Merge branch 'develop'HEADv0.23.03releasemain

11 files changed, 556 insertions, 47 deletions

diff --git a/test/extractor/generic/test_constant.py b/test/extractor/generic/test_constant.py
index 9dbaced..77ee02b 100644
--- a/test/extractor/generic/test_constant.py
+++ b/test/extractor/generic/test_constant.py
@@ -1,10 +1,5 @@
-"""
 
-Part of the bsie test suite.
-A copy of the license is provided with the project.
-Author: Matthias Baumgartner, 2022
-"""
-# imports
+# standard imports
 import unittest
 
 # bsie imports
@@ -20,11 +15,11 @@ class TestConstant(unittest.TestCase):
     def test_extract(self):
         schema = '''
             bse:author rdfs:subClassOf bsfs:Predicate ;
-                rdfs:domain bsfs:Entity ;
+                rdfs:domain bsn:Entity ;
                 rdfs:range xsd:string ;
                 bsfs:unique "true"^^xsd:boolean .
             bse:comment rdfs:subClassOf bsfs:Predicate ;
-                rdfs:domain bsfs:Entity ;
+                rdfs:domain bsn:Entity ;
                 rdfs:range xsd:string ;
                 bsfs:unique "false"^^xsd:boolean .
             '''
@@ -33,33 +28,33 @@ class TestConstant(unittest.TestCase):
             (ns.bse.comment, 'the quick brown fox jumps over the lazy dog.'),
             ]
         ext = Constant(schema, tuples)
-        node = _node.Node(ns.bsfs.Entity, '') # Blank node
+        node = _node.Node(ns.bsn.Entity, '') # Blank node
         p_author = ext.schema.predicate(ns.bse.author)
         p_comment = ext.schema.predicate(ns.bse.comment)
-        entity = ext.schema.node(ns.bsfs.Node).get_child(ns.bsfs.Entity)
-        string = ext.schema.literal(ns.bsfs.Literal).get_child(ns.xsd.string)
+        entity = ext.schema.node(ns.bsfs.Node).child(ns.bsn.Entity)
+        string = ext.schema.literal(ns.bsfs.Literal).child(ns.xsd.string)
         # baseline
         self.assertSetEqual(set(ext.extract(node, None, (p_author, p_comment))),
             {(node, p_author, 'Me, myself, and I'),
              (node, p_comment, 'the quick brown fox jumps over the lazy dog.')})
         # predicates is respected
-        p_foobar = ext.schema.predicate(ns.bsfs.Predicate).get_child(ns.bse.foobar, domain=entity, range=entity)
+        p_foobar = ext.schema.predicate(ns.bsfs.Predicate).child(ns.bse.foobar, domain=entity, range=entity)
         self.assertSetEqual(set(ext.extract(node, None, (p_author, p_foobar))),
             {(node, p_author, 'Me, myself, and I')})
         self.assertSetEqual(set(ext.extract(node, None, (p_comment, p_foobar))),
             {(node, p_comment, 'the quick brown fox jumps over the lazy dog.')})
-        p_barfoo = ext.schema.predicate(ns.bse.author).get_child(ns.bse.comment, domain=entity, range=string)
+        p_barfoo = ext.schema.predicate(ns.bse.author).child(ns.bse.comment, domain=entity, range=string)
         self.assertSetEqual(set(ext.extract(node, None, (p_foobar, p_barfoo))), set())
 
     def test_construct(self):
         # schema compliance
         schema = '''
             bse:author rdfs:subClassOf bsfs:Predicate ;
-                rdfs:domain bsfs:Entity ;
+                rdfs:domain bsn:Entity ;
                 rdfs:range xsd:string ;
                 bsfs:unique "true"^^xsd:boolean .
             bse:comment rdfs:subClassOf bsfs:Predicate ;
-                rdfs:domain bsfs:Entity ;
+                rdfs:domain bsn:Entity ;
                 rdfs:range xsd:string ;
                 bsfs:unique "false"^^xsd:boolean .
             '''
@@ -80,13 +75,13 @@ class TestConstant(unittest.TestCase):
     def test_eq(self):
         schema_a = '''
             bse:author rdfs:subClassOf bsfs:Predicate ;
-                rdfs:domain bsfs:Entity ;
+                rdfs:domain bsn:Entity ;
                 rdfs:range xsd:string ;
                 bsfs:unique "true"^^xsd:boolean .
             '''
         schema_b = '''
             bse:comment rdfs:subClassOf bsfs:Predicate ;
-                rdfs:domain bsfs:Entity ;
+                rdfs:domain bsn:Entity ;
                 rdfs:range xsd:string ;
                 bsfs:unique "false"^^xsd:boolean .
             '''
diff --git a/test/extractor/generic/test_path.py b/test/extractor/generic/test_path.py
index 820f402..0beb37e 100644
--- a/test/extractor/generic/test_path.py
+++ b/test/extractor/generic/test_path.py
@@ -1,14 +1,9 @@
-"""
 
-Part of the bsie test suite.
-A copy of the license is provided with the project.
-Author: Matthias Baumgartner, 2022
-"""
-# imports
+# standard imports
 import unittest
 
 # bsie imports
-from bsie.base import extractor
+from bsie.extractor import base
 from bsie.utils import bsfs, node as _node, ns
 
 # objects to test
@@ -29,31 +24,31 @@ class TestPath(unittest.TestCase):
 
     def test_schema(self):
         self.assertEqual(Path().schema,
-            bsfs.schema.Schema.from_string(extractor.SCHEMA_PREAMBLE + '''
+            bsfs.schema.from_string(base.SCHEMA_PREAMBLE + '''
                 bse:filename rdfs:subClassOf bsfs:Predicate ;
-                    rdfs:domain bsfs:File ;
+                    rdfs:domain bsn:Entity ;
                     rdfs:range xsd:string ;
-                    bsfs:unique "false"^^xsd:boolean .
+                    bsfs:unique "true"^^xsd:boolean .
                 '''))
 
     def test_extract(self):
         ext = Path()
-        node = _node.Node(ns.bsfs.File, '') # Blank node
+        node = _node.Node(ns.bsn.Entity, '') # Blank node
         content = '/tmp/foo/bar'
         p_filename = ext.schema.predicate(ns.bse.filename)
-        entity = ext.schema.node(ns.bsfs.Node).get_child(ns.bsfs.Entity)
-        string = ext.schema.literal(ns.bsfs.Literal).get_child(ns.xsd.string)
+        entity = ext.schema.node(ns.bsfs.Node).child(ns.bsn.Entity)
+        string = ext.schema.literal(ns.bsfs.Literal).child(ns.xsd.string)
 
         # baseline
         self.assertSetEqual(set(ext.extract(node, content, (p_filename, ))),
             {(node, p_filename, 'bar')})
         # predicates parameter is respected
-        p_foo = ext.schema.predicate(ns.bsfs.Predicate).get_child(ns.bse.foo, domain=entity, range=string) # unsupported predicate
+        p_foo = ext.schema.predicate(ns.bsfs.Predicate).child(ns.bse.foo, domain=entity, range=string) # unsupported predicate
         self.assertSetEqual(set(ext.extract(node, content, (p_filename, p_foo))),
             {(node, p_filename, 'bar')})
         self.assertSetEqual(set(ext.extract(node, content, (p_foo, ))), set())
         # predicates are validated
-        p_bar = p_foo.get_child(ns.bse.filename) # same URI but different hierarchy
+        p_bar = p_foo.child(ns.bse.filename) # same URI but different hierarchy
         self.assertSetEqual(set(ext.extract(node, content, (p_filename, p_bar))),
             {(node, p_filename, 'bar')})
         self.assertSetEqual(set(ext.extract(node, content, (p_bar, ))), set())
diff --git a/test/extractor/generic/test_stat.py b/test/extractor/generic/test_stat.py
index 3441438..0e83e24 100644
--- a/test/extractor/generic/test_stat.py
+++ b/test/extractor/generic/test_stat.py
@@ -1,15 +1,10 @@
-"""
 
-Part of the bsie test suite.
-A copy of the license is provided with the project.
-Author: Matthias Baumgartner, 2022
-"""
-# imports
+# standard imports
 import os
 import unittest
 
 # bsie imports
-from bsie.base import extractor
+from bsie.extractor import base
 from bsie.utils import bsfs, node as _node, ns
 
 # objects to test
@@ -30,31 +25,31 @@ class TestStat(unittest.TestCase):
 
     def test_schema(self):
         self.assertEqual(Stat().schema,
-            bsfs.schema.Schema.from_string(extractor.SCHEMA_PREAMBLE + '''
+            bsfs.schema.from_string(base.SCHEMA_PREAMBLE + '''
                 bse:filesize rdfs:subClassOf bsfs:Predicate ;
-                    rdfs:domain bsfs:File ;
+                    rdfs:domain bsn:Entity ;
                     rdfs:range xsd:integer ;
-                    bsfs:unique "false"^^xsd:boolean .
+                    bsfs:unique "true"^^xsd:boolean .
                 '''))
 
     def test_extract(self):
         ext = Stat()
-        node = _node.Node(ns.bsfs.File, '') # Blank node
+        node = _node.Node(ns.bsn.Entity, '') # Blank node
         content = os.stat(__file__)
         p_filesize = ext.schema.predicate(ns.bse.filesize)
-        entity = ext.schema.node(ns.bsfs.Node).get_child(ns.bsfs.Entity)
-        string = ext.schema.literal(ns.bsfs.Literal).get_child(ns.xsd.string)
+        entity = ext.schema.node(ns.bsfs.Node).child(ns.bsn.Entity)
+        string = ext.schema.literal(ns.bsfs.Literal).child(ns.xsd.string)
 
         # baseline
         self.assertSetEqual(set(ext.extract(node, content, (p_filesize, ))),
             {(node, p_filesize, content.st_size)})
         # predicates parameter is respected
-        p_foo = ext.schema.predicate(ns.bsfs.Predicate).get_child(ns.bse.foo, domain=entity, range=string) # unsupported predicate
+        p_foo = ext.schema.predicate(ns.bsfs.Predicate).child(ns.bse.foo, domain=entity, range=string) # unsupported predicate
         self.assertSetEqual(set(ext.extract(node, content, (p_filesize, p_foo))),
             {(node, p_filesize, content.st_size)})
         self.assertSetEqual(set(ext.extract(node, content, (p_foo, ))), set())
         # predicates are validated
-        p_bar = p_foo.get_child(ns.bse.filesizse) # same URI but different hierarchy
+        p_bar = p_foo.child(ns.bse.filesizse) # same URI but different hierarchy
         self.assertSetEqual(set(ext.extract(node, content, (p_filesize, p_bar))),
             {(node, p_filesize, content.st_size)})
         self.assertSetEqual(set(ext.extract(node, content, (p_bar, ))), set())
diff --git a/test/extractor/image/__init__.py b/test/extractor/image/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/test/extractor/image/__init__.py
diff --git a/test/extractor/image/test_colors_spatial.py b/test/extractor/image/test_colors_spatial.py
new file mode 100644
index 0000000..902ab6d
--- /dev/null
+++ b/test/extractor/image/test_colors_spatial.py
@@ -0,0 +1,95 @@
+
+# standard imports
+import os
+import unittest
+
+# external imports
+import PIL.Image
+
+# bsie imports
+from bsie.extractor import base
+from bsie.utils import bsfs, ns, node as _node
+
+# objects to test
+from bsie.extractor.image.colors_spatial import ColorsSpatial
+
+
+## code ##
+
+class TestColorsSpatial(unittest.TestCase):
+    def setUp(self):
+        # content id with default constructors (width=32, height=32, exp=4)
+        self.instance_prefix = 'https://schema.bsfs.io/ie/Literal/Array/Feature/ColorsSpatial'
+        self.predicate_prefix = 'https://schema.bsfs.io/ie/Node/Entity#colors_spatial_'
+        self.uuid = 'adee8d6c43687021e1c5bffe56bcfe727f1638d792744137181304ef889dac2a'
+
+    def test_essentials(self):
+        # clones are equal
+        self.assertEqual(ColorsSpatial(32, 32, 4), ColorsSpatial(32, 32, 4))
+        self.assertEqual(hash(ColorsSpatial(32, 32, 4)), hash(ColorsSpatial(32, 32, 4)))
+        # equal respects type
+        self.assertNotEqual(ColorsSpatial(32, 32, 4), 'hello world')
+        self.assertNotEqual(hash(ColorsSpatial(32, 32, 4)), hash('hello world'))
+        # equals respects width
+        self.assertNotEqual(ColorsSpatial(32, 32, 4), ColorsSpatial(16, 32, 4))
+        self.assertNotEqual(hash(ColorsSpatial(32, 32, 4)), hash(ColorsSpatial(16, 32, 4)))
+        # equals respects height
+        self.assertNotEqual(ColorsSpatial(32, 32, 4), ColorsSpatial(32, 16, 4))
+        self.assertNotEqual(hash(ColorsSpatial(32, 32, 4)), hash(ColorsSpatial(32, 16, 4)))
+        # equals respects exp
+        self.assertNotEqual(ColorsSpatial(32, 32, 4), ColorsSpatial(32, 32, 8))
+        self.assertNotEqual(hash(ColorsSpatial(32, 32, 4)), hash(ColorsSpatial(32, 32, 8)))
+        # string representation
+        self.assertEqual(str(ColorsSpatial()), 'ColorsSpatial')
+        self.assertEqual(repr(ColorsSpatial(64, 16, 2)), 'ColorsSpatial(64, 16, 2)')
+
+    def test_dimension(self):
+        self.assertEqual(ColorsSpatial.dimension(32, 32, 4), 3 * (32*32 + 8*8 + 2*2))
+        self.assertEqual(ColorsSpatial.dimension(16, 16, 8), 3 * (16*16 + 2*2))
+        self.assertEqual(ColorsSpatial.dimension(64, 64, 16), 3 * (64*64 + 4*4))
+
+    def test_schema(self):
+        schema = bsfs.schema.from_string(base.SCHEMA_PREAMBLE + f'''
+            <{self.instance_prefix}> rdfs:subClassOf bsa:Feature ;
+                # annotations
+                rdfs:label "Spatially dominant colors"^^xsd:string ;
+                schema:description "Domiant colors of subregions in an image."^^xsd:string ;
+                bsfs:dtype xsd:integer .
+
+            <{self.instance_prefix}#{self.uuid}> rdfs:subClassOf <{self.instance_prefix}> ;
+                bsfs:dimension "3276"^^xsd:integer ;
+                # annotations
+                <{self.instance_prefix}/args#width> "32"^^xsd:integer ;
+                <{self.instance_prefix}/args#height> "32"^^xsd:integer ;
+                <{self.instance_prefix}/args#exp> "4"^^xsd:float .
+
+            <{self.predicate_prefix}{self.uuid}> rdfs:subClassOf bsfs:Predicate ;
+                rdfs:domain bsn:Entity ;
+                rdfs:range <{self.instance_prefix}#{self.uuid}> ;
+                bsfs:unique "true"^^xsd:boolean .
+            ''')
+        self.assertEqual(schema, ColorsSpatial().schema)
+
+    def test_extract(self):
+        ext = ColorsSpatial(2,2,2)
+        img = PIL.Image.open(os.path.join(os.path.dirname(__file__), 'testimage.jpg'))
+        node = _node.Node(ns.bsn.Entity, bsfs.URI('http://example.com/entity#1234'))
+        principals = set(ext.principals)
+        self.assertEqual(len(principals), 1)
+        # valid invocation yields feature
+        ret = list(ext.extract(node, img, principals))
+        self.assertEqual(ret[0], (
+            node,
+            list(principals)[0],
+            (91, 127, 121, 94, 138, 167, 163, 134, 190, 138, 170, 156, 121, 142, 159)))
+        # principals is respected
+        self.assertListEqual(list(ext.extract(node, img, {})), [])
+
+
+
+## main ##
+
+if __name__ == '__main__':
+    unittest.main()
+
+## EOF ##
diff --git a/test/extractor/image/test_photometrics.py b/test/extractor/image/test_photometrics.py
new file mode 100644
index 0000000..fb219e2
--- /dev/null
+++ b/test/extractor/image/test_photometrics.py
@@ -0,0 +1,143 @@
+
+# standard imports
+import unittest
+
+# bsie imports
+from bsie.extractor import base
+from bsie.utils import bsfs, node as _node, ns
+
+# objects to test
+from bsie.extractor.image.photometrics import Exif, _gps_to_dec
+
+
+## code ##
+
+class TestExif(unittest.TestCase):
+
+    def test_gps_to_dec(self):
+        # deg+min+sec format
+        self.assertAlmostEqual(_gps_to_dec('29/1 58/1 45/1'.split()), 29.979167, 6)
+        self.assertAlmostEqual(_gps_to_dec('31 08 03'.split()), 31.134167, 6)
+        self.assertAlmostEqual(_gps_to_dec('20 40 586/10'.split()), 20.682944, 6)
+        self.assertAlmostEqual(_gps_to_dec('88/1 34 68/10'.split()), 88.568556, 6)
+        # deg+min format
+        self.assertAlmostEqual(_gps_to_dec('13 472167/10000 0/1 '.split()), 13.786945, 6)
+        self.assertAlmostEqual(_gps_to_dec('104/1 3215/100 0/1'.split()), 104.535833, 6)
+
+    def test_eq(self):
+        # identical instances are equal
+        self.assertEqual(Exif(), Exif())
+        self.assertEqual(hash(Exif()), hash(Exif()))
+        # comparison respects type
+        class Foo(): pass
+        self.assertNotEqual(Exif(), Foo())
+        self.assertNotEqual(hash(Exif()), hash(Foo()))
+        self.assertNotEqual(Exif(), 1234)
+        self.assertNotEqual(hash(Exif()), hash(1234))
+        self.assertNotEqual(Exif(), None)
+        self.assertNotEqual(hash(Exif()), hash(None))
+
+    def test_schema(self):
+        self.assertSetEqual({pred.uri for pred in Exif().schema.predicates()}, {
+            ns.bsfs.Predicate,
+            ns.bse.exposure,
+            ns.bse.aperture,
+            ns.bse.iso,
+            ns.bse.focal_length,
+            ns.bse.width,
+            ns.bse.height,
+            ns.bse.orientation,
+            ns.bse.orientation_label,
+            ns.bse.altitude,
+            ns.bse.latitude,
+            ns.bse.longitude,
+            })
+
+    def test_extract(self):
+        ext = Exif()
+        node = _node.Node(ns.bsfs.File, '') # Blank node
+        content = {
+            'Exif.Photo.ExposureTime': '10/600',
+            'Exif.Photo.FNumber': '48/10',
+            'Exif.Photo.ISOSpeedRatings': '400',
+            'Exif.Photo.FocalLength': '460/10',
+            'Exif.Photo.PixelXDimension': '4288',
+            'Exif.Photo.PixelYDimension': '2848',
+            'Exif.Image.Orientation': '1',
+            'Exif.GPSInfo.GPSAltitude': '431/1',
+            'Exif.GPSInfo.GPSLatitude': '46/1 11397/625 0/1',
+            'Exif.GPSInfo.GPSLongitude': '7/1 131250/2500 0/1',
+            }
+
+        # invalid principals are ignored
+        self.assertSetEqual(set(ext.extract(node, content, {ns.bse.filename})), set())
+        # extract finds all relevant information
+        self.assertSetEqual(set(ext.extract(node, content, {ext.schema.predicate(ns.bse.exposure)})),
+            {(node, ext.schema.predicate(ns.bse.exposure), 60.0)})
+        self.assertSetEqual(set(ext.extract(node, content, {ext.schema.predicate(ns.bse.aperture)})),
+            {(node, ext.schema.predicate(ns.bse.aperture), 4.8)})
+        self.assertSetEqual(set(ext.extract(node, content, {ext.schema.predicate(ns.bse.iso)})),
+            {(node, ext.schema.predicate(ns.bse.iso), 400)})
+        self.assertSetEqual(set(ext.extract(node, content, {ext.schema.predicate(ns.bse.focal_length)})),
+            {(node, ext.schema.predicate(ns.bse.focal_length), 46.0)})
+        self.assertSetEqual(set(ext.extract(node, content, {ext.schema.predicate(ns.bse.width)})),
+            {(node, ext.schema.predicate(ns.bse.width), 4288)})
+        self.assertSetEqual(set(ext.extract(node, content, {ext.schema.predicate(ns.bse.height)})),
+            {(node, ext.schema.predicate(ns.bse.height), 2848)})
+        self.assertSetEqual(set(ext.extract(node, content, {ext.schema.predicate(ns.bse.orientation)})),
+            {(node, ext.schema.predicate(ns.bse.orientation), 1)})
+        self.assertSetEqual(set(ext.extract(node, content, {ext.schema.predicate(ns.bse.orientation_label)})),
+            {(node, ext.schema.predicate(ns.bse.orientation_label), 'landscape')})
+        self.assertSetEqual(set(ext.extract(node, content, {ext.schema.predicate(ns.bse.altitude)})),
+            {(node, ext.schema.predicate(ns.bse.altitude), 431.0)})
+        self.assertSetEqual(set(ext.extract(node, content, {ext.schema.predicate(ns.bse.latitude)})),
+            {(node, ext.schema.predicate(ns.bse.latitude), 46.30392)})
+        self.assertSetEqual(set(ext.extract(node, content, {ext.schema.predicate(ns.bse.longitude)})),
+            {(node, ext.schema.predicate(ns.bse.longitude), 7.875)})
+
+        # check orientation label
+        self.assertSetEqual(set(ext.extract(
+            node, {
+                'Exif.Photo.PixelXDimension': '4288',
+                'Exif.Photo.PixelYDimension': '2848',
+                'Exif.Image.Orientation': '5',
+                },
+            {ext.schema.predicate(ns.bse.orientation_label)})),
+            {(node, ext.schema.predicate(ns.bse.orientation_label), 'portrait')})
+
+        # can pass multiple principals
+        self.assertSetEqual(set(ext.extract(node, content, {
+            ext.schema.predicate(ns.bse.exposure),
+            ext.schema.predicate(ns.bse.iso),
+            ext.schema.predicate(ns.bse.focal_length),
+            })), {
+            (node, ext.schema.predicate(ns.bse.exposure), 60.0),
+            (node, ext.schema.predicate(ns.bse.iso), 400),
+            (node, ext.schema.predicate(ns.bse.focal_length), 46.0),
+            })
+
+        # principals w/o content are ignored
+        self.assertSetEqual(set(ext.extract(
+            node,
+            content={'Exif.Photo.ExposureTime': '10/600'},
+            principals={
+                ext.schema.predicate(ns.bse.exposure),
+                ext.schema.predicate(ns.bse.iso),
+                ext.schema.predicate(ns.bse.focal_length),
+                })
+            ), {
+            (node, ext.schema.predicate(ns.bse.exposure), 60.0),
+            })
+
+        # empty content is acceptable
+        self.assertSetEqual(set(ext.extract(node, {}, set(ext.principals))), set())
+        # no principals is acceptable
+        self.assertSetEqual(set(ext.extract(node, content, set())), set())
+
+
+## main ##
+
+if __name__ == '__main__':
+    unittest.main()
+
+## EOF ##
diff --git a/test/extractor/image/testimage.jpg b/test/extractor/image/testimage.jpg
new file mode 100644
index 0000000..c80bb48
--- /dev/null
+++ b/test/extractor/image/testimage.jpg
diff --git a/test/extractor/test_base.py b/test/extractor/test_base.py
new file mode 100644
index 0000000..81865e1
--- /dev/null
+++ b/test/extractor/test_base.py
@@ -0,0 +1,65 @@
+
+# standard imports
+import unittest
+
+# bsie imports
+from bsie.utils import bsfs, ns
+
+# objects to test
+from bsie.extractor import base
+
+
+## code ##
+
+class StubExtractor(base.Extractor):
+    def __init__(self):
+        super().__init__(bsfs.schema.from_string(base.SCHEMA_PREAMBLE + '''
+            bse:author rdfs:subClassOf bsfs:Predicate ;
+                rdfs:domain bsn:Entity ;
+                rdfs:range xsd:string ;
+                bsfs:unique "false"^^xsd:boolean .
+            bse:comment rdfs:subClassOf bsfs:Predicate ;
+                rdfs:domain bsn:Entity ;
+                rdfs:range xsd:string ;
+                bsfs:unique "false"^^xsd:boolean .
+        '''))
+
+    def extract(self, subject, content, predicates):
+        raise NotImplementedError()
+
+class StubSub(StubExtractor):
+    pass
+
+class TestExtractor(unittest.TestCase):
+    def test_essentials(self):
+        ext = StubExtractor()
+        self.assertEqual(str(ext), 'StubExtractor')
+        self.assertEqual(repr(ext), 'StubExtractor()')
+        self.assertEqual(ext, StubExtractor())
+        self.assertEqual(hash(ext), hash(StubExtractor()))
+
+        sub = StubSub()
+        self.assertEqual(str(sub), 'StubSub')
+        self.assertEqual(repr(sub), 'StubSub()')
+        self.assertEqual(sub, StubSub())
+        self.assertEqual(hash(sub), hash(StubSub()))
+        self.assertNotEqual(ext, sub)
+        self.assertNotEqual(hash(ext), hash(sub))
+
+    def test_principals(self):
+        schema = bsfs.schema.Schema()
+        entity = schema.node(ns.bsfs.Node).child(ns.bsn.Entity)
+        string = schema.literal(ns.bsfs.Literal).child(ns.xsd.string)
+        p_author = schema.predicate(ns.bsfs.Predicate).child(ns.bse.author, domain=entity, range=string)
+        p_comment = schema.predicate(ns.bsfs.Predicate).child(ns.bse.comment, domain=entity, range=string)
+        ext = StubExtractor()
+        self.assertSetEqual(set(ext.principals),
+            {p_author, p_comment} | set(schema.predicates()) - {schema.predicate(ns.bsfs.Predicate)})
+
+
+## main ##
+
+if __name__ == '__main__':
+    unittest.main()
+
+## EOF ##
diff --git a/test/extractor/test_builder.py b/test/extractor/test_builder.py
new file mode 100644
index 0000000..fbb0895
--- /dev/null
+++ b/test/extractor/test_builder.py
@@ -0,0 +1,98 @@
+
+# standard imports
+import unittest
+
+# bsie imports
+from bsie.utils import errors
+
+# objects to test
+from bsie.extractor import ExtractorBuilder
+
+
+## code ##
+
+class TestExtractorBuilder(unittest.TestCase):
+    def test_iter(self):
+        # no specifications
+        self.assertListEqual(list(ExtractorBuilder([])), [])
+        # some specifications
+        builder = ExtractorBuilder([
+            {'bsie.extractor.generic.path.Path': {}},
+            {'bsie.extractor.generic.stat.Stat': {}},
+            {'bsie.extractor.generic.path.Path': {}},
+            ])
+        self.assertListEqual(list(builder), [0, 1, 2])
+
+    def test_build(self):
+        # simple and repeated extractors
+        builder = ExtractorBuilder([
+            {'bsie.extractor.generic.path.Path': {}},
+            {'bsie.extractor.generic.stat.Stat': {}},
+            {'bsie.extractor.generic.path.Path': {}},
+            ])
+        ext = [builder.build(0), builder.build(1), builder.build(2)]
+        import bsie.extractor.generic.path
+        import bsie.extractor.generic.stat
+        self.assertListEqual(ext, [
+            bsie.extractor.generic.path.Path(),
+            bsie.extractor.generic.stat.Stat(),
+            bsie.extractor.generic.path.Path(),
+            ])
+        # out-of-bounds raises KeyError
+        self.assertRaises(IndexError, builder.build, 3)
+
+        # building with args
+        builder = ExtractorBuilder([
+            {'bsie.extractor.generic.constant.Constant': {
+                'schema': '''
+                    bse:author rdfs:subClassOf bsfs:Predicate ;
+                        rdfs:domain bsn:Entity ;
+                        rdfs:range xsd:string ;
+                        bsfs:unique "true"^^xsd:boolean .
+                    bse:rating rdfs:subClassOf bsfs:Predicate ;
+                        rdfs:domain bsn:Entity ;
+                        rdfs:range xsd:integer ;
+                        bsfs:unique "true"^^xsd:boolean .
+                    ''',
+                'tuples': [
+                    ('https://schema.bsfs.io/ie/Node/Entity#author', 'Me, myself, and I'),
+                    ('https://schema.bsfs.io/ie/Node/Entity#rating', 123),
+                    ],
+            }}])
+        obj = builder.build(0)
+        import bsie.extractor.generic.constant
+        self.assertEqual(obj, bsie.extractor.generic.constant.Constant('''
+                    bse:author rdfs:subClassOf bsfs:Predicate ;
+                        rdfs:domain bsn:Entity ;
+                        rdfs:range xsd:string ;
+                        bsfs:unique "true"^^xsd:boolean .
+                    bse:rating rdfs:subClassOf bsfs:Predicate ;
+                        rdfs:domain bsn:Entity ;
+                        rdfs:range xsd:integer ;
+                        bsfs:unique "true"^^xsd:boolean .
+                    ''', [
+            ('https://schema.bsfs.io/ie/Node/Entity#author', 'Me, myself, and I'),
+            ('https://schema.bsfs.io/ie/Node/Entity#rating', 123),
+            ]))
+
+        # building with invalid args
+        self.assertRaises(errors.BuilderError, ExtractorBuilder(
+            [{'bsie.extractor.generic.path.Path': {'foo': 123}}]).build, 0)
+        # non-dict build specification
+        self.assertRaises(TypeError, ExtractorBuilder(
+            [('bsie.extractor.generic.path.Path', {})]).build, 0)
+        # multiple keys per build specification
+        self.assertRaises(TypeError, ExtractorBuilder(
+            [{'bsie.extractor.generic.path.Path': {},
+              'bsie.extractor.generic.stat.Stat': {}}]).build, 0)
+        # non-dict value for kwargs
+        self.assertRaises(TypeError, ExtractorBuilder(
+            [{'bsie.extractor.generic.path.Path': 123}]).build, 0)
+
+
+## main ##
+
+if __name__ == '__main__':
+    unittest.main()
+
+## EOF ##
diff --git a/test/extractor/test_preview.py b/test/extractor/test_preview.py
new file mode 100644
index 0000000..6526783
--- /dev/null
+++ b/test/extractor/test_preview.py
@@ -0,0 +1,123 @@
+
+# standard imports
+import io
+import os
+import unittest
+
+# external imports
+import PIL.Image
+
+# bsie imports
+from bsie.extractor import base
+from bsie.utils import bsfs, node as _node, ns
+from bsie.reader.preview import Preview as Reader
+
+# objects to test
+from bsie.extractor.preview import Preview
+
+
+## code ##
+
+class TestPreview(unittest.TestCase):
+    def test_eq(self):
+        # identical instances are equal
+        self.assertEqual(Preview([1,2,3]), Preview([1,2,3]))
+        self.assertEqual(hash(Preview([1,2,3])), hash(Preview([1,2,3])))
+        # comparison respects max_sides
+        self.assertNotEqual(Preview([1,2,3]), Preview([1,2]))
+        self.assertNotEqual(hash(Preview([1,2,3])), hash(Preview([1,2])))
+        self.assertNotEqual(Preview([1,2]), Preview([1,2,3]))
+        self.assertNotEqual(hash(Preview([1,2])), hash(Preview([1,2,3])))
+        # comparison respects type
+        class Foo(): pass
+        self.assertNotEqual(Preview([1,2,3]), Foo())
+        self.assertNotEqual(hash(Preview([1,2,3])), hash(Foo()))
+        self.assertNotEqual(Preview([1,2,3]), 123)
+        self.assertNotEqual(hash(Preview([1,2,3])), hash(123))
+        self.assertNotEqual(Preview([1,2,3]), None)
+        self.assertNotEqual(hash(Preview([1,2,3])), hash(None))
+
+    def test_schema(self):
+        self.assertEqual(Preview([1,2,3]).schema,
+            bsfs.schema.from_string(base.SCHEMA_PREAMBLE + '''
+                bsn:Preview rdfs:subClassOf bsfs:Node .
+                bsl:BinaryBlob rdfs:subClassOf bsfs:Literal .
+                <https://schema.bsfs.io/ie/Literal/BinaryBlob/JPEG> rdfs:subClassOf bsl:BinaryBlob .
+
+                bse:preview rdfs:subClassOf bsfs:Predicate ;
+                    rdfs:domain bsn:Entity ;
+                    rdfs:range bsn:Preview ;
+                    bsfs:unique "false"^^xsd:boolean .
+
+                bsp:width rdfs:subClassOf bsfs:Predicate ;
+                    rdfs:domain bsn:Preview ;
+                    rdfs:range xsd:integer ;
+                    bsfs:unique "true"^^xsd:boolean .
+
+                bsp:height rdfs:subClassOf bsfs:Predicate ;
+                    rdfs:domain bsn:Preview ;
+                    rdfs:range xsd:integer ;
+                    bsfs:unique "true"^^xsd:boolean .
+
+                bsp:asset rdfs:subClassOf bsfs:Predicate ;
+                    rdfs:domain bsn:Preview ;
+                    rdfs:range <https://schema.bsfs.io/ie/Literal/BinaryBlob/JPEG> ;
+                    bsfs:unique "true"^^xsd:boolean .
+
+                '''))
+
+    def test_extract(self):
+        # setup dependents
+        rdr = Reader()
+        subject = _node.Node(ns.bsn.Entity)
+        path = os.path.join(os.path.dirname(__file__), 'testimage.jpg')
+
+        # setup extractor
+        ext = Preview(max_sides=[10])
+        principals = set(ext.principals)
+        self.assertEqual(principals, {ext.schema.predicate(ns.bse.preview)})
+        # skip unknown predicates
+        gen = rdr(path)
+        self.assertSetEqual(set(), set(ext.extract(subject, gen,
+            {ext.schema.predicate(ns.bsfs.Predicate).child(ns.bse.unknown)})))
+        gen(10) # NOTE: consume some image to avoid resource error warning
+        # extract a preview
+        triples = set(ext.extract(subject, rdr(path), principals))
+        thumbs = {node for node, _, _ in triples if node.node_type == ns.bsn.Preview}
+        self.assertEqual(len(thumbs), 1)
+        thumb = list(thumbs)[0]
+        # test properties
+        self.assertTrue(triples.issuperset({
+            (subject, ext.schema.predicate(ns.bse.preview), thumb),
+            (thumb, ext.schema.predicate(ns.bsp.width), 10),
+            (thumb, ext.schema.predicate(ns.bsp.height), 10),
+            }))
+        # test image data
+        rawdata = {val for _, pred, val in triples if pred == ext.schema.predicate(ns.bsp.asset)}
+        self.assertEqual(len(rawdata), 1)
+        data = io.BytesIO(list(rawdata)[0])
+        data.seek(0)
+        img = PIL.Image.open(data)
+        self.assertEqual(img.size, (10, 10))
+        self.assertEqual(sum(band for pix in img.getdata() for band in pix), 0)
+
+        # setup extractor
+        ext = Preview(max_sides=[10, 20])
+        principals = set(ext.principals)
+        self.assertEqual(principals, {ext.schema.predicate(ns.bse.preview)})
+        # extract a preview
+        triples = set(ext.extract(subject, rdr(path), principals))
+        thumbs = {node for node, _, _ in triples if node.node_type == ns.bsn.Preview}
+        self.assertEqual(len(thumbs), 2)
+        self.assertSetEqual({10, 20}, {
+            value for _, pred, value in triples if pred == ext.schema.predicate(ns.bsp.width)})
+        self.assertSetEqual({10, 20}, {
+            value for _, pred, value in triples if pred == ext.schema.predicate(ns.bsp.height)})
+
+
+## main ##
+
+if __name__ == '__main__':
+    unittest.main()
+
+## EOF ##
diff --git a/test/extractor/testimage.jpg b/test/extractor/testimage.jpg
new file mode 100644
index 0000000..4c2aca5
--- /dev/null
+++ b/test/extractor/testimage.jpg