Which approach between top-down and bottom-up methodologies best fits with a SOA in regards of Service identification?

SOA is a type of architecture. The building architecture is a Top-Down, not Bottom-Up, process. The most persuasive justification for claiming that Web Services are not SOA is that they are technical in nature and are frequently created from the ground up. Building a Bottom-Up SOA is a bad idea since it might result in bloated architecture or even no architecture at all. However, developing SOA entirely from the top down may result in perceptual architecture with no run-time artifacts, thus some SOA activities should be done from the bottom up. To summarise, SOA is a Top-Down method at first, but a pragmatic approach needs to combine Top-Down and Bottom-Up Approaches.