra pointers, so a B-tree only takes

about 10% more than the number of frames used by a SELECT list of the items being indexed. For

example, if a SELECT list of a vendor file takes about 200 frames, than a B-tree for the same file will

probably take about 220 frames. Each data files can have any number of B-trees. B-trees are stored in

their own file space, any number of B-trees can be saved in one file, and B-trees and indexed data

files can grow to any size. As only item identifiers are saved, a B-tree takes the same amount of space


7/7

regardless of how the data file is indexed and sorted. For example, a B-tree for vendor lookups by ZIP

codes takes the same amount of space as a B-tree for lookups by company name or by phone number

or by invoice date.

Q5. B-trees are better than inverted files justify the proposition

Answer:

Inverted files usually fail if the inverted list of identifiers grows beyond the Pick item limit of 32K,

and can require slow sequential searches of those large items. B-tree items always stay very small and

never run into any Pick size limitations.

Inverted files can only find actual keys known to already exist in the data. If a look up for any ZIP

code 95003, and it's not in the file, an inverted file can do nothing. But a B-tree can tell the next

closest match, such as ZIP 95005, and even identify any size "neighborhood" of adjacent records

before and after the match.

Inverted files only allow searches for a complete key. However, with B-trees search for the name

JOTIN, or just JOT, or just the letter J, or as many characters correctly specified and B-TREE-P will

immediately find the closest match. If an inverted file tries to store all those substrings, it requires

enormous amounts of disk space.

Inverted files cannot step sequentially through the index file. Whereas B-trees can start at any key,

then step sequentially through all preceding or following keys.

Inverted files allow searches for a primary key only ,while with B-trees immediate retrieval of the list

of items having ZIP 10020..

Software for inverted files is usually tied closely to the data being indexed, and must often be

modified if a new type of data file or field is to be indexed. B-trees are much more efficient, flexible,

and user-friendly than inverted files.

Q6. How were B-trees invented?

Answer:

B-tree algorithms were developed by various computer manufacturers and independent research

groups beginning in about the late 1960s, and are now the basis for many commercial database

systems, although not the Pick system.

After deciding to abandon the use of inverted files on its Pick system in late 1985, Semaphore

Corporation developed its own B-tree software to simplify and improve various applications used

internally at the company. Articles published by Semaphore about those efforts attracted numerous

requests from other Pick users asking to acquire the software, so it was packaged as B-TREE-P

beginning in April 1986.

Web for Database Management Systems BCA 4th Sem

Documents

Transcript of Web for Database Management Systems BCA 4th Sem