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Understanding Cardinality

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When you define a relationship, you can specify a minimum, maximum, and default cardinality. Cardinality refers to the quantity of the products the user can select from a relationship. For example, you define a relationship called Hard Drives. It contains a 20 GB drive and a 30 GB drive. If you set the minimum cardinality to 2, the user must pick 2 items from this relationship. The user can do this in any of the following ways:

Pick one 20 GB drive and one 30 GB drive
Pick two 20 GB drives
Pick two 30 GB drives

The three types of cardinality you can define for a relationship are as follows:

Minimum Cardinality. Governs whether or not selecting items from this relationship is optional or is required. If you set the minimum cardinality to 0, selecting items is optional. If you set the minimum cardinality to greater than 0, the user must select that number of items from the relationship.
Maximum Cardinality. Sets the maximum number of items that the user can select from a relationship. If you set the minimum cardinality to greater than 0, you must set the maximum cardinality to a number at least as large If you do not enter a maximum cardinality, the default is 999. To revise this default, refer to Revising the System Default Cardinalities.
Default Cardinality. Specifies what quantity of the default product is automatically added to the initial solution that the user sees. Default cardinality must be equal to or greater than the minimum cardinality and must be less than or equal to the maximum cardinality.

If you specify a default cardinality and do not specify a default product, the system uses the first product that displays when you expand the relationship folder in the Product Designer.

Table 17 describes several combinations for setting cardinality. The table shows what the user will see in the initial solution and what actions that the user can take. In the table, N is the quantity of the default product in the initial solution. In all the cases where the Min Card is greater than 0, the user can substitute other products for the default product.

Table 17. Combinations of Cardinality

Min Card	Default Card	Max Card	System Adds Default Product?	User Pick Reqd?	Initial Solution	User Actions Allowed
=0	= Min Card	>Default Card	No	No	No items	Increase item quantities to Max Card.
=0	> Min Card	=Default Card	No	No	N=Max Card	Decrease Item quantities to 0 but cannot increase them.
=0	> Min Card	>Default Card	No	No	N=Default Card	Increase item quantities to Max Card or decrease them to 0.
>0	= Min Card	=Default Card	Yes	Yes	N=Min, Default, Max	Cannot increase or decrease item quantities.
>0	= Min Card	> Default Card	Yes	Yes	N=Min	Can increase item quantities to Max Card but cannot decrease them.
>0	> Min Card	= Default Card	Yes	Yes	N=Default	Can decrease item quantities to Min Card but cannot increase them.
>0	> Min Card	>Default Card	Yes	Yes	N=Default	Can decrease item quantities to Min Card or increase them to Max Card.

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