I get the following error when attempting to create a one to many relationship between 2 classes
SAXParseException: Attribute "column" must be declared for element type "one-to-many".
I'm pretty new to Hibernate. I'm using hibernate 2.1. What am I doing wrong?

<hibernate-mapping>
<class name="com.aaa.bbb.dao.Query_Group" table="titan.Query_Group">
<id name="id" column="query_group_id" type="long">
<generator class="increment"/>
</id>
<property name="interval" />

<set name="Queries" table="titan.Report_Query">
<key column="query_group_id"/>
<one-to-many column="group_id" class="com.aaa.bbb.dao.ReportQuery"/>
</set>
</class>
</hibernate-mapping>


public class Query_Group {
private long id;
private String interval;
private Set queries = new HashSet();

public Set getQueries() {
return queries;
}

public void setQueries(Set sQueries) {
queries = sQueries;
}

public long getId() {
return id;
}

public void setId(long query_group_id) {
this.id = query_group_id;
}

public String getInterval() {
return interval;
}

public void setInterval(String interval) {
this.interval = interval;
}
}

public class ReportQuery {

private long id;
private long group_id;
private String name;
private String description;

public long getId() {
return id;
}

public void setId(long id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public String getDescription() {
return description;
}

public void setDescription(String description) {
this.description = description;
}

public long getGroup_id() {
return group_id;
}

public void setGroup_id(long query_group_id) {
this.group_id = query_group_id;
}
}

Nobody knows???