Output Links

You can have any number of output links from your Transformer stage.

You might want to pass some data straight through the Transformer stage unaltered, but it's likely that you'll want to transform data from some input columns before outputting it from the Transformer stage.

You can specify such an operation by entering a BASIC expression or by selecting a transform to apply to the data. IBM® InfoSphere® DataStage® has many built-in transforms, or you can define your own custom transforms that are stored in the repository and can be reused as required.

The source of an output link column is defined in that column's Derivation cell within the Transformer Editor. You can use the Expression Editor to enter expressions or transforms in this cell. You can also simply drag an input column to an output column's Derivation cell, to pass the data straight through the Transformer stage.

In addition to specifying derivation details for individual output columns, you can also specify constraints that operate on entire output links. A constraint is a BASIC expression that specifies criteria that data must meet before it can be passed to the output link. You can also specify a reject link, which is an output link that carries all the data not output on other links, that is, columns that have not met the criteria.

Each output link is processed in turn. If the constraint expression evaluates to TRUE for an input row, the data row is output on that link. Conversely, if a constraint expression evaluates to FALSE for an input row, the data row is not output on that link.

Constraint expressions on different links are independent. If you have more than one output link, an input row might result in a data row being output from some, none, or all of the output links.

For example, if you consider the data that comes from a paint shop, it might include information about any number of different colors. If you want to separate the colors into different files, you would set up different constraints. You could output the information about green and blue paint on LinkA, red and yellow paint on LinkB, and black paint on LinkC.

When an input row contains information about yellow paint, the LinkA constraint expression evaluates to FALSE and the row is not output on LinkA. However, the input data does satisfy the constraint criterion for LinkB and the rows are output on LinkB.

If the input data contains information about white paint, this does not satisfy any constraint and the data row is not output on Links A, B or C, but will be output on the reject link. The reject link is used to route data to a table or file that is a "catch-all" for rows that are not output on any other link. The table or file containing these rejects is represented by another stage in the job design.