1 files changed, 129 insertions, 0 deletions
diff --git a/rdflib/void.py b/rdflib/void.py
new file mode 100644
index 00000000..8a23f569
--- /dev/null
+++ b/rdflib/void.py
@@ -0,0 +1,129 @@
+import collections
+
+from rdflib import URIRef, Graph, Literal
+from rdflib.namespace import VOID, RDF
+
+
+def generateVoID(g, dataset=None, res=None, distinctForPartitions=True):
+    """
+    Returns a new graph with a VoID description of the passed dataset
+
+    For more info on Vocabulary of Interlinked Datasets (VoID), see:
+    http://vocab.deri.ie/void
+
+    This only makes two passes through the triples (once to detect the types
+    of things)
+
+    The tradeoff is that lots of temporary structures are built up in memory
+    meaning lots of memory may be consumed :)
+    I imagine at least a few copies of your original graph.
+
+    the distinctForPartitions parameter controls whether
+    distinctSubjects/objects are tracked for each class/propertyPartition
+    this requires more memory again
+
+    """
+
+    typeMap = collections.defaultdict(set)
+    classes = collections.defaultdict(set)
+    for e, c in g.subject_objects(RDF.type):
+        classes[c].add(e)
+        typeMap[e].add(c)
+
+    triples = 0
+    subjects = set()
+    objects = set()
+    properties = set()
+    classCount = collections.defaultdict(int)
+    propCount = collections.defaultdict(int)
+
+    classProps = collections.defaultdict(set)
+    classObjects = collections.defaultdict(set)
+    propSubjects = collections.defaultdict(set)
+    propObjects = collections.defaultdict(set)
+
+    for s, p, o in g:
+
+        triples += 1
+        subjects.add(s)
+        properties.add(p)
+        objects.add(o)
+
+        # class partitions
+        if s in typeMap:
+            for c in typeMap[s]:
+                classCount[c] += 1
+                if distinctForPartitions:
+                    classObjects[c].add(o)
+                    classProps[c].add(p)
+
+        # property partitions
+        propCount[p] += 1
+        if distinctForPartitions:
+            propObjects[p].add(o)
+            propSubjects[p].add(s)
+
+    if not dataset:
+        dataset = URIRef("http://example.org/Dataset")
+
+    if not res:
+        res = Graph()
+
+    res.add((dataset, RDF.type, VOID.Dataset))
+
+    # basic stats
+    res.add((dataset, VOID.triples, Literal(triples)))
+    res.add((dataset, VOID.classes, Literal(len(classes))))
+
+    res.add((dataset, VOID.distinctObjects, Literal(len(objects))))
+    res.add((dataset, VOID.distinctSubjects, Literal(len(subjects))))
+    res.add((dataset, VOID.properties, Literal(len(properties))))
+
+    for i, c in enumerate(classes):
+        part = URIRef(dataset + "_class%d" % i)
+        res.add((dataset, VOID.classPartition, part))
+        res.add((part, RDF.type, VOID.Dataset))
+
+        res.add((part, VOID.triples, Literal(classCount[c])))
+        res.add((part, VOID.classes, Literal(1)))
+
+        res.add((part, VOID["class"], c))
+
+        res.add((part, VOID.entities, Literal(len(classes[c]))))
+        res.add((part, VOID.distinctSubjects, Literal(len(classes[c]))))
+
+        if distinctForPartitions:
+            res.add(
+                (part, VOID.properties, Literal(len(classProps[c]))))
+            res.add((part, VOID.distinctObjects,
+                    Literal(len(classObjects[c]))))
+
+    for i, p in enumerate(properties):
+        part = URIRef(dataset + "_property%d" % i)
+        res.add((dataset, VOID.propertyPartition, part))
+        res.add((part, RDF.type, VOID.Dataset))
+
+        res.add((part, VOID.triples, Literal(propCount[p])))
+        res.add((part, VOID.properties, Literal(1)))
+
+        res.add((part, VOID.property, p))
+
+        if distinctForPartitions:
+
+            entities = 0
+            propClasses = set()
+            for s in propSubjects[p]:
+                if s in typeMap:
+                    entities += 1
+                for c in typeMap[s]:
+                    propClasses.add(c)
+
+            res.add((part, VOID.entities, Literal(entities)))
+            res.add((part, VOID.classes, Literal(len(propClasses))))
+
+            res.add((part, VOID.distinctSubjects,
+                    Literal(len(propSubjects[p]))))
+            res.add((part, VOID.distinctObjects,
+                    Literal(len(propObjects[p]))))
+
+    return res, dataset