2nd PUC Computer Science Question Bank Chapter 13 Database Concepts

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Karnataka 2nd PUC Computer Science Question Bank Chapter 13 Database Concepts

2nd PUC Computer Science Database Concepts One Mark Questions and Answers

Question 1.
What is data?
Answer:
Data is a collection of facts, figures or statistics, which can be processed to produce meaningful information.

Question 2.
What is information?
Answer:
Information is processed data with some definite meaning.

Question 3.
What is database?
Answer:
A data organised & recorded in a format that establishes a relationship in a form that-can-be handled by a computer.

Question 4.
What is a file?
Answer:
File is basic unit of storage in computer system which contains collection of related data.

Question 5.
What is a record?
Answer:
A single entry in a table is called a Record or Row & it represnts a related data.

Question 6.
What is an entity?
Answer:
An entity is an object such as a table or form.

Question 7.
What is an instance?
Answer:
The most recently used data in a databare table gives the instance of relation.

Question 8.
What is an attribute?
Answer:
Each column of a table is identified with a distinct header called attribute.

Question 9.
What us domain?
Answer:
The range of vales that an attribute can have is called the pomain.

Question 10.
What is a relation?
Answer:
Data organised in two – dimentional tables are called relation.

Question 11.
What is a table?
Answer:
A table is a collection of data elements organized in terms of rows & columns.

Question 12.
What is a normalization?
Answer:
Normalization is the process of organizing data in a database.

Question 13.
What is a key?
Answer:
The key is a set of one or more columns whose combined values are unique among all occurrence in a given table.

Question 14.
Give the symbol notation for project.
Answer:
PROJECT π p (pi)

Question 15.
What is data mining?
Answer:
Data mining is concerned with the analysis and picking out relevant information. It is the computer, which is responsible for finding the patterns by identifing the underling rules of the features in the data.

2nd PUC Computer Science Database Concepts Two Marks Questions and Answers

Question 1.
How database helps us?
Answer:
Today the data base is used everywhere and all walks of life. The database is becoming the backbone of all the software from standalone, client-server, online, mainframe, super computers etc. for ex-use in business, government agency, service organization etc. & database can be used in schools, for ex: The fees payment software. The basic reguirments for new student admission.

Question 2.
How do we get data?
Answer:
The data may be in the form of letters, numbers, symbols, images, sound, video etc. The origin of fact can be from the organization/within or outside the organization or any part of universe. For example the marks obtained by the exam 80 is the fact, on the marks card the 80 entered will be in numeric symbols which is data.

Question 3.
Name the data types supported by DBMS.
Answer:

• INTEGER
• Single & double precision
• Logical data type
• Characters
• Strings
• Memo data type
• Index fields
• Currency fields
• Data fields
• Text fields.

Question 4.
What is generalization?
Answer:
Generalization is a bottom-up approach in which two lower level entities combine to form a higher level entity. In generalization, the higher level entity also combine with other lower level entity to make further higher level entity.

Question 5.
What is specification?
Answer:
‘Specification’ is opposite to Generalization. It is a topdown approach in which one higher level entity can be broken down into lower level entity. In specialisation, same higher level entities may not have lower level entity sets at all.

Question 6.
What is the difference between serial & direct access file organization?
Answer:
With serial file organization, records are arranged one after another , in no particular order-other than, the chronological order in which records are added to the file Direct access file organization allow immediate direct access to individual records on the file. The record are stored & retrieved using a relative record number.

Question 7.
Give the advantages and disadvantages of Index sequential Access Method.
Answer:
Advantages:

1. ISAM permits efficient & economical use of sequential processing techniques when the activity ratio is high.
2. Permits direct assess processing of records in a relatively efficient way when the activity ratio is low. .

Disadvantages:

1. Files must be stored in a direct access storage device. Hence relatively expensive hardware & software resources are required.
2. Access to records may be slower maybe slower than direct file.
3. Less efficient in the use of storage space than some other alternatives.

Question 8.
Classify various types of keys used in database.
Answer:

1. Candidate key [ck]
2. primary key [pk]
3. Alternate Key (AK) Secondary Key (SK)
4. Super key
5. foring key (fk)

Question 9.
What is relation algebra?
Answer:
Relational algebra is:

1. The formal description of how a relational database operates.
2. On interface to the data stored in the database itself.
3. The mathematics which underpin SQL operations.

Question 10.
Give an example for relation selection with example.
Answer:
Relation SELECT
SELECT: is used to obtain a subset of the tuples of a relation that satisty a select condition, for example: find all employees born after 14th Feb 2014: SELECT dob 14/Feb/2014 (employee).

Question 11.
What is Cartesian product?
Answer:
It combines the tuples of one relation with all the tuples of the other relation.

Question 12.
What is Join operation?
Answer:
JOIN is used to combine related tuple from tus relation:
JOIN allows you to evaluate a join condition between the attributes of the relation on which the join is undertaken.

Question 13.
what is data warehouse?
Answer:
A data warehouse is a repository of an organization’s electronically stored data. Data warehouses are designed to facilitate reporting & supporting data analysis. The concept of data warehouses was introduced in late 1980’s. The concept was introduced to meet the growing demands for management information & analysis that could not be met by operational systems.

Question 14.
What is data mining?
Answer:
Data mining is concerned with the analysis & picking out relevant information. It ist the computer, which is responsible for finding the patterns by identifying the underling rules of the features in the data.

2nd PUC Computer Science Database Concepts Three Marks Questions and Answers

Question 1.
Mention the applications of database.
Answer:

1. Banking
2. Water meter billing
3. Rail & Airlines
4. Colleagues
5. Credit card transactions.

Question 2.
List different forms of data (any three).
Answer:

• Document.
• Spreadsheet.
• Image.
• Drawing.
• Audio.
• Video.

Question 3.
Give the difference between manual & Electronic file systems.
Answer:
Manual file:

1. The volume of the data, which can be processed, is limited in a desirable time.
2. Manual data processing requires large quantity of paper.
3. The speed & accuracy at which the Job is executed is limited.
4. Labour cost is high.
5. Storage medium is paper.

Ellectronic file:

1. The volume of data which can be processed can be very large.
2. Reasonable less amount of paper is used.
3. The Job executed is faster & Accurate.
4. Labour cost is economical.
5. Storage medium is secondary storage medium.

Question 4.
Explan Boyce & codd form (BCNF).
Answer:
Boyce & Codd Normal form (BCNF) is a higher version of the third Normal form. This form deals with certain type of anamoly that is not handled by 3 NF A 3NF table which does not have multiple overlapping candidate key is said to be in BCNF.”

1. When a relation has more than one candidate, anomalies may result even though the relation is in 3NF.
2. 3NF does not deal satisfactorily with the case of a relation with overlapping candidate.

Question 5.
Give the different notations for E-R diagram.
Answer:
Entity:
An entity is represented using rectangles. Double rectangle represents weak entity.
In E – R diagram

An attribute is represented using eclipse

Composite Attribute Example

Relationship is represented using diamonds.

Question 6.
Explain any three components of E-R diagram.
Answer:

1. Entity: An Entity can be any object, place, person or class. In E-R Diagram, an entity is represented using rectangles.
2. Attribute: An attribute describes a property or characteristic of an entity. For Example. Name, age, address etc. Can be attributs of a student. An attribut is represented using eclipse.
3. Relationship: A Relationship describes relation between entities. Relationship is represented using diamonds.

Question 7.
What is relationship? Classify & give example.
Answer:
A relationship describes relations between entities Relationship is represented using diamonds.
Relationship:

Thre are the types of relationship that exist between entities:

• Binary Relationship
• Recursive Relationship
• Ternary Relationship

Question 8.
Explain Chen style & martin style of relation.
Answer:
Chen style

M : N Ordinality	Cardinality
Describe the minimum (optional vs mandatory)	Describe the maximum

1:N (n =0, 1, 2, 3,…)
one to zero or more
M:N (m&n=0, 1, 2, 3…)
Zero or more to zero or more
(Many to many)
1:1
One to one

Question 9.
Explain physical data independence.
Answer:
The physical storage of data should not matter to system. If say, some file supporting table were renamed or moved from one disk to another, it should not effect the application.

Question 10.
Explain ISAM with example.
Answer:
ISAM means indexed sequential Access method. It is the hybrid between sequential and direct access file organization. The records within the file are stored sequentially but direct access to individual records is possible through an index. Example: ISAM permits efficient and economical use at sequential processing techniques when the activity ratio is high.

Question 11.
Explain database users.
Answer:
DBMS users:
The broad classification DBMS users are,

1. Application programmers & system analysts: system analysts determine the requirements of end users, and develop specification for transactions that meet these requirments. Application programmers implement these parameters in programs.
2. End-users: People who require access to the database for querying, updating & ‘ generating reports. The database exists primarily for/ their use.
3. Database Administrator (DBA): DBA is responsible for authorisation access to the database for coordinating & monitoring its use. & for acquiring the needed software & hardware resources.
4. Database designers: Database designers are responsible for identifying the data to be stored in the database for choosing appropriate structures to represent & Store the data.

Question 12.
Explain hierarchical data model.
Answer:
This data model organises the data in a tree- like structure, in which each child node (also known as dependents) can have only one parent node. The database on the hierachical data model comprises a set of records connected to one another through links. The link is an association between two or more records. The top of tree structure consists of a single node that does not have any parent and is called the root node.

The root may have any number of dependents each of these dependents may have any numbers of lower level dependents. Each child node can have only one parent node and a parent node can have any number of (many) child nodes. It, therefore, represents only one-to-one and – to – many relationships. The collection of same type of records is known as a record type.

For simplicity only few fields of each record type are shown. One complete record of each record type represents a node. In this model each entity has only one parent but can” Have several children. At the top of hierarchy there is only one entity which is called Root.

Question 13.
Explain relational data model.
Answer:
The relation data model was developed by E.F Codd in 1970. In the relational data model, unlike the hierarchical and models, there are no physical links all data is maintained in the form of tables [generally known as relations) consisting of rows and columns. Each row (record) represents an entity and a column (field) represents an attribute of the entity.
The relationship between the two tables is implemented through a common attribute in the tables and not by physical links or pointers. This makes the querying much easier in a relational database system than in the hierarchical or network database systams.

Thus the relational model has become more programmer friendly and much more dominant and popular in both industrial and academic scenarios, oracle, Sybase, DBZ, Ingres, informix, ms – server are few of the popular relational DBMSs.

Question 14.
Explain outer Join with example.
Answer:
An outer Join retains the information that would have been lost from the tables, replacing missing data with nulls There are three forms of the outer join, depending on which data is be kept.

1. LEFT OUTER JOIN – Keep data from the left-hand table.
2. RIGHT OUTER JOIN – Keep data from the right- hand table.
3. FULL OUTER JOIN – Keep data from both tables.

OUTER JOIN example 1:

Question 15.
List the components of, data warehouse.
Answer:
1. Data Sources:
Data sources refer to any electronic repository of information that contains data of interest for management use or anaytics. Data needs to be passed from these to systems to the data warehouse either on the transaction-by-transaction basis for real-time data warehouses or on a regular cycle (e.g daily or weekly) of offline data warehouse.

2. Data transformation:
The data transformation layer recieve data from the data sources cleaned & standardizes & loads it into the data repository. This is often called “staging”data as data often passes through a temporary database whilst it is being transformed.

3. Reporting:
The data in the data warehouse must be available to the organization’s staff if the data warehouse is to be useful. There are a very large number of applications that perform this function or reporting can be custom-developed. Some are Bussiness intelligence tools, Executive information system, online Analytical processing (OLAP) Tools, Data Mining etc.,

4. Metadata:
Metadata or “Data about data” is used to inform operators & uses of the data
warehouses about its status & the information held within the data warehouses.

5. Operations:
Data warehouses operations comprisces of the processes of loading, manipulating & extracting data from the data warehouse. Operations also cover uses management security, capacity management & related functions.

6. Optional components:
In addition the following components also exist in same data warehouse:

• Dependent data marts.
• Logical data marts.
• Operational data store.

2nd PUC Computer Science Database Concepts Five Marks Questions and Answers

Question 1.
Explain data processing cycle.
Answer:
Data processing is the process of restructuring, manipulating & Storing data, which is recovered from various sources by people or a machine, to increase its usefulness & value of usage. Processing in whatever form invovles a sequence of tarks to be permed. The fundamental functions involves the following.
1. Gathering data, facts & statistics (Data collection):
Data requeired for an organization may be available at various places. For ex – the data about the employee is present within the organization & data about a product may be available in the market which is outside the organization.

This task basically involves the operation of finding out where data is going to orginate. The source may include documents such as invoice, sales orders purchase orders & So on which Some thimes may be available within an orgaization or sometimes environment.

2. Data input:
as the data, which is necessary, has been gathered, it is necessary to input this data to the data processing system. The input of stored data should be done in a form that is acceptable by the data processing system. For example, the marks of the test of a student may be recorded in the marks list. This has to be transferred to the data processing system so that a proper marks card of the student may be generated.

3. Processing of data:
The first step involved inprocessing is classifying the data into a proper format based on one or more charcteristics i.e the classifying of data into a proper formate based on one or more characterstics i.e, the classifying of data involves the identification of like data on one more charactersties. The characteristic identified may include elements such as class for a student or department for an employee.

The next step involves sorting the data base. Sorting is the process of arranging the data in a required form. Such as in the order of register number for a student. The process of sorting ensures that the remaining operations are easily & defficiently performed. Once data has been sorted it has to be verified to check for inconsistencies & duplication.

Inconsistencies may be due to errors which were induced in the process of input, or due to other factors. Proper verfication increases the accuracy of the data processing system. Finally the arithmetic manipulation of data is performed so that proper results are generated. Calculation is the most important task in the data processing.

During the process of calculation intermediate results may be generated, these results may be recorded so that they may be used for further processing. The next step involves summerising the result of’calculations, so that it can be organized into a desired form & meaningful information in generated.

4. Data storge :
The storage of data and the generated results is basically nesssary so that the data generated can be used in future. Storage of data can be done on any device as identified & useful to the organization. Identification of the storage device depends on the amount of data generated and the effective cost of storage. Data storage may be on devices such as floppies, hard distk, tape & so on or a hard copy may be maintained in files.

5. Data output:
Once all the above-described operations have been performed, it is necessary to put the results forward so that it helps in proper decision & the generation of more information. The output of data processing system in the form of a report.

Question 2.
Explain various data types used in DBMS.
Answer:

1. Integer: Hold whole number without fractions.
2. Single and double precision: Seven significant value for u number.
3. Logical data type: Store data that has only two values true or false.
4. Characters: It include letter, number, spaces, symbols and punctuation, character fields or variables store text information like name, address, etc.
5. Strings: String is a sequence at character contain more than one. Fixed length is 0 to 63kb and dynamics strings length range from 0 to 2 billion characters.
6. Memo data type: Store morethan 255 characters. A memo fields can store up to 65536 characters.
7. Index fields: Used to store relevant information along with the documents.
8. Currency fields: It accepts data in dollar from by default.
9. Date fields: This field accepts data entored in date format.
10. Texts field: Accepts data as an alpha – numeric text string.

Question 3.
Explain Normalization with classifications & example.
Answer:
Normalization:
Normalization the process of organising data in a data base. This includes creating tables & establishing relationships between those tables according to rules designed both to protect the data & to make the database more flexible, Normalisation redundancy and inconsistent dependency.
Normalization rules are divided into following normal form.

1. First Normal Form
2. Second Normal form
3. Third Normal form
4. BCNF

1. First Normal form (INF):
A row of data cannot contain repeating group of data i.e each column must have a unique value identifier i.e* Primary key*

2. Second Norm Form (2NF):
A table to be normalized to second normal form should meet all the needs of first normal form and there must not be any partial dependency of any column on primary key Now all these three table comply with second Normal form.

Question 4.
Explain cardinality with example.
Answer:
Cardinality specifies how many instances of an entity relate to one instance of another entity. Originality is also closely linked to cardinality, while cardinality specifies the occurances of a relationslip, ordinality describes the relationship as either, mandatory or optional.

In other words cardinality specifies the maximum number of relationships & ordinality specifies the absolute minimum number of relationships, when the minimum number is zero, & when the minimum number is one or more, the relationship is usually called mandatory.

Question 5.
Explain data independence in detail.
Answer:
Data Independence is an ability of a database to modify a schma definition at one level without affecting a schema in the next higher level (The ability to change the conceptual schema without affecting the external schemas or application programs). Data independence occurs because when the schema is changed at one level, the schema at next level remain unchanged & only the mapping between the two levels is changs two types of data independace are:

1. Logical data independence
2. Physical data independence

All schemas are logical & actual data is stored in but bit format on the disk, Namely storage medium Hard disk (all the fies will be stored), floppies, drum, tapes, SD etc., system designs choose to organize, access & process *files in different ways depending on the type of application & the need of users. The three commonly used file organizations used im DBMS/RDBMS data processing applications are sequential, direct & indexed sequential access method.

Question 6.
Discuss file organization with respect to physical data independence.
Answer:
All schemas are logical and actual data is stored in bit format on the disk namely storage medium: Hard disk (all the files will be stored), floppies, drum, tapes, SD cards etc. System designs choose to organize, access and process records and filet in different ways depending On the type of application and the needs of users. The three commonly used file organizations used in DBMS/RDBMS data processing applications are:

1. Sequential processing
2. Direct processing
3. Indexed sequential access method (ISAM).

The selection at a particular file organization depends upon the application used. To access a record some key field or unique identifying value that is found in every record in a file is used.

Question 7.
Explain the features of database system.
Answer:
1. Controlled data redundancy:
During Database design, various files are intergrated & each logical data item is stored at central location. This eliminates replicating (duplication) the data item in defferent files & ensource consistency & not saves the storage space.

2. Enforcing Data integrity:
In database apporach. enforcing data integrity is much easier. Data integrity refers to the validity of data & it can be compromised in a number of ways. Data integrity constraints can be enforced automatically by the DBMS, & others may have to be checked by the application programs.

3. Data sharing:
The data stored in the database can be shared among multiple users or application programs. Moreover, new applications can be developed to use the same stored data.

4. Earefo application development:
The application programmer needs to develop the application programs to the user needs. The other issues like concurrent access. Security, data integrity, etc., are handled by RDBMS itself.

5. Data Security:
Since the data is stored centrally, enforcing security constraints is much easier. The ‘RDBMS ensures that only the means of access to the database is through authorized channel only.

6. Multiple uses interfaces:
In order to meet the need of various users having different technical knowledge, DBMS provides different types of interfaces such as query languages, application program interfaces, & graphical user interfaces (GUI) that include forms-style & menu- drive interfaces.

7. Backup & recovery:
The RDBMS provides backup and recovery subsystem that is responsible for recovery from hardware & software failures.

Question 8.
Explain DBMS architecture.
Answer:
DBMS architecture can be seen as single tier or multi-tier. N-tier architecture divides the whole system into related but indepent n modules, which can be independently modified, altered, charged or replaced.
Data base architecture is logically divided into three types:

1. Logical one-tier In -1 tier architecture,
2. Logical tow-tier client/ server architecture
3. Logical three-tier client/server architecture

In 1- tier architecture, DBMS is the only entity where user directly sits on DBMS & uses it. Any changes done here will directly be done on DBMS itself. It does not provide handy tools for end users & preferably database designer and programers use single-tier architecture.
Two-tier client/ server architecture:
Structures and conceptual tools that is used to describe the structure (data types, relationships. & constraints) of a database. Also defines a set of operations that can be performed on the data. A data model generally consists of data model theory, which is a formal description of how data may be structured & data model instance, which is a practical data model designed for a particular application.

The processes of applying a data model theory to create a data model instance is known as data modelling. A database model provides the necessary means to achive data abstraction.

Question 9.
Explain database model.
Answer:
A database model or simply a data model is an abstract model that describes how the data is represented & used. A data model consists of a set model of a set of data structures & conceptual fools that is used to describe the structure (data types, relationship, & constrains) of a database. Also defines a set of operations that can be performed & on the data.

A data model generally consists of data model theory, which is a formal description of how data may be structured & used, and data model instance which is a parctical data model designed for a particular application. The process of applying a data model theory to create a data model instance is knwon as data modelling.

A database model provides the necessary means to active data abstraction. A Database model define the logical design of data. The model describes the relationship between different parts of the data.

Question 10.
Explain Codd’s rules for database management.
Answer:
Rule zero:
This rule states that for a system to quality as an RDBMS, it must be able to manage database entity through the relational capabilities.

Rule No – 1: Information rule.
All information (including meta -data) is to be represented as stored data in cells of tables. The rows and columns have to be strictly unordered.

Rule – 2: Guaranteed access.
Each unique piece of data (atomic value) should be accessible by: Table Nam + primary Key (row) + Attibute (Column).

Rule – 3: Systematic treatment of Null
Null has server meanings, it can mean missing data, not applicable or no value, It should be handled consistently, primary key must not be null. Expression on null must give NDLL.

Rule – 4: Active online catalog.
Database dictionary (catalog) must have description of database, catalog to be governed by some rule as rest of the database.

Rule – 5: Powerful Language.
One well defined language must be there to provide all manners of access to data, for ex: SQL.

Rule – 6: view updation rule.
All view that are theoritically updatable should be updatable system.

Rule – 7: Relational Level Operation.
There must be Insert, delete, update operations at each level of relations. Set operation like union, Intersection and minus should also be supported.

Rule – 8: Physical Data Independence.
The physical storage of data should not matter to the system.

Rule – 9: Logical Data Independence.
If there is change in the logical structure (table structure) of the data base the user view of data should not change.

Rule – 10: Integrity Independence.
The database should be able to con – force its own intergiry rather than using other programs.

Rule – 11: Distribution Independence.
A database should work properly regardless of its distribution across a network. This lays foundation of distributed database.

Rule – 12: Non – subversion rule.
If low level access is allowed to a system it should not be able to subvert or bypass intergrity rule to change data. This can be achieved by some sort of looking or encryption.

Question 11.
Write comparing RA and SQL.
Answer:
Relational Algebra (RA):

1. RA is the formal description D7 how a relational database operates.
2. RA is an interface to the data stored in the database itself.
3. RA is the mathematics that underpin SQL operations.
4. RA has simple semantics.

SQL:

1. SQL is a superset of relational algebra.
2. SQL has convenient formatting features.
3. SQL provides aggregate functions.
4. SQL has complicated semantics.
5. SQL is an end-user language.

Question 12.
List any five types of relational keys.
Answer:

1. Candidate Key (CK)
2. Primary Key (PK)
3. Alternate Key/Secondary Key (SK)
4. Super Key
5. Foreign Key (FK)

Question 13.
Explain Entity-Relationship Model in detail.
Answer:
The ER Model defines the conceptual view of a database. If woks around real-world entities and the associations among them. At view level, the ER model is considered a good option for designing databases.
The ER model has 3 main components:
1. Entity:
An entity can be any object, place, person or class. In ER diagram an entity is represented using rectangles. Consider an example of an organization. Employee, Manager, Department, Product and many more can be taken as entities from an organization.

2. Attribute :
An attribute describes a property or characteristic of an Entity. For example, Name, Age, Address etc. can be attributes of a student. An attribute is represented using eclipse.
Different types of attributes are:

1. Simple attribute
2. Composite attribute
3. Derived attribute
4. Single – value attribute
5. Multi-value attribute

3. Relationship:
A relationship describes relations between entities. Relationship-is represented using diamonds. There are 3 types of relationship that exist between entities.

1. Binary relationship
2. Recursive relationship
3. Ternary relationship

Question 14.
Explain the concept of Data abstraction.
Answer:
Database systems are made – up of complex data structures. Ter ease the user interaction with database, the developers hide internal irrelevent details from users. This process of hiding irrelevent details from user is called data abstraction.
1. Physical level:
This is the lowest level of data abstraction. It describes how data is.actually stored in database. You can get the complex data structure details at this level.

2. Logical level:
This is the middle level of 3 – level data abstraction architecture. It describes what data is stored in database.

3. View level:
This is the highest level of data abstraction. This level describes the user interaction with database system.

Question 15.
Describe and explain the phases of data mining.
Answer:
Data mining is concerned with the analysis and picking out relevant information. It is the computer, which is responsible for finding the patterns by identifying the underling rules of the features in the data.
Phases of Data mining:
1. Selection:
Selecting or segmenting the data according to some criteria. For Example all those people who won a car, in this way subsets of the data can be determined.

2. Preprocessing:
This is the data cleaning stage’ where certain information is removed which deemed unnecessary and may slow down queries for example gender of the patient.

3. Transformation:
The data is not merely transferred, but transformed. For example, demographic overlays commonly used in market research. The data is made useable and navigable.

4. Data mining:
This stage is concerned with the extraction of patterns from the data.

5. Interpretation and Evaluation:
The patterns identified by the system are interpret1 *o knowldge which Can be used to support human decision – making. For example prediction and classification tasks, summarizing the content of a database or explaining observed phenomena.

2nd PUC Computer Science Database Concepts Additional Questions and Answers

Question 1.
Write any two advantages of electronic data processing.
Answer:
The use of computers has eliminated the use of papers to solve problams. Involves very high speeds and greater accuracy.

Question 2.
Write any two dis advantages of manual data processing.
Answer:
Since the data is stored using physical means, it involves the usage of a large amount of paper. The speed and accuracy at which a job is executed is limited.

Question 3.
Explain selection operations in database.
Answer:
The selection operation is used when we would like to view only certain tuples from a table based on our requirement. For example form the table EMPLOYEE our we many want to see only those tuples who are drawing salary for more than Rs. 7500. Thus the selection on a table is that only those tuple where the value in a particular column or a combination of columns satisfies the requirement condition, which is specified i.e, the output of the selection operator also results in a table, with the same number of attributes and whose contents are a subset of the original table.

The contents are chosen such that they satify a required condition. The condition in the selection operation is denoted using relational operators such as (=) equal to, (< >) not equal to, (>) greatet than, (>+) greater than or. equal to, (<) less than and (<=1) less than or equal.

Multiple conditions are combined using the logical operators and, or, not, Eg: select* from employ will display contents of employ table. Insert into student values (167: Anand”, 20-Dec – 89″, PCMB 5950) will insert value into the table student.

Question 4.
Explain insertion operation in database.
Answer:
The insert operation is performed to include a new tuple into the database. It is done by providing a set of values for each attribute in the relation scheme. While inserting new values into the database care has to be taken to see that the various constraints are not violated. The constraints are:

1. No key value should be duplicated.
2. A value must be specified for every attribute in a row.

Question 5.
Explain foreign key with an example.
Answer:
For example consider two relation schemes.
Employee (Empno, Empname, Deptno, salary)
Department (Deptno, Deptname, No-of-employee, Expert-area)
In these two relation scheme the attribute ‘dept no’ refers to two different tuples, each from one relation. Such sets of attributes from the first selections scheme which can be used to uniquely identity tuples from another relation scheme is termed as foreign key.

Depno is called the foreign key. A non – key attribute, whose values are derived from the primary key of some other table is known as foreign key in its current table.

Question 6.
Explain alternate key with an example.
Answer:
For example consider the relation scheme.
STUDENT (Regno, Name, Comb, Class, Fees)
All attributes combinations inside a relation that can serve as primary key are candidate keys as they are candidats for the primary key position. In the tables Regno and Name are Candidate Keys. A candidate key that is not the primary key is called an alternate key or secondary key. In example STUDENT relations Name is the alternate key.

Question 7.
Mention any two merits of Indexed sequential file organization.
Answer:
Two merits of Indexed sequential file organization are:

1. It combines the best features of sequential access, and direct access.
2. Permits quick access of records with a high activity ratio.

Question 8.
Write any two advantages of DBMS.
Answer:

1. DBMS has efficient searching and update of data.
2. It has ability to enforce integrity constraints.

Question 9.
Write any two advantages of direct access file organization.
Answer:
The two advanlages of direct access file organization are:

1. No index is used to store records, thus saving storage space.
2. Since mapping exists between the record key and its corresponding physical storage location, access is fast as very little searching is involved.

Question 10.
Mention any two database operations.
Answer:
2 database operations are

• Selection operation and
• Update operation.