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Do people often use the word "entity" to refer to what will latter become a table? If yes, isn't this technically incorrect because it's the entity sets that typically become tables?

It seems to me that often times people say entity when they mean entity set. When I see a square on a diagram, that actually represents an entity set right? For example if there were a square that said movies that wouldn't be one particular movie (like an entity) but a collection of movies (entity set), right?

For example this is the first website that came up on Google when I typed in E/R diagram tutorial and it claims that squares represents entities, which is technically wrong.

Celeritas
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1 Answers1

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The E/R diagram wording is in the singular - e.g. 'A teacher teaches a class'.

So there would be a rectangle for 'teacher', a rectangle for 'class' and a diamond for 'teaches'.

However strictly speaking, yes, the modelling is of the sets, and is translated to tables such that 'teacher' is the table (set) of 'teachers' and 'class' is the table (set) of 'classes' and depending on the cardinality, the 'teaches' would probably be a 'teacher-class' table

Chamila Chulatunga
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  • So what I'm asking is, in your example, is it more correct to say `teacher` is an "entity" or "entity set" or are they both equally correct? – Celeritas Dec 05 '12 at 09:51
  • A 'teacher' is an entity, but the rectangle in the diagram represents the set of teachers (i.e. the entity set) that may exist in the 'world' that we are trying to model – Chamila Chulatunga Dec 05 '12 at 09:54