- From: Ruben Verborgh <ruben.verborgh@ugent.be>
- Date: Wed, 19 Mar 2014 15:28:43 +0000
- To: Martynas Jusevičius <martynas@graphity.org>
- Cc: Olaf Hartig <ohartig@uwaterloo.ca>, Linked Data community <public-lod@w3.org>, "semantic-web@w3.org Web" <semantic-web@w3.org>
Hi Martynas, I'm fully with Olaf here, except for two side-remarks: >> How does LDF compare to [SQUIN]? > > I understand LDF more as an alternative practice for publishing (Linked) data > on the Web. However, the primary purpose for proposing this practice (as Ruben > and his colleagues emphasize in their LDOW paper) his to facilitate > distributed querying without putting most of the burden on the servers. So distributed querying is indeed an important part of what we want to achieve. In general: SQUIN: solving queries through Linked Data dereferencing Linked Data Fragments: publishing Linked Data in a low-cost, queryable way Linked Data Fragments: client: solving queries through Linked Data Fragments > So, the primary difference between querying LDFs and the aforementioned Linked > Data query processing is that querying LDFs is a form of distributed query > processing, that is, some part of the execution of a given user query is > distributed to LDF servers (which provide a limited form of query processing > functionality). In contrast, Linked Data query processing is _not_ a form of > distributed query processing. Instead, for Linked Data query processing > approaches, the whole execution of a query happens within the Linked Data > query processing system (e.g., SQUIN), simply because these approaches do not > assume / rely on server-side query processing functionality (servers in this > setting are only required to answer URI lookup requests). Here, it depends on how you define "querying". You could say that a regular Linked Data server offers querying, because you give it a URI, and it will look up the resource associated with that URI. So in that sense, regular Linked Data servers offer a { <s> ?p ?o } querying interface. For instance, few would disagree that http://dbpedia.org/page/Barack_Obama is the result of querying. For another definition, you could say that basic Linked Data Fragment servers _don't_ do querying: they just offer a finite set of resources you can retrieve. Only it's not dereferencing, but a little more flexible. Or you could say they do offer { ?s ?p ?o } querying; depends on how you look at it. But note that basic LDF servers do not necessarily need a query processor; they might as well offer a set of pre-generated HTML files. So the main difference with regular Linked Data servers is that basic Linked Data servers offer a more specific interface that just HTTP dereferencing; each basic Linked Data Fragment is subject to these constraints: - they offer data corresponding to a triple pattern - they offer the total count of all patterns that match the triple pattern - they offer hypermedia controls to all basic LDFs of the same dataset Best, Ruben
Received on Wednesday, 19 March 2014 15:29:25 UTC