Split and create relations
To keep our data organized, it's good practice to categorize our information into logical groups.
We want to keep independent entities separate
and create relations between them. This process is called normalisation.
Simply by the GUI (e.g. using buttons, dropdown menues and input/tick boxes), the Galaxy and Morphology data can be
structured into two separate tables (say MORPHOLOGY and GALAXY), as shown in Figures 5 to 7.
We now have created the relation between the tables, having the morphology
data independent to the galaxy data, and associating each galaxy to a specific morphology.
From Figures 5 and 6, we can see the relationship between MORPHOLOGY and GALAXY
is built on the attribute morphologyNo. This was made possible by setting up the
"Foreign Key" during the creation of the table GALAXY with
Therefore, when we will want to insert a new galaxy along with its morphology,
we will get an error if we do not provide a valid morphologyNo.
In other word, the insertion won't happen if we want to assign a morphology that doesn't exist.
Extra information about PRIMARY KEY.
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