Construct XML Map Iteration Rules

In an XML Map transform, iteration rules define how the output data set for the selected output schema is calculated.

An iteration rule is associated only with a repeatable target node, and defines how to construct the instances of the target schema from the source data. It is a mechanism to specify the input data sets and the way to combine them to create the target data set.

In the iteration rule tab, a hierarchical tree represents the logical combination of operations and input schemas that form a rule. Each operation in the rule is displayed as a node and may contain other operations or input schemas as children.

Use the iteration rule tab to create iteration rules for each repeatable schema in your output:

Adding a new element to a rule

From the Create icon, choose Create Rule Operator and specify the type of operation to perform.

Elements that can be added to an iteration rule include the following:

Element	Description
INNER JOIN	Performs a SQL INNER JOIN on the sources. Create the expression to use for the join condition in the On area of the Iteration Rule tab. When you create the expression, you can use the following types of columns: Source columns from the sources under the current operation and the left side of the current iteration rule tree. Source columns from the sources that appear in the iteration rules associated with the parent schemas of the selected target schema. Target columns from the parent schemas of the selected target schema. Restriction When using a source column, the path from the column being used to the source schema must contain no repeatable schemas. Restriction When using a target column, it must be a scalar column and descend from the parent schema of the selected target schema. In addition, the path from the parent schema to the target column must contain no repeatable schemas.
LEFT OUTER JOIN	Performs a SQL LEFT OUTER JOIN on the sources. Create the expression to use for the join condition in the On area of the Iteration Rule tab. When you create the expression, you can use the following types of columns: Source columns from the sources under the current operation and the left side of the current iteration rule tree. Source columns from the sources that appear in the iteration rules associated with the parent schemas of the selected target schema. Target columns from the parent schemas of the selected target schema. Restriction When using a source column, the path from the column being used to the source schema must contain no repeatable schemas. Restriction When using a target column, it must be a scalar column and descend from the parent schema of the selected target schema. In addition, the path from the parent schema to the target column must contain no repeatable schemas.
* - Cross operation	Performs a Cartesian product of two or more sources. When the sources have no parent-child relationship, the behavior is the same as a standard SQL CROSS JOIN. When the sources have a parent-child relationship, the Cartesian operation provides a mechanism to iterate through all instances of the repeatable elements identified by the source schemas in the operation in the document order.
\|\| - Parallel operation	Combines corresponding rows from two or more sources to generate the output set. For example, the first rows in a pair of input tables are combined to become the first row of the output set, the second rows are combined to become the second output row, and so on. If the sources have different numbers of rows, the output set will contain the same number of rows as the largest source. For extra rows in the output set that contain data from only one source, the additional columns that would contain data from the other sources are considered empty. Note The Parallel operation is not a standard SQL operation.
Available input schemas

Note

There is no limit to the number of sources that may be used in an iteration rule.

Automatic rule generation

The iteration rule can be generated automatically. After you have created mappings for the columns under the selected target schema, select Propose rule in the Iteration Rule tab. The software generates the iteration rule tree. Always validate that the generated iteration rule matches your requirements. Modify the rule as needed, and add the ON condition expression when appropriate.

Remember

Automatic rule generation is a best-guess function. For example, the software cannot know the ON condition, or whether to use INNER JOIN or LEFT OUTER JOIN. Use the automatic rule generation as a guide and always verify that the iteration rule that it creates fits your needs.