• An item of data means the smallest piece
of data that may be a single name or a
• A field is a area of a record reserved for
one particular type of data.
• Each field contain one or more data items.
• Record is a group of related items of data which
together can be treated as a unit.
• The records are similar to one another in the type
• A file is organized collection of related records.
• In computing a file is usually on backing store.
Name Phone# DOB
1 Ali 042-78888 12/12/98
2 Ahmed 544545 09/4/97
A Students Files
Reasons for using files
• In any situations requiring a
permanent source of data.
• In computer when the main store is
so small for amount of data being
• A key field is field that may be used to
search a file.
• It is always useful to have one field which
is unique to a particular record.
• Admission form no of each student.
• With the library system, the key field
would be the number given to the book
Fixed and variable length
• Fields may be of fixed or variable length.
• If the fields are of fixed length then a given
field in a record has a set number of characters
positions reserved for it.
• We specify how long each field is going to be
when we set up the structure of a database
• If the fields are of variable length, the number
of characters in each is not determined
Advantages of variable
over fixed length
• There is no waste of storage space
• Advantages of fixed over variable length
• Computer operations such as searching can
be carried out quickly.
• Allocation of storage space is more
• Updating the file is much easier
Types of Files
• 1.Master file
• Is a file used as a reference for a
particular computer application
• It may be updated when necessary
• It is the most complete and up-to date
version of a file.
• If the master file is lost or damaged and
it is only copy, the whole system will break
• Is a file of temporary data which has been
prepared in order to carry out a
processing operation with the data on a
• It is used to update master file.
• A transaction is a piece of a business.
• Transaction can occur in any order, so it is
necessary to sort a transaction file into
the same order as the master file
Backup or security files
• Backup copies of files are in kept in case the
original file is damaged or lost or cannot be used
• The importance of master file, back up copies of
it should be taken at regular intervals in case it is
stolen, lost or corrupted.
• Looking after your disks is not enough you should
always keep backup copies of all important data.
Transaction log files
• Are bits of business such as placing
an order, updating the stock, making
File Access Methods
• Serial access
• Sequential access
• Random Access
• To read a serial file ,a computer has to
read each record until it reaches the one
• The records do not follow each other in
any particular order.
• So if another record needs to be added it
can just be added to the end of the file.
• Access to a file is sequential when records
can only be written to or read from it in
order one after another.
• So if just one record is required then
method is slow but if all the records are
required then it becomes fast
• Sequential files can be stored on
• Magnetic tape
Direct or Random Access
• When any record can be accessed
without having to access other
• It store data on direct access.
• You can access both sequential and
random files directly
Advantages of direct access
over sequential access
• Selected records can be accessed far
more quickly from direct access files.
• Records can be accessed in any chosen
• Records do not have to be put into any
particular order before the file is created
Advantages of Sequential
access over direct access
• Sequential files can be stored on
most media including magnetic tape
,paper tape and punched card
• For the programmer ; it is usually
easier to write programs to handle
Factors for choice of
• How may records are to accessed. If the records
are to be accessed singly or few then direct
access is used.
• How large the file is. If a file is small the time
delay in searching it is not important therefore a
sequential file is acceptable.
• Sequential files is often suitable for batch
• The type of storage medium being used. If
magnetic tape is to used then files may have
• Manual File System
• Mechanical File System
• Electronic File Systems
• File is Processed manually without using
any machine or tool.
• Accessing the same information in same of
two people can not possible.
• If a file is placed in wrong place then
finding it again can be problem
• Updating the file is difficult.
Mechanical File System
• File is processed by using different
device like typewriters, mechanical
• That method is faster and more
accurate than manual file.
• File is processed through computers
• Files and set of instructions are
given to the computer as input and
computer automatically processed
• Information is stored only once, since
most database software allows you to
access information from several files.
• Files can be linked together which means
that if you update one of the files.
• Changing is in easy way
• Data loss is less chance
• Validations checks may be made on the
data as it is being entered into database.
• If the computer breaks down you are
not able to access the details.
• It is easy to copy computer file so
there is a need to protect sensitive
• Training is needed to use the system
• Database is organized collection of
information or data.
• Collection of related data stored in
an efficient and compact manner.
• Flight Details
• Hotmail Or Yahoo Or Google
• Library in Schools
• Complete data is located at a single
computer and all the users access
this single database.
• Its an efficient way to access and
• Used in computer network
• Is a single database which is spread
physically across multiple computers
over wide area network .
• It may be
• Database management system is
computerized record keeping system.
• Is a collection of programs, which are
used to define ,create and maintain
Database System of a
• Involves bringing a file up-to-date
with any changes that have occurred.
• There are various process that can
take place during updating.
• A new entry in the file.
• Suppose we had a file containing the
details of pupils in a school.
• A new pupil may have joined the
school and so that pupil’s details will
need to be added to the file.
• A delete record in the file.
• A pupil could have moved to a new
school so that the pupil’s detail will
need to be removed from the file.
• Some changes occur in the field of
• A pupil has moved house so the
address field needs changing.
• Some time a field need to be sorted
in particular order.
• It may be
• Sometimes we want to combine the
contents of two files to form a single
• The process of combining the files is
• If the two files to be merged are on
magnetic tape then we must sort the tapes
into order before merging them.
• Merging is very important when we want to
divide the work.