schema ordering

1 files changed, 35 insertions, 0 deletions

diff --git a/bsfs/schema/schema.py b/bsfs/schema/schema.py
index 0e053c0..b6f37a7 100644
--- a/bsfs/schema/schema.py
+++ b/bsfs/schema/schema.py
@@ -103,6 +103,41 @@ class Schema():
 
     SchemaDiff = namedtuple('SchemaDiff', ['nodes', 'literals', 'predicates'])
 
+    def _issubset(self, other: 'Schema') -> bool:
+        # inconsistent schema can't be ordered.
+        if not self.consistent_with(other):
+            return False
+        # since schemas are consistent, it's sufficient to compare their URIs.
+        # self's sets are fully contained in other's sets
+        # pylint: disable=protected-access
+        return set(self._predicates) <= set(other._predicates) \
+           and set(self._nodes) <= set(other._nodes) \
+           and set(self._literals) <= set(other._literals)
+
+    def __lt__(self, other: typing.Any) -> bool:
+        """Return True if *other* is a true subset of *self*."""
+        if not isinstance(other, Schema): # other is not a Schema
+            return NotImplemented
+        return self != other and self._issubset(other)
+
+    def __le__(self, other: typing.Any) -> bool:
+        """Return True if *other* is a subset of *self*."""
+        if not isinstance(other, Schema): # other is not a Schema
+            return NotImplemented
+        return self == other or self._issubset(other)
+
+    def __gt__(self, other: typing.Any) -> bool:
+        """Return True if *other* is a true superset of *self*."""
+        if not isinstance(other, Schema): # other is not a Schema
+            return NotImplemented
+        return self != other and other._issubset(self)
+
+    def __ge__(self, other: typing.Any) -> bool:
+        """Return True if *other* is a superset of *self*."""
+        if not isinstance(other, Schema): # other is not a Schema
+            return NotImplemented
+        return self == other or other._issubset(self)
+
     def diff(self, other: 'Schema') -> SchemaDiff:
         """Return node, literals, and predicates that are in *self* but not in *other*."""
         return self.SchemaDiff(