database design - Data modeling diagram notation, what is this? -


what type of notation mean in logical data model? there 3 tables in diagram , x inside "half moon". so, "x inside half moon". not find e.g. different diagramming conventions mentioned in wikipedia.

             _________             |_________|             |         |             |_________|                  |                  |                  -----               /__x__\                  |           _______|_________     _____|_____        ____|______    |___________|      |___________|    |           |      |           |    |           |      |           |    |___________|      |___________|

it means 2 child entities exclusive subtypes of parent super type.

this "information engineering" notation

for example, see erwin notes (at bottom) http://www.isqa.unomaha.edu/wolcott/tutorials/erwin/erwin.html


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