Java library for XML Schema to Instance Conversion

[Dianela]

I need to convert a given XML instance to its Schema. I also need to do the conversion from a given XML Schema to its corresponding instance. Also, if a user gives a XML instance with data, i need to convert it to a proper instance.( Proper instance means the one in which occurrence of multiple tuples are reduced to single entry.)Currently am using Apache XMLBeans library(xbean.jar). But it is taking too much time when i give a huge xml of 12k lines. Also, it generates multiple schema nodes for few instances, instead of one.Is there any other Java library which performs this conversion? Thanks in advance.