Monday, May 21, 2007
PatHelland's WebLog : SOA and Newton's Universe: "Classic database/transaction approaches to Consistency choose to emphasize read-write semantics. To preserve Read-Write-Consistency, you lock the data. We've been at this for over 30 years. What I see happening in loosely-coupled systems is identical to how businesses operated 150-200 years ago when messages were sent with couriers running across the city between businesses. You allocated (i.e. reserved) the ability to perform an operation and then later on you would take the confirming step to ensure the completion of the work. Today, you make a reservation at a hotel and then later on you show up to complete the operation. What is the definition of consistency in this world? It is the successful remembering of the reservation and then keeping a room for you. The reserved room count is not locked waiting for you to decide if you want the reservation, waiting for you to cancel, nor while waiting to see if you show up. The definition of consistency evolves to one that is explicitly including independence and loose-coupling."