Q.1 What is a database? Describe the advantages and disadvantages of using of DBMS.

Ans: Database – A database is a collection of related data and/or information stored so that it is available to many users for different purposes. 

Advantages Of DBMS:-

1. database system is that the organization can exert, via the DBA, centralized unnecessary duplication of data and effectively reduces the total amount of data

2. Reduction of Redundancies and Inconsistencies - Centralized control avoids storage required. Removing redundancy eliminates inconsistencies.

3  Data Integrity - Data integrity means that the data contained in the database is both

4  Data Sharing - A database allows the sharing of data under its control by any number of application programs or users. accurate and consistent. Centralized control can also ensure that adequate checks. The DBA who has the ultimate responsibility for the data in the DBMS can ensure incorporated in the DBMS to provide data integrity.

5. Data Security - Data is of vital importance to an organization and may be confidential. Such confidential data must not be accessed by unauthorized persons. one level of a database system without having to change the schema at the next that proper access procedures are followed. Different levels of security could be implemented for various types of data and operations. independence is the capacity to change the conceptual schema without having to

6. Data Independence - Data independence is the capacity to change the schema at  level. It is usually considered from two points of view: physical data independence the internal schema without having to change conceptual schema. Logical data and logical data independence. Physical data independence is the capacity to change change external schemas or application programs. hardware and/or software failures.

7. Providing Storage Structures for Efficient Query Processing - Database systems
provide capabilities for efficiently executing queries and updates. Auxiliary files
called indexes are used for this purpose.

Disadvantages Of DBMS

1. Cost of Software/Hardware and Migration - A significant disadvantage of the DBMS system is cost.
2. Reduced Response and Throughput - The processing overhead introduced by the DBMS to implement security, integrity, and sharing of the data causes a degradation of the response and throughput times.
from a single source namely the database. This increases the potential of security breaches and disruption of the operation of the organization because of downtimes and failures.


Q.2 Explain five duties of Database Administrator.
Ans:

1. DBA administers the three levels of the database and, in consultation with the overall user community, sets up the definition of the global view or conceptual level

2. Mappings between the internal and the conceptual levels, as well as between the of the database.
conceptual and external levels, are also defined by the DBA. database and that the database is not accessible to unauthorized users.

3. DBA ensures that appropriate measures are in place to maintain the integrity of the

4. DBA is responsible for granting permission to the users of the database and stores the profile of each user in the database with minimal loss of data.

5. DBA is responsible for defining procedures to recover the database from failures




Q.3 Explain the terms primary key, candidate key and foreign key.

Ans: Primary Key – Primary key is one of the candidate keys that uniquely identifies each row in the relation.

Candidate Key – A candidate key of an entity set is a minimal superkey, that uniquely identifies each row in the relation.

Foreign Key – Let there are two relations (tables) R and S. Any candidate key of the relation R which is referred in the relation S is called the foreign key in the relation S and referenced key in the relation R. The relation R is also called as parent table and relation S is also called as child table.


Q.4 Differentiate between logical database design and physical database design. Show how this separation leads to data independence.

Ans: Basis Logical Database Design Physical Database Design Task Maps or transforms the conceptual schema (or an ER schema) from the high-level data model into a relational database schema. The specifications for the stored database in terms of physical storage structures, record placement, and indexes are designed. Choice of criteria The mapping can proceed in two stages:

-        System-independent mapping but data model-dependent
-        Tailoring the schemas to a specific DBMS 


The following criteria are often used to guide the choice of physical database design options:

-        Response Time
-         Space Utilization
-        Transaction Throughput

          Result DDL statements in the language of the chosen DBMS that specify the conceptual and external level schemas of the database system. But if the DDL statements include some physical design parameters, a complete DDL specification must wait until after the physical  database design phase is completed. An initial determination of storage structures and the access paths for the database files. This corresponds to defining the internal schema in terms of Data Storage Definition Language. The database design is divided into several phases. The logical database design and physical database design are two of them. This separation is generally based on the system which is independent from the output of the physical database design that is concept of three-level architecture of DBMS, which provides the data independence.
               Therefore, we can say that this separation leads to data independence because the output of the logical database design is the conceptual and external level schemas of the database internal schema.


Q.6 What is ODBC? How does Oracle act as ODBC and give examples of front end uses with
ODBC.

Ans:
ODBC – Open DataBase Connectivity (ODBC) enable the integration of SQL with a general-purpose programming language. ODBC expose database capabilities in a standardized way to the application programmer through an application programming interface (API). Using ODBC, an application can access not just one DBMS but several different ones simultaneously. ODBC achieve portability at the level of the executable by introducing an extra level of indirection. All direct interaction with a specific DBMS happens through a DBMS specific driver. A driver is a software program that translates the ODBC calls into DBMS specific calls. Drivers are loaded dynamically on demand since the DBMSs the application is going to access are known only at run-time. Available drivers are registered with a driver manager. The Oracle database driver translates the SQL commands from the application into equivalent commands that the Oracle DBMS understands and takes the result from the DBMS and translate into equivalent form for the application. Example: Let there be a DSN named EMPLOYEE through, which we want to access the Oracle database in Visual Basic.


Dim CN As New ADODB. Connection Dim RS As New ADODB. 
Recordset

CN.Open “DSN=employee”, “scott”, “tiger”
RS.Open “Select * From Emp”, CN


Q. 7 Differentiate between the following:
(i) Theta Join. (ii) Equi Join. (iii) Natural Join (iv) Outer Join.

Ans:(i) Theta Join – The theta join operation is an extension to the natural-join operation that allows us to combine selection and a Cartesian product into a single operation. Consider relations r(R) and s(S), and let _ be a predicate on attributes in the schema R ??S. The theta join operation r __ ??s is defined as follows: r __ ??s = ???(r x s)

(ii) Equi Join – It produces all the combinations of tuples from two relations that satisfy a join condition with only equality comparison (=).

(iii) Natural Join - Same as equi-join except that the join attributes (having same names) are not included in the resulting relation. Only one sets of domain compatible attributes involved in the natural join are present.

(iv) Outer Join - If there are any values in one table that do not have corresponding value(s) in the other, in an equi-join that will not be selected. Such rows can be forcefully selected by using the outer join. The corresponding columns for that row will have NULLs. There are actually three forms of the outer-join operation: left outer join ( X), right outer join (X ) and full outer join ( X ).


Q.8 Draw and explain the three level architecture of the database system.
Ans:

A DBMS provides three levels of data is said to follow three-level architecture. The goal of the three-schema architecture is to separate the user applications and the physical database. The view at each of these levels is described by a schema. The processes of transforming requests and results between levels are called mappings. In this architecture, schemas can be defined at the following three levels:

External Level or Subschema – It is the highest level of database abstraction where
only those portions of the database of concern to a user or application program are
included. Any number of user views (some of which may be identical) may exist for a
given global or conceptual view. Each external view is described by means of a schema
called an external schema or subschema.

Conceptual Level or Conceptual Schema - At this level of database abstraction all the database entities and the relationships among them are included. One conceptual view represents the entire database. This conceptual view is defined by the conceptual schema. There is only one conceptual schema per database. The description of data at this level is in a format independent of its physical representation. It also includes features that specify the checks to retain data consistency and integrity.

Internal Level or Physical Schema – It is closest to the physical storage method used. It indicates how the data will be stored and describes the data structures and access methods to be used by the database. The internal view is expressed by the internal schema.


Q.9 Explain (a) Heap file (b) Sorted file. Also discuss their advantages and disadvantages.

Ans: 

Heap File is an unordered set of records, stored on a set of pages. This class provides basic support for inserting, selecting, updating, and deleting records. Temporary heap files are used for external sorting and in other relational operators. A sequential scan of a heap file (via the Scan class) is the most basic access method. Sorted file The sort utility shall perform one of the following functions:

Sort lines of all the named files together and write the result to the specified output.

Merge lines of all the named (presorted) files together and write the result to the specified
output.

               Check that a single input file is correctly presorted. Comparisons shall be based on one or more sort keys extracted from each line of input (or, if no sort keys are specified, the entire line up to, but not including, the terminating <newline>), and shall be performed using the collating sequence of the current locale.


Q.10 Explain the integrity constraints: Not Null, Unique, Primary Key with an example each. Is the combination ‘Not Null, Primary Key’ a valid combination. Justify.
Ans:
Not Null – Should contain valid values and cannot be NULL.
Unique – An attribute or a combination of two or more attributes must have a unique value in each row. The unique key can have NULL values.
Primary Key – It is same as unique key but cannot have NULL values. A table can have at most one primary key in it.

For example:
STUDENT
Roll No Name
City Mobile
17 Ankit Vats Delhi 9891663808
16 Vivek Rajput Meerut 9891468487
6 Vanita Punjab NULL
75 Bhavya Delhi 9810618396

_ Roll No is a primary key.
_ Name is defined with NOT NULL, means each student must have a name.
_ Mobile is unique.
‘Not Null, Primary Key’ is a valid combination. Primary key constraint already includes
‘Not Null’ constraint in it but we can also add ‘Not Null’ constraint with it. The use of
‘Not Null’ with ‘Primary Key’ will not have any effect. It is same as if we are using just
‘Primary Key’.


Q.11 Explain the followings :
(i) Nested Queries.
(ii) Cursors in SQL.
(iii) RDBMS.
(iv) View
(v) Application Programming Interface (14)

Ans:

(i) Nested Queries – A SELECT query can have subquery(s) in it. When a  SELECT query having another SELECT query in it, is called as nested query. Some operations cannot be performed with single SELECT command or with join operation. There are some operations which can be performed with the help of nested queries (also referred to as subqueries). For example, we want to compute the second highest salary:
SELECT MAX(SAL) FROM EMP WHERE SAL < (SELECT MAX(SAL) FROM EMP)

Some operations can be performed both by Join and subqueries. The Join operation is costlier in terms of time and space. Therefore, the solution based on subqueries is preferred.

(ii) Cursors in SQL – An object used to store the output of a query for row-by-row processing by the application programs. Cursors are constructs that enable the user to name a private memory area to hold a specific statement for access at a later time. Cursors are used to process multi-row result sets one row at a time. Additionally, cursors keep track of which row is currently being accessed, which allows for interactive processing of the active set.

(iii) RDBMS – RDBMS is a database management system (DBMS) that stores data in the form of relations. Relational databases are powerful because they require few assumptions about how data is related or how it will be extracted from the database. As a result, the same database can be viewed in many different ways. An important feature of relational system is that a single database can be spread across several tables. This differs from flat-file databases, in which each database is self-contained in a single table.

(iv) View – A view is a relation (virtual rather than base) and can be used in query expressions, that is, queries can be written using the view as a relation. In other words, a view is a named table that is represented, not by its own physically separate stored data, but by its definition in terms of other named tables (base tables or views). The base relations on which a view is based are sometimes called the existing relations. The definition of a view in a create view statement is stored in the system catalog. The syntax to create a view is:

CREATE [OR REPLACE] VIEW <view_name> [(<aliases>)] AS
<query> WITH {READ ONLY|CHECK OPTION [CONSTRAINT
<constraint_name>]};

(v) Application Programming Interface – Commercial SQL implementations take one of the two basic techniques for including SQL in a programming language – embedded SQL and application program interface (API). In the application program interface approach, the program communicates with the RDBMS using a set of functions called the Application Program Interface (API). The program passes the SQL statements to the RDBMS using API calls and uses API calls to retrieve the results. In this method, the precompiler is not required.





Q.12What is data independence? Explain the difference between physical and logical data independence. 
Ans:
Data independence is the capacity to change the schema at one level of a database system without having to change the schema at the next level. The three-schema architecture allows the feature of data independence. Data independence occurs because when the schema is changed at some level, the schema at the next level remains unchanged; only the mapping between the two levels is changed.

Types of data independence are:

Physical Data Independence – It is capacity to change the internal schema without having to change conceptual schema. Hence, the external schemas need not be changed as well. Changes to the internal schema may be needed because some physical files had to be reorganized to improve the performance of retrieval or update. If the same data as before remains in the database, the conceptual schema needs not be changed.

Logical Data Independence - It is the capacity to change the conceptual schema without having to change external schemas or application programs. The conceptual schema may be changed to expand the database (by adding a record type or data item), to change constraints, or to reduce the database (by removing a record type or data item). Only the view definition and the mappings need be changed in a DBMS that supports logical data independence. Changes to constraints can be applied to the
conceptual schema without affecting the external schemas or application programs.


Q.13 Write short notes on :
(i) Weak and strong entity sets.
(ii) Types of attributes.
(iii) Oracle Instance.
(iv) Mid square method of hashing. (4 x 4 = 16 )

Ans:
(i) Weak and Strong entity sets: A strong entity set has a primary key. All tuples in the set are distinguishable by that key. A weak entity set has no primary key unless attributes of the strong entity set on which it depends are included. Tuples in a weak entity set are partitioned according to their relationship with tuples in a strong entity set. Tuples within each partition are distinguishable by a discriminator, which is a set of attributes. A strong entity set has a primary key. All tuples in the set are distinguishable by that key. A weak entity set has no primary key unless attributes of the strong entity set
on which it depends are included. Tuples in a weak entity set are partitioned according to their relationship with tuples in a strong entity set. Tuples within each partition are distinguishable by a discriminator, which is a set of attributes.

(ii) Types of attributes: An attribute's type determines the kind of values that are allowed in the attribute. For example, the value version 1 is not valid for an attribute defined as an integer, but the value 1 is valid. Numeric types (such as integer or real) can also be limited to a predefined range by their attribute definition.
Choice :
An attribute with a list of predefined values.
ID Reference: An attribute with a value that is a Unique ID value from another element.
It is typically used for element-based cross-references.
ID References: An attribute with a value of one or more Unique ID values from another element.
Integer: An attribute with a whole number value (no decimal parts). Examples of valid
integers are 22, -22, and +322. An integer can be defined to fall within a range.
Integers: An attribute with a value of one or more integers. Enter each number on a separate line in the Attribute Value text box.
Real An attribute with a real number value, with or without a decimal part (the value can also be expressed in scientific notation). Examples of valid real numbers are 2, 22.4, - 0.22, and 2.3e-1. A real number can be defined to fall within a range.
Reals: An attribute with a value of one or more real numbers. Enter each number on a
separate line in the Attribute Value text box.
String: An attribute with a value of a series of characters (text).
Strings: An attribute with a value of one or more strings. Enter each string on a
separate line in the Attribute Value text box.                              
Unique ID: An attribute with a value of a unique text string. An element can have only
one ID attribute (which can be of type Unique ID or Unique IDs). All ID values must be
unique in the document or book. An element with a Unique ID attribute can be the source
for an element-based cross-reference.
Unique IDs: An attribute with a value of one or more unique text strings. Enter each
string on a separate line in the Attribute Value text box.

(iii) Oracle Instances: An instance is the (executed) Oracle software and the memory
they use. It is the instance that manipulates the data stored in the database. It can be
started independent of any database. It consists of:
1) A shared memory area that provides the communication between various processes.
2) Upto five background processes which handled various tasks Whenever an oracle instance starts, the file ‘INIT.ORA’ is executed.

(iv)  Mid square method of hashing: In mid square hashing, the key is squared and the
address selected from the middle of the squared number.
Mid square method
* Square K.
* Strip predetermined digits from front and rear.
* e.g., use thousands and ten thousands places.


Q.14 Discuss the correspondence between the E-R model construct and the relation model construct.
Show how each E-R model construct can be mapped to the relational model using the
suitable example?

Ans: An entity-relationship model (ERM): An entity-relationship model (ERM) is an abstract conceptual representation of structured data. Entity-relationship modeling is a relational schema database modeling method, used in software engineering to produce a type of conceptual data model (or semantic data model) of a system, often a relational database, and its requirements in a top-down fashion. Diagrams created using this process are called entity-relationship diagrams, or ER diagrams or ERDs for short.
ER-to-Relational Mapping Algorithm:

1) Step 1: Mapping of regular entity types: For each strong entity type E, create a relation T that includes all the simple attributes of a composite attribute.
2) Step2: Mapping of weak entity types: For each weak entity type W with owner entity type E, create relation R and include all simple attributes (or simple components of composite attributes) of W as attributed of R. In addition, include as foreign key attributes of R, the primary key attribute (s) of relation(s) that correspond to the owner(s) and the partial key of the weak entity type W, if any.
3) Mapping of relationship types: form a relation R, for relationship with primary keys of participating relations A and B as foreign keys in R. In addition to this, any attributes of relationship become an attribute of R also.
4) Mapping of multivalued attributes: For each multilvalued attribute A, create a new relation R. This relation R will include an attribute corresponding to A, plus primary key attribute K-as a foreign key in R-of the relation that represents the entity type or relationship type that has A as an attribute.



Q.15 Explain the concept of a data model. What data models are used in database management systems?
Ans:

Data Model – Model is an abstraction process that hides irrelevant details while highlighting details relevant to the applications at hand. Similarly, a data model is a collection of concepts that can be used to describe structure of a database and provides the necessary means to achieve this abstraction. Structure of database means the data types, relationships, and constraints that should hold for the data. In general a data model consists of two elements:


1. mathematical notation for expressing data and relationships.
2.perations on the data that serve to express queries and other manipulations of the data.

Data Models used in DBMSs:

Hierarchical Model - It was developed to model many types of hierarchical organizations that exist in the real world. It uses tree structures to represent relationship among records. In hierarchical model, no dependent record can occur without its parent record occurrence and no dependent record occurrence may be connected to more than one parent record occurrence.

Network Model - It was formalised in the late 1960s by the Database Task Group of the Conference on Data System Language (DBTG/CODASYL). It uses two different data structures to represent the database entities and relationships between the entities, namely record type and set type. In the network model, the relationships as well as the navigation through the database are predefined at database creation time.

Relational Model - The relational model was first introduced by E.F. Codd of the IBM Research in 1970. The model uses the concept of a mathematical relation (like a table of values) as its basic building block, and has its theoretical basis in set theory and first-order predicate logic. The relational model represents the database as a collection of relations.

Object Oriented Model – This model is based on the object-oriented programming language paradigm. It includes the features of OOP like inheritance, object-identity, encapsulation, etc. It also supports a rich type system, including structured and collection types.

Object Relational Model – This model combines the features of both relational model and object oriented model. It extends the traditional relational model with a variety of features such as structured and collection types.





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