Very interesting, thank you. To give a little more detail, I will share a quote from their whitepaper:
'Sovrin utilizes a “public permissioned” distributed ledger design (Fig 4). The easiest analogy is to the global ATM network: anyone can use an ATM (public), but only those who’ve been given special permission can add a new ATM to the ATM network (permissioned). With the Sovrin Identity Network, it is the Sovrin Foundation that grants permission for “nodes” (akin to ATMs in the metaphor) to join the network.'
[0] https://sovrin.org