# Re: Some reflections on the semantics of embedded triples

• From: Dörthe Arndt <doerthe.arndt@ugent.be>
• Date: Mon, 30 Nov 2020 16:22:43 +0100
• Message-ID: <a7132e16-a27c-31c1-9b53-cc1fe3214776@ugent.be>
```Dear Antoine,

> In the current semantics, blank nodes that appear in embedded triples
> are behaving differently from blank nodes outside. This leads to
> peculiarities of semantics with possibly unforseen consequences.
>
> TL;DR: In short, blank nodes inside embedded triples can be understood
> as "placeholders", as opposed to existentials when they are outside
> embedded triples.

I would not say that they are placeholders,  the idea was originally to
let them be quantified outside of the embedding.

Taking  your example from below,  the question is whether a triple

:mike :says <<_:x :in :house >>.

should mean (in pseudo FOL, I  am aware  that the below has  no actual
meaning, but I hope you still get the idea)

∃x: says(mike, in(x, house))

"There is someone (or  something) about whom Mike  says that he is in house"

or

says(mike, (∃x: in(x, house)))

"Mike  says that someone (or something) is in house."

so, it is important to decide where exactly the blank node would be
quantified.

If  we choose the first option,  the blank nodes occurring in the
"normal" RDF graph correspond to the referred blank nodes with the same
name. So, if there is  for example a person of which  mike says that he
is in house, we could  state;

_:x a :Person.
:mike :says <<_:x :in :house >>.

and the two occurrences of _:x would actually refer to the same instance.

In the second interpretation, the blank node would have local scope and
the two _:x could refer to two different domain elements. The second
interpretation would reflect the situation that Mike  actually stated
that there is someone in house. So, if we have  a graph of statements
from Mike and that  graph contains the triple _:x :in :house.

Both interpretations have  advantages, but we have to choose one of
them.  I would say that choice should depend of our  intended use of
RDF*. So far I understood from the discussions that a correspondence
between a blank node in an embedded triple and a "normal" triple  is
what we want.  To get that we have to give up the local quantification.

But I guess  we will have the discussion anyway when it comes to the
discussion of examples containing bank nodes in our next meeting.

Kind regards,
Dörthe
```

Received on Monday, 30 November 2020 15:23:00 UTC