Added Graph.create_literal() and Graph.create_typed_literal()

Also added an `Enum` with XSD datatype URIs

example.py

@@ -6,14 +6,15 @@
 
 graph1 = dataset.default_graph
 resource1 = graph1.create_resource("http://example.org/subject1")
-resource1.add_property(graph1.create_property("http://example.org/property1"), Literal("Object1"))
+resource1.add_property(graph1.create_property("http://example.org/property1"), graph1.create_literal("Object1"))
 resource1.add_property(graph1.create_property("http://example.org/property2"), graph1.create_resource("http://example.org/object"))
+resource1.add_property(graph1.create_property("http://example.org/property2"), graph1.create_typed_literal(42))
 
 graph2 = dataset.get_named_graph("http://example.org/graph2")
 resource2 = graph2.create_resource()
-resource2.add_property(graph2.create_property("http://example.org/property3"), Literal("Object2"))
+resource2.add_property(graph2.create_property("http://example.org/property3"), graph2.create_literal("Object2"))
 resource3 = graph2.create_resource("http://example.org/subject3")
-resource3.add_property(graph2.create_property("http://example.org/property4"), Literal("Object3"))
+resource3.add_property(graph2.create_property("http://example.org/property4"), graph2.create_literal("Object3"))
 
 graph3 = dataset.get_named_graph("http://example.org/graph3")
 graph3.add(graph1)
@@ -37,6 +38,9 @@
 serialize(list(graph1.list_triples()), output, "application/n-triples") # "application/n-quads" should work
 print(output.getvalue())
 
+print("\nlen(graph1):\n")
+print(len(graph1))
+
 print("\nresource1.uri:\n")
 print(resource1.uri)
 

oxijen/model_impl/impl.py

@@ -1,6 +1,7 @@
 from oxijen.rdf_model import Resource, Property, Graph, Dataset
+from oxijen.model_impl.xsd import XSD
 from pyoxigraph import Store, Triple, BlankNode, NamedNode, Literal, Quad, DefaultGraph
-from typing import Iterator, Union, Optional
+from typing import Iterator, Union, Optional, Any
 
 class ResourceImpl(Resource):
 
@@ -62,13 +63,34 @@ def create_resource(self, uri: Optional[str] = None) -> Resource:
     def create_property(self, uri: str) -> Property:
         return ResourceImpl(NamedNode(uri), self)
 
+    def create_literal(self, value: str) -> Literal:
+        return Literal(value) # should it be xsd:string-typed by default as per RDF 1.1?
+
+    def create_typed_literal(self, value: Any, type_uri: Optional[str] = None) -> Literal:
+        if type_uri is None:
+            match value:
+                case int():
+                    type_uri = XSD.INTEGER.value
+                case str():
+                    type_uri = XSD.STRING.value
+                case float():
+                    type_uri = XSD.FLOAT.value
+                # TO-DO: support more types
+                case _:
+                    raise TypeError('Unsupported type conversion')
+
+        return Literal(str(value), datatype=NamedNode(type_uri))
+
 
 class GraphStoreImpl(GraphImpl):
 
     def __init__(self, store: Store, name: Union[BlankNode, NamedNode]):
         self.store = store
         self.name = name
 
+    def __len__(self) -> int:
+        return len(list(self.list_triples()))
+
     def list_triples(self) -> Iterator[Triple]:
         quads = self.store.quads_for_pattern(None, None, None, self.name)
 

oxijen/model_impl/xsd.py

@@ -0,0 +1,9 @@
+from enum import Enum
+
+class XSD(Enum):
+
+    NS : str = "http://www.w3.org/2001/XMLSchema#"
+
+    INTEGER = NS + "integer"
+    STRING = NS + "string"
+    FLOAT = NS + "float"

oxijen/rdf_model.py

@@ -1,5 +1,5 @@
 from abc import ABC, abstractmethod
-from typing import Iterator, Union, Optional
+from typing import Iterator, Union, Optional, Any
 from pyoxigraph import Store, Triple, Quad, Literal, NamedNode, BlankNode
 
 class Resource(ABC):
@@ -53,6 +53,10 @@ class Property(Resource):
 
 class Graph(ABC):
 
+    @abstractmethod
+    def __len__(self) -> int:
+        pass
+
     @abstractmethod
     def create_resource(self, uri: Optional[str] = None) -> Resource:
         pass
@@ -61,6 +65,14 @@ def create_resource(self, uri: Optional[str] = None) -> Resource:
     def create_property(self, uri: str) -> Property:
         pass
 
+    @abstractmethod
+    def create_literal(self, value: str) -> Literal:
+        pass
+
+    @abstractmethod
+    def create_typed_literal(self, value: Any, type_uri: Optional[str] = None) -> Literal:
+        pass
+
     @abstractmethod
     def list_triples(self) -> Iterator[Triple]:
         pass