Page 52 - DLIS408_INFORMATION_TECHNOLOGY-APPLICATIONSL SCIENCES

Unit 4: Database

it must include all necessary data relationships, to support the variety of different uses to Notes
which data is put;
it must have common approach to retrieval, additions and deletions and amendments to
data.

Notes A database can be analysed from two viewpoints: The physical storage of the data or
logical or conceptual view of data.
Files are used to physically store data in a database. Most databases use either direct files or
indexed files or a combination of the both to physically store data on disk. Users and applications
do not need to know anything about the physical data storage. Stored with actual data will be a
description of the database, which enables the DBMS to retrieve information from the database
and to store new data in appropriate places in the database establishing relationships with other
data if relevant.
The logical or conceptual database is concerned with how the data is logically organised and how
the data can be retrieved for information purposes. In case access is required to a series of linked
files, it is necessary to have guidelines regarding allocation of data to specific files within the
database system, and defining the optimum links between files. Based on the model followed for
the structuring of data there are three basic types of databases and the associated DBMS namely:
hierarchical, network and relational.
Hierarchical databases are structured in such a way that the relationships between data items follow
a branching tree-type arrangement. In other words, the database consists of elements, which act, in
a parent-child relationship. The relationships within the database are established when the database
is created, that is to say that the database designer defines which is a child element of the parent
element. An element within a database can have only one parent element. The data stored in the
lower levels of a hierarchy database can only be accessed through the parent element.
The network database approach is based on explicit links or pointers between related entities. In a
network model of database, there is more direct link between the data items at various levels. This
is achieved by the use of pointers linking data at different levels. This approach requires a large
number of links established between data elements, which occupy a large amount of storage space.
Relational databases use a type of data structure, which has been commonly adopted in database
systems. In relational database systems, information is held in a set of relations or in the form of
tables. Rows in such tables correspond to records while columns in these tables are equivalent to
fields. The data items in various relations are linked through a series of keys. Relational databases
are designed using a technique known as ‘normalisation’. ‘Normalisation’ is used to break data
into tables so that the fields in each table are dependent only on one key field and not linked to any
other key. This process ensures that insertions, deletions and amendments may be made on to the
data without any difficulty.
In addition to the above-discussed types of databases, other types of database structures such as
multimedia databases and object oriented databases are also in existence. Multimedia structures
are used to manage such databases, which deal with pictures, animation, sound and text as well as
tables. The storage needs of these materials are certainly different from the types discussed earlier.
The Multi Media DBMS (MM-DBMS) attempts to use a range of technologies like relational
technology for tables, image storage devices for graphics and animation, and provide facilities to
the users.

Types of Databases
There are many ways of categorising databases. One of the categorisations might be a numerical
and textual database. Another way of looking at them is by their coverage i.e., local, regional and
global. Databases are generally stored on magnetic or optical media such as disks and accessed

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