CUSTOMER_CODE
SMUDE
DIVISION_CODE
SMUDE
EVENT_CODE
OCTOBER15
ASSESSMENT_CODE MIT202_OCTOBER15
QUESTION_TYPE
DESCRIPTIVE_QUESTION
QUESTION_ID
13025
QUESTION_TEXT
What are the attribute types used in the E-R model. Explain the steps in
E-R Modeling
SCHEME OF
EVALUATION
The attribute used in the E-R model can be characterized by the
following attribute types.
Simple
Each entity has a single atomic value for the attribute. For example, SSN
or Sex.
Composite
The attribute may be composed of several components. For example,
Address (Apt#, House#, Street, City, State, ZipCode, Country) or Name
(FirstName, MiddleName, LastName). Composition may form a
hierarchy where some components are themselves composite.
Single valued
An entity having single value for that attribute. For example, loannumber in the loan entity.
Multi-valued
An entity may have multiple values for that attribute. For example, Color
of a CAR or PreviousDegrees of a STUDENT. Denoted as {Color} or
{PreviousDegrees}.
Null attribute
A null value is used when an entity does not have a value for an
attribute. For an instance an employee has no dependent.
Derived attribute
The value for this type of attribute can be derived from the values of
other related attributes or entities. For instance, account number and
balance. Here balance attribute is derived from account number attribute.
An attribute of an entity type for which each entity must have a unique
value, is called a key attribute of the entity type. For example, SSN is the
key attribute of EMPLOYEE relation schema. A key attribute may be
composite. For example, VehicleTagNumber is a key of the CAR entity
type with components (Number, State).
(5 Marks)
Steps in E-R Modeling
Usually the following six steps are followed to generate E-R Models.
Identify the entities: Look for general nouns in the requirement
specification document which are of business interest to business users.
Find relationships: Identify the natural relationship and their cardinalities
between the entities.
Identify the key attributes for every entity: Identify the attribute or set of
attributes which can identify the instance of the entity uniquely.
Identify other relevant attributes: Identify other attributes which are
interest to business users and which they want to store the information in
database.
Complete E-R diagram: Draw a complete E-R diagram with all
attributes, including primary key.
Review your results with your business users: Look at the list of
attributes associated with each entity to see if anything has been omitted.
(5 Marks)
QUESTION_TYPE
DESCRIPTIVE_QUESTION
QUESTION_ID
72999
QUESTION_TEXT
Give an account of various Keys used in DBMS.
SCHEME OF
EVALUATION
Keys: The key uniquely differentiates one entity instance from all others in
the entity. A key is an identifier.
Primary Key: Identifier used to uniquely identify one particular instance of an
entity.
A primary key
• Can be one or more attributes
• Must be unique within the domain
• Its value should not change over time
• Must always have a value
• Is created when no obvious attribute exists. Each instance has a value.
• Candidate Key: When multiple possible identifiers exist, each of them is
a candidate key.
• Concatenated Key: Key made up of parts which, when combined,
become a unique identifier. Multiple attribute keys are concatenated keys.
• Foreign Keys: Foreign keys reference a related table through the
primary key of that related table.
QUESTION_TYPE
DESCRIPTIVE_QUESTION
QUESTION_ID
73001
QUESTION_TEXT
Explain different types of Databases.
SCHEME OF
EVALUATION
• Design databases: Engineering design databases are useful in computeraided design / manufacturing / software engineering (CAD / CAM / CASE)
systems. In such systems, complex objects can be recursively partitioned into
smaller objects. Furthermore, an object can have different representations at
different levels of abstraction.
• Multimedia databases: In modern office information or other multimedia
systems, data includes not only text and numbers but also images, graphics
and digital audio and video. Such multimedia data is typically stored as
sequences of bytes with variable lengths, and segments of data are linked
together for easy reference.
• Knowledge bases: Artificial intelligence and expert systems represent
information as facts and rules that can be collectively viewed as a knowledge
base. In typical AI applications, knowledge representation requires data
structures with rich semantics that go beyond the simple structure of the
relational model. Artificial decomposition and mapping would be necessary if a
relational DBMS were used.
QUESTION_TYPE
DESCRIPTIVE_QUESTION
QUESTION_ID
118840
QUESTION_TEXT
Define a block. Explain the techniques for improving the speed of access
to the blocks on disk.
SCHEME OF
EVALUATION
A block is a contiguous sequence of sectors from a single track of one
platter. Block sizes range from 512 bytes to several kilobytes. Data is
transferred between disk and main memory in units of blocks. (2marks)
Techniques for improving the speed of access to the blocks on disk.
•
Scheduling: If several blocks from a cylinder need to be
transferred from disk to main memory, we may be able to save access
time by requesting the blocks in the order in which they will pass under
the heads. Two examples for scheduling algorithms are: Disk-arm
scheduling and elevator algorithm.
•
File Organization: To reduce block access time we can organize
blocks on disk in a way that corresponds closely to the way we expect
data to be accessed. Example: If a file is to be accessed sequentially,
then it is ideal to keep all the blocks of the file sequentially on adjacent
cylinders.
•
Nonvolatile write buffers: Since the contents of the main
memory are lost in a power failure, information about database updates
has to be recorded on disk to survive possible system crashes. For this
reason, the performance of update-intensive database applications such
as transaction processing systems.
•
Log disk: Another approach o reducing write latencies is to use
a log disk. That is, a disk devoted to writing a sequential log- in much
the same way as a nonvolatile RAM buffer. All access to the log disk is
sequential, essentially eliminating seek time. (2 X 4= 8 marks)
QUESTION_TYPE
DESCRIPTIVE_QUESTION
QUESTION_ID
118844
Explain the different types of Normal forms with examples.
QUESTION_TEXT
SCHEME OF EVALUATION
i.
ii.
First Normal form – 2 Marks
Second normal form – 2 Marks
iii.
iv.
v.
Third normal form – 2 Marks
Fourth Normal Form – 2 Marks
Boyce Cod Normal Form – 2 Marks
QUESTION_TYPE
DESCRIPTIVE_QUESTION
QUESTION_ID
118847
QUESTION_TEXT
List and explain the important responsibilities of Database manager.
SCHEME OF
EVALUATION
The important responsibilities of Database Manager:
a.
Interaction with file manager: The raw data is stored on the disk
using the file system which is usually provided by a conventional
operating system. Database manager is responsible for the actual storing,
retrieving and updating of data in the database.
b.
Integrity enforcement: The data values stored in the database
must satisfy certain types of consistency constraints. Example: the
balance of a bank account may never fall below a prescribed amount. In
such cases database manager can check the system.
c.
Security enforcement: Not every user of the database needs to
have access to the entire content of the database. It is the job of the
database manager to enforce these security requirements.
d.
Backup and recovery: A computer system like any other system
may fail; hence the information concerning the database is lost. It is the
responsibility of the Database manger to detect such failures, and restore
the database.
e.
Concurrency Control: When several users update the database
concurrently, the consistency of data may no longer be preserved. It is
necessary for the system to control the interaction among concurrent
users and achieving such a control is one of the responsibilities of
database manager. (2 X 5= 10 marks)