diff --git a/transforge/bag.py b/transforge/bag.py
index 8ed2d4e..b4230e9 100644
--- a/transforge/bag.py
+++ b/transforge/bag.py
@@ -5,8 +5,13 @@
 from collections.abc import MutableSet
 
 class TypeUnion(MutableSet[Type]):
+    """A disjunction of types. Can be either the most specific types (ie for a 
+    hierarchy with B, C subtypes of A, the disjunction B OR C OR A will be 
+    equivalent to B OR C) or the most general types (ie the disjunction B OR C 
+    OR A will be A)."""
 
-    def __init__(self, xs: Iterable[Type] = ()) -> None:
+    def __init__(self, xs: Iterable[Type] = (), specific: bool = True) -> None:
+        self.specific = specific
         self.data: set[Type] = set()
         for x in xs:
             self.add(x)
@@ -34,10 +39,16 @@ def is_subtype(self, other: Type | "TypeUnion") -> bool:
     def add(self, new: Type) -> None:
         to_remove = set()
         for t in self.data:
-            if new.is_subtype(t):
-                to_remove.add(t)
-            elif t.is_subtype(new):
-                return
+            if self.specific:
+                if new.is_subtype(t):
+                    to_remove.add(t)
+                elif t.is_subtype(new):
+                    return
+            else:
+                if new.is_subtype(t):
+                    return
+                elif t.is_subtype(new):
+                    to_remove.add(t)
         self.data -= to_remove
         self.data.add(new)
 
diff --git a/transforge/query.py b/transforge/query.py
index 3c480d9..4d16e26 100644
--- a/transforge/query.py
+++ b/transforge/query.py
@@ -277,11 +277,23 @@ def io(self) -> Iterator[str]:
             else:
                 path = "?workflow :output/:type/rdfs:subClassOf*"
 
-            yield from union(path, self.graph.objects(output, TF.type))
+            # TODO general method for this
+            type_set = TypeUnion((self.lang.parse_type_uri(t)
+                for t in self.graph.objects(output, TF.type)
+                    if isinstance(t, URIRef)),
+                specific=False)
+
+            yield from union(path, (self.lang.uri(t) for t in type_set))
 
         for input in self.graph.objects(self.root, TF.input):
+
+            type_set = TypeUnion((self.lang.parse_type_uri(t)
+                for t in self.graph.objects(input, TF.type)
+                    if isinstance(t, URIRef)),
+                specific=False)
+
             yield from union("?workflow :input/:type/rdfs:subClassOf*",
-                self.graph.objects(input, TF.type))
+                (self.lang.uri(t) for t in type_set))
 
     def chronology(self) -> Iterator[str]:
         """
@@ -338,6 +350,10 @@ def chronology(self) -> Iterator[str]:
             type_set = TypeUnion(self.lang.parse_type_uri(t)
                 for t in self.type.get(current, ()) if isinstance(t, URIRef))
 
+            type_set = TypeUnion((self.lang.parse_type_uri(t)
+                for t in self.type.get(current, ()) if isinstance(t, URIRef)),
+                specific=False)
+
             yield from union(f"{current.n3()} :via",
                 self.operator.get(current, ()))
             yield from union(f"{current.n3()} :type/rdfs:subClassOf*",