SP and SA Databases
The not-so-current documents
describe the concept of the Security Policy and Security Association databases.
Here is an example of how the SP and SA reference each other:
As can be seen from the example, all interfaces share common SPs. An interface can have specific SPs, also. All the common SPs must be entered before the specific SPs. This is accomplished by having all the common SPs entered with smaller SP index values than the specific SPs.