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Data modeling diagram notation, what is it?

What does this type of notation mean in a logical data model? There are three tables in this diagram and x inside the crescent. So what is this "x inside the crescent." I could not find it, for example. from the various schema conventions mentioned in Wikipedia .

_________ |_________| | | |_________| | | ----- /__x__\ | _______|_________ _____|_____ ____|______ |___________| |___________| | | | | | | | | |___________| |___________|
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This means that 2 children are exclusive subtypes of the parent super-type.

This is the notation "Information Engineering"

For example, see ERWin notes (below) http://www.isqa.unomaha.edu/wolcott/tutorials/erwin/erwin.html

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There is already the right answer, but I thought the following might be useful for future visitors.

In ER modeling, this pattern is known as specialization / generalization. In languages ​​like Java, “subtypes” may be known as “subclasses”.

When you switch from an ER modeling model to SQL (relational), you will probably be at a loss for a good presentation of this template. Introductory material about database design often does not include this pattern, although it repeats itself over and over.

Fortunately, the design technique is well understood here. If you visit class-table-inheritance and click on "learn more" you will get an overview of one useful technique and links to two related methods.

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Source: https://habr.com/ru/post/1480858/

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