What is the basic difference between x. 509 and pgp in terms of key hierarchy and key trust?

In terms of key hierarchy, you have to request to a Certification Authority in order for them to issue you an X. 509 certificate. On the other hand, you can creat your own pgp.

In terms of key trust, X. 509 supports only a sole key owner. It can support only one digital signature to confirm the key's validity. This does not work for pgp.