Schema Evolution publication categorizer

Schema evolution is of two kinds: (a) those requiring instance transformation because the application is simpler to develop when it works only with one version of the schema, and (b) those in which the old data must be preserved and instance transformation must be avoided. The latter is important in practice but has received scant attention in the literature. Data conforming to multiple versions of the XML schema must be maintained, indexed, and manipulated using the same query. Microsoft’s SQL Server 2005 introduces XML schema collections to address both types of schema evolution.