Slug = sluggified version of the taxon name.
Permalink = is meant to be like PHPCR node name.

So for a hierarchy Category -> Men -> T-Shirts.
Slug = "t-shirts"
Permalink = "category/men/t-shirts"

Currently the permalink generation is kinda broken, I plan to introduce a separate service which will handle this.

The slug should be unique inside the particular taxonomy. I think that the "permalink" would be redundant with the phpcr node name, right? That being said, we need it for the ORM / other implementations.