The TScPolicyMapping class corresponds to a single policy mapping.
The following paragraph is taken from RFC 5280, section 126.96.36.199:
"The Policy Mappings extension is used in CA certificates. It lists one or more pairs of OIDs; each pair includes an IssuerDomainPolicy and a SubjectDomainPolicy. The pairing indicates the issuing CA considers its IssuerDomainPolicy equivalent to the subject CA's SubjectDomainPolicy."