RDF Nodes cannot exist without at least one edge, to another node or to themselves.
IRI: Internationalized Resource Identifier, generalized URI
used for proper things
URLs are not officially recognised as a type of RDF node
Literal: string, number, date, etc.
used for values
XML schema datatypes
Blank Nodes: avoid if possible
make querying RDF Data harder
don't carry persistent labels
used in skos:collection, skos:OrderedCollection to build up linked lists
A directed graph
:Bugs_Bunny :name "Bugs Bunny"
: Colon is a prefix for the "base URI" or the default namespace
:name is a relative IRI - snake case is common
"Bugs Bunny" is a literal
PREFIX rdf: http://www.w3.org/1999/02/22-rdf-syntax-ns#
PREFIX : http://looneytunes-graph.com/
:Bugs_Bunny :name "Bugs Bunny" ;
:species "Hare" ;
:gender "Male" .
:Bugs_Bunny rdf:type :Looney_Tunes_Character.
:Bugs_Bunny a :Looney_Tunes_Character.
- the
rdf:type is so common that it has a shorthand "a"
Looney TUnes
- plan complex queeries (pencil+paper, pseudo-code, comments)
- write lean queries using prefixes and semicolons, commas
- (short) varnames that match what you are looking for (?m for "movies")
- use DISTINCT often to avoid duplicates
- use LIMIT 5 to avoid long waits
- combine LIMIT with ORDER BY DESC(?var) to get top n results
- use OFFSET to page through results
- OPTIONAL for Left-join equivalent
- you can follow different approaches to design queries
- DESCRIBE :item to get all triples about an item (ingoing and outgoing links 1 hop away)
- ASK :item to check if an item exists or if a fact is true (Logicians proposition)
- often used to check if a triple exists, especially in federated queries
- CONSTRUCT to build a new graph from a query, or new properties/relationships (similar to a view in relational databases)
- can get the data for a new graph, or to infer new relationships. Useful with federated queries
BIND to execute expressions and assign the result to a variable
- useful for calculations, string manipulations, and conditional tests
VALUES to provide a list of possible values for a variable
COALESCE to provide default values, or COALESCE( IF()) as a cleaner conditional test
CONSTRUCT queries
We can, of course, further customise the output and include other triples if we wanted to: for example, let's calculate some birth dates, and use a custom predicate identified as :birth_date, hit "run", and we get a slightly bigger sub-graph.
What I personally like about CONSTRUCT queries, is that idea of customising the output of following graph patterns. CONSTRUCT queries are a very flexible construct in SPARQL and useful for building inferred graphs on-the-fly.
Use LOAD 👍
LOAD file:///$HOME/data/_my-turtle.ttl INTO GRAPH http://example.com/demo/Info_Graph;
LOAD ...
In Blazegraph, select the "SPARQL Update" selectionlist, use N-Quads, because we want to create named graphs.
Most basic query:
select *
where { ?s ?p ?o }usable for small custom knowledge graphs
PREFIX : <http://looneytunes-graph.com/>
select ?s ?p ?o
where { ?s ?p ?o .
?s a :Looney_Tunes_Character
}Add query modifiers after the WHERE clause. Most common are:
LIMIT
OFFSET
ORDER BY
Very similar to Turtle Syntax
PREFIX : <http://looneytunes-graph.com/>
SELECT ?n
WHERE {
:Bugs_Bunny :name ?n
}
LIMIT 5PREFIX : <http://looneytunes-graph.com/>
SELECT ?p ?n
WHERE {
:Bugs_Bunny :created_by ?p .
?p :name ?n .
}# what are the debut release dates for looney tunes characters?
PREFIX : <http://looneytunes-graph.com/>
SELECT ?n ?m ?d
WHERE {
?c a :Looney_Tunes_Character ;
:name ?n ;
:made_debut_appearance_in ?m .
?m :release_date ?d;
}
order by desc(?d)#
# list the lifespan of each Looney Tunes character creator.
# In the tabulated results make sure to list each creator along with their corresponding lifespan value in years.
#
PREFIX : <http://looneytunes-graph.com/>
SELECT DISTINCT ?p1 ?bd ?dd ?lifespan
WHERE {
?c a :Looney_Tunes_Character ;
:created_by ?p1 .
?p1 :born_on ?bd;
:died_on ?dd .
BIND(year(?bd) as ?bYear ) .
BIND(year(?dd) as ?dYear ) .
BIND((?dYear - ?bYear) as ?lifespan )
}
#
# list the lifespan of each Looney Tunes character creator.
# In the tabulated results make sure to list each creator along with their corresponding lifespan value in years.
#
PREFIX : <http://looneytunes-graph.com/>
SELECT DISTINCT ?p1 ?bd ?dd ?lifespan ?period
WHERE {
?c a :Looney_Tunes_Character ;
:created_by ?p1 .
?p1 :born_on ?bd;
:died_on ?dd .
BIND(year(?bd) as ?bYear )
BIND(year(?dd) as ?dYear )
BIND((?dYear - ?bYear) as ?lifespan )
# uses 1/0 error to force a FALSE value
BIND(COALESCE( IF (?bYear < 1900, "Born pre-1900", 1/0),
IF (?bYear >= 1900, "Born post-1900", 1/0),
"NA")
as ?period )
}
# property paths
## Inverse path
PREFIX : <http://looneytunes-graph.com/>
SELECT ?c ?p
WHERE {
?p ^:created_by ?c
}## What are the possible paths I can take between two nodes (e.g. between Bugs Bunny & Daffy Duck)?
## will probably work with a small graph only
PREFIX : <http://looneytunes-graph.com/>
SELECT DISTINCT ?subject ?predicate ?object
WHERE {
VALUES ?start { :Bugs_Bunny }
VALUES ?end { :Daffy_Duck }
?start (:|!:)* ?subject .
?subject ?predicate ?object .
?object (:|!:)* ?end
}# BIND()/BOUND() : use this
# if some OPTIONAL values are NULL and there is nothing to bind
#....
OPTIONAL { ?clang :language_variant ?langVar. }
# !BOUND checks if there is no bound ?langVar
# - if this is true, then simply ?langN is returned,
# otherwise, the string function CONCAT concatenates the necessary strings as ?langWithVariant
BIND(IF(!(BOUND(?langVar)),
?langN,
CONCAT(?langN, "[", ?langVar, "]")) AS ?langWithVariant)