Merge pull request #1289 from RDFLib/dataset_example

dataset examples file

examples/datasets.py

@@ -0,0 +1,146 @@
+"""
+An RDFLib Dataset is a slight extension to ConjunctiveGraph: it uses simpler terminology
+and has a few additional convenience method extensions, for example add() can be used to
+add quads directly to a specific Graph within the Dataset.
+
+This example file shows how to decalre a Dataset, add content to it, serialise it, query it
+and remove things from it.
+"""
+
+from rdflib import Dataset, URIRef, Literal, Namespace
+
+#
+#   Create & Add
+#
+
+# Create an empty Dataset
+d = Dataset()
+# Add a namespace prefix to it, just like for Graph
+d.bind("ex", Namespace("http://example.com/"))
+
+# Declare a Graph URI to be used to identify a Graph
+graph_1 = URIRef("http://example.com/graph-1")
+
+# Add an empty Graph, identified by graph_1, to the Dataset
+d.graph(identifier=graph_1)
+
+# Add two quads to Graph graph_1 in the Dataset
+d.add((
+    URIRef("http://example.com/subject-x"),
+    URIRef("http://example.com/predicate-x"),
+    Literal("Triple X"),
+    graph_1
+))
+d.add((
+    URIRef("http://example.com/subject-z"),
+    URIRef("http://example.com/predicate-z"),
+    Literal("Triple Z"),
+    graph_1
+))
+
+# Add another quad to the Dataset to a non-existent Graph:
+# the Graph is created automatically
+d.add((
+    URIRef("http://example.com/subject-y"),
+    URIRef("http://example.com/predicate-y"),
+    Literal("Triple Y"),
+    URIRef("http://example.com/graph-2")
+))
+
+# printing the Dataset like this: print(d.serialize(format="trig"))
+# produces a result like this:
+"""
+@prefix ex: <http://example.com/> .
+
+ex:graph-1 {
+    ex:subject-x ex:predicate-x "Triple X" .
+
+    ex:subject-z ex:predicate-z "Triple Z" .
+}
+
+ex:graph-2 {
+    ex:subject-y ex:predicate-y "Triple Y" .
+}
+"""
+print("Printing Serialised Dataset:")
+print("---")
+print(d.serialize(format="trig"))
+print("---")
+print()
+print()
+
+#
+#   Use & Query
+#
+
+# print the length of the Dataset, i.e. the count of all triples in all Graphs
+# we should get
+"""
+3
+"""
+print("Printing Dataset Length:")
+print("---")
+print(len(d))
+print("---")
+print()
+print()
+
+# Query one graph in the Dataset for all it's triples
+# we should get
+"""
+(rdflib.term.URIRef('http://example.com/subject-z'), rdflib.term.URIRef('http://example.com/predicate-z'), rdflib.term.Literal('Triple Z'))
+(rdflib.term.URIRef('http://example.com/subject-x'), rdflib.term.URIRef('http://example.com/predicate-x'), rdflib.term.Literal('Triple X'))
+"""
+print("Printing all triple from one Graph in the Dataset:")
+print("---")
+for triple in d.triples((None, None, None, graph_1)):
+    print(triple)
+print("---")
+print()
+print()
+
+# Query the union of all graphs in the dataset for all triples
+# we should get Nothing:
+"""
+"""
+# A Dataset's default union graph does not exist by default (default_union property is False)
+print("Attempt #1 to print all triples in the Dataset:")
+print("---")
+for triple in d.triples((None, None, None, None)):
+    print(triple)
+print("---")
+print()
+print()
+
+# Set the Dataset's default_union property to True and re-query
+d.default_union = True
+print("Attempt #2 to print all triples in the Dataset:")
+print("---")
+for triple in d.triples((None, None, None, None)):
+    print(triple)
+print("---")
+print()
+print()
+
+
+#
+#   Remove
+#
+
+# Remove Graph graph_1 from the Dataset
+d.remove_graph(graph_1)
+
+# printing the Dataset like this: print(d.serialize(format="trig"))
+# now produces a result like this:
+
+"""
+ex:graph-2 {
+    ex:subject-y ex:predicate-y "Triple Y" .
+}
+"""
+print("Printing Serialised Dataset after graph_1 removal:")
+print("---")
+print(d.serialize(format="trig").strip())
+print("---")
+print()
+print()