This document provides an introduction to files and file systems. It defines what files are, including that they are containers for storing information and come in different types like text, data, binary and graphic files. It outlines key file attributes like name, size, permissions. It also describes different file access methods like sequential, direct/random, and indexed sequential access. File operations like create, write, read, delete and truncate are also covered. The document concludes with definitions of flat file databases and their advantages and disadvantages compared to relational databases.

1. Presented by,
V.Santhi,
Assistant Professor,
Department of Computer Applications,
Bon Secours College for Women,
Thanjavur
I n t r o d u c t i o n t o
O R A C L E A N D
S Q L

2. files

3.  In general, A large amount of information or
data that lives a very long time
 File is a container in a computer system for
storing information.
 Files used in computers are similar in features to
that of paper documents used in library and
office files.
 A file is a sequence of bits, bytes, lines or records
whose meaning is defined by the files creator and
user.
What are files?

4. What are files?
 There are different types of files such as text files, data
files, directory files, binary and graphic files, and
these different types of files store different types of
information.
 In a computer operating system, files can be stored on
optical drives, hard drives or other types of storage
devices.
 The file can be indexed, structured, etc. The file is an
entry in a directory.
 The file may have attributes (name, creator, date, type,
permissions).

5. File attributes
 Name – only information kept in human-readable form
 Identifier – unique tag (number) identifies file within file
system
 Type – needed for systems that support different types
 Location – pointer to file location on device
 Size – current file size
 Protection – controls who can do reading, writing,
executing
 Time, date, and user identification– data for
protection, security, and usage monitoring
 Information about files are kept in the directory structure,
which is maintained on the disk

6. File Systems and Disks
User view
File is a named, persistent collection of data
OS & file system view
File is collection of disk blocks — i.e., a container
File System maps file names and offsets to disk blocks

7. File structure
 File structure is a structure, which is according to
a required format that operating system can
understand.
 A file has a certain defined structure according to
its type.
 A text file is a sequence of characters organized
into lines.
 source file is a sequence of procedures and
functions.
 An object file is a sequence of bytes organized into
blocks that are understandable by the machine.

8. File operations
 Create
 Write (Store)
 Read
 Reposition within file
 Delete
 Truncate

9. File types

10. Functions of file system
 File system in OS provide the way to create
and access the files.
 How the memory is allocated to files and how
the addresses are saved regarding to each file.

11. File access methods
 File access refers to the
manner in which the records of a file
may be accessed.
There are several ways to access files
 Sequential access
 Direct/Random access
 Indexed sequential access

12. Sequential access
 A sequential access is that in which the records are
accessed in some sequence i.e the information in the file
is processed in order, one record after the other.

13.  This access method is the most common one.
 Example: Compilers usually access files in this fashion.
 Retrieving from sequential file:
 To access records, it is necessary to read the file from beginning to
examine each record in sequence until the desired record is located.
 Appending a sequential file:
The append operation refers to adding more records to an
existing file.
The following operations are done for the purpose of appending a
file.
 Open the file.
Read the file till EOF is encountered.
Read the data to be added.
Write the data on the file.
Close the file.





14. Direct / random access
 Random access file organization provides, accessing the records
directly.
 Each record has its own address on the file with by the help of
which it can be directly accessed for reading or writing.
 The records need not be in any sequence within the file and they
need not be in adjacent locations on the storage medium.

15.  Method useful for disks.
 There are no restrictions on which blocks are read/written
in any order.
 User now says "read n" rather than "read next".

17. Indexed sequential access
 This approach combines the advantages of both
sequential and direct file access.
 Anindex is created for each file which contains
pointers to various blocks.
 Indexis searched sequentially and its pointer is
used to access the file directly.

18. Example to understand Indexed
Sequential Access
(Prime Area)

19. FLAT FILE
 A flat file database is a database that stores data in a
plain text file.
 Each line of the text file holds one record, with fields
separated by delimiters, such as commas or tabs.
 While it uses a simple structure, a flat file database
cannot contain multiple tables like a relational database can
 Flat file is also a type of computer file system that stores
all data in a single directory There are no folders or paths
used organize the data.
 While this is a simple way to store files, a flat file system
becomes increasingly inefficient as more data is added.

20. Advantages OF Flat file System
Easy to understand.
Easy to implement.
Less hardware and software requirements.
Less Skills set are required to handle flat database
systems.
Best for small databases.

21. Disadvantages OF Flat file System
Less security easy to extract information.
Data Inconsistency
Redundancy
Sharing of information is cumbersome task
Slow for huge database
Searching process is time consuming

22. Thank you