"SOM clustering: Conversion of non-numeric attributes to numeric?"

As you might have seen in my other posts, I'm trying to perform Clustering of the data using SOM method. I'm able to generate the Clusters. But, I assume that to create meaningful clustering, I'll have to convert all the non-numerical attributes (categorical, timestamp) to the numeric attributes without affecting the meaning of those attributes while deciding the cluster. Is my understanding correct? What is the support from Rapidminer for doing that?
What are the operators I have to use, to achieve that?