398 O. Povel and C. Giraud-Carrier
the intended object. A similar result is achieved in Weka’s new Knowledge Flow GUI, where sets of operations are listed as icons under context-sensitive tabs.
Furthermore, comments may be attached to all steps, thus allowing the user to record specific insight or clarification. Comment fields are absent from most DM software, yet they often prove essential in documenting the DM process, facilitating maintenance (changes to models, etc.) and knowledge transfer.
A small note on streams involving more than one pre-processing step is worth making. Although one is indeed able to apply pre-processing to a pre-processed step (i.e., some object in the Pre-processing panel), one should avoid doing so as only one object can be highlighted in the top-level stream. Hence, only one (here, the last one) of the pre-processing steps will be highlighted. Instead, one should use a single pre-processing step and edit it at will since each pre-processing step is essentially a sub-stream. There is nothing to be gained in functionality in having more than one pre-processing steps, since they are linked sequentially anyway, which can be handled at the sub-stream level (see Section 3.7).
Figure 4. Data Mining Streams