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Essay example - DATABASE SYSTEMS COURSEWORK
Pages 6 (1506 words)
The above table of entities and their attributes follows from the analysis of the case study. These entities form the master entities and others will follow from the logical and conceptual relationships between these entities.
b. The relationship type 'rents' is linking the student and the room…
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This conceptual model depicts all the entities and their relations; it gives the overall picture and understanding of the system to a novice. This can also be called a logical model as it does not take into consideration any DBMS in mind and shows the logical association of the system.
Next we are constructing the logical system which has the cardinality ratios. A cardinality ratio of a binary relation is the maximum number of instances an entity can participate in a given relationship type.
Special note: The attribute named 'lease' to the relationship named 'rent' has been shifted to the rent table as the cardinality ratio is 1:1 so any attribute of the relationship type must be shifted on either side.
The arrows show the functional dependencies. The single arrow with no point head determines all the attributes of the entire entity. In the table 'Responsible_For' which was previously a relationship between student and staff had a cardinality ratio of M:N. The relationship type will form a separate table with the same name having the primary keys of both the aligned tables.
a. Only the table 'Room' has an attribute called 'Room Type' which can have both 'single' and 'double' rooms in a particular hall. ...
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