Looks like the Category end of the bidirectional association on page 228 has the many-to-many class mentioned as Item.

<class name="Item" table="ITEM">
...
<set name="categories"
table="CATEGORY_ITEM"
lazy="true"
inverse="true"
cascade="save-update">
<key column="ITEM_ID"/>
<many-to-many class="Item" column="CATEGORY_ID"/>
</set>
</class>

The many-to-many class I believe should be Category.
I believe it also the same problemwith the bag mapping shown at the end of the page 228 continued on to page 229

Thanks, will be fixed in reprint.