Feature: document metadata (#123)

* Rework metadata structure in processing messages to be a subgraph
* Add subgraph creation for tg-load-pdf and tg-load-text based on command-line passing of doc attributes
* Document metadata is added to knowledge graph with subjectOf linkage to extracted entities

trustgraph-base/trustgraph/knowledge/organization.py

@@ -0,0 +1,40 @@
+
+from . defs import *
+from .. schema import Triple, Value
+
+class Organization:
+    def __init__(self, id, name=None, description=None):
+        self.id = id
+        self.name = name
+        self.description = description
+
+    def emit(self, emit):
+
+        emit(Triple(
+            s=Value(value=self.id, is_uri=True),
+            p=Value(value=IS_A, is_uri=True),
+            o=Value(value=ORGANIZATION, is_uri=True)
+        ))
+
+        if self.name:
+
+            emit(Triple(
+                s=Value(value=self.id, is_uri=True),
+                p=Value(value=LABEL, is_uri=True),
+                o=Value(value=self.name, is_uri=False)
+            ))
+
+            emit(Triple(
+                s=Value(value=self.id, is_uri=True),
+                p=Value(value=NAME, is_uri=True),
+                o=Value(value=self.name, is_uri=False)
+            ))
+
+        if self.description:
+
+            emit(Triple(
+                s=Value(value=self.id, is_uri=True),
+                p=Value(value=DESCRIPTION, is_uri=True),
+                o=Value(value=self.description, is_uri=False)
+            ))
+