tuplizer

I came across a post that mentioned Tuplizer in NHibernate, can anybody provide a good definition or reference for Tuplizer? From ITuplizer's source code : A tuplizer defines the contract for things which know how to manage a particular representation of a piece of data, given that representation's EntityMode (the entity-mode essentially defining which representation). If that given piece of data is thought of as a data structure, then a tuplizer is the thing which knows how to: create such a data structure appropriately extract values from and inject values into such a data structure For

I'm trying to use Hibernate to persist a class that looks like this: public class Item implements Serializable, Comparable<Item> { // Item id private Integer id; // Description of item in inventory private String description; // Number of items described by this inventory item private int count; //Category item belongs to private String category; // Date item was purchased private GregorianCalendar purchaseDate; public Item() { } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getDescription() { return description; } public void