This article uses the following assumptions:
You are familiar with both LDAP databases and schema basics.
You already have an earlier version of Sun Java System Calendar Server or Sun Java System Messaging Server software installed.
You need to determine which of the Schema versions to use when you upgrade to the 6.3 versions of Calendar Server and Messaging Server software.
This article should supply you with enough information to understand the differences between the Schema versions and help you determine which version is best suited to your needs.