The `org.apache.ddlutils.io` package contains a classes for input and output of both the database schemas and data files. Specifically, the {@link org.apache.ddlutils.io.DatabaseIO} class reads from and writes to schema XML files, and the {@link org.apache.ddlutils.io.DataReader} and {@link org.apache.ddlutils.io.DataWriter} classes to the same for data XML files. The DTD for these data XML files is generated via the {@link org.apache.ddlutils.io.DataDtdWriter} class.