In order to keep in line with the self contained concept, scm dependencies should be kept to a minimum. The only dependency that an scm should have is one of the large toolkits or maybe python. Things like alsa/OSS, flash, are optional and can just be mentioned in the info file. The team has agreed that no tcz's should be in the dep file of an scm, only other scms can be included. Below is the current list of allowed dependencies. In the future, other candidates will be judiciously considered.
python2.7.scm, python3.2.scm, gtk2.scm, gtk3.scm, qt4.scm (if and when it materializes).
These are the allowed set of deps, but is always ok to build these toolkits into any scm to eliminate any external dependency. With TC, we have a challenge in creating self contained apps that is not seen in larger distros, since things like gtk2/gtk3, qt, python, perl, etc, etc are usually part of what larger distros consider their standard system. Therefore our making use of a shared scm of a large toolkits makes the self contained process easier and more efficient in their creation and runtime use.