The RDB DAS provides a straightforward mechanism for support of
OptimisticConcurrencyControl. To enable OCC a client must
designate an integer version column in the configuration
(usually via a config xml file). The following example is an
example of a cofig file that identifies a version column:
<Config xsi:noNamespaceSchemaLocation="http:///org.apache.tuscan
y.das.rdb/config.xsd" xmlns:xsi="">        <Command name="select
book 1" SQL="select * from BOOK where BOOK_ID = 1"
kind="Select"/>       <Table tableName="BOOK">         <Column
columnName="BOOK_ID" primaryKey="true"/>         <Column
columnName="OCC" collision="true" managed="true"/>  This line in
the config file <Column columnName="OCC" collision="true"
managed="true"/> designates the column named "OCC" as the
version column and also sets "managed" to true. The "managed"
attribute has to do with how the version column is changed. In
order for OCC to work, some agent must change the value of the
version column each time the row is modified. A new va