Expressing No-Value Information in RDF
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The document discusses the limitations of RDF and SPARQL in representing non-existence of information, introducing a no-value framework that characterizes empty queries and their implications. It presents a no-value theorem that connects the evaluation of BGPs to the emptiness of queries, and suggests that this framework can be implemented using standard semantic web tools for tasks like data cleaning. An example illustrates the application of the no-value statements in determining the non-existence of Obama's male children.
![Expressing No-Value Information in RDF
Fariz Darari, Radityo Eko Prasojo, Werner Nutt
Free University of Bozen-Bolzano, Italy
Problem Statement
Elizabeth I had no children
RDF cannot represent
non-existence of information
SPARQL cannot distinguish whether
a query returns the empty answer
due to possibly incomplete information or
non-existence of information
No-Value Framework
Definition: No-Value Statements
BGP-based statements
for declaring non-existence
Definition: Empty Queries
Queries that always give
the empty answer
Definition: Emptiness Entailment
No-value statements entail
that a query is empty
No-Value Theorem
The emptiness entailment holds
iff
the evaluation of the BGPs
of the no-value statements
over the frozen version
of the query is not empty
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Discussion
The entailment characterization can be implemented using standard Semantic Web frameworks like Jena
Can also be used to represent negative ground facts like “Fariz is not Obama’s child”
Useful also for data cleaning, assuming that no-value statements are always faithful
Example
Nob : Obama has no male children
No(obama child ?c . ?c gender male)
ex:stmtObama a ex:NoValStatement ;
ex:hasPattern [ ex:subj ex:Obama ;
ex:pred ex:child ;
ex:obj [ex:varName "c"]] ;
ex:hasPattern [ ex:subj [ex:varName "c"] ;
ex:pred ex:gender ;
ex:obj ex:male ] .
Qob : What are the schools of
Obama’s male children?
SELECT ?c ?s
WHERE { ex:Obama ex:child ?c .
?c ex:gender ex:male .
?c ex:school ?s }
We can conclude that:
The query returns the empty answer due to
non-existence of information per the statement
Nob Empty(Qob )
X
SPARQLW3C
RDFW3C](https://image.slidesharecdn.com/posterfinal-150928094700-lva1-app6892/85/Expressing-No-Value-Information-in-RDF-1-320.jpg)
Expressing No-Value Information in RDF
- 1. Expressing No-Value Information in RDF Fariz Darari, Radityo Eko Prasojo, Werner Nutt Free University of Bozen-Bolzano, Italy Problem Statement Elizabeth I had no children RDF cannot represent non-existence of information SPARQL cannot distinguish whether a query returns the empty answer due to possibly incomplete information or non-existence of information No-Value Framework Definition: No-Value Statements BGP-based statements for declaring non-existence Definition: Empty Queries Queries that always give the empty answer Definition: Emptiness Entailment No-value statements entail that a query is empty No-Value Theorem The emptiness entailment holds iff the evaluation of the BGPs of the no-value statements over the frozen version of the query is not empty [[ Sponsored by ]] Discussion The entailment characterization can be implemented using standard Semantic Web frameworks like Jena Can also be used to represent negative ground facts like “Fariz is not Obama’s child” Useful also for data cleaning, assuming that no-value statements are always faithful Example Nob : Obama has no male children No(obama child ?c . ?c gender male) ex:stmtObama a ex:NoValStatement ; ex:hasPattern [ ex:subj ex:Obama ; ex:pred ex:child ; ex:obj [ex:varName "c"]] ; ex:hasPattern [ ex:subj [ex:varName "c"] ; ex:pred ex:gender ; ex:obj ex:male ] . Qob : What are the schools of Obama’s male children? SELECT ?c ?s WHERE { ex:Obama ex:child ?c . ?c ex:gender ex:male . ?c ex:school ?s } We can conclude that: The query returns the empty answer due to non-existence of information per the statement Nob Empty(Qob ) X SPARQLW3C RDFW3C