=over 4 =item 1 Design is large, or is likely to become large =item 2 When data is aggregated into obvious structures, especially if there's a lot of data in each aggregate For instance, an IP address is not a good candidate: There's only 4 bytes of information related to an IP address. An immigrant going through customs has a lot of data related to him, such as name, country of origin, luggage carried, destination, etc.