[Model] Create Entity data type for cross-entity relationships

[luis100]

A entity can have a property which is a relation to another entity. For example, the entity Repository can have the following properties with type Entity:

• Content (which is the content profile of the repository)
• Events (which is the information to come from the Report API)

The relations can be bi-directional, repository can point to content and content to repository.

@peshkira This can also be used to relate format distribution within content profile with formats or do we need a entity-integer dictionary data type?

[peshkira]

I think EntityInteger Dictionary or even StringInteger Dictionary is better and simple for the distributions because the introduction of the new Entity FormatDistribution won't spare us the dictionaries.
It will be ContentProfile -> FormatDistribution -> (still needs dictionary to represent the triples)

Don't you think? However, if there is another advantage on the core side, I don't mind changing the adaptor

[luis100]

I think that making to many entities and entity types will make the knowledge base too confusing and impossible to browse on.

Nevertheless, there is a problem with the EntityInteger Dictionary approach, as there is no assurance that a format that is detected on the content profile will exist as a format. Actually, it should be the DataLinker that creates this relationships when available, but not really sure on how to represent this information...

[peshkira]

I agree with both arguments.
The problem with the current profile is, that it shows the format distribution (but does not include the format version).
I can improve that in the next version as I have also the mime and the format version. Until then, I will say we use the current dictionary (String String), or a new one.