Cardinality

In an E-R Model, we can constrain the number of entities that participate in a relationship. This is often reffered to as Cardinality.

When many entities of an entity set may participate in a relationship, we express this by connecting the entity set with the relationship by an undecorated line.

Connect the Account entity set with the CustAcc relationship set with an undecorated line:

1. Select the "Connection" tool.
2. Move the mouse over the "Account" entity set
3. Press the mouse button and drag the mouse to the "CustAcc" entity set.
4. Release the mouse button.

When only one entity of an entity set may participate in a relationship, we express this by connecting the entity set with the relationship by an arrowed line

Connect the Customer entity set with the CustAcc relationship set with an arrowed line.

1. Select the "Connection" tool and connect the Customer entity set with the CustAcc relationship set as described above.
2. Move the mouse over the line, and press the mouse button for a second until the popup menu opens.
3. Choose the menu item "Cardinality > 1". This turns the connection into an arrowed line

Click at the "Compare with Solution" button to see if your diagram is correct

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Source: http://www.cs.sfu.ca/CC/354/zaiane/material/notes/Chapter2/node8.html

DLOB M2: Conceptual Data Modelling