What Up With Linked Data Platform

downstairs
December 11, 2012

Eric Prud'hommeaux, <eric@w3.org>
- Sanitation Engineer, W3C

Intro

Excipientia is starting into the antidepressant business with Damitol™.
They're tracking marketing and outreach todo lists.
Entries include domain-spefific details on coatings and packaging.
Also interoperates with supply chain management tools.

@prefix o: <http://pharma.example/data/> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
@prefix dcterms: <http://purl.org/dc/terms/> .
[] a o:ExploitationOpportunity ; dcterms:title "sad folks" ;
   o:appraisal 10000000.00 ; dcterms:date "2012-01-01"^^xsd:date .

Approaches

SOAP protocol -- Create a web service with a detailed domain-specific interface.
(probably backed by a relational database.)
SPARQL protocol -- Put stuff in a triple store. Clients issue SPARQL requests.
REST protocol -- transport information as Web documents, access with AtomPub.
SemWeb protocol -- transport information as RDF documents, access/manipulate with HTTP verbs.

SemWeb protocol

server creates/hosts new data.
server provides effective indexing/access.
client manages "containers" of POSTed data.
server manages any replication.
server manages any ACID transactions.

Needn't be backed by triple store.

Geneology

IBM et al decide to interface on data patterns instead of procedures.
http://open-services.net/
data manipulation for REST-heads instead of SPARQL-heads.

Linked Data

re-hash of old RDF best practices. ← controversial statement
emphasizes the use of HTTP verbs to GET and manipulate graphs.

Linked Data Basic Profile

LD Resources

subset of XSD:
{boolean, date, dateTime, decimal, double, float, integer, string, XMLLiteral}.
blue types are required by SPARQL.
encourage certain vocabs: Dublin Core (RDF, RDFS).
obvious GET/PUT/DELETE behavior, no POST behavior (SPARQL GSP appends).

LD Containers

membership: bp:membershipSubject , bp:membershipPredicate
paging: bp:Page , bp:pageOf , bp:nextPage
POST to add entries.

User Storie

http://www.w3.org/2012/ldp/wiki/Use_Cases_And_Requirements

Issues

http://www.w3.org/2012/ldp/track/issues/open

10 ETags.
11 sequestering of encouraged vocas (who controls dc:creator).
12,17,27 Patch-related (pretty relevent to SemWeb community).
28 ACID commit/rollback.
30,36 containers of containers.
34 containership (bulk erase vs. move R1 from C1 to C2 without breaking R1).

(sort of) implementable in SPARQL

https://github.com/ericprud/SWObjects/blob/sparql11/tests/test_LDP.cpp#L306

PREFIX container: <http://example.org/netWorth/nw1/assetContainer>
PREFIX page: <http://example.org/netWorth/nw1/assetContainer?p=>
PREFIX membership: <http://example.org/netWorth/nw1>
PREFIX asset: <http://example.org/netWorth/nw1/assetContainer/>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX dcterms: <http://purl.org/dc/terms/>
PREFIX bp: <http://open-services.net/ns/basicProfile#>
PREFIX o: <http://example.org/ontology/>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>

DELETE    { GRAPH ?LastTail { ?LastTail bp:nextPage ?NewNil } }
INSERT    {
  GRAPH ?LastTail { ?LastTail bp:nextPage ?NewTail }
  GRAPH ?NewTail {
    container: a bp:Container ;
        dcterms:title "The assets of JohnZSmith" ;
        bp:membershipSubject membership: ;
        bp:membershipPredicate o:asset .
      ?NewTail a bp:Page ; bp:pageOf container: .
  }
  GRAPH ?CurTail {
      ?CurTail bp:nextPage rdf:nil .
      membership: a o:NetWorth ; o:asset ?NewObj .
      ?NewObj a ?type ; dcterms:title ?title ; o:value ?value
  }
  GRAPH ?NewObj { ?NewObj a ?type ; dcterms:title ?title ; o:value ?value ; dcterms:date ?date }
}
CONSTRUCT { ?NewObj a ?type }
WHERE     {
  ?oldObj a ?type ; dcterms:title ?title ; o:value ?value ; dcterms:date ?date
  BIND (ldp:newObj  (asset:a) AS ?NewObj)
  BIND (ldp:lastTail(container:, membership:, o:asset, 4) AS ?LastTail)
  BIND (ldp:newTail (container:, membership:, o:asset, 4) AS ?NewTail)
  BIND (ldp:newNil  (container:, membership:, o:asset, 4) AS ?NewNil)
  BIND (ldp:curTail (container:, membership:, o:asset, 4) AS ?CurTail)
}

Page Management SPARQL

POST

@prefix o: <http://example.org/ontology/> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
@prefix dcterms: <http://purl.org/dc/terms/> .
[] a o:Stock ; dcterms:title "IBM" ;
   o:value 100.00 ; dcterms:date "2012-01-01"^^xsd:date .

match

  ?oldObj a ?type ; dcterms:title ?title ; o:value ?value ; dcterms:date ?date
  BIND (ldp:newObj  (asset:a) AS ?NewObj)
  BIND (ldp:lastTail(container:, membership:, o:asset, 4) AS ?LastTail)
  BIND (ldp:newTail (container:, membership:, o:asset, 4) AS ?NewTail)
  BIND (ldp:newNil  (container:, membership:, o:asset, 4) AS ?NewNil)
  BIND (ldp:curTail (container:, membership:, o:asset, 4) AS ?CurTail)

(pivoted) results by page

attr	1st value	last on page	first on new page
?oldObj	_:b1	_:b1	_:b1
?type	o:Stock	o:Stock	o:Stock
?NewObj	asset:a1	asset:a4	asset:a5
?LastTail	page:1	page:1	page:2
?NewTail	NULL	NULL	page:2
?NewNil	NULL	rdf:nil	NULL
?CurTail	page:1	page:1	page:2

vs. Graph Store Protocol

Comparing operations on a LDP Container and a GDP endpoint.
details at http://www.w3.org/2012/ldp/wiki/ISSUE-37

operation	SPARQL GSP	LDP
POST /interface/	create new graph G return 201/204, Location: G	create new graph G return 201, Location: G
PUT /interface/	new graph G return 201, Location: G
GET G	return 200, G	return 200, G
PUT G	return 200, replace G	return 200, replace G
DELETE G	return 200, delete G	return 200, delete G
GET /interface/	SPARQL service description graph	return 200, page1 with ref to G

Miscegenation

Can an LDP Container and a GDP endpoint cohabitate?

Sure, they just need to know which they are.

Multiple Personality Disorder

Can one endpoint be both an LDP Container and a GDP endpoint?

Conflicts on:

GET - page info vs. undefined -- so OK.
POST - paging maintenance -- so not OK.

Discussion

use cases
approaches
resources
containers
alternatives