DATABASE

	To give consistency over the database development, all modeling should be carried out at the conceptual level. Performing database modeling at the conceptual level is closer to the business domain that the database being designed is required to satisfy.
	Conceptual Models allow for greater flexibility in the design process, by working with entities and their relationships to one another allows for changes to be made once, change the name of a column or its attributes, which may result in multiple changes to the physical model that will be handled through the toolset.
	By working on the physical level multiple copies of the database schema would need to be kept or a migration path developed, one for each of the target databases, which would soon get out of sync, as each required target database generally has their own extensions and limitations that need to be taken into account. The number of changes that would need to be made to a physical model if for example the Policy Number column attributes changed would be fairly high and prone to possible errors, but would only require one change at the conceptual level.
	Currently the modeling tool of choice is PowerDesigner from Sybase, this provides a flexible platform for describing the conceptual level of the database, and has built in capability to generate approximately 38 different physical database models, with the option to create your own physical database definition if the need arises.

http://www.sybase.com/products/enterprisemodeling/powerdesigner