I'm a little confused about terminology in the Host Identity Protocol (HIP)
The two distinct terms Host Identity and Host Identifier are described in https://tools.ietf.org/html/rfc4423#section-3 (section 3.2) as
Host Identity | An abstract concept assigned to a 'computing platform'
Host Identifier | A public key used as a name for a Host Identity.
It is also described earlier
Each host will have at least one Host Identity, but it will typically have more than one. Each Host Identity uniquely identifies a single host; i.e., no two hosts have the same Host Identity. The Host Identity, and the corresponding Host Identifier, can be either public (e.g., published in the DNS) or unpublished. Client systems will tend to have both public and unpublished Identities. There is a subtle but important difference between Host Identities and Host Identifiers. An Identity refers to the abstract entity that is identified. An Identifier, on the other hand, refers to the concrete bit pattern that is used in the identification process.
It is stated "a Host Identity is an abstract concept" which is rather vague. What actually is it? It is also described that an "Host Identity uniquely identifies a single host", but not how. On the other hand a Host Identifier is very concret and easily understandable: It's a public key used as a name (identifier) for a host.
What also confuses me is that two books about HIP I started reading already got in wrong on the first pages. E.g. "Towards the secure mobile Internet": "The transport protocols use a cryptographic host identity instead of IP addresses." (whereas the Host Identifier should be used here, as it is cryptographic)
Also "Host Identity Protocol (HIP): Towards the Secure Mobile Internet Andrei Gurtov 2008 John Wiley & Sons, Ltd. ISBN: 978-0-470-99790-1" states on Chapter 1 Overview Page 1:
"HIP also includes security as an inherent part of its design, because its “host identities” are cryptographic keys that can be used with many established security algorithms"
Am I right in saying the books got in wrong? What actually is a Host Identity?