Transmission Line
A transmission line is the material medium or structure that forms all or part of a path from one place to another for directing the transmission of energy, such as electromagnetic waves or acoustic waves, as well as electric power transmission. Components of transmission lines include wires, coaxial cables, dielectric slabs, optical fibers, electric power lines, and waveguides.

An electric transmission line can be generally represented by a series combination of resistance,inductance and shunt combination of conductance and capacitace

The transmission line model represents the transmission line as an infinite series of two-port elementary components, each representing an infinitesimally short segment of the transmission line:

Transmission lines are basically circuits with distributed constants i.e R,L,C and G are distributed along the whole length of line.each small length at any section of the line will have its own values and concentration of all such parameters for complete length of line in to a single one is not possible.In the above figure

• The distributed resistance R of the conductors is represented by a series resistor (expressed in ohms per unit length).
• The distributed inductance L (due to the magnetic field around the wires, self-inductance, etc.) is represented by a series inductor (henries per unit length).
• The capacitance C between the two conductors is represented by a shunt capacitor C (farads per unit length).
• The conductance G of the dielectric material separating the two conductors is represented by a conductance G shunted between the signal wire and the return wire (siemens per unit length).

Among the parameters R,L,G and C , R and G are least important in the sense that they do not affect much the total equivalent impedance of the line and hence the transmission capacity.They are very much important when transmission efficiency and economy are to be evaluated as they completely determine the real transmission line losses.

Practical types of electrical transmission line

Coaxial cable
Coaxial lines confine the electromagnetic wave to the area inside the cable, between the center conductor and the shield. The transmission of energy in the line occurs totally through the dielectric inside the cable between the conductors. Coaxial lines can therefore be bent and twisted (subject to limits) without negative effects, and they can be strapped to conductive supports without inducing unwanted currents in them.

In radio-frequency applications up to a few gigahertz, the wave propagates in the transverse electric and magnetic mode (TEM), which means that the electric and magnetic fields are both perpendicular to the direction of propagation. However, above a certain frequency called the cutoff frequency, the cable behaves as a waveguide, and propagation switches to either a transverse electric (TE) or a transverse magnetic (TM) mode or a mixture of modes. This effect enables coaxial cables to be used at microwave frequencies, although they are not as efficient as the more expensive, purpose-built waveguides.

The most common use for coaxial cables is for television and other signals with bandwidth of multiple Megahertz. In the middle 20th Century they carried long distance telephone connections.

Microstrip
A microstrip circuit uses a thin flat conductor which is parallel to a ground plane. Microstrip can be made by having a strip of copper on one side of a printed circuit board (PCB) or ceramic substrate while the other side is a continuous ground plane. The width of the strip, the thickness of the insulating layer (PCB or ceramic) and the dielectric constant of the insulating layer determine the characteristic impedance.

Stripline
A stripline circuit uses a flat strip of metal which is sandwiched between two parallel ground planes. The insulating material of the substrate forms a dielectric. The width of the strip, the thickness of the substrate and the relative permittivity of the substrate determine the characteristic impedance of the strip which is a transmission line.

Balanced lines

Lecher lines
Lecher lines are a form of parallel conductor that can be used at UHF for creating resonant circuits. They are used at frequencies between HF/VHF where lumped components are used, and UHF/SHF where resonant cavities are more practical.

General applications of transmission lines

Transferring signals from one point to another
Electrical transmission lines are very widely used to transmit high frequency signals over long or short distances with minimum power loss. One familiar example is the down lead from a TV or radio aerial to the receiver.

Pulse generation
Transmission lines are also used as pulse generators. By charging the transmission line and then discharging it into a resistive load, a rectangular pulse equal in length to twice the electrical length of the line can be obtained, although with half the voltage. A Blumlein transmission line is a related pulse forming device that overcomes this limitation. These are sometimes used as the pulsed energy sources for radar transmitters and other devices.

Stub filters
If a short-circuited or open-circuited transmission line is wired in parallel with a line used to transfer signals from point A to point B, then it will function as a filter. The method for making stubs is similar to the method for using Lecher lines for crude frequency measurement, but it is ‘working backwards’. One method recommended in the RSGB’s radiocommunication handbook is to take an open-circuited length of transmission line wired in parallel with the feeder delivering signals from an aerial. By cutting the free end of the transmission line, a minimum in the strength of the signal observed at a receiver can be found. At this stage the stub filter will reject this frequency and the odd harmonics, but if the free end of the stub is shorted then the stub will become a filter rejecting the even harmonics.

THIS IS COLLECTED FROM

http://www.powerelectrical.blogspot.com/

A GOOD BLOG FOR ELECTRICALS

the motor speed is controlled by the use of transistor as control switch

varying the dutycycle of the switching signal to the transistor varies the power of the motor.

the operation is quiet simple,with the help optocoupler speed is measured and will be in digital form so can be given directly to micro controller .microcontroller sends the control signal to uln2003 which magnifies current and causes the variation off duty cycle . inthis way speed off d.c motor can be controlled. with lcd display we can see the speed also.

the motor is a small d.c motor .

by writting suitable code ,you should successfully control the speed of the motor

1.    What are the various registers in 8085? – Accumulator register, Temporary register, Instruction register, Stack Pointer, Program Counter are the various registers in 8085 .
2.    In 8085 name the 16 bit registers? – Stack pointer and Program counter all have 16 bits.
3.    What are the various flags used in 8085? – Sign flag, Zero flag, Auxillary flag, Parity flag, Carry flag.
4.    What is Stack Pointer? – Stack pointer is a special purpose 16-bit register in the Microprocessor, which holds the address of the top of the stack.
5.    What is Program counter? – Program counter holds the address of either the first byte of the next instruction to be fetched for execution or the address of the next byte of a multi byte instruction, which has not been completely fetched. In both the cases it gets incremented automatically one by one as the instruction bytes get fetched. Also Program register keeps the address of the next instruction.
6.    Which Stack is used in 8085? – LIFO (Last In First Out) stack is used in 8085.In this type of Stack the last stored information can be retrieved first.
7.    What happens when HLT instruction is executed in processor? – The Micro Processor enters into Halt-State and the buses are tri-stated.
8.    What is meant by a bus? – A bus is a group of conducting lines that carriers data, address, & control signals.
9.    What is Tri-state logic? – Three Logic Levels are used and they are High, Low, High impedance state. The high and low are normal logic levels & high impedance state is electrical open circuit conditions. Tri-state logic has a third line called enable line.
10.    Give an example of one address microprocessor? – 8085 is a one address microprocessor.
11.    In what way interrupts are classified in 8085? – In 8085 the interrupts are classified as Hardware and Software interrupts.
12.    What are Hardware interrupts? – TRAP, RST7.5, RST6.5, RST5.5, INTR.
13.    What are Software interrupts? – RST0, RST1, RST2, RST3, RST4, RST5, RST6, RST7.
14.    Which interrupt has the highest priority? – TRAP has the highest priority.
15.    Name 5 different addressing modes? – Immediate, Direct, Register, Register indirect, Implied addressing modes.
16.    How many interrupts are there in 8085? – There are 12 interrupts in 8085.
17.    What is clock frequency for 8085? – 3 MHz is the maximum clock frequency for 8085.
18.    What is the RST for the TRAP? – RST 4.5 is called as TRAP.
19.    In 8085 which is called as High order / Low order Register? – Flag is called as Low order register & Accumulator is called as High order Register.
20.    What are input & output devices? – Keyboards, Floppy disk are the examples of input devices. Printer, LED / LCD display, CRT Monitor are the examples of output devices.
21.    Can an RC circuit be used as clock source for 8085? – Yes, it can be used, if an accurate clock frequency is not required. Also, the component cost is low compared to LC or Crystal.
22.    Why crystal is a preferred clock source? – Because of high stability, large Q (Quality Factor) & the frequency that doesn’t drift with aging. Crystal is used as a clock source most of the times.
23.    Which interrupt is not level-sensitive in 8085? – RST 7.5 is a raising edge-triggering interrupt.
24.    What does Quality factor mean? – The Quality factor is also defined, as Q. So it is a number, which reflects the lossness of a circuit. Higher the Q, the lower are the losses.
25.    What are level-triggering interrupt? – RST 6.5 & RST 5.5 are level-triggering interrupts

8086 Interview Questions:
1.    What are the flags in 8086? – In 8086 Carry flag, Parity flag, Auxiliary carry flag, Zero flag, Overflow flag, Trace flag, Interrupt flag, Direction flag, and Sign flag.
2.    What are the various interrupts in 8086? – Maskable interrupts, Non-Maskable interrupts.
3.    What is meant by Maskable interrupts? – An interrupt that can be turned off by the programmer is known as Maskable interrupt.
4.    What is Non-Maskable interrupts? – An interrupt which can be never be turned off (ie.disabled) is known as Non-Maskable interrupt.
5.    Which interrupts are generally used for critical events? – Non-Maskable interrupts are used in critical events. Such as Power failure, Emergency, Shut off etc.,
6.    Give examples for Maskable interrupts? – RST 7.5, RST6.5, RST5.5 are Maskable interrupts
7.    Give example for Non-Maskable interrupts? – Trap is known as Non-Maskable interrupts, which is used in emergency condition.
8.    What is the Maximum clock frequency in 8086? – 5 Mhz is the Maximum clock frequency in 8086.
9.    What are the various segment registers in 8086? – Code, Data, Stack, Extra Segment registers in 8086.
10.    Which Stack is used in 8086? – FIFO (First In First Out) stack is used in 8086.In this type of Stack the first stored information is retrieved first.
11.    What are the address lines for the software interrupts? -
RST 0    0000 H
RST1    0008 H
RST2    0010 H
RST3    0018 H
RST4    0020 H
RST5    0028 H
RST6    0030 H
RST7    0038 H
12.    What is SIM and RIM instructions? – SIM is Set Interrupt Mask. Used to mask the hardware interrupts. RIM is Read Interrupt Mask. Used to check whether the interrupt is Masked or not.
13.    Which is the tool used to connect the user and the computer? – Interpreter is the tool used to connect the user and the tool.
14.    What is the position of the Stack Pointer after the PUSH instruction? – The address line is 02 less than the earlier value.
15.    What is the position of the Stack Pointer after the POP instruction? – The address line is 02 greater than the earlier value.
16.    Logic calculations are done in which type of registers? – Accumulator is the register in which Arithmetic and Logic calculations are done.
17.    What are the different functional units in 8086? – Bus Interface Unit and Execution unit, are the two different functional units in 8086.
18.    Give examples for Micro controller? – Z80, Intel MSC51 &96, Motorola are the best examples of Microcontroller.
19.    What is meant by cross-compiler? – A program runs on one machine and executes on another is called as cross-compiler.
20.    What are the address lines for the hardware interrupts? -
RST 7.5    003C H
RST 6.5    0034 H
RST 5.5    002C H
TRAP    0024 H
21.    Which Segment is used to store interrupt and subroutine return address registers? – Stack Segment in segment register is used to store interrupt and subroutine return address registers.
22.    Which Flags can be set or reset by the programmer and also used to control the operation of the processor? – Trace Flag, Interrupt Flag, Direction Flag.
23.    What does EU do? – Execution Unit receives program instruction codes and data from BIU, executes these instructions and store the result in general registers.
24.    Which microprocessor accepts the program written for 8086 without any changes? – 8088 is that processor.
25.    What is the difference between 8086 and 8088? – The BIU in 8088 is 8-bit data bus & 16- bit in 8086.Instruction queue is 4 byte long in 8088and 6 byte in 8086.

Rahul is an Indian technical writer living in South Korea working for Samsung. You can read more about the lessons he talks about from his ten lessons learned post.

Here’s a snapshot of the 10 lessons:

• Lesson 1: Choose the Right Words
• Lesson 2: Strike a Rapport with Your Audience
• Lesson 3: Pay Attention to Details
• Lesson 4: Meet the Expectations
• Lesson 5: Break the Mediocrity
• Lesson 6: Know Your Role Well
• Lesson 7: Steer Away from the Usual Rut
• Lesson 8: Don’t Network for the Heck of It
• Lesson 9: Education is only a Catalyst
• Lesson 10: Don’t Suppress the Writer in You

full link http://techwritervoices.com/2007/01/13/rahulprabhakar/

his blog http://idratherbewriting.com/

[Q001]. What will be the output of the following program :
struct {
int i;
float f;
}var;
void main()
{
var.i=5;
var.f=9.76723;
printf(“%d %.2f”,var.i,var.f);
}
(a)Compile-Time Error    (b)5 9.76723        (c)5 9.76        (d)5 9.77
Ans. (d) Though both <struct type name> and <structure variables> are optional, one of the two
must appear. In the above program, <structure variable> i.e. var is used. (2 decimal places or)
2-digit precision of 9.76723 is 9.77
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[Q002]. What will be the output of the following program :
struct {
int i;
float f;
};
void main()
{
int i=5;
float f=9.76723;
printf(“%d %.2f”,i,f);
}
(a)Compile-Time Error    (b)5 9.76723            (c)5 9.76        (d)5 9.77
Ans. (d) Both <struct type name> and <structure variables> are optional. Thus the structure
defined in the above program has no use and program executes in the normal way.
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[Q003]. What will be the output of the following program :
struct values{
int i;
float f;
};
void main()
{
struct values var={555,67.05501};
printf(“%2d %.2f”,var.i,var.f);
}
(a)Compile-Time Error    (b)55 67.05            (c)555 67.06        (d)555 67.05
Ans. (c) The members of a structure variable can be assigned initial values in much the same
manner as the elements of an array. The initial values must appear in order in which they will be
assigned to their corresponding strucutre members, enclosed in braces and separated by commas.
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[Q004]. What will be the output of the following program :
typedef struct {
int i;
float f;
}values;
void main()
{
static values var={555,67.05501};
printf(“%2d %.2f”,var.i,var.f);
}
(a)Compile-Time Error    (b)55 67.05            (c)555 67.06        (d)555 67.05
Ans. (c) In the above program, values is the user-defined structure type or the new user-defined
data type. Structure variables can then be defined in terms of the new data type.
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[Q005]. What will be the output of the following program :
struct my_struct{
int i=7;
float f=999.99;
}var;
void main()
{
var.i=5;
printf(“%d %.2f”,var.i,var.f);
}
(a)Compile-Time Error    (b)7 999.99            (c)5 999.99        (d)None of these
Ans. (a) C language does not permit the initialization of individual structure members within the
template. The initialization must be done only in the declaration of the actual variables. The
correct way to initialize the values is shown in [Q003] or [Q004].
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[Q006]. What will be the output of the following program :
struct first{
int a;
float b;
}s1={32760,12345.12345};
typedef struct{
char a;
int b;
}second;
struct my_struct{
float a;
unsigned int b;
};
typedef struct my_struct third;
void main()
{
static second s2={‘A’,- -4};
third s3;
s3.a=~(s1.a-32760);
s3.b=-++s2.b;
printf(“%d %.2f\n%c %d\n%.2f %u”,(s1.a)–,s1.b+0.005,s2.a+32,s2.b,++(s3.a),–s3.b);
}
(a)Compile-Time Error    (b)32760 12345.12        (c)32760 12345.13    (d)32760 12345.13
A 4                   a -5               a 5
1 -5                   0.00 65531            0.00 65530
Ans. (d) Illustrating 3 different ways of declaring the structres : first, second and third are
the user-defined structure type. s1, s2 and s3 are structure variables. Also an expression of the
form ++variable.member is equivalent to ++(variable.member), i.e. ++ operator will apply to the
structure member, not the entire structure variable.
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[Q007]. What will be the output of the following program :
struct {
int i,val[25];
}var={1,2,3,4,5,6,7,8,9},*vptr=&var;
void main()
{
printf(“%d %d %d\n”,var.i,vptr->i,(*vptr).i);
printf(“%d %d %d %d %d %d”,var.val[4],*(var.val+4),vptr->val[4],*(vptr->val+4),(*vptr).val[4],*((*vptr).val+4));
}
(a)Compile-Time Error    (b)1 1 1            (c)1 1 1        (d)None of these
6 6 6 6 6 6               5 5 5 5 5 5
Ans. (b) Since value of the member ‘i’ can be accessed using var.i, vptr->i and (*vptr).i
Similarly 5th value of the member ‘val’ can be accessed using var.val[4], *(var.val+4),
vptr->val[4], *(vptr->val+4), (*vptr).val[4] and *((*vptr).val+4)
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[Q008]. What will be the output of the following program :
typedef struct {
int i;
float f;
}temp;
void alter(temp *ptr,int x,float y)
{
ptr->i=x;
ptr->f=y;
}
void main()
{
temp a={111,777.007};
printf(“%d %.2f\n”,a.i,a.f);
alter(&a,222,666.006);
printf(“%d %.2f”,a.i,a.f);
}
(a)Compile-Time error    (b)111 777.007        (c)111 777.01        (d)None of these
222 666.006           222 666.01
Ans. (c) This program illustrates the transfer of a structure to a function by passing the
structure’s address (a pointer) to the function.
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[Q009]. What will be the output of the following program :
typedef struct {
int i;
float f;
}temp;
temp alter(temp tmp,int x,float y)
{
tmp.i=x;
tmp.f=y;
return tmp;
}
void main()
{
temp a={111,777.007};
printf(“%d %.3f\n”,a.i,a.f);
a=alter(a,222,666.006);
printf(“%d %.3f”,a.i,a.f);
}
(a)Compile-Time error    (b)111 777.007        (c)111 777.01        (d)None of these
222 666.006           222 666.01
Ans. (b) This program illustrates the transfer of a structure to a function by value. Also the
altered structure is now returned directly to the calling portion of the program.
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[Q010]. What will be the output of the following program :
typedef struct {
int i;
float f;
}temp;
temp alter(temp *ptr,int x,float y)
{
temp tmp=*ptr;
printf(“%d %.2f\n”,tmp.i,tmp.f);
tmp.i=x;
tmp.f=y;
return tmp;
}
void main()
{
temp a={65535,777.777};
a=alter(&a,-1,666.666);
printf(“%d %.2f”,a.i,a.f);
}
(a)Compile-Time error    (b)65535 777.777        (c)65535 777.78        (d)-1 777.78
-1 666.666                  -1 666.67           -1 666.67
Ans. (d) This program illustrates the transfer of a structure to a function by passing the
structure’s address (a pointer) to the function. Also the altered structure is now returned
directly to the calling portion of the program.
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[Q011]. What will be the output of the following program :
struct my_struct1{
int arr[2][2];
};
typedef struct my_struct1 record;
struct my_struct2{
record temp;
}list[2]={1,2,3,4,5,6,7,8};
void main()
{
int i,j,k;
for (i=1; i>=0; i–)
for (j=0; j<2; j++)
for (k=1; k>=0; k–)
printf(“%d”,list[i].temp.arr[j][k]);
}
(a)Compile-Time Error    (b)Run-Time Error        (c)65872143          (d)56781243
Ans. (c) This program illustrates the implementation of a nested structure i.e. structure inside
another structure.
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[Q012]. What will be the output of the following program :
struct my_struct{
int i;
unsigned int j;
};
void main()
{
struct my_struct temp1={-32769,-1},temp2;
temp2=temp1;
printf(“%d %u”,temp2.i,temp2.j);
}
(a)32767 -1        (b)-32769 -1            (c)-32769 65535        (d)32767 65535
Ans. (d) An entire structure variable can be assigned to another structure variable, provided
both variables have the same composition.
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[Q013]. What will be the output of the following program :
struct names {
char str[25];
struct names *next;
};
typedef struct names slist;
void main()
{
slist *list,*temp;
list=(slist *)malloc(sizeof(slist)); // Dynamic Memory Allocation
strcpy(list->str,”Hai”);
list->next=NULL;
temp=(slist *)malloc(sizeof(slist)); // Dynamic Memory Allocation
strcpy(temp->str,”Friends”);
temp->next=list;
list=temp;
while (temp != NULL)
{
printf(“%s”,temp->str);
temp=temp->next;
}
}
(a)Compile-Time Error    (b)HaiFriends            (c)FriendsHai        (d)None of these
Ans. (c) It is sometimes desirable to include within a structure one member i.e. a pointer to the
parent structure type. Such structures are known as Self-Referencial structures. These structures
are very useful in applications that involve linked data structures, such as lists and trees.
[A linked data structure is not confined to some maximum number of components. Rather, the data
structure can expand or contract in size as required.]
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[Q014]. Which of the following declarations is NOT Valid :
(i)  struct A{
int a;
struct B {
int b;
struct B *next;
}tempB;
struct A *next;
}tempA;

(ii) struct B{
int b;
struct B *next;
};
struct A{
int a;
struct B tempB;
struct A *next;
};

(iii)struct B{
int b;
}tempB;
struct  {
int a;
struct B *nextB;
};

(iv) struct B {
int b;
struct B {
int b;
struct B *nextB;
}tempB;
struct B *nextB;
}tempB;
(a) (iv) Only        (b) (iii) Only            (c)All of the these    (d)None of these
Ans. (d) Since all the above structure declarations are valid in C.
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[Q015]. What will be the output of the following program :
union A{
char ch;
int i;
float f;
}tempA;
void main()
{
tempA.ch=’A';
tempA.i=777;
tempA.f=12345.12345;
printf(“%d”,tempA.i);
}
(a)Compile-Time Error    (b)12345            (c)Erroneous output    (d)777
Ans. (c) The above program produces erroneous output (which is machine dependent). In effect,
a union creates a storage location that can be used by any one of its members at a time. When a
different member is assigned a new value, the new value supercedes the previous member’s value.
[NOTE : The compiler allocates a piece of storage that is large enough to hold the largest
variable type in the union i.e. all members share the same address.]
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[Q016]. What will be the output of the following program :
struct A{
int i;
float f;
union B{
char ch;
int j;
}temp;
}temp1;
void main()
{
struct A temp2[5];
printf(“%d %d”,sizeof temp1,sizeof(temp2));
}
(a)6 30            (b)8 40                (c)9 45            (d)None of these
Ans. (b) Since int (2 bytes) + float (4 bytes) = (6 bytes) + Largest among union is int (2 bytes)
is equal to (8 bytes). Also the    total number of bytes the array ‘temp2′ requires :
(8 bytes) * (5 bytes) = (40 bytes).
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[Q017]. What will be the output of the following program :
void main()
{
static struct my_struct{
unsigned a:1;
unsigned b:2;
unsigned c:3;
unsigned d:4;
unsigned  :6; // Fill out first word
}v={1,2,7,12};
printf(“%d %d %d %d”,v.a,v.b,v.c,v.d);
printf(“\nSize=%d bytes”,sizeof v);
}
(a)Compile-Time Error    (b)1 2 7 12            (c)1 2 7 12        (d)None of these
Size=2 bytes               Size=4 bytes
Ans. (b) The four fields within ‘v’ require a total of 10 bits and these bits can be accomodated
within the first word(16 bits). Unnamed fields can be used to control the alignment of bit fields
within a word of memory. Such fields provide padding within the word.
[NOTE : Some compilers order bit-fields from righ-to-left (i.e. from lower-order bits to high-
order bits) within a word, whereas other compilers order the fields from left-to-right (high-
order to low-order bits).
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[Q018]. What are the largest values that can be assigned to each of the bit fields defined in
[Q017] above.
(a)a=0 b=2 c=3 d=4    (b)a=1 b=2 c=7 d=15        (c)a=1 b=3 c=7 d=15    (d)None of thes
Ans. (c)a=1  (1 bit: 0 or 1)
b=3  (2 bits: 00 or 01 or 10 or 11),
c=7  (3 bits: 000 or 001 or 010 or 011 or 100 or 101 or 110 or 111)
d=15 (4 bits: 0000 or 0001 or 0010 or 0011 or 0100 or 0101 or 0110 or 0111 or 1000 or
1001 or 1010 or 1011 or 1100 or 1101 or 1110 or 1111)
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[Q019]. What will be the output of the following program :

void main()
{
struct sample{
unsigned a:1;
unsigned b:4;
}v={0,15};
unsigned *vptr=&v.b;
printf(“%d %d”,v.b,*vptr);
}
(a)Compile-Time Error    (b)0 0                (c)15 15        (d)None of these
Ans. (a) Since we cannot take the address of a bit field variable i.e. Use of pointer to access
the bit fields is prohibited. Also we cannot use ‘scanf’ function to read values into a bit field
as it requires the address of a bit field variable. Also array of bit-fields are not permitted
and a function cannot return a bit field.
_________________________________________________________________________________________________

[Q020]. What will be the output of the following program :
void main()
{
static struct my_struct{
unsigned a:1;
int i;
unsigned b:4;
unsigned c:10;
}v={1,10000,15,555};
printf(“%d %d %d %d”,v.i,v.a,v.b,v.c);
printf(“\nSize=%d bytes”,sizeof v);
}
(a)Compile-Time Error    (b)1 10000 15 555         (c)10000 1 15 555    (d)10000 1 15 555
Size=4 bytes               Size=4 bytes           Size=5 bytes
Ans. (d) Here the bit field variable ‘a’ will be in first byte of one word, the variable ‘i’ will
be in the second word and the bit fields ‘b’ and ‘c’ will be in the third word. The variables
‘a’, ‘b’ and ‘c’ would not get packed into the same word. [NOTE: one word=2 bytes]
_________________________________________________________________________________________________

This test consists of 50 questions. The Set Code for this paper is D.

1. The C language terminator is
(a) semicolon                        (b) colon                        (c) period                                (d) exclamation mark

2. What is false about the following — A compound statement is
(a) A set of simple statements                                                (b) Demarcated on either side by curly brackets
(c) Can be used in place of simple statement                          (d) A C function is not a compound statement.

3. What is true about the following C Functions
(a) Need not return any value                                                 (b) Should always return an integer
(c) Should always return a float                                              (d) Should always return more than one value

4. Main must be written as
(a) The first function in the program                                        (b) Second function in the program
(c) Last function in the program                                              (d) Any where in the program

5. Which of the following about automatic variables within a function is correct ?
(a) Its type must be declared before using the variable             (b) They are local
(c) They are not initialized to zero                                           (d) They are global

6. Write one statement equivalent to the following two statements:   x=sqr(a);  return(x);
Choose from one of the alternatives
(a) return(sqr(a));                                    (b) printf(“sqr(a)”);
(c) return(a*a*a);                                    (d) printf(“%d”,sqr(a));

7. Which of the following about the C comments is incorrect ?
(a) Comments can go over multiple lines
(b) Comments can start any where in the line
(c) A line can contain comments with out any language statements
(d) Comments can occur within comments

8. What is the value of y in the following code?
x=7;
y=0;
if(x=6) y=7;
else y=1;
(a) 7                                    (b) 0                                (c) 1                                 (d) 6

9. Read the function conv() given below
conv(int t)
{
int u;
u=5/9 * (t-32);
return(u);
}
What is returned
(a) 15                                    (b) 0                                (c) 16.1                            (d) 29

10. Which of the following represents true statement either x is in the range of 10 and 50 or y is zero
(a) x >= 10 && x <= 50 || y = = 0                                (b) x<50
(c) y!=10 && x>=50                                                    (d) None of these

11. Which of the following is not an infinite loop ?
(a) while(1)\{ ….}                                                    (b) for(;;){…}
(c) x=0;                                                                   (d) # define TRUE 0
do{ /*x unaltered within the loop*/                                …
…..}while(x = = 0);                                                while(TRUE){ ….}

12. What does the following function print?
func(int i)
{
if(i%2)return 0;
else return 1;
}
main()
{
int =3;
i=func(i);
i=func(i);
printf(“%d”,i);
}
(a) 3                                (b) 1                                (c) 0                                (d) 2

13. How does the C compiler interpret the following two statements
p=p+x;
q=q+y;
(a) p= p+x;                     (b)p=p+xq=q+y;                (c)p= p+xq;                      (d)p=p+x/q=q+y;
q=q+y;                                                                    q=q+y;

For questions 14,15,16,17 use the following alternatives:
a.int                                 b.char                                 c.string                              d.float

14. ’9′

15. “1 e 02″

16. 10e05

17. 15
18. Read the folllowing code
# define MAX 100
# define MIN 100
….
….
if(x>MAX)
x=1;
else if(x<MIN)
x=-1;
x=50;
if the initial value of x=200,what is the value after executing this code?
(a) 200                                (b) 1                                (c) -1                                (d) 50

19. A memory of 20 bytes is allocated to a string declared as char *s then the following two statements are executed:
s=”Entrance”
l=strlen(s);
what is the value of l ?
(a)20                                (b)8                                (c)9                                (d)21
20. Given the piece of code
int a[50];
int *pa;
pa=a;
To access the 6th element of the array which of the following is incorrect?
(a) *(a+5)                                (b) a[5]                     (c) pa[5]                           (d) *(*pa + 5}
21. Consider the following structure:
struct num nam
{
int no;
char name[25];
}
struct num nam n1[]={{12,”Fred”},{15,”Martin”},{8,”Peter”},{11,Nicholas”}};
…..
…..
printf(“%d%d”,n1[2],no,(*(n1 + 2),no) + 1);
What does the above statement print?
(a) 8,9                            (b) 9,9                            (c) 8,8                            (d) 8,unpredictable value
22. Identify the in correct expression
(a)a=b=3=4;               (b)a=b=c=d=0;                (c)float a=int b= 3.5;        (d)int a; floatb;a=b=3.5;
23. Regarding the scope of the varibles;identify the incorrect statement:
(a) automatic variables are automatically initialized to 0    (b) static variables are are automatically initialized to 0
(c) the address of a register variable is not accessible       (d) static variables cannot be initialized with any expression

24. cond 1?cond 2?cond 3?:exp 1:exp 2:exp 3:exp 4;
is equivalent to which of the following?
(a) if cond 1
exp 1;
else if cond 2
exp 2;
else if cond 3
exp 3;
else exp 4;
(b) if cond 1
if cond 2
if cond 3
exp 1;
else exp 2;
else exp 3;
else exp 4;
(c) if cond 1 && cond 2 && cond 3
exp 1 |exp 2|exp 3|exp 4;
(d) if cond 3
exp 1;
else if cond 2 exp 2;
else if cond 3 exp 3;
else exp 4;

25. The operator for exponentiation is
(a) **                            (b) ^                            (c) %                            (d) not available

26. Which of the following is invalid
(a) a+=b                        (b) a*=b                       (c) a>>=b                    (d) a**=b

27. What is y value of the code if input x=10
y=5;
if (x==10)
else if(x==9)
else y=8;
(a)9                            (b)8                                 (c)6                            (d)7

28. What does the following code do?
fn(int n, int p, int r)
{
static int a=p;
switch(n)
{
case 4:a+=a*r;
case 3:a+=a*r;
case 2:a+=a*r;
case 1:a+=a*r;
}
}
(a) computes simple interest for one year                (b) computes amount on compound interest for 1 to 4 years
(c) computes simple interest for four year                (d) computes compound interest for 1 year

29.
a=0;
while(a<5)
printf(“%d\\n”,a++);
How many times does the loop occurs?
(a) infinite                                    (b)5                                    (c)4                                    (d)6

30. How many times does the loop iterated ?
for(i=0;i=10;i+=2)
printf(“Hi\\n”);
(a)10                                          (b) 2                                    (c) 5                                    (d) None of these

31. What is incorrect among the following
A recursive function
(a) calls itself                                            (b) is equivalent to a loop
(c) has a termination condition                  (d) does not have a return value at all

32. Which of the following go out of the loop if expn 2 becoming false
(a) while(expn 1)\{…if(expn 2)continue;}        (b) while(!expn 1)\{if(expn 2)continue;…}
(c) do{..if(expn 1)continue;..}while(expn 2);   (d) while(!expn 2)\{if(expn 1)continue;..\}

33. Consider the following program
main()
{
unsigned int i=10;
while(i>=0)
{
printf(“%u”,i)
i–;
}
}
How many times the loop will get executed
(a)10                                (b)9                                (c)11                                (d) infinite

34.Pick out the odd one out
(a) malloc()                       (b) calloc()                     (c) free()                           (d) realloc()

35.Consider the following program
main()
{
int a[5]={1,3,6,7,0};
int *b;
b=&a[2];
}
The value of b[-1] is
(a) 1                            (b) 3                                (c) -6                                (d) none

36.                       # define prod(a,b)=a*b
main()
{
int x=2;
int y=3;
printf(“%d”,prod(x+2,y-10));
}
the output of the program is
(a) 8                            (b) 6                                (c) 7                                (d) None

37.Consider the following program segment
int n,sum=1;
switch(n)
{
case 2:sum=sum+2;
case 3:sum*=2;
break;
default:sum=0;
}
If n=2, what is the value of sum
(a) 0                            (b) 6                                (c) 3                                    (d) None of these

38. Identify the incorrect one
1.if(c=1)
2.if(c!=3)
3.if(a<b)then
4.if(c==1)
(a) 1 only                     (b) 1&3                            (c) 3 only                            (d) All of the above

39. The format specified for hexa decimal is
(a) %d                          (b) %o                             (c) %x                                (d) %u

40. Find the output of the following program
main()
{
int x=5, *p;
p=&x
printf(“%d”,++*p);
}
(a) 5                                    (b) 6                                    (c) 0                                    (d) none of these

41.Consider the following C code
main()
{
int i=3,x;
while(i>0)
{
x=func(i);
i–;
}
int func(int n)
{
static sum=0;
sum=sum+n;
return(sum);
}
}
The final value of x is
(a) 6                                (b) 8                                (c) 1                                    (d) 3

43. Int *a[5] refers to
(a) array of pointers        (b) pointer to an array        (c) pointer to a pointer          (d) none of these

44.Which of the following statements is incorrect
(a)                 typedef struct new
{
int n1;
char n2;
} DATA;

(b)                typedef struct
{
int n3;
char *n4;
}ICE;

(c)                typedef union
{
int n5;
float n6;
} UDT;

(d)                        #typedef union
{
int n7;
float n8;
} TUDAT;

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. Advantages of DBMS?
� Redundancy is controlled.
� Unauthorised access is restricted.
� Providing multiple user interfaces.
� Enforcing integrity constraints.
� Providing backup and recovery.

5. Disadvantage in File Processing System?
� Data redundancy & 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:
� Physical level: The lowest level of abstraction describes how data are stored.
� Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data.
� View level: The highest level of abstraction describes only part of entire database.

7. Define the “integrity rules”
There are two Integrity rules.
� Entity Integrity: States that �Primary key cannot have NULL value�
� 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?
Extension -
It is the number of tuples present in a table at any instance. This is time dependent.
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
� Research Storage
� System Relational Data System.

10. How is the data structure of System R different from the relational structure?
Unlike Relational systems in System R
� Domains are not supported
� Enforcement of candidate key uniqueness is optional
� Enforcement of entity integrity is optional
� 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:
� Physical Data Independence: Modification in physical level should not affect the logical level.
� 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.

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

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

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

28. 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.

29. What is DML (Data Manipulation Language)?
This language that enable user to access or manipulate data as organised by appropriate data model.
� Procedural DML or Low level: DML requires a user to specify what data are needed and how to get those data.
� Non-Procedural DML or High level: DML requires a user to specify what data are needed without specifying how to get those data.

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

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

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

34. 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.

35. 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.

36. 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.

37. 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.

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

39. 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
� Minimizing redundancy
� Minimizing insertion, deletion and update anomalies.

40. 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.

41. When is a functional dependency F said to be minimal?
� Every dependency in F has a single attribute for its right hand side.
� We cannot replace any dependency X A in F with a dependency Y A where Y is a proper subset of X and still have a set of dependency that is equivalent to F.
� We cannot remove any dependency from F and still have set of dependency that is equivalent to F.

42. What is Multivalued dependency?
Multivalued dependency denoted by X Y specified on relation schema R, where X and Y are both subsets of R, specifies the following constraint on any relation r of R: if two tuples t1 and t2 exist in r such that t1[X] = t2[X] then t3 and t4 should also exist in r with the following properties
� t3[x] = t4[X] = t1[X] = t2[X]
� t3[Y] = t1[Y] and t4[Y] = t2[Y]
� t3[Z] = t2[Z] and t4[Z] = t1[Z]
where [Z = (R-(X U 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
� X is a Super-key of R.
� 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. 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.

50. 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.

51. 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.

52. What are partial, alternate,, artificial, compound and natural key?
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.
Alternate Key:
All Candidate Keys excluding the Primary Key are known as Alternate Keys.
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.
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.

53. 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

54. 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.

55. 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.

56. 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.

57. 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.

58. What do you mean by atomicity and aggregation?
Atomicity:
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.

59. 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.

60. 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.

61. What are the different phases of transaction?
Different phases are
� Analysis phase
� Redo Phase
� Undo phase

62. 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.

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

64. 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.

65. 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.

66. 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)

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

68. Name the buffer in which all the commands that are typed in are stored
�Edit� Buffer

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

70. 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.

71. 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
.
72. 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

73. 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.

74. 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.

75. 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)

77. 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.

78. 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.

79. 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

80. 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).

81. 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.

82. 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

83. 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.

84. 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.

85. 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.

86. 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.

87. 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.

88. 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.

89. 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

(b) Are always in 1NF

90. 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)