400+ TOP DBMS LAB VIVA Questions and Answers

DBMS LAB VIVA Questions :-

1. What is database?
A database is a logically coherent collection of data with some inherent meaning, representing some
aspect of real world and which is designed, built and populated with data for a specific purpose.

2. What is DBMS?
It is a collection of programs that enables user to create and maintain a database. In other words it is
general-purpose software that provides the users with the processes of defining, constructing and
manipulating the database for various applications.

3. What is a Database system?
The database and DBMS software together is called as Database system.

4. What are the advantages of DBMS?

  1. Redundancy is controlled.
  2. Unauthorised access is restricted.
  3. Providing multiple user interfaces.
  4. Enforcing integrity constraints.
  5. Providing backup and recovery.

5. What are the disadvantage in File Processing System?

  • Data redundancy and inconsistency.
  • Difficult in accessing data.
  • Data isolation.
  • Data integrity.
  • Concurrent access is not possible.
  • Security Problems.

6. Describe the three levels of data abstraction?
The are three levels of abstraction:

  1. Physical level: The lowest level of abstraction describes how data are stored.
  2. Logical level: The next higher level of abstraction, describes what data are stored in
    database and what relationship among those data.
  3. View level: The highest level of abstraction describes only part of entire database.

7. Define the “integrity rules”?
There are two Integrity rules.
1. Entity Integrity: States that “Primary key cannot have NULL value”
2. Referential Integrity: States that “Foreign Key can be either a NULL value or should be
Primary Key value of other relation.

8. What is extension and intension?
1. Extension: It is the number of tuples present in a table at any instance. This is time
dependent.
2. Intension: It is a constant value that gives the name, structure of table and the constraints
laid on it.

9. What is System R? What are its two major subsystems?
System R was designed and developed over a period of 1974-79 at IBM San Jose Research Center. It
is a prototype and its purpose was to demonstrate that it is possible to build a Relational System that
can be used in a real life environment to solve real life problems, with performance at least
comparable to that of existing system.
Its two subsystems are
1. Research Storage
2. System Relational Data System.

10. How is the data structure of System R different from the relational structure?
Unlike Relational systems in System R
1. Domains are not supported
2. Enforcement of candidate key uniqueness is optional
3. Enforcement of entity integrity is optional
4. Referential integrity is not enforced

11. What is Data Independence?
Data independence means that “the application is independent of the storage structure and access
strategy of data”. In other words, The ability to modify the schema definition in one level should not
affect the schema definition in the next higher level.
Two types of Data Independence:
1. Physical Data Independence: Modification in physical level should not affect the logical
level.
2. Logical Data Independence: Modification in logical level should affect the view level.
NOTE: Logical Data Independence is more difficult to achieve

12. What is a view? How it is related to data independence?
A view may be thought of as a virtual table, that is, a table that does not really exist in its own right
but is instead derived from one or more underlying base table. In other words, there is no stored file
that direct represents the view instead a definition of view is stored in data dictionary.

Growth and restructuring of base tables is not reflected in views. Thus the view can insulate users
from the effects of restructuring and growth in the database. Hence accounts for logical data
independence.

13. What is Data Model?
A collection of conceptual tools for describing data, data relationships data semantics and constraints.

14. What is E-R model?
This data model is based on real world that consists of basic objects called entities and of relationship
among these objects. Entities are described in a database by a set of attributes.

15. What is Object Oriented model?
This model is based on collection of objects. An object contains values stored in instance variables
with in the object. An object also contains bodies of code that operate on the object. These bodies of
code are called methods. Objects that contain same types of values and the same methods are
grouped together into classes.

16. What is an Entity?
It is a ‘thing’ in the real world with an independent existence.

17. What is an Entity type?
It is a collection (set) of entities that have same attributes.

18. What is an Entity set?
It is a collection of all entities of particular entity type in the database.

19. What is an Extension of entity type?
The collections of entities of a particular entity type are grouped together into an entity set.

20. What is Weak Entity set?
An entity set may not have sufficient attributes to form a primary key, and its primary key
compromises of its partial key and primary key of its parent entity, then it is said to be Weak Entity
set.

21. What is an attribute?
It is a particular property, which describes the entity.

22. What is a Relation Schema and a Relation?
A relation Schema denoted by R(A1, A2, …, An) is made up of the relation name R and the list of
attributes Ai that it contains. A relation is defined as a set of tuples. Let r be the relation which
contains set tuples (t1, t2, t3, …, tn). Each tuple is an ordered list of n-values t=(v1,v2, …, vn).

23. What is degree of a Relation?
It is the number of attribute of its relation schema.

24. What is Relationship?
It is an association among two or more entities.

25. What is Relationship set?
The collection (or set) of similar relationships.

26. What is Relationship type?
Relationship type defines a set of associations or a relationship set among a given set of entity types.

27. What is degree of Relationship type?
It is the number of entity type participating.

28. What is DDL (Data Definition Language)?
A data base schema is specifies by a set of definitions expressed by a special language called DDL.

29. What is VDL (View Definition Language)?
It specifies user views and their mappings to the conceptual schema.

30. What is SDL (Storage Definition Language)?
This language is to specify the internal schema. This language may specify the mapping between two
schemas.

31. What is Data Storage – Definition Language?
The storage structures and access methods used by database system are specified by a set of
definition in a special type of DDL called data storage-definition language.

32. What is DML (Data Manipulation Language)?
This language that enable user to access or manipulate data as organised by appropriate data model.

  1. Procedural DML or Low level: DML requires a user to specify what data are needed and
    how to get those data.
  2. Non-Procedural DML or High level: DML requires a user to specify what data are needed without specifying how to get those data.

33. What is DML Compiler?
It translates DML statements in a query language into low-level instruction that the query evaluation
engine can understand.

34. What is Query evaluation engine?
It executes low-level instruction generated by compiler.

35. What is DDL Interpreter?
It interprets DDL statements and record them in tables containing metadata.

36. What is Record-at-a-time?
The Low level or Procedural DML can specify and retrieve each record from a set of records. This
retrieve of a record is said to be Record-at-a-time.

37. What is Set-at-a-time or Set-oriented?
The High level or Non-procedural DML can specify and retrieve many records in a single DML
statement. This retrieve of a record is said to be Set-at-a-time or Set-oriented.

38. What is Relational Algebra?
It is procedural query language. It consists of a set of operations that take one or two relations as
input and produce a new relation.

39. What is Relational Calculus?
It is an applied predicate calculus specifically tailored for relational databases proposed by E.F. Codd.
E.g. of languages based on it are DSL ALPHA, QUEL.

40. How does Tuple-oriented relational calculus differ from domain-oriented relational calculus?
1. The tuple-oriented calculus uses a tuple variables i.e., variable whose only permitted values
are tuples of that relation. E.g. QUEL
2. The domain-oriented calculus has domain variables i.e., variables that range over the
underlying domains instead of over relation. E.g. ILL, DEDUCE.

41. What is normalization?
It is a process of analysing the given relation schemas based on their Functional Dependencies (FDs)
and primary key to achieve the properties
(1).Minimizing redundancy, (2). Minimizing insertion, deletion and update anomalies.

42. What is Functional Dependency?
A Functional dependency is denoted by X Y between two sets of attributes X and Y that are subsets of
R specifies a constraint on the possible tuple that can form a relation state r of R. The constraint is for
any two tuples t1 and t2 in r if t1[X] = t2[X] then they have t1[Y] = t2[Y]. This means the value of X
component of a tuple uniquely determines the value of component Y.

43. What is Lossless join property?
It guarantees that the spurious tuple generation does not occur with respect to relation schemas after
decomposition.

44. What is 1 NF (Normal Form)?
The domain of attribute must include only atomic (simple, indivisible) values.

45. What is Fully Functional dependency?
It is based on concept of full functional dependency. A functional dependency X Y is full functional
dependency if removal of any attribute A from X means that the dependency does not hold any more.

46. What is 2NF?
A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully functionally
dependent on primary key.

47. What is 3NF?
A relation schema R is in 3NF if it is in 2NF and for every FD X A either of the following is true
1. X is a Super-key of R.
2. A is a prime attribute of R.
In other words, if every non prime attribute is non-transitively dependent on primary key.

48. What is BCNF (Boyce-Codd Normal Form)?
A relation schema R is in BCNF if it is in 3NF and satisfies an additional constraint that for every FD X
A, X must be a candidate key.

49. Define Entity Set.
Compilation of all entries of any particular type of entry in the database is called Entity Set.

50. What do you mean by Entity type extension?
Compilation of similar entity types into one particular type which is grouped together as an entity set.

DBMS LAB VIVA Questions and Answers ::

51. What is 4NF?
A relation schema R is said to be in 4NF if for every Multivalued dependency X Y that holds over R, one of following is true
–> X is subset or equal to (or) XY = R.
–> X is a super key.

52. What is 5NF?
A Relation schema R is said to be 5NF if for every join dependency {R1, R2, …, Rn } that holds R, one the following is true
–> Ri = R for some i .
–> The join dependency is implied by the set of FD, over R in which the left side is key of R.

53. What is Domain-Key Normal Form?
A relation is said to be in DKNF if all constraints and dependencies that should hold on the the constraint can be enforced by simply enforcing the domain constraint and key constraint on the relation.

54. What are partial, alternate,, artificial, compound and natural key?

  1. Partial Key:
    It is a set of attributes that can uniquely identify weak entities and that are related to same owner entity. It is sometime called as Discriminator.
  2. Alternate Key:
    All Candidate Keys excluding the Primary Key are known as Alternate Keys.
  3. Artificial Key:
    If no obvious key, either stand alone or compound is available, then the last resort is to simply create a key, by assigning a unique number to each record or occurrence. Then this is known as developing an artificial key.
  4. Compound Key:
    If no single data element uniquely identifies occurrences within a construct, then combining multiple elements to create a unique identifier for the construct is known as creating a compound key.
    Natural Key:
    When one of the data elements stored within a construct is utilized as the primary key, then it is called the natural key.

55. What is indexing and what are the different kinds of indexing?
Indexing is a technique for determining how quickly specific data can be found.
Types:

  • Binary search style indexing
  • B-Tree indexing
  • Inverted list indexing
  • Memory resident table
  • Table indexing

56. What is system catalog or catalog relation? How is better known as?
A RDBMS maintains a description of all the data that it contains, information about every relation and index that it contains. This information is stored in a collection of relations maintained by the system called metadata. It is also called data dictionary.

57. What is meant by query optimization?
The phase that identifies an efficient execution plan for evaluating a query that has the least estimated cost is referred to as query optimization.

58. What is join dependency and inclusion dependency?

  • Join Dependency:
    A Join dependency is generalization of Multivalued dependency.A JD {R1, R2, …, Rn } is said to hold over a relation R if R1, R2, R3, …, Rn is a lossless-join decomposition of R . There is no set of sound and complete inference rules for JD.
  • Inclusion Dependency:
    An Inclusion Dependency is a statement of the form that some columns of a relation are contained in other columns. A foreign key constraint is an example of inclusion dependency.

59. What is durability in DBMS?
Once the DBMS informs the user that a transaction has successfully completed, its effects should persist even if the system crashes before all its changes are reflected on disk. This property is called durability.

60. What do you mean by atomicity and aggregation?

  • nAtomicity:
    Either all actions are carried out or none are. Users should not have to worry about the effect of incomplete transactions. DBMS ensures this by undoing the actions of incomplete transactions.
  • Aggregation:
    A concept which is used to model a relationship between a collection of entities and relationships. It is used when we need to express a relationship among relationships.

61. What is a Phantom Deadlock?
In distributed deadlock detection, the delay in propagating local information might cause the deadlock detection algorithms to identify deadlocks that do not really exist. Such situations are called phantom deadlocks and they lead to unnecessary aborts.

62. What is a checkpoint and When does it occur?
A Checkpoint is like a snapshot of the DBMS state. By taking checkpoints, the DBMS can reduce the amount of work to be done during restart in the event of subsequent crashes.

63. What are the different phases of transaction?
Different phases are

  1. Analysis phase
  2. Redo Phase
  3. Undo phase

64. What do you mean by flat file database?
It is a database in which there are no programs or user access languages. It has no cross-file capabilities but is user-friendly and provides user-interface management.

65. What is “transparent DBMS”?
It is one, which keeps its Physical Structure hidden from user.

66. Brief theory of Network, Hierarchical schemas and their properties
Network schema uses a graph data structure to organize records example for such a database management system is CTCG while a hierarchical schema uses a tree data structure example for such a system is IMS.

67. What is a query?
A query with respect to DBMS relates to user commands that are used to interact with a data base. The query language can be classified into data definition language and data manipulation language.

68. What do you mean by Correlated subquery ?
Subqueries , or nested queries, are used to bring back a set of rows to be used by the parent query. Depending on how the subquery is written, it can be executed once for the parent query or it can be executed once for each row returned by the parent query. If the subquery is executed for each row of the parent, this is called a correlated subquery .
A correlated subquery can be easily identified if it contains any references to the parent subquery columns in its WHERE clause. Columns from the subquery cannot be referenced anywhere else in the parent query. The following example demonstrates a non-correlated subquery .
E.g. Select * From CUST Where ’10/03/1990′ IN (Select ODATE From ORDER Where CUST.CNUM = ORDER.CNUM)

69. What are the primitive operations common to all record management systems?
Addition, deletion and modification.

70. Name the buffer in which all the commands that are typed in are stored
‘Edit’ Buffer

71. What are the unary operations in Relational Algebra?
PROJECTION and SELECTION.

72. Are the resulting relations of PRODUCT and JOIN operation the same?
No.
PRODUCT: Concatenation of every row in one relation with every row in another.
JOIN: Concatenation of rows from one relation and related rows from another.

73. What is RDBMS KERNEL?
Two important pieces of RDBMS architecture are the kernel, which is the software, and the data dictionary, which consists of the system-level data structures used by the kernel to manage the database
You might think of an RDBMS as an operating system (or set of subsystems), designed specifically for controlling data access; its primary functions are storing, retrieving, and securing data. An RDBMS maintains its own list of authorized users and their associated privileges; manages memory caches and paging; controls locking for concurrent resource usage; dispatches and schedules user requests; and manages space usage within its table-space structures .

74. Name the sub-systems of a RDBMS
I/O, Security, Language Processing, Process Control, Storage Management, Logging and Recovery, Distribution Control, Transaction Control, Memory Management, Lock Management

75. Which part of the RDBMS takes care of the data dictionary? How
Data dictionary is a set of tables and database objects that is stored in a special area of the database and maintained exclusively by the kernel.

76. What is the job of the information stored in data-dictionary?
The information in the data dictionary validates the existence of the objects, provides access to them, and maps the actual physical storage location.

77. Not only RDBMS takes care of locating data it also
determines an optimal access path to store or retrieve the data

76. How do you communicate with an RDBMS?
You communicate with an RDBMS using Structured Query Language (SQL)

78. Define SQL and state the differences between SQL and other conventional programming Languages
SQL is a nonprocedural language that is designed specifically for data access operations on normalized relational database structures. The primary difference between SQL and other conventional programming languages is that SQL statements specify what data operations should be performed rather than how to perform them.

79. Name the three major set of files on disk that compose a database in Oracle
There are three major sets of files on disk that compose a database. All the files are binary. These are

  • Database files
  • Control files
  • Redo logs

The most important of these are the database files where the actual data resides. The control files and the redo logs support the functioning of the architecture itself.
All three sets of files must be present, open, and available to Oracle for any data on the database to be useable. Without these files, you cannot access the database, and the database administrator might have to recover some or all of the database using a backup, if there is one.

80. What is an Oracle Instance?
The Oracle system processes, also known as Oracle background processes, provide functions for the user processes—functions that would otherwise be done by the user processes themselves
Oracle database-wide system memory is known as the SGA, the system global area or shared global area. The data and control structures in the SGA are shareable, and all the Oracle background processes and user processes can use them.
The combination of the SGA and the Oracle background processes is known as an Oracle instance

81. What are the four Oracle system processes that must always be up and running for the database to be useable
The four Oracle system processes that must always be up and running for the database to be useable include DBWR (Database Writer), LGWR (Log Writer), SMON (System Monitor), and PMON (Process Monitor).

82. What are database files, control files and log files. How many of these files should a database have at least? Why?
Database Files
The database files hold the actual data and are typically the largest in size. Depending on their sizes, the tables (and other objects) for all the user accounts can go in one database file—but that’s not an ideal situation because it does not make the database structure very flexible for controlling access to storage for different users, putting the database on different disk drives, or backing up and restoring just part of the database.
You must have at least one database file but usually, more than one files are used. In terms of accessing and using the data in the tables and other objects, the number (or location) of the files is immaterial.
The database files are fixed in size and never grow bigger than the size at which they were created Control Files
The control files and redo logs support the rest of the architecture. Any database must have at least one control file, although you typically have more than one to guard against loss. The control file records the name of the database, the date and time it was created, the location of the database and redo logs, and the synchronization information to ensure that all three sets of files are always in step. Every time you add a new database or redo log file to the database, the information is recorded in the control files.
Redo Logs
Any database must have at least two redo logs. These are the journals for the database; the redo logs record all changes to the user objects or system objects. If any type of failure occurs, the changes recorded in the redo logs can be used to bring the database to a consistent state without losing any committed transactions. In the case of non-data loss failure, Oracle can apply the information in the redo logs automatically without intervention from the DBA.
The redo log files are fixed in size and never grow dynamically from the size at which they were created.

83. What is ROWID?
The ROWID is a unique database-wide physical address for every row on every table. Once assigned (when the row is first inserted into the database), it never changes until the row is deleted or the table is dropped.
The ROWID consists of the following three components, the combination of which uniquely identifies the physical storage location of the row.
–> Oracle database file number, which contains the block with the rows
–> Oracle block address, which contains the row
–> The row within the block (because each block can hold many rows)
The ROWID is used internally in indexes as a quick means of retrieving rows with a particular key value. Application developers also use it in SQL statements as a quick way to access a row once they know the ROWID

84. What is Oracle Block? Can two Oracle Blocks have the same address?
Oracle “formats” the database files into a number of Oracle blocks when they are first created—making it easier for the RDBMS software to manage the files and easier to read data into the memory areas.
The block size should be a multiple of the operating system block size. Regardless of the block size, the entire block is not available for holding data; Oracle takes up some space to manage the contents of the block. This block header has a minimum size, but it can grow.
These Oracle blocks are the smallest unit of storage. Increasing the Oracle block size can improve performance, but it should be done only when the database is first created.
Each Oracle block is numbered sequentially for each database file starting at 1. Two blocks can have the same block address if they are in different database files.

85. What is database Trigger?
A database trigger is a PL/SQL block that can defined to automatically execute for insert, update, and delete statements against a table. The trigger can e defined to execute once for the entire statement or once for every row that is inserted, updated, or deleted. For any one table, there are twelve events for which you can define database triggers. A database trigger can call database procedures that are also written in PL/SQL.

86. Name two utilities that Oracle provides, which are use for backup and recovery.
Along with the RDBMS software, Oracle provides two utilities that you can use to back up and restore the database. These utilities are Export and Import.
The Export utility dumps the definitions and data for the specified part of the database to an operating system binary file. The Import utility reads the file produced by an export, recreates the definitions of objects, and inserts the data
If Export and Import are used as a means of backing up and recovering the database, all the changes made to the database cannot be recovered since the export was performed. The best you can do is recover the database to the time when the export was last performed.

87. What are stored-procedures? And what are the advantages of using them.
Stored procedures are database objects that perform a user defined operation. A stored procedure can have a set of compound SQL statements. A stored procedure executes the SQL commands and returns the result to the client. Stored procedures are used to reduce network traffic.

88. How are exceptions handled in PL/SQL? Give some of the internal exceptions’ name
PL/SQL exception handling is a mechanism for dealing with run-time errors encountered during procedure execution. Use of this mechanism enables execution to continue if the error is not severe enough to cause procedure termination.
The exception handler must be defined within a subprogram specification. Errors cause the program to raise an exception with a transfer of control to the exception-handler block. After the exception handler executes, control returns to the block in which the handler was defined. If there are no more executable statements in the block, control returns to the caller.
User-Defined Exceptions
PL/SQL enables the user to define exception handlers in the declarations area of subprogram specifications. User accomplishes this by naming an exception as in the following example:
ot_failure EXCEPTION;
In this case, the exception name is ot_failure . Code associated with this handler is written in the EXCEPTION specification area as follows:
EXCEPTION
when OT_FAILURE then
out_status_ code : = g_out_status_code ;
out_msg := g_out_msg ;
The following is an example of a subprogram exception:
EXCEPTION
when NO_DATA_FOUND then
g_out_status_code := ‘FAIL’;
RAISE ot_failure ;
Within this exception is the RAISE statement that transfers control back to the ot_failure exception handler. This technique of raising the exception is used to invoke all user-defined exceptions.
System-Defined Exceptions
Exceptions internal to PL/SQL are raised automatically upon error. NO_DATA_FOUND is a system-defined exception. Table below gives a complete list of internal exceptions.

PL/SQL internal exceptions.
PL/SQL internal exceptions.

Exception Name Oracle Error
CURSOR_ALREADY_OPEN ORA-06511
DUP_VAL_ON_INDEX ORA-00001
INVALID_CURSOR ORA-01001
INVALID_NUMBER ORA-01722
LOGIN_DENIED ORA-01017
NO_DATA_FOUND ORA-01403
NOT_LOGGED_ON ORA-01012
PROGRAM_ERROR ORA-06501
STORAGE_ERROR ORA-06500
TIMEOUT_ON_RESOURCE ORA-00051
TOO_MANY_ROWS ORA-01422
TRANSACTION_BACKED_OUT ORA-00061
VALUE_ERROR ORA-06502
ZERO_DIVIDE ORA-01476

In addition to this list of exceptions, there is a catch-all exception named OTHERS that traps all errors for which specific error handling has not been established.

89. Does PL/SQL support “overloading”? Explain
The concept of overloading in PL/SQL relates to the idea that you can define procedures and functions with the same name. PL/SQL does not look only at the referenced name, however, to resolve a procedure or function call. The count and data types of formal parameters are also considered.
PL/SQL also attempts to resolve any procedure or function calls in locally defined packages before looking at globally defined packages or internal functions. To further ensure calling the proper procedure, you can use the dot notation. Prefacing a procedure or function name with the package name fully qualifies any procedure or function reference.

90. Tables derived from the ERD
a) Are totally unnormalised
b) Are always in 1NF
c) Can be further denormalised
d) May have multi-valued attributes

91. Spurious tuples may occur due to
i . Bad normalization
ii. Theta joins
iii. Updating tables from join
a) i & ii b) ii & iii
c) i & iii d) ii & iii

(a) i & iii because theta joins are joins made on keys that are not primary keys.

92. A B C is a set of attributes. The functional dependency is as follows
AB -> B
AC -> C
C -> B
a) is in 1NF
b) is in 2NF
c) is in 3NF
d) is in BCNF

(a) is in 1NF since (AC)+ = { A, B, C} hence AC is the primary key. Since C B is a FD given, where neither C is a Key nor B is a prime attribute, this it is not in 3NF. Further B is not functionally dependent on key AC thus it is not in 2NF. Thus the given FDs is in 1NF.

93. In mapping of ERD to DFD
a) entities in ERD should correspond to an existing entity/store in DFD
b) entity in DFD is converted to attributes of an entity in ERD
c) relations in ERD has 1 to 1 correspondence to processes in DFD
d) relationships in ERD has 1 to 1 correspondence to flows in DFD

94. A dominant entity is the entity
a) on the N side in a 1 : N relationship
b) on the 1 side in a 1 : N relationship
c) on either side in a 1 : 1 relationship
d) nothing to do with 1 : 1 or 1 : N relationship

95. Select ‘NORTH’, CUSTOMER From CUST_DTLS Where REGION = ‘N’ Order By
CUSTOMER Union Select ‘EAST’, CUSTOMER From CUST_DTLS Where REGION = ‘E’ Order By CUSTOMER
The above is
a) Not an error
b) Error – the string in single quotes ‘NORTH’ and ‘SOUTH’
c) Error – the string should be in double quotes
d) Error – ORDER BY clause

(d) Error – the ORDER BY clause. Since ORDER BY clause cannot be used in UNIONS

96. What is Storage Manager?
It is a program module that provides the interface between the low-level data stored in database, application programs and queries submitted to the system.

97. What is Buffer Manager?
It is a program module, which is responsible for fetching data from disk storage into main memory and deciding what data to be cache in memory.

98. What is Transaction Manager?
It is a program module, which ensures that database, remains in a consistent state despite system failures and concurrent transaction execution proceeds without conflicting.

99. What is File Manager?
It is a program module, which manages the allocation of space on disk storage and data structure used to represent information stored on a disk.

100. What is Authorization and Integrity manager?
It is the program module, which tests for the satisfaction of integrity constraint and checks the authority of user to access data.

dbms lab viva questions and answers ::

101. What are the four objectives of the selection of a data type?
A data type should be selected so that all possible values are represented using minimal storage
space. The data type should help to ensure data integrity and support all possible data manipulations (i.e., cannot place a letter in a field such as salary where a number is required).

102. Describe the four types of indexes.
A unique primary index is unique and is used to find and store a row. A nonunique primary index is not unique and is used to find a row but also where to store a row (based on its unique primary
index). A unique secondary index is unique for each row and used to find table rows. A nonunique secondary index is not unique and used to find table rows.

103. What is denormalization and why would someone consider doing so?
Denormalization is the process of taking normalized relations and changing them so that they are not longer normalized. This process may lead to anomalies and create data redundancy as negative consequences. However, the revised relations should improve database performance.

104. Compare a hierarchical and network database model?
The hierarchical model is a top-down structure where each parent may have many children but each child can have only one parent. This model supports one-to-one and one-to-many relationships. The network model can be much more flexible than the hierarchical model since each parent can have multiple children but each child can also have multiple parents. This model supports one-to-one, one to- many, and many-to-many relationships.

105. Describe the differences between vertical and horizontal portioning.
Horizontal portioning is where the rows in a relation are separated by some criteria and placed into a new relation or file with the same layout as the original relation (in this case only the records in each file differ). Vertical portioning is where the columns in a relation are separated by some criteria and placed into a new relation or file with a different layout as the original relation.

106. Explain the difference between a dynamic and materialized view.
A dynamic view may be created every time that a specific view is requested by a user. A materialized view is created and or updated infrequently and it must be synchronized with its associated base table(s).

107. Discuss some of the techniques that can be used to tune operational performance.
Choosing primary and secondary keys can increase the speed of row selection, joining, and row
ordering. Selecting the appropriate file organization for base tables and indexes can also improve
performance. Clustering related rows together and maintaining statistics about tables and indexes can lead to increased efficiency.

108. Briefly describe the three types of SQL commands.
Data definition language commands are used to create, alter, and drop tables. Data manipulation
commands are used to insert, modify, update, and query data in the database. Data control language commands help the DBA to control the database.

109. What are the steps to follow when preparing to create a table?
1. Identify the data type, length, and precision for each attribute. 2. Identify the columns that can
accept a null value. 3. Identify the columns that need to be unique. 4. Identify primary and related foreign keys with the parent table being created before the child. 5. Determine default values. 6. Determine where the domain values are that need to be constrained. 7. Create the indexes.

110. What are some disadvantages of a standard language such as SQL?
A standard language can hinder the effort to create a new language. One standard is never enough to meet all of the business needs. A standard can be a compromise among interested parties which can cause the standard to not be ideal. If a standard is altered by some, than portability between

111. Explain a join between tables
A join allows tables to be linked to other tables when a relationship between the tables exists. The
relationships are established by using a common column in the tables and often uses the
primary/foreign key relationship.

112. Describe and contrast a trigger and a procedure.
Triggers are stored and controlled in the DBMS. A trigger is executed automatically when a condition is met (INSERT, UPDATE, or DELETE). A procedure is also stored in a database. A procedure is not executed automatically.

113. Briefly describe an outer join.
An outer join includes the records that match and those that do not have a matching value in another table. Outer joins can be a LEFT outer join (includes all records from the first table listed) or a RIGHT outer join (includes all records from the second table listed). Outer joins are not easily used with more than two tables.

114. Describe a subquery.
A subquery is a query that is composed of two queries. The first query (inner query) is within the
WHERE clause of the other query (outer query). In some cases the inner query provides results for the outer query to process. In other cases, the outer query results provide results for the inner query (correlated subquery).

115. Describe the difference between embedded and dynamic SQL.
Embedded SQL is the process of including hard coded SQL statements. These statements do not
change unless the source code is modified. Dynamic SQL is the process of generating SQL on the fly. The statements generated do not have to be the same each time.

116. Explain the difference between two and three-tier architectures.
A three-tier architecture includes a client and two server layers. The application code is stored on the application server and the database is stored on the database server. A two-tier architecture includes a client and one server layer. The database is stored on the database server.

117. Describe and contrast SQL and QBE.
QBE is a direct-manipulation database language that uses a graphical approach to query construction. Some database systems translate QBE queries into SQL. QBE does not adhere to a standard but SQL does. Both SQL and QBE are relational database languages.

118. Describe ODBC
ODBC is a standard that contains an interface that provides a common language for application
programs to access and process SQL databases. In order to use ODBC, a driver, server name,
database name, user id, and password are required. ODBC is important for Internet applications and has gained wide acceptance.

119. Compare a thin and a fat client.
A fat client is a PC that is responsible where most processing occurs on the client rather than the
server. Some of the fat client activities include processing, presentation logic, and business rules logic. A thin client is a PC where only limited processing occurs. In these cases, more processing should occur on the application server.

120. Describe some reasons that someone familiar with Microsoft Access will want to learn
VBA.
You can perform more complex functions and error handling can be accommodated by VBA. VBA code will execute faster since code runs faster than macros and maintenance is easier because VBA modules are stored with the forms and reports. Reading VBA is easier because you can see the entire code. Finally, you can pass parameters and use OLE automation better.

121. Describe middleware applications that ease the connection of databases to Web
applications.
Both ASP and ColdFusion are middleware that ease the connection of databases to Web applications. Both require the use of several files. Both use tags and are executed on the server. Both Internet Explorer and Netscape can access these files. The programmer does not need to be concerned with the client when they work with this middleware.

122. Describe JavaScript and VBScript.
JavaScript shares many features with Java. Developers use it to achieve interactivity. JavaScript is an open language and does not require a license. It is supported by both Internet Explorer and Netscape. VBScript is similar to JavaScript. It is based on Visual Basic but is simpler. Microsoft developed this language.

123. Describe Web Services.
Web Services are improving the ability of computers to communicate over the Internet. These services use XML programs and usually run in the background. Easier integration of applications may be possible because developers do not need to be familiar with the technical details with applications that are being integrated. UDDI is a technical specification for creating a distributed registry of Web services and businesses that are open to communicating through Web services.

124. Provide an overview of XML.
XML is used to structure and manipulate data involved with a browser and is becoming the standard for e-commerce. XML uses tags that are similar to HTML in that they use the angle brackets, but XML describes the content whereas HTML describes the appearance. The XML schema standard was published in May 2001 by W3C.

125. Describe Website security issues.
Website security issues include unauthorized access to the several aspects of one’s Website. Security measures should include all aspects of the system such as the network, operating level, database, and Web server. Regular monitoring and security testing by a company should help to avoid intrusion into one’s system.

126. Explain the role of metadata for the three-layer architecture.
Each of the three layers has a metadata layer linked with it. The metadata layer describes the
properties or characteristics of the data. The operational metadata describe the data used in the
various operational and external systems. The enterprise data warehouse metadata describe the
reconciled data layer. The data mart metadata describes the derived data layer.

127. Describe why operational and informational systems are separate.
Operational systems are used to run the business in real time on a daily basis and contain current
data. Non-managers and non-analysts work in this type of system. Operational systems must process large volumes of data. Informational systems are used to support decisions and contain historical data. Managers and analysts work in this type of system. Informational systems have periodic batch
updates.

128. Describe a data warehouse.
A data warehouse is organized around specific subjects. The data is defined using consistent naming, format, and encoding structure standards. The data contains a time element, so that the data can be studied for trends. No data in a data warehouse can be updated by end users.

129. Explain why an information gap exists in most organizations.
One reason that an information gap exists is the fact that systems have been developed in separate, segmented efforts. This has helped the data from being stored in an integrated database and thus the data is in an inconsistent structure. The other reason for the gap is that most systems are created to support the operational aspect of an organization. The systems were not developed for decision
making.

130. Describe the differences between a data warehouse and data mart.
A data warehouse is for the enterprise and contains multiple subjects. A data mart is for a specific
functional area and focuses on one subject. A data warehouse is flexible and data-oriented and
contains detailed historical data. A data mart is restrictive and project-oriented and contains some historical data.

131. Describe the difference between data and database administration.
Data administration is responsible for the overall management of data resources. Some of the core roles include the creation of data polices, procedures and standards, resolve data ownership issues,and manage the information repository. Database administration is physical database oversight. Some of the core duties include the selection of the DBMS and software tools, the installation and upgrade of the DBMS, and database performance tuning.

132. What are some of the important security features of a DBMS?
One of the features includes the use of views which allows the presentation of only data needed by someone and limits the capability of database updates. The use of integrity controls includes such things as domains, assertions, and checks. Also authorization rules, user-defined procedures,encryption, authentication schemes, and backups are important.

133. Describe concurrency control.
Concurrency control is the process managing simultaneous operations against a database so that
database integrity is not compromised. There are two approaches to concurrency control. The pessimistic approach involves locking and the optimistic approach involves versioning.

134. Explain locking.
Locking is denying others the ability to update a record until someone completes the update or
releases the record. Locking can occur on many different levels in a database. It can occur at the
database, table, record, or field level. A lock can be shared (another can read the record while an
update is in progress) or exclusive (no one can read the record while an update is in progress).

135. Explain issues for database performance.
The installation of the database is an important issue since the better the installation, the better the
performance could be. Memory usage is learning how the DBMS uses main memory and then using
that knowledge to enable better performance. I/O is usually very intense in a DB, so understanding
how users will use the data will help to prepare the database better. CPU usage and application tuning
are also important considerations.

136. Describe the difference between homogeneous and heterogeneous distributed database.
A homogenous database is one that uses the same DBMS at each node. Either each node can work
independently or a central DBMS may coordinate database activities. A heterogeneous database is one that may have a different DBMS at each node. It may support some or all of the functionality of one logical database. It may support full Distributed DBMS functionality or partial Distributed DBMS functionality.

137. What is a distributed database?
A distributed database is a single logical database that is spread across more than one node or
locations that are all connected via some communication link. It requires multiple DBMSs, running at
each remote site. A distributed database can be either homogenous (same DBMS at each node) or
heterogeneous (different DBMS at some nodes).

138. What is the difference between horizontal and vertical partitioning?
Horizontal partitioning is where some rows of a table are placed into the base relations at one site and
other rows are placed at another site. Vertical partitioning is where some columns of a table are
placed into the base relations at one site and other columns are placed at another site but each all of
these relations must share a common domain.

139. Explain concurrency transparency.
Concurrency transparency is where each transaction in a distributed database is treated as if it is the
only one in the system. Therefore if several transactions are running at one time, the results will be
the same as if each transaction was run in serial order. The transaction manager helps to provide
concurrency control. The three methods that may be used are locking, versioning, and timestamping.

140. Explain snapshot replication.
Snapshot replication can be used when an application does not require that the data always be
current. These applications can be updated by periodic table copying or snapshots. As part of the
snapshot effort, all of the data to be included in the snapshot is collected at a primary point. Then a
read-only snapshot is taken and the snapshot is sent to each site so that the update can be made.

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