I have 3 tables
The first one:

PRODUCTS
-------------------
id
name
-------------------

The second one:
_____________
SPECIFICATIONS
---------------------------
id
name
dat
beg_dat
end_dat
____________

the link between them is many-to-many, but the "link table" must have not 2 fields(product_id,specification_id). It should have structure like this

LINKSPECPROD
----------------------------
ID*
----------------------------
spec_id
---------------------------
product_id
---------------------------
price
---------------------------

How can i do it?

ps

my mapping files are:
<class name="tables.Product" table="PRODUCTS">
<id name="id" column="PRODUCT_ID" type="long">
<generator class="native"/>
</id>
<property name="name" type="string" length="30" not-null="true" />
<set name="specifications" table="LinkSpecProd">
<key column="product_id"/>
<many-to-many class="tables.Specification">
<column name="spec_id"/>
</many-to-many>
<!--<many-to-many column="spec_id" class="tables.Specification/>-->
</set>
</class>

<class name="tables.Specification" table="SPECIFICATIONS">
<id name="id" column="ID" type="long">
<generator class="native"/>
</id>
<property name="name" type="string" length="30" not-null="true" />
<property name="dat" type="timestamp" not-null="true" />
<property name="beg_date" type="timestamp" not-null="false" />
<property name="end_date" type="timestamp" not-null="false" />
<set name="products" table="LinkSpecProd" inverse="true">
<key column="spec_id"/>
<!--<many-to-many column="product_id" class="tables.Product"/>-->
<many-to-many class="tables.Product">
<column name="product_id"/>
</many-to-many>
</set>
</class>

TIA, Constantine.

Well, your link table is not a link table. It is a distinct entity. So you will need to create another class and mapping and make two many-to-one relationships between this new entity and the classes it relate; you should also have inverse one-to-many reference on the attribute(s) that would hold the many-to-many relationship.

thanks