Data Redundancy

Data Redundancy:
• A well-designed organisation has all the data required
by the organisation in the one place
• When data is updated immediately, any information
extracted from the database is accurate and up to date.
• Accuracy of data is needed when making decisions.
• Data redundancy occurs when the same data is stored
in a multiple locations in an organisation
• Thus, only one correct record is required in an
organisation
• Having details in multiple places causes data
redundancy
Implications of data redundancy:
1) Data inconsistency because of different and conflicting
versions of the same data in multiple locations leading
to lack of data integrity
2) Data redundancy leads to data anomalies; this is
because changes in data need to occur in different
places rather than just in the one place
3) Data anomalies can be modification, insertion and
deletion anomalies
Data Anomalies:
1) Modification anomalies occur when a field values is
changed; changes must be made to all the record
pertaining else there could be a loss of data integrity;
Data inconsistency will occur
2) Insertion anomalies occur when a new information is
entered into the customer file
3) Deletion anomalies occur when the deletion of data
about an entity inadvertently deletes data about another
entity
Database Modelling:
Conceptual models provide a logical representation of what
the database contains. It is a graphical representation of the
complexities of the real world data entities and their
relationships with one another. Database designs can depict
the data structure, relations, characteristics and constraints
on the design using a database model.
Reasons for database modelling:
– good database design is a foundation of good database
modelling; it provides a blue print to build tables and
relationships that are required in a database
application.
– Different people such as managers, admin staff,
programmers view data differently. While managers see
data from a decision-making perspective, the
administration staff see it from a more ease of use
perspective. Programmers want simplicity than anything
else
Symbols used in entity-relationship:
Entity
Relationship line
Relationship
One (1) symbol: 1 one to one : II

Composite entity
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