What;s Coming In SPARQL2?

What’s coming with SPARQL 2?
Slides available online at:
http://www.slideshare.net/LeeFeigenbaum/whats-coming-in-sparql2
Comments & questions to:
Lee Feigenbaum <lee@cambridgesemantics.com>
VP Technology & Standards, Cambridge Semantics
Co-chair, W3C SPARQL Working Group

For More Details
SPARQL By Example
http://www.cambridgesemantics.com/2008/09/sparql-by-example/
SPARQL Cheat Sheet
http://www.slideshare.net/LeeFeigenbaum/sparql-cheat-sheet
SPARQL2 Status
http://www.slideshare.net/LeeFeigenbaum/sparql2-status

Why SPARQL?
SPARQL is the query language of the Semantic Web. SPARQL lets us:
Pull values from structured and semi-structured data
Explore data by querying unknown relationships
Perform complex joins of disparate data sources in a single, simple query
Transform RDF data from one vocabulary to another

Structure of a SPARQL Query
A SPARQL query comprises, in order:
Prefix declarations, for abbreviating URIs
Dataset definition, stating what RDF graph(s) are being queried
A result clause, identifying what information to return from the query
The query pattern, specifying what to query for in the underlying dataset
Query modifiers, slicing, ordering, and otherwise rearranging query results

Anatomy of a SPARQL Query
PREFIXfoo:<…>
PREFIXbar:<…>
…
SELECT …
FROM <…>
FROM NAMED <…>
WHERE{
…
}
ORDER BY …
LIMIT …
OFFSET …
Declare prefix
shortcuts
(optional)
Query result
clause
Define the
dataset (optional)
Query pattern
Query modifiers
(optional)

An Example SPARQL Query
Find the name of all landlocked countries with a population bigger than 15 million
PREFIXrdfs:<http://www.w3.org/2000/01/rdf-schema#>
PREFIXtype:<http://dbpedia.org/class/yago/>
PREFIXprop: <http://dbpedia.org/property/>
SELECT?country_name ?population
WHERE{
?countryatype:LandlockedCountries;
rdfs:label?country_name;
prop:populationEstimate?population.
FILTER(?population>15000000).
}

SPARQL Over HTTP (the SPARQL Protocol)
http://host.domain.com/sparql/endpoint?<parameters>
where <parameters>can include:
query=<encoded query string>
e.g. SELECT+*%0DWHERE+{…
default-graph-uri=<encoded graph URI>
e.g. http%3A%2F%2Fexmaple.com%2Ffoo…
n.b. zero of more occurrences of default-graph-uri
named-graph-uri=<encoded graph URI>
e.g. http%3A%2F%2Fexmaple.com%2Fbar…
n.b. zero of more occurrences of named-graph-uri
HTTP GET or POST. Graphs given in the protocol override graphs given in the query.

Some Public SPARQL Endpoints

Disclaimer
The SPARQL Working Group has not yet decided many of the technical questions surveyed in these slides. All examples are subject to change; please do not construe them as indicators or endorsements of specific technical designs/decisions.
All opinions are Lee Feigenbaum’s alone.

Naming
I use “SPARQL2” to collectively refer to the work of the 2nd SPARQL Working Group. The actual languages being worked on are known as:SPARQL/Query 1.1SPARQL/Update 1.0

Where are we now?
Today
August 2010
March 2009
???
Last Call and beyond of core SPARQL specifications
July 2009
FPWD of SPARQL New Features and Rationales document
October 2009
FPWD of core SPARQL specifications

Overview

Projected Expressions
Select expressions other than variables (literals, functions on literals and variables, etc.)
Issues around:
Do expressions require an aliased name?
Syntax (main issue here)
SELECT ?price * ?qty AS ?total_price
WHERE {
…
}

Aggregates
À la SQL aggregates (MIN, MAX, COUNT, AVG, etc.)
Issues around:
Which aggregates to include
Aggregates over mixed datatypes
Syntax, keywords, custom aggregates
SELECT MIN(?price) AS ?min_price …
WHERE { … }
GROUP BY ?item

Subqueries
Nested queries allow multiple queries to be combined into one.
Issues around:
Variable scope & evaluation model
Precise syntax
SELECT ?article ?authorWHERE { ?article ex:author ?author . { SELECT ?article WHERE { … ?article … } ORDER BY … LIMIT … }}

Negation
Supplant the mystifying OPTIONAL/!bound method of negation with a dedicated construct
Issues around:
Filter semantics vs. set-difference semantics
Choice of keyword(s)
SELECT … WHERE { ?person a foaf:Person .
NOT {
?person foaf:mbox ?email
}
}

Service Description
A standard discovery mechanism and vocabulary for describing the capabilities, extensions, data sets, and more for a SPARQL endpoint
Discovery. How can a client find the RDF that describes a SPARQL endpoint at a particular URI?
Description. What predicates, classes, values, etc. should a client expect to find (and be able to query) once it locates a service description?
Issues around:
Choice of discovery mechanism
Which predicates and enumerations to define URIs for

Update Language
Based on the SPARQL Update member submission
Batch insert & delete
Insert & delete based on triple patterns
Graph management (creation, removal)
Issues around:
Graph stores vs. triple stores
Which language statements to include?
Transactions/atomicity/concurrency?

Update Protocol
The ability to issue SPARQL/Update language statements via a standard protocol (e.g. via HTTP POST)
Issues around:
Relation to existing SPARQL (Query) Protocol
Security
Need for WSDL description? SOAP bindings?

RESTful Update
Where appropriate, map RESTful HTTP requests to SPARQL/Update operations
DELETE /foo/g1 …-> DELETE DATA FROM ex:g1 …
Issues around:
Which mappings to include?
Updating graphs with URIs that are not under the control of the SPARQL endpoint

Property Paths
Support arbitrary-length predicate paths in triple patterns – “regular expressions” on predicates?
Query hierarchical structures such as RDF collections
Issues around:
Can variables be used in path expressions?
Can the length of a path be found?
Are paths first-class datatypes?
SELECT … WHERE { ?person foaf:knows+ ?network .
}

Basic Federated Query
Initial scaffolding for authoring federated SPARQL queries
Likely will involve a keyword to explicitly target portions of a query to specific endpoints
Initial plan: Start with ARQ’s SERVICE keyword
SELECT … WHERE { … SERVICE ex:books {
…
}
}

Entailment Regime Semantics
SPARQL/Query 1.0 defines a mechanism to extend SPARQL semantics for additional entailment regimes
Use this mechanism to define the semantics of SPARQL queries for:
RDF Schema
OWL flavors
RIF rule sets
…
Issues around:
Requiring consistency checks
How to limit infinite results (e.g. from axiomatic inferences)

Common Functions
Extend the set of functions that SPARQL engines must support to include some of…
Common string functions (e.g. substr)
Common date/time/datetime functions
Logical functions (COALESCE, IF, …?)
Limited discussion to date about which functions to include

Get Involved
Join.
Email team-sparql-chairs@w3.org
Follow.
WG materials at http://www.w3.org/2009/sparql/wiki/
Comment.
Public feedback at public-rdf-dawg-comments@w3.org
Use.
Discuss SPARQL at public-sparql-dev@w3.org

SPARQL Resources
The SPARQL Specification
http://www.w3.org/TR/rdf-sparql-query/
SPARQL implementations
http://esw.w3.org/topic/SparqlImplementations
SPARQL endpoints
http://esw.w3.org/topic/SparqlEndpoints
SPARQL Frequently Asked Questions
http://www.thefigtrees.net/lee/sw/sparql-faq
SPARQL 2 Working Group
http://www.w3.org/2009/sparql/wiki/
Common SPARQL extensions
http://esw.w3.org/topic/SPARQL/Extensions

What;s Coming In SPARQL2?

by LeeFeigenbaum

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What;s Coming In SPARQL2? Presentation Transcript