Client Server General

these two are SQL concepts

TRigger is a special type of stored procedure that

automatically takes effect when the data in a specified

table is modified.

triggers invoked in response to an INSERT,UPDATE OR DELETE

STATEMENT EXECUTED.

TRIGGERS are used to handle some exceptional conditions

if u r moving data 40 MB into data base,But data base having

only 30 mB free space then the trigger fires automatically

and the entire transaction automativcally roll backs.

Rules:

Rules are database objects used to enforce data integrity.

this object bound to column or userdefined data types.

to ensure that only valid values are allowed to insert in

to columns.

so trigger acts automatically nad rollbacks the transaction

when error is occured.

rule is used to enforce data integrity on a column or user

defined data type.

A super-server or sometimes called a service dispatcher is a

type of daemon run generally on Unix-like systems.

Usage

It starts other servers when needed, normally with access to

them checked by 'tcpd'. It uses no (or very little)

resources when in idle state. This can be ideal for

workstations used for local web development, client/server

development or low traffic daemons with occasional usage

such as ident and SSH.

Performance

There is a slight delay in connecting, thus when compared to

pre-spawn servers, a 'super-server' setup may not be all

that quick in reaction to connection attempts, especially

when under high load. Some servers, such as hpa-tftpd,

therefore takeover the socket and listen on it themselves

for some specified interval, anticipating more connections

to come.

Program Execution

The purpose of a computer systems is to allow the user to

execute programs. So the operating systems provides an

environment where the user can conveniently run programs.

The user does not have to worry about the memory allocation

or multitasking or anything. These things are taken care of

by the operating systems.

Running a program involves the allocating and deallocating

memory, CPU scheduling in case of multiprocess. These

functions cannot be given to the user-level programs. So

user-level programs cannot help the user to run programs

independently without the help from operating systems.

I/O Operations

Each program requires an input and produces output. This

involves the use of I/O. The operating systems hides the

user the details of underlying hardware for the I/O. All

the user sees is that the I/O has been performed without

any details. So the operating systems by providing I/O

makes it convenient for the users to run programs.

For efficiently and protection users cannot control I/O so

this service cannot be provided by user-level programs.

File System Manipulation

The output of a program may need to be written into new

files or input taken from some files. The operating systems

provides this service. The user does not have to worry

about secondary storage management. User gives a command

for reading or writing to a file and sees his her task

accomplished. Thus operating systems makes it easier for

user programs to accomplished their task.

This service involves secondary storage management. The

speed of I/O that depends on secondary storage management

is critical to the speed of many programs and hence I think

it is best relegated to the operating systems to manage it

than giving individual users the control of it. It is not

difficult for the user-level programs to provide these

services but for above mentioned reasons it is best if this

service s left with operating system.

Communications

There are instances where processes need to communicate

with each other to exchange information. It may be between

processes running on the same computer or running on the

different computers. By providing this service the

operating system relieves the user of the worry of passing

messages between processes. In case where the messages need

to be passed to processes on the other computers through a

network it can be done by the user programs. The user

program may be customized to the specifics of the hardware

through which the message transits and provides the service

interface to the operating system.

Error Detection

An error is one part of the system may cause malfunctioning

of the complete system. To avoid such a situation the

operating system constantly monitors the system for

detecting the errors. This relieves the user of the worry

of errors propagating to various part of the system and

causing malfunctioning.

This service cannot allowed to be handled by user programs

because it involves monitoring and in cases altering area

of memory or deallocation of memory for a faulty process.

Or may be relinquishing the CPU of a process that goes into

an infinite loop. These tasks are too critical to be handed

over to the user programs. A user program if given these

privileges can interfere with the correct (normal)

operation of the operating systems.