Re: Understanding linked data fragments

Hi Nathan,

> What I don't understand though is that, from the LDF spec itself, it says:
> 
> "A Linked Data Fragment of a Linked Data dataset is a set of RDF triples that consists of three parts:
> data: all triples of this dataset that match a specific selector;
> metadata: triples that describe the dataset and/or the Linked Data Fragment;
> controls: hypermedia links and/or forms that lead to other Linked Data Fragments."

Linked Data Fragments is a view that was created post-factum:
i.e., SPARQL, data dumps, Linked Data documents, existed already.
But we can retrofit, for instance, the SPARQL interface into Linked Data Fragments.
We do this exercise for common interface types here:
http://www.hydra-cg.com/spec/latest/linked-data-fragments/#existing-linked-data-fragments
However, we cannot (and do not) change their format.

> I guess I'm confused about the relationship of TPF to LDF because the above description is what I thought I was describing in the last part of my previous message: "And the standardized response format (LDF) facilitates the universal applicability of any smart client built around it."

Triple Pattern Fragments are one possible interface to Linked Data;
hence, they can be described using the Linked Data Fragments view.

In contrast to other interfaces, TPF was made after LDF,
so we can use the LDF conceptual framework (data / metadata / controls)
to define and describe TPF.

> Is a TPF therefore just a specific LDF response format?

A Triple Pattern Fragments is a specific Linked Data Fragment, where "specific" means:
- its data consists of (a page of) triples matching a triple pattern
- its metadata consists of an estimated total match count
- its controls give access to all other TPFs of the same dataset.

I.e., from http://www.hydra-cg.com/spec/latest/triple-pattern-fragments/#aim-scope-and-intended-audience:

>> This document defines Triple Pattern Fragments, a Linked Data Fragments type, by specifying their representation and effect on the application state. This allows to publish and consume Linked Data through a Triple Pattern Fragments interface.

In other words: Triple Pattern Fragments are a subclass of Linked Data Fragments.

> the following sentence in the LDF spec - "The goal of Linked Data Fragments is to provide a uniform view on all possible interfaces to Linked Data" - suggests that LDF simply defines the composition of any response that qualifies as LDF, of which TPF would be just one.

Yes, that interpretation is correct.

> Perhaps the confusion was in my use of the word "format"?

Maybe, yes!
Because a data dump is a Linked Data Fragment,
a Linked Data document is a Linked Data Fragment,
a SPARQL endpoint response is a Linked Data Fragment.

In that sense, the response _format_ is not standardized,
as it can take any shape. We can however, in an abstract sense,
view each response as a combination of data/metadata/controls.

Triple Pattern Fragments provide a concrete implementation,
in which we do know what the response will look like.

However:
> the standardized response format (LDF) facilitates the universal applicability of any smart client built around it.

is thus hard to say, because LDF itself does not specify any concrete format.

Hope that makes things clear; if not, continue asking :-)

Best,

Ruben

Received on Friday, 6 February 2015 11:44:17 UTC