public AttributeIndexDescription( 
   Index attributeIndex,
   TableDescription tableDescription
)

public void CreatingTableWithIndex(SchemaBuilder schemaBuilder)
{
  FieldDescription nameFieldDescription = FieldDescription.CreateStringField("Name", 50);
  FieldDescription addressFieldDescription = FieldDescription.CreateStringField("Address", 200);

  // Creating a feature class, 'Buildings' with two fields
  TableDescription tableDescription = new TableDescription("Buildings", new List<FieldDescription>() { nameFieldDescription, addressFieldDescription });

  // Enqueue DDL operation to create a table
  TableToken tableToken = schemaBuilder.Create(tableDescription);

  // Creating an attribute index named as 'Idx'
  AttributeIndexDescription attributeIndexDescription = new AttributeIndexDescription("Idx", new TableDescription(tableToken),
    new List<string> { nameFieldDescription.Name, addressFieldDescription.Name });

  // Enqueue DDL operation to create an attribute index
  schemaBuilder.Create(attributeIndexDescription);

  // Execute build indexes operation
  bool isBuildSuccess = schemaBuilder.Build();
}

public void RemoveAttributeIndex(SchemaBuilder schemaBuilder, FeatureClassDefinition featureClassDefinition, string attributeIndexName)
{
  // Find a index to be removed 
  ArcGIS.Core.Data.Index indexToRemove = featureClassDefinition.GetIndexes().First(f => f.GetName().Equals(attributeIndexName));

  // Index description of the index to be removed 
  AttributeIndexDescription indexDescriptionToRemove = new AttributeIndexDescription(indexToRemove, new TableDescription(featureClassDefinition));

  // Enqueue the DDL operation to remove index 
  schemaBuilder.Delete(indexDescriptionToRemove);

  // Execute the delete index operation
  bool isDeleteIndexSuccess = schemaBuilder.Build();
}