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# SOS Attributes

These are SOS attributes, meaning that they are associated with specific special-ordered set constraints in the model. You should use one of the various `get` routines to retrieve the value of an attribute. These are described at the beginning of this section. For the object-oriented interfaces, SOS attributes are retrieved by invoking the `get` method on an SOS object. For attributes that can be modified directly by the user, you can use one of the various `set` methods.

Attempting to query an attribute that is not available will produce an error. In C, the attribute query routine will return a DATA_NOT_AVAILABLE error code. The object-oriented interfaces will throw an exception.

## IISSOS

- Type: `int`

- Modifiable: `No`

For an infeasible model, indicates whether the SOS constraint participates in the computed Irreducible Inconsistent Subsystem (IIS). Only available after you have computed an IIS.

For examples of how to query or modify attributes, refer to our Attribute Examples.

## IISSOSForce

- Type: `int`

- Modifiable: `Yes`

When computing an Irreducible Inconsistent Subsystem (IIS) for an infeasible model, indicates whether the SOS constraint should be included or excluded from the IIS.

The default value of -1 lets the IIS algorithm decide.

If the attribute is set to 0, the constraint is not eligible for inclusion in the IIS.

If the attribute is set to 1, the constraint is included in the IIS and the IIS algorithm never considers the possibility of removing it.

Note that setting this attribute to 0 may make the resulting subsystem feasible (or consistent), which would then make it impossible to construct an IIS. Trying anyway will result in a IIS_NOT_INFEASIBLE error. Similarly, setting this attribute to 1 may result in an IIS that is not irreducible. More precisely, the system would only be irreducible with respect to the model elements that have force values of -1 or 0.

See the `Model.computeIIS` documentation for more details.

For examples of how to query or modify attributes, refer to our Attribute Examples.

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