shacl utilities: Add new SHACL path building utility with correspondi…

…ng tests

rdflib/extras/shacl.py

@@ -6,18 +6,28 @@
 
 from typing import TYPE_CHECKING
 
-from rdflib import Graph, Literal, URIRef, paths
+from rdflib import BNode, Graph, Literal, URIRef, paths
+from rdflib.collection import Collection
 from rdflib.namespace import RDF, SH
 from rdflib.paths import Path
 
 if TYPE_CHECKING:
     from rdflib.graph import _ObjectType
+    from rdflib.term import IdentifiedNode
 
 
 class SHACLPathError(Exception):
     pass
 
 
+# Map the variable length path operators to the corresponding SHACL path predicates
+_PATH_MOD_TO_PRED = {
+    paths.ZeroOrMore: SH.zeroOrMorePath,
+    paths.OneOrMore: SH.oneOrMorePath,
+    paths.ZeroOrOne: SH.zeroOrOnePath,
+}
+
+
 # This implementation is roughly based on
 # pyshacl.helper.sparql_query_helper::SPARQLQueryHelper._shacl_path_to_sparql_path
 def parse_shacl_path(
@@ -93,3 +103,110 @@ def parse_shacl_path(
         raise SHACLPathError(f"Cannot parse {repr(path_identifier)} as a SHACL Path.")
 
     return path
+
+
+def _build_path_component(
+    graph: Graph, path_component: URIRef | Path
+) -> IdentifiedNode:
+    """
+    Helper method that implements the recursive component of SHACL path
+    triple construction.
+
+    :param graph: A :class:`~rdflib.graph.Graph` into which to insert triples
+    :param graph_component: A :class:`~rdflib.term.URIRef` or
+        :class:`~rdflib.paths.Path` that is part of a path expression
+    :return: The :class:`~rdflib.term.IdentifiedNode of the resource in the
+        graph that corresponds to the provided `path_component
+    """
+    # Literals or other types are not allowed
+    if not isinstance(path_component, (URIRef, Path)):
+        raise TypeError(
+            f"Objects of type {type(path_component)} are not valid "
+            + "components of a SHACL path."
+        )
+
+    # If the path component is a URI, return it
+    elif isinstance(path_component, URIRef):
+        return path_component
+    # Otherwise, the path component is represented as a blank node
+    bnode = BNode()
+
+    # Handle Sequence Paths
+    if isinstance(path_component, paths.SequencePath):
+        # Sequence paths are a Collection directly with at least two items
+        if len(path_component.args) < 2:
+            raise SHACLPathError(
+                "A list of SHACL Sequence Paths must contain at least two path items."
+            )
+        Collection(
+            graph,
+            bnode,
+            [_build_path_component(graph, arg) for arg in path_component.args],
+        )
+
+    # Handle Inverse Paths
+    elif isinstance(path_component, paths.InvPath):
+        graph.add(
+            (bnode, SH.inversePath, _build_path_component(graph, path_component.arg))
+        )
+
+    # Handle Alternative Paths
+    elif isinstance(path_component, paths.AlternativePath):
+        # Alternative paths are a Collection but referenced by sh:alternativePath
+        # with at least two items
+        if len(path_component.args) < 2:
+            raise SHACLPathError(
+                "List of SHACL alternate paths must have at least two path items."
+            )
+        coll = Collection(
+            graph,
+            BNode(),
+            [_build_path_component(graph, arg) for arg in path_component.args],
+        )
+        graph.add((bnode, SH.alternativePath, coll.uri))
+
+    # Handle Variable Length Paths
+    elif isinstance(path_component, paths.MulPath):
+        # Get the predicate corresponding to the path modifiier
+        pred = _PATH_MOD_TO_PRED.get(path_component.mod)
+        if pred is None:
+            raise SHACLPathError(f"Unknown path modifier {path_component.mod}")
+        graph.add((bnode, pred, _build_path_component(graph, path_component.path)))
+
+    # Return the blank node created for the provided path_component
+    return bnode
+
+
+def build_shacl_path(
+    path: URIRef | Path, target_graph: Graph | None = None
+) -> tuple[IdentifiedNode, Graph | None]:
+    """
+    Build the SHACL Path triples for a path given by a :class:`~rdflib.term.URIRef` for
+    simple paths or a :class:`~rdflib.paths.Path` for complex paths.
+
+    Returns an :class:`~rdflib.term.IdentifiedNode` for the path (which should be
+    the object of a triple with predicate `sh:path`) and the graph into which any
+    new triples were added.
+
+    :param path: A :class:`~rdflib.term.URIRef` or a :class:`~rdflib.paths.Path`
+    :param target_graph: Optionally, a :class:`~rdflib.graph.Graph` into which to put
+        constructed triples. If not provided, a new graph will be created
+    :return: A (`path_identifier`, `graph`) tuple where:
+      - `path_identifier`: If `path` is a :class:`~rdflib.term.URIRef`, this is simply
+        the provided `path`. If `path` is a :class:`~rdflib.paths.Path`, this is
+        the :class:`~rdflib.term.BNode` corresponding to the root of the SHACL
+        path expression added to the graph.
+      - `graph`: `None` if `path` is a :class:`~rdflib.term.URIRef` (as no new triples
+        are constructed). If `path` is a :class:`~rdflib.paths.Path`, this is either the
+        `target_graph` provided or a new graph into which the path triples were added.
+    """
+    # If a path is a URI, that's the whole path. No graph needs to be constructed.
+    if isinstance(path, URIRef):
+        return path, None
+
+    # Create a graph if one was not provided
+    if target_graph is None:
+        target_graph = Graph()
+
+    # Recurse through the path to build the graph representation
+    return _build_path_component(target_graph, path), target_graph

test/test_extras/test_shacl_extras.py

@@ -4,8 +4,9 @@
 
 import pytest
 
-from rdflib import Graph, URIRef
-from rdflib.extras.shacl import SHACLPathError, parse_shacl_path
+from rdflib import Graph, Literal, URIRef, paths
+from rdflib.compare import graph_diff
+from rdflib.extras.shacl import SHACLPathError, build_shacl_path, parse_shacl_path
 from rdflib.namespace import SH, Namespace
 from rdflib.paths import Path
 
@@ -248,3 +249,49 @@ def test_parse_shacl_path(
             parse_shacl_path(path_source_data, path_root)  # type: ignore[arg-type]
     else:
         assert parse_shacl_path(path_source_data, path_root) == expected  # type: ignore[arg-type]
+
+
+@pytest.mark.parametrize(
+    ("resource", "path"),
+    (
+        # Single SHACL Path
+        (EX.TestPropShape1, EX.pred1),
+        (EX.TestPropShape2a, EX.pred1 / EX.pred2 / EX.pred3),
+        (EX.TestPropShape3, ~EX.pred1),
+        (EX.TestPropShape4a, EX.pred1 | EX.pred2 | EX.pred3),
+        (EX.TestPropShape5, EX.pred1 * "*"),  # type: ignore[operator]
+        (EX.TestPropShape6, EX.pred1 * "+"),  # type: ignore[operator]
+        (EX.TestPropShape7, EX.pred1 * "?"),  # type: ignore[operator]
+        # SHACL Path Combinations
+        (EX.TestPropShape8, ~EX.pred1 * "*"),
+        (
+            EX.TestPropShape10a,
+            ~EX.pred1
+            * "*"
+            / (~EX.pred1 * "*" | EX.pred1 | EX.pred2 * "+" | EX.pred3 * "*"),  # type: ignore[operator]
+        ),
+        (TypeError, Literal("Not a valid path")),
+        (SHACLPathError, paths.SequencePath(SH.targetClass)),
+        (SHACLPathError, paths.AlternativePath(SH.targetClass)),
+    ),
+)
+def test_build_shacl_path(
+    path_source_data: Graph, resource: URIRef | type, path: Union[URIRef, Path]
+):
+    if isinstance(resource, type):
+        with pytest.raises(resource):  # type: ignore[arg-type]
+            build_shacl_path(path)
+    else:
+        expected_path_root = path_source_data.value(resource, SH.path)
+        actual_path_root, actual_path_graph = build_shacl_path(path)
+        if isinstance(expected_path_root, URIRef):
+            assert actual_path_root == expected_path_root
+            assert actual_path_graph is None
+        else:
+            assert isinstance(actual_path_graph, Graph)
+            expected_path_graph = path_source_data.cbd(expected_path_root)  # type: ignore[arg-type]
+            in_both, in_first, in_second = graph_diff(
+                expected_path_graph, actual_path_graph
+            )
+            assert len(in_first) == 0
+            assert len(in_second) == 0