-Overwriting: Until now, SEXTANTE algorithms could just generate new layers and never modify existing ones. While this is a good idea most of the times, in certain cases it must be better to just alter an input layer instead. This is the case, for instance, with the "calculate geometrical properties of polygons", which adds new fields to the attributes table of a vector layer. I have done some changes to take that into account, so algorithms now can define a link between input layers and output ones. If such a link exists, the parameter setting dialog will give the option to overwrite the corresponding input layer instead of typing an output filename.
To make this easier, I have changed the output filename panel and its behaviour. Before this, it was just a text box with a small button. Clicking on the button caused the fiel selection dialog to appear, and the textbox contained the selected filename. A blank filename forced SEXTANTE to use a temporary filename.
Now, when you click on the button, you see a more complex dialog with several tabs. In the first tab, there are two buttons: one to select a temporary output file and another one to overwrite the corresponding input, in case it is possible. The second tab is used to select a filename. More tabs can be easily added, defining different ways of storing the resulting layer. In the case of vector layer, a "database" tab appears. However, this is not functional yet, but will allow the user to select a database table as the destination for the layer to create.
The overwrite functionality is compatible not only with file-based outputs, but also with other ones, like databases. I still have to solve what happens when a layer that cannot be overwritten is selected as input, and other similar small issues. Apart from that, I think that this is also a great advance in SEXTANTE and opens many new possibilities. Once this is fully functional, I will have to adapt some algorithms, but I hope that it will not take long to do.
These functionalities (the ones detailed in this post) come mostly from the suggestions from the Deputacion de Pontevedra, who needs this kind of capabilities for their work and pointed us in the right direction (apart from funding the project that resulted in the implementation of this ideas!), so we would like to thank them for their suppport.