1. In a database system, a method for performing a schema evolution operation using partial data copy, the method comprising: to convert one or more XML documents that conform to a first version of an XML schema to a second version of the XML schema that is different from the first version, determining an affected portion of data in each of the one or more XML documents that is affected by converting said one or more XML documents from the first version of the XML schema to the second version of the XML schema; wherein a first object-relational database representation is used to store the XML documents conforming to said first version of the XML schema; determining one or more first object-relational database structures within said first object-relational database representation that are used to store at least said affected portion of said data; based on the one or more first object-relational database structures, determining one or more second object-relational database structures in a second database representation used to store XML documents conforming to said second version of the XML schema; wherein the first object-relational database representation is different from the second object-relational database representation; wherein determining the one or more second object-relational database structures includes determining to remove or modify at least one particular first object-relational database structure of said one or more first-object relational database structures; populating at least one particular second object-relational database structure of the one or more second object-relational database structures based on said affected portion of data in the one or more XML documents that conform to the first version of the XML schema; and wherein the method is performed by one or more computing devices.