1. II. DATA BASE CONCEPTS
1. Data are some instances of the attributes of the entities of the system
2. Occurrences of instances of these attributes of each of the entities are known as data.
3. Data is like a raw material and the information is like the product made using the raw
material.
4. Metadata is the “DATA ABOUT DATA”. I.e. information for accessing the data.
5. A field is the lowest level of data item of an entity which is alternatively called as an
attribute of the entity.
6. Record is the collection of fields/attributes of entity in a desired sequence.
7. File is a collection of records having the same set of fields arranged in the same
sequence.
8. A field is said to be key field/primary key if it can identify a record uniquely in a
file.
9. A field is said to be non-key field/secondary key if it can not identify a record
uniquely in a file.
10. Schema is a schematic representation/overview of all the files in a database.
11. A portion of the schema of a database is called as subschema.
12. Association between fields of a file is the relationship in terms of occurrence of
data of a file.
13. Association between two files is the relationship between the records of these two
files or between any two record types.
14. One-to-One Association: A record of one file is associated with only one record
of another file.
15. One-to-many Association: A record of one file will be associated with one or
more records of another file.
16. Many-to-Many Association: In this type of association, each and every record of
one file will be associated with one or more records of another file.
17. Many-to-One Association: In this type of association, many record of the first
file will be associated with a single record of the second file.
18. Multiple Association: When there will be more than one type of association
between two files. This type of association is known as multiple association.
19. One-to-One Conditional Association: In this type of association, a particular
record of a file will be associated to only one record of another file for only
certain temporarily.
20. Recursive Association: Recursive association is the association between entities
of the same entity class.
21. File organizations can be classified into three categories as listed below.
1. Sequential file organization.
2. Indexed sequential file organization.
3. Direct access file organization.
22. In the sequential file organization, the records of the file will be arranged as per
the desired order of its key field one after another. This arrangement helps the
user to retrieve/update all the records one after another as per the order of storage
of records in the file.

2. 23. This type of organization is more suitable for situations which require processing
actions on all the records of the file.
24. In the indexed sequential file organization, the records of the file are stored in the
physical storage area as per the desired order of the key field. But this type of
organization will create a set of index values which will help in accessing the
records from the physical storage area randomly without accessing other records
from the beginning of the file to the location of the record. This file organization
can also be used to access all the records of the file sequentially.
25. In random file organization, each and every record of the file can be accessed
randomly without accessing other records of the file. This type of the file
organization is more suitable for on-line processing systems.
26. The files are stored in the secondary storage area, namely magnetic disk.
27. A track in disk is a circular storage position on that disk area. All the data in a
track of a disk can be accessed by placing the ‘read/write’ head at the radius of
that particular track.
28. A block is a sector of a track which stores a set of records. There will be a gap
between adjacent blocks on a track to indicate the ending of a particular block and
the beginning of another block.
29. A cylinder is a collection of tracks of different magnetic disks mounted one over
another with a constant radius or a collection of adjacent tracks in the same disk.
30. Access assembly consists of access arm and ‘read/write’ heads.
31. The direct file organization can be of two types, viz. relative addressed direct file
organization and hashed addressed direct file organization.
32. Relative addressed direct file organization: In this type of file organization, the
relative address of a desired record from the base address, 0 must be given by the
user.
Under such situation, the user should necessarily refer the base document to
identify the relative address of the record of integers.
33. Hashed addressed direct file organization:
i. The keys of records in the hashed addressed direct file organization are
scattered randomly throughout an area called hashing table which enables
the users to access each and every record in a rapid manner directly
without using indexes. Hence, it is considered to be the most efficient
method for accessing files in most of the on-line systems.
ii. Each bucket has a set of slots.
iii. Each and every key value of a record will be stored in a slot of a bucket
using a given hashing algorithm.