10 basic rules to overcome ontology engineering deadlocks in
collaborative ontology engineering tasks
Why do they call it Linked Data when they want to say?
Keynote atThe 6th International Workshop on Consuming Linked
Data (COLD)12/10/2015Oscar
[email protected]@ocorchohttps://www.slideshare.com/ocorcho
The four Linked Data publishing principles established in 2006
seem to be quite clear and well understood by people inside and
outside the core Linked Data and Semantic Web community. However,
not only when discussing with outsiders about the goodness of
Linked Data but also when reviewing papers for the COLD workshop
series, I find myself, in many occasions, going back again to the
principles in order to see whether some approach for Web data
publication and consumption is actually Linked Data or not. In this
talk we will review some of the current approaches that we have for
publishing data on the Web, and we will reflect on why it is
sometimes so difficult to get into an agreement on what we
understand by Linked Data. Furthermore, we will take the
opportunity to describe yet another approach that we have been
working on recently at the Center for Open Middleware, a joint
technology center between Banco Santander and Universidad
Politcnica de Madrid, in order to facilitate Linked Data
consumption.
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Why do they call it Linked Data when they want to say? by O.
CorchoNon-commercialShare-Alike
MotivationI want to consume Linked Data. What do I use?
SQUINLinked Data PlatformLinked Data FragmentsJSON-LDCSV on the
WebSPARQL endpoints
Outline of the talkWhere do we start from?A few examples of
applications that we have built by consuming RDF
Application 1. 3cixty
http://www.3cixty.com/
3cixty. Planning our visit to a city
3cixty. Exploiting the wishlist while in the city
Check it at the poster and demo session, for the Semantic Web
Challenge
Application 2. Geomarketing
Application 3. Buyer profile at Zaragoza
http://www.zaragoza.es/ciudad/gestionmunicipal/contratos/
Application 4. Smart Developer Hub
http://www.smartdeveloperhub.org/
How are all these applications built?ApplicationHow is data
stored & published?How is data consumed?3cixtyCentralised
SPARQL endpointLinked Data (Virtuoso)SPARQL queries (webapp)Ad-hoc
API (mobile app) Linked Data (not used yet)Geomarketing
Centralised SPARQL endpointLinked Data (ELDA)Linked DataAd-hoc
API for RDF Data CubeBuyer profile at Zaragoza
Oracle DBLinked Data (ad-hoc software)SOLRCentralised SPARQL
endpointLinked DataSOLRSPARQL for complex queries????
Outline of the talkWhere do we start from?A few examples of
applications that we have built by consuming RDFQuiz time: what do
we understand by Linked Data?
What do papers in COLD tell us about Linked Data?KR2RML: An
Alternative Interpretation of R2RML for Heterogenous
SourcesLeveraging Linked Data to Infer Semantic Relations within
Structured SourcesLOTUS: Linked Open Text UnleaShedOptimizing RDF
Data Cubes for Efficient Processing of Analytical Queries
Pattern-Based Linked Data Publication: The Linked Chess Dataset
CasePolicies Composition based on Data Usage Context Towards
Crawling the Web for Structured Data: Pitfalls of Common Crawl for
E-Commerce Uniqueness, Density, and Keyness: Exploring Class
Hierarchies
TopicsMakes use of Linked Data principles, including
dereferencingInvolves direct use of multiple, real-world Linked
Datasets
Linked Data principlesUse URIs as names for things Use HTTP URIs
so that people can look up those names. When someone looks up a
URI, provide useful information, using standards (RDF, SPARQL)
Include links to other URIs, so that they can discover more
things
Quiz time
What is Linked Data for you?
Quiz 1. Is this Linked Data?
They call it API. Do they mean Linked
Data?http://www.zaragoza.es/docs-api/
16
Quiz 1. A few hintsLets try to runcurl -X GET --header "Accept:
application/x-turtle"
"http://www.zaragoza.es/api/recurso/urbanismo-infraestructuras/callejero/via?rf=html&results_only=false"
Or a more specific one for one streetcurl -X GET --header
"Accept: application/ld+json"
"http://www.zaragoza.es/api/recurso/urbanismo-infraestructuras/callejero/via/20?rf=html"
Then, what do we think about it?
Quiz 2. And what about this?
http://datos.localidata.com/recurso/comercio/Provincia/Madrid/Municipio/madrid/Local/Distrito/Label/Tetun
Quiz 2. A few more hintsHowever, this is giving me access to
lots of
URIshttp://datos.localidata.com/recurso/comercio/Provincia/Madrid/Municipio/madrid/Local/11029404L0-PlantaPB-Local214-ID36963
Which I could then use in order to start applying a Linked
traversal approach with bound subjects (e.g., as in SQUIN)
In summarySeveral approaches for Linked Data exposure that go
beyond pure Linked DataCombining REST APIs that provide you access
to lots of URIs with pure Linked Data approaches
Outline of the talkWhere do we start from?A few examples of
applications that we have built by consuming RDFQuiz time: what do
we understand by Linked Data?A summary of current Linked Data
consumption approaches
A summary of Linked Data consumption approachesStealing some
copyrighted material from the Linked Data Fragments folksThey will
surely be better than me explaining this ;-)
A summary of Linked Data consumption approaches
?
Outline of the talkWhere do we start from?A few examples of
applications that we have built by consuming RDFQuiz time: what do
we understand by Linked Data?A summary of current Linked Data
consumption approachesYet another approach: AGORAPlus some demos
(compulsory when talking about Linked Data)
Attention!!Ongoing workSneak-previewNo technical paper yetWe
have to sit down and write everything carefullyHighly driven by our
initial use caseNow in the process of generalising it
Our research hypothesisCan we go a bit beyond triple pattern
fragments whilemaintaining the good behaviour
server-side,exploiting Linked Data about subjects, andkeeping to
the Web paradigm?
Basic graph pattern fragments?
BGPs-lite, that is, BGPs with somerestrictionsThe Agora (/r/;
Ancient Greek: Agor) was a central spot in ancient Greek
city-states. The literal meaning of the word is "gathering place"
or "assembly". [Wikipedia]
Our assumptions on BGPsBGPs composed of triple patterns
withSubjects are always variablesProperties must be URIsObjects can
be variables, URIs or literals (will only work with equality)Easy
extensions (not done because of lack of time)Allowing URIs as
subjectsExtending properties to property pathsAdding more types of
FILTERSDifficult extensions (need to think a bit more about
them)Properties as variablesPROCESSABLE{?x ci:codebase ?y}{?s
doap:name "jenkins" . ?s scm:hasBranch ?b}{?a ci:hasBuild ?b . ?b
ci:hasExecution ?c . ?c ci:hasResult ?d}
NOT PROCESSABLE{?x ?p "jenkins}{?x ?p ?y}
A few more assumptionsRDF data has been created according to
some vocabularyResources are typed ( a )Vocabularies may be
lightweight or heavyweightHowever, we are not exploiting all types
of domain and range restrictions, or inferences, yet
Step 1. Provide some vocabularies to use for planningTell AGORA
(our fountain) which are the vocabularies that it has to
understandNote: relevant for the production of query plans
Post to http://localhost:9001/vocabs the OWL fileLets check the
resultshttp://localhost:9001/typeshttp://localhost:9001/properties
Step 2. Provide/get some seed URIs to start query plansTell
AGORAs seed collector which are the seeds that it can take to start
the link traversal approachNote: those seed URIs need to be
connected to all dataStored in redis
Post to http://localhost:9001/seeds every seed URIOne may be
enough if it provides access to other URIsLets check the
resultshttp://localhost:9001/seeds
Step 2. Provide/get some seed URIs to start query plansSeeds may
be obtained from a list of URIs, queries to SPARQL endpoints,
ad-hoc wrappers, etc.
Step 3. Obtain a query/search planRequest a query plan to AGORAs
planner, for a given graph pattern
Lets check the resultshttp://localhost:9001/plan?gp={?a
ci:hasBuild ?b}
Step 3. Obtain a query/search plan[] a agora:SearchTree ;
agora:fromType ci:CIHarvester ; agora:hasSeed ; agora:length 1 ;
agora:next [ agora:byPattern _:tp_0 ; agora:expectedType
ci:CIHarvester ] .
[] a agora:SearchSpace ; agora:definedBy _:tp_0 .
_:var_a a agora:Variable ; rdfs:label "?a"^^xsd:string .
_:var_b a agora:Variable ; rdfs:label "?b"^^xsd:string .
_:tp_0 a agora:TriplePattern ; agora:object _:var_b ;
agora:predicate ci:hasBuild ; agora:subject _:var_a .
Lets check the resultshttp://localhost:9001/plan?gp={?a
ci:hasBuild ?b}
Lets check this URI
Looking up for that URI
Step 3. Obtain a query/search plan[] a agora:SearchTree ;
agora:fromType ci:CIHarvester ; agora:hasSeed ; agora:length 52 ;
agora:next [ agora:byPattern _:tp_2 ; agora:expectedType
ci:CIHarvester ; agora:next [ agora:byPattern _:tp_0 ;
agora:expectedType ci:Build ; agora:next [ agora:byPattern _:tp_1 ;
agora:expectedType oslc_auto:AutomationRequest ] ; agora:onProperty
ci:hasExecution ] ; agora:onProperty ci:hasBuild ] .
[] a agora:SearchSpace ; agora:definedBy _:tp_0, _:tp_1, _:tp_2
.
_:var_a a agora:Variable ; rdfs:label "?a"^^xsd:string .
_:var_d a agora:Variable ; rdfs:label "?d"^^xsd:string .
_:tp_0 a agora:TriplePattern ; agora:object _:var_c ;
agora:predicate ci:hasExecution ; agora:subject _:var_b .
..Lets check the results of a more complex
queryhttp://localhost:9001/plan?gp={?a ci:hasBuild ?b . ?b
ci:hasExecution ?c . ?c ci:hasResult ?d}
What is a query/search plan for a BGP?Composed by:A set of seed
URIsA set of search pathsWhat is a seed URI?The subject of one of
the triples contained in the AgoraWhat is a search path?A finite
and executable queue of search stepsIts execution starts by
dereferencing the seed URIs, which initializes theset of
query-relevant triples
property 1...property N
Step 4. Evaluate the query plan by dereferencing
Lets check the resultshttp://localhost:9001/fragment?gp={?a
ci:hasBuild ?b}
Lets now do a demo with dbpediaYeah, all this was working in a
controlled environment. What about Dbpedia?Obviuosly, DBpedia
understood from a pure Linked Data perspective.
We will open a brand new AGORA and will tell it to understand
about movies
A few operations to be doneFirst of all, load the vocabulary in
AGORA and provide a few seedsThrough a SPARQL query to DBpedia, but
could be a list of URIsThen, we can start
inspectinghttp://localhost:9000/graph/
http://localhost:9000/typeshttp://localhost:9000/propertiesLets
start queryingFirst lets see a
plan:http://localhost:9000/plan?gp={?f%20dbpedia-owl:starring%20?a}http://localhost:9000/plan/view?gp={?f%20dbpedia-owl:starring%20?a}And
then execute the query
A few other queriesGet all relations between the films and the
actors who star on themhttp://localhost:9000/fragment?gp={?f
dbpedia-owl:starring ?a}Same as previous query, but also getting
the name of these actorshttp://localhost:9000/fragment?gp={?f
dpedia-owl:starring ?a. ?a dbp:birthName ?n}Get all films, their
distributors and known locations of each
themhttp://localhost:9000/fragment?gp={?f dbpedia-owl:distributor
?d. ?d dbpedia-owl:location ?l}
Outline of the talkWhere do we start from?A few examples of
applications that we have built by consuming RDFQuiz time: what do
we understand by Linked Data?A summary of current Linked Data
consumption approachesYet another approach: AGORAPlus some demos
(compulsory when talking about Linked Data)Where do we go next?
Whats next for AGORA?An additional bit of engineeringExtending
to other parts of SPARQLExploiting caching even
morePaginationBuilding the vocabularies automatically for all those
cases where there is no vocabulary (using LOUPE)etc.(basically, all
those things already very well done by LDF)SPARQL UpdatesSome
Linked Data Platform (ldp4j) technology behind the scenesSitting
down to write everything carefullyThe whole frameworkThe query
planning algorithmEvaluations and comparisons with other
approachesIs this approach really worth it?
What have we been talking about?
WAIT FOR OUR PAPER TO BE PUBLISHED
And now the main conclusionsConsumption of Linked Data is
normally associated to SPARQL querying over some dataset of the LOD
cloudMy feeling after having read many papers that talk about
Linked Data consumptionNothing against that (look at the original
examples that I gave earlier), but we have to understand, as a
community, whether there are any challenges that pure Linked Data
approaches allows performing betterWhy do all people talk about
REST APIs and we dont?So, more work needed onApproaches that
exploit the features of pure Linked Data (e.g., SQUIN and Linked
Traversal querying)Approaches that exploit the Web dimension
infrastructure (e.g. Linked Data Fragments)
Conclusions (II)We should continue exploring this space
But probably these dimensions are not enough
And many open challenges stillFederated query processing
techniques (adaptive)
AGORA
And the last (bonus) slide
And this is what you should remember from the talk
Source: "Linking Open Data cloud diagram 2014, by Max
Schmachtenberg, Christian Bizer, Anja Jentzsch and Richard
Cyganiak. http://lod-cloud.net/"
Why do they call it Linked Data when they want to say?
Acknowledgements to the SDH team at the Center for Open
Middleware:Fernando Serena, Carlos Blanco, Alejandro Fernndez,
Alejandro Vera, Miguel Esteban, Andrs Garca, Javier Soriano,
Asuncin GmezOscar
[email protected]@ocorchohttps://www.slideshare.com/ocorcho
