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I’m using an online tool yEd Live to model a MER diagram. However, there are some elements that use terms in which leave me with some doubts.
Those terms are:
Therefore, I would like to know what those terms are and what the differences between them are?
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Weakentity
It is the entity that cannot exist by itself, it always depends on the existence of another entity that sustains it, that associates it. The classic example is the item line of a tax note, it alone cannot exist, it depends on the existence of a tax note that it is associated with. She demands a strong relationship.
Weakrelationship
It’s the relationship between strong entities, so they can exist on their own, so you just need a simple identification of what to relate. A student with a course for example, they are related when there is interest in both, otherwise the relationship is not necessary.
One Optional
It means that the relationship may have zero or a connected entity. Zero indicates optionality and it is clear that you cannot have more than one.
One Mandatory
It means that the relationship needs a connected entity, but only one, no more.
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Weak Relationship’s response is tolerably wrong, the correct' is the relationship of an Entity with a Weak Entity, and an example would be a table person and a blood type, blood type needs a person to exist, in practice the week Relationship will only have the person id and the blood type id if it has other values it ceases to be a week Relationship or even a week Entity
– HudsonPH