  Data consistency is very desirable because strong semantic properties make it
easier to write correct programs that perform as users expect. However, there
are good reasons why consistency may have to be weakened to achieve other
business goals. In this CIDR 2009 Perspectives paper, we present real-world
reasons inconsistency may be necessary, offer principles for managing
inconsistency coherently, and describe implementation approaches we are
investigating for sustainably scalable systems that offer comprehensible user
experiences despite inconsistency.
