Annotopia: Creation/updates with Open Annotation (?)

I am currently developing the Annotopia Open Annotation server [GitHub, Living Slides, Talk 'I Annotate 2014'] and there are a few topics related to the application of the Open Annotation Model that might need further discussion within the community. I will start with one

:: Date/agent of annotation creation and update ::

Even if we don't have the need to support versioning (this will be subject of a future post) and in the unlikely event that the annotation cannot be edited we often need to be able to keep track of who/when the annotation has been created and, eventually, updated. 

Open Annotation Provenance Model

The Open Annotation Model now supports the following provenance relationships/properties:

Vocabulary Item	Type	Description
oa:annotatedBy	Relationship	[subProperty of prov:wasAttributedTo] The object of the relationship is a resource that identifies the agent responsible for creating the Annotation. This may be either a human or software agent. There SHOULD be exactly 1 oa:annotatedBy relationship per Annotation, but MAY be 0 or more than 1, as the Annotation may be anonymous, or multiple agents may have worked together on it.
oa:annotatedAt	Property	The time at which the Annotation was created. There SHOULD be exactly 1 oa:annotatedAt property per Annotation, and MUST NOT be more than 1. The datetime MUST be expressed in the xsd:dateTime format, and SHOULD have a timezone specified.
oa:serializedBy	Relationship	[subProperty of prov:wasAttributedTo] The object of the relationship is the agent, likely software, responsible for generating the Annotation's serialization. There MAY be 0 or more oa:serializedBy relationships per Annotation.
oa:serializedAt	Property	The time at which the agent referenced by oa:serializedBy generated the first serialization of the Annotation, and any subsequent substantially different one. The annotation graph MUST have changed for this property to be updated, and as such represents the last modified datestamp for the Annotation. This might be used to determine if it should be re-imported into a triplestore when discovered. There MAY be exactly 1 oa:serializedAt property per Annotation, and MUST NOT be more than 1. The datetime MUST be expressed in the xsd:dateTime format, and SHOULD have a timezone specified.

So we can encode when the annotation has been created and usually that coincides with the time when the user created the annotation on the user interface of the annotation client.

Then the annotation is sent to the server to be persisted.

Do nothing approach

One possible approach, that I would rather not advocate for, is to forget about the concepts of creation and update: 'every time a change is performed on an annotation, the old instance is swapped with the new one. The new one replaces entirely the previous annotation and shares the same URI.'. In this case, 'annotatedAt' is always referring to the latest annotation event (no matter if it was the original creation or following updates). 

Use a richer provenance model

To be a little more exhaustive, in Annotopia, as I was doing in Domeo and Annotation Ontology, I could use a series of properties of PAV (Provenance, Authoring and Versioning) ontology [paper]: pav:createdOn (when it has been created), pav:createdBy (who created it), pav:lastUpdateOn (when it has been last updated), pav:lastUpdateBy (who last updated the annotation).

So I could say:

Option A: Add lastUpdateOn

In this scenario we use annotatedAt/annotatedBy for the annotation creation and lastUpdateOn/lastUpdateBy for the last update.

{
    "@id" : "http://host/s/annotation/830ED7EE-BF7B-4A18-8AE1-A9AF96AC135B",
    "@type" : "oa:Annotation",
    "annotatedAt" : "2014-02-17T09:46:11EST",
    "annotatedBy" : {
      "@id" : "http://orcid.org/0000-0002-5156-2703",
      "@type" : "foaf:Person",
      "name" : "Paolo Ciccarese"
    },
    "pav:lastUpdateOn" : "2014-03-11T11:46:11EST",
    "pav:lastUpdateBy" : {
      "@id" : "http://example.org/johndoe",
      "@type" : "foaf:Person",
      "name" : "John Doe"
    }
...
}

In this case, both events would refer to when the act has been performed on the user interface (?).

Option B: Add createdOn and lastUpdateOn

Here we make use of annotatedAt/annotatedBy, createdOn/createdBy and  lastUpdateOn/lastUpdateBy

{
    "@id" : "http://host/s/annotation/830ED7EE-BF7B-4A18-8AE1-A9AF96AC135B",
    "@type" : "oa:Annotation",
    "pav:previousVersion" : "urn:temp:001",
    "annotatedAt" : "2014-02-17T09:46:11EST",
    "annotatedBy" : {
      "@id" : "http://orcid.org/0000-0002-5156-2703",
      "@type" : "foaf:Person",
      "name" : "Paolo Ciccarese"
    },
    "pav:createdOn" : "2014-02-17T09:48:11EST",
    "pav:createdBy" : {
      "@id" : "http://orcid.org/0000-0002-5156-2703",
      "@type" : "foaf:Person",
      "name" : "Paolo Ciccarese"
    },
    "pav:lastUpdateOn" : "2014-03-11T11:46:11EST",
    "pav:lastUpdateBy" : {
      "@id" : "http://example.org/johndoe",
      "@type" : "foaf:Person",
      "name" : "John Doe"
    }
...
}

In this case it is necessary to agree on the semantics of all those properties. I could use:
(i) 'createdOn/createdBy' for the original creation on the (Annotopia) server
(ii) 'lastUpdateOn/lastUpdateBy' for the last update on the (Annotopia)  server
(iii) and what is  'annotatedAt' going to indicate? The original creation or the latest update? And how do I keep track of the agents involved?