In the item descriptor provided, what is the column book_index used for?
<item-descriptor name = “author”>
<table name = “PRJ_AUTHOR” type = “primary” id-column-name = “ID”>
<property name = “id” column-name = “ID” data-type = “string”/>
<property name = “Last Name” column-name = LAST_NAME”
data-type = “string”/>
</table>
<table name = “PRJ_BOOK_AUTHORS” type = “multi”
id-column-name= “AUTHOR_ID” multi-column-name= “Book_inDEX”>
<property name = “booksWritten” data-type = “list”
Component-item-type = “book” column-name = “book_id”/>
</table>
</item-descriptor>
A.
It is used for storing the databaseindex of the books table.
B.
It is used for storing the sequence of books by the author.
C.
It is used to store the primary key of the prj_book_author table as the author_id column is not
unique.
D.
It is a reference to auxiliary table not presentinthis item descriptor that stores the values.
E.
It is a legacy field and not used.
Explanation:
The multi-column-name attribute ensures that the ordering of the multi-values are
maintained. The column specified by the multi-column-name attribute is used for multi-valued
properties of data type array, map, and list and is not used for sets (which are unordered). For
map type properties, the values in the column specifiedy by the multi-column-name attribute must
be a string. For list or array type properties, these values should be an integer or numeric type,
and must be sequential.