public MergePolicy MergePolicy {get; set;}

// Create a CodedValueDomain description for water pipes
CodedValueDomainDescription codedValueDomainDescription = new CodedValueDomainDescription("WaterPipeTypes", FieldType.String,
  new SortedList<object, string> { { "Copper", "C_1" },
    { "Steel", "S_2" } })
{
  SplitPolicy = SplitPolicy.Duplicate,
  MergePolicy = MergePolicy.DefaultValue
};

SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

// Create a coded value domain 
CodedValueDomainToken codedValueDomainToken = schemaBuilder.Create(codedValueDomainDescription);
schemaBuilder.Build();