Page 54 - DLIS408_INFORMATION_TECHNOLOGY-APPLICATIONSL SCIENCES

Unit 4: Database

abstracts Notes
full text
indexing terms or keywords or phrases
citations including the total number of references
language of the document
call number or location
Each of these items is known as a data element and is represented by a field. There are different
bibliographic record formats and there is considerable variation between them. It may be mentioned
here that the components listed above do not generally (except in case of those containing abstracts)
give information of the text of the document but only indicate where the information might be
found. Of course, a good informative abstract, if provided for each reference may furnish valuable
information to the user and enhance the utility of the database.

Database Architechture

The architecture of a database is commonly viewed in terms of three separate levels of description:
conceptual, external and internal.
The overall logical description of the entire database is the conceptual level. This overall description
is commonly known as a schema. It may also be called a community user view. Subsets of the
schema that contain only the data needed for particular applications may be defined. These are
called sub-schemas or user views. The sub-schemas provide a description at the external level. The
description of physical storage structures used to store database on a specific computer system is
the internal description.
Explained in simple language, it might be stated that a database can be analysed from two view-
points—the physical storage of the data and the 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 two to physically store data on a disk.
The logical or conceptual view of a database is concerned with how data is logically organised and
how data can be retrieved for information purposes. There are three different methods (architectures)
of logically organising data in a database. They are hierarchy model, network model and relational
model.

Advantages of Database Systems
The Database Systems provide the following advantages over the traditional file system
1. Controlled redundancy: In a traditional file system, each application program has its own
data, which causes duplication of common data items in more than one file. This duplica-
tion/redundancy requires multiple updations for a single transaction and wastes a lot of
storage space. We cannot eliminate all redundancy due to technical reasons. But in a data-
base, this duplication can be carefully controlled, that means the database system is aware
of the redundancy and it assumes the responsibility for propagating updates.
2. Data consistency: The problem of updating multiple files in traditional file system leads to
inaccurate data as different files may contain different information of the same data item at
a given point of time. This causes incorrect or contradictory information to its users. In
database systems, this problem of inconsistent data is automatically solved by controlling
the redundancy.
3. Program data independence: The traditional file systems are generally data dependent, which
implies that the data organization and access strategies are dictated by the needs of the
specific application and the application programs are developed accordingly- However,
the database systems provide an independence between the file system and application
program, that allows for changes at one level of the data without affecting others. This
property of database systems allow to change data without changing the application pro-
grams that process the data.
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