diff --git a/stix2/v21/observables.py b/stix2/v21/observables.py
index ed560a6..68115a0 100644
--- a/stix2/v21/observables.py
+++ b/stix2/v21/observables.py
@@ -760,6 +760,7 @@ class Software(_Observable):
         ('id', IDProperty(_type, spec_version='2.1')),
         ('name', StringProperty(required=True)),
         ('cpe', StringProperty()),
+        ('swid', StringProperty()),
         ('languages', ListProperty(StringProperty)),
         ('vendor', StringProperty()),
         ('version', StringProperty()),

Changes made to Software SCO, and its usage.
See https://github.com/oasis-tcs/cti-stix2/issues/220
diff --git a/stix2/test/v21/test_observed_data.py b/stix2/test/v21/test_observed_data.py
index 71bad46..abcbb7b 100644
--- a/stix2/test/v21/test_observed_data.py
+++ b/stix2/test/v21/test_observed_data.py
@@ -1300,6 +1300,7 @@ def test_software_example():
     s = stix2.v21.Software(
         name="Word",
         cpe="cpe:2.3:a:microsoft:word:2000:*:*:*:*:*:*:*",
+        swid="com.acme.rms-ce-v4-1-5-0",
         version="2002",
         vendor="Microsoft",
     )

pip install -e .[dev]
parse_log_pytest
requirements.txt
pytest pytest-cov pytest-xdist pytest-mock pytest-asyncio
3.6
requirements.txt
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
alabaster==0.7.13
antlr4-python3-runtime==4.9.3
async-generator==1.10
attrs==22.2.0
Babel==2.11.0
backcall==0.2.0
bleach==4.1.0
bump2version==1.0.1
bumpversion==0.6.0
certifi==2021.5.30
cfgv==3.3.1
charset-normalizer==2.0.12
coverage==6.2
decorator==5.1.1
defusedxml==0.7.1
distlib==0.3.9
docutils==0.17.1
entrypoints==0.4
execnet==1.9.0
filelock==3.4.1
identify==2.4.4
idna==3.10
imagesize==1.4.1
importlib-metadata==4.8.3
importlib-resources==5.2.3
iniconfig==1.1.1
ipython==7.16.3
ipython-genutils==0.2.0
jedi==0.17.2
Jinja2==3.0.3
jsonschema==3.2.0
jupyter-client==7.1.2
jupyter-core==4.9.2
jupyterlab-pygments==0.1.2
MarkupSafe==2.0.1
mistune==0.8.4
nbclient==0.5.9
nbconvert==6.0.7
nbformat==5.1.3
nbsphinx==0.4.3
nest-asyncio==1.6.0
nodeenv==1.6.0
packaging==21.3
pandocfilters==1.5.1
parso==0.7.1
pexpect==4.9.0
pickleshare==0.7.5
platformdirs==2.4.0
pluggy==1.0.0
pre-commit==2.17.0
prompt-toolkit==3.0.36
ptyprocess==0.7.0
py==1.11.0
Pygments==2.14.0
pyparsing==3.1.4
pyrsistent==0.18.0
pytest==7.0.1
pytest-asyncio==0.16.0
pytest-cov==4.0.0
pytest-mock==3.6.1
pytest-xdist==3.0.2
python-dateutil==2.9.0.post0
pytz==2025.2
PyYAML==6.0.1
pyzmq==25.1.2
requests==2.27.1
simplejson==3.20.1
six==1.17.0
snowballstemmer==2.2.0
Sphinx==1.8.6
sphinx-prompt==1.5.0
sphinxcontrib-serializinghtml==1.1.5
sphinxcontrib-websupport==1.2.4
-e git+https://github.com/oasis-open/cti-python-stix2.git@c2b71672f5504b975b113e3671e3279ceb503a65#egg=stix2
stix2-patterns==2.0.0
testpath==0.6.0
toml==0.10.2
tomli==1.2.3
tornado==6.1
tox==3.28.0
traitlets==4.3.3
typing_extensions==4.1.1
urllib3==1.26.20
virtualenv==20.16.2
wcwidth==0.2.13
webencodings==0.5.1
zipp==3.6.0

name: cti-python-stix2
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - certifi=2021.5.30=py36h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.3=he6710b0_2
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=1.1.1w=h7f8727e_0
  - pip=21.2.2=py36h06a4308_0
  - python=3.6.13=h12debd9_1
  - readline=8.2=h5eee18b_0
  - setuptools=58.0.4=py36h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - wheel=0.37.1=pyhd3eb1b0_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - alabaster==0.7.13
      - antlr4-python3-runtime==4.9.3
      - async-generator==1.10
      - attrs==22.2.0
      - babel==2.11.0
      - backcall==0.2.0
      - bleach==4.1.0
      - bump2version==1.0.1
      - bumpversion==0.6.0
      - cfgv==3.3.1
      - charset-normalizer==2.0.12
      - coverage==6.2
      - decorator==5.1.1
      - defusedxml==0.7.1
      - distlib==0.3.9
      - docutils==0.17.1
      - entrypoints==0.4
      - execnet==1.9.0
      - filelock==3.4.1
      - identify==2.4.4
      - idna==3.10
      - imagesize==1.4.1
      - importlib-metadata==4.8.3
      - importlib-resources==5.2.3
      - iniconfig==1.1.1
      - ipython==7.16.3
      - ipython-genutils==0.2.0
      - jedi==0.17.2
      - jinja2==3.0.3
      - jsonschema==3.2.0
      - jupyter-client==7.1.2
      - jupyter-core==4.9.2
      - jupyterlab-pygments==0.1.2
      - markupsafe==2.0.1
      - mistune==0.8.4
      - nbclient==0.5.9
      - nbconvert==6.0.7
      - nbformat==5.1.3
      - nbsphinx==0.4.3
      - nest-asyncio==1.6.0
      - nodeenv==1.6.0
      - packaging==21.3
      - pandocfilters==1.5.1
      - parso==0.7.1
      - pexpect==4.9.0
      - pickleshare==0.7.5
      - platformdirs==2.4.0
      - pluggy==1.0.0
      - pre-commit==2.17.0
      - prompt-toolkit==3.0.36
      - ptyprocess==0.7.0
      - py==1.11.0
      - pygments==2.14.0
      - pyparsing==3.1.4
      - pyrsistent==0.18.0
      - pytest==7.0.1
      - pytest-asyncio==0.16.0
      - pytest-cov==4.0.0
      - pytest-mock==3.6.1
      - pytest-xdist==3.0.2
      - python-dateutil==2.9.0.post0
      - pytz==2025.2
      - pyyaml==6.0.1
      - pyzmq==25.1.2
      - requests==2.27.1
      - simplejson==3.20.1
      - six==1.17.0
      - snowballstemmer==2.2.0
      - sphinx==1.8.6
      - sphinx-prompt==1.5.0
      - sphinxcontrib-serializinghtml==1.1.5
      - sphinxcontrib-websupport==1.2.4
      - stix2-patterns==2.0.0
      - testpath==0.6.0
      - toml==0.10.2
      - tomli==1.2.3
      - tornado==6.1
      - tox==3.28.0
      - traitlets==4.3.3
      - typing-extensions==4.1.1
      - urllib3==1.26.20
      - virtualenv==20.16.2
      - wcwidth==0.2.13
      - webencodings==0.5.1
      - zipp==3.6.0
prefix: /opt/conda/envs/cti-python-stix2

stix2/test/v21/test_observed_data.py::test_software_example
stix2/test/v21/test_observed_data.py::test_observed_data_example stix2/test/v21/test_observed_data.py::test_observed_data_example_with_refs stix2/test/v21/test_observed_data.py::test_observed_data_example_with_object_refs stix2/test/v21/test_observed_data.py::test_observed_data_object_constraint stix2/test/v21/test_observed_data.py::test_observed_data_example_with_bad_refs stix2/test/v21/test_observed_data.py::test_observed_data_example_with_non_dictionary stix2/test/v21/test_observed_data.py::test_observed_data_example_with_empty_dictionary stix2/test/v21/test_observed_data.py::test_parse_observed_data[{\n stix2/test/v21/test_observed_data.py::test_parse_observed_data[data1] stix2/test/v21/test_observed_data.py::test_parse_artifact_valid["0": stix2/test/v21/test_observed_data.py::test_parse_artifact_invalid["0": stix2/test/v21/test_observed_data.py::test_artifact_example_dependency_error stix2/test/v21/test_observed_data.py::test_parse_autonomous_system_valid["0": stix2/test/v21/test_observed_data.py::test_parse_email_address[{\n stix2/test/v21/test_observed_data.py::test_parse_email_message[\n stix2/test/v21/test_observed_data.py::test_parse_email_message_not_multipart[\n stix2/test/v21/test_observed_data.py::test_parse_file_archive["0": stix2/test/v21/test_observed_data.py::test_parse_email_message_with_at_least_one_error[\n stix2/test/v21/test_observed_data.py::test_parse_basic_tcp_traffic[\n stix2/test/v21/test_observed_data.py::test_parse_basic_tcp_traffic_with_error[\n stix2/test/v21/test_observed_data.py::test_observed_data_with_process_example stix2/test/v21/test_observed_data.py::test_artifact_example stix2/test/v21/test_observed_data.py::test_artifact_mutual_exclusion_error stix2/test/v21/test_observed_data.py::test_directory_example stix2/test/v21/test_observed_data.py::test_directory_example_ref_error stix2/test/v21/test_observed_data.py::test_domain_name_example stix2/test/v21/test_observed_data.py::test_domain_name_example_invalid_ref_type stix2/test/v21/test_observed_data.py::test_file_example stix2/test/v21/test_observed_data.py::test_file_example_with_NTFSExt stix2/test/v21/test_observed_data.py::test_file_example_with_empty_NTFSExt stix2/test/v21/test_observed_data.py::test_file_example_with_PDFExt stix2/test/v21/test_observed_data.py::test_file_example_with_PDFExt_Object stix2/test/v21/test_observed_data.py::test_file_example_with_RasterImageExt_Object stix2/test/v21/test_observed_data.py::test_raster_image_ext_parse stix2/test/v21/test_observed_data.py::test_raster_images_ext_create stix2/test/v21/test_observed_data.py::test_file_example_with_WindowsPEBinaryExt stix2/test/v21/test_observed_data.py::test_file_example_encryption_error stix2/test/v21/test_observed_data.py::test_ipv4_address_example stix2/test/v21/test_observed_data.py::test_ipv4_address_valid_refs stix2/test/v21/test_observed_data.py::test_ipv4_address_example_cidr stix2/test/v21/test_observed_data.py::test_ipv6_address_example stix2/test/v21/test_observed_data.py::test_mac_address_example stix2/test/v21/test_observed_data.py::test_network_traffic_example stix2/test/v21/test_observed_data.py::test_network_traffic_http_request_example stix2/test/v21/test_observed_data.py::test_network_traffic_icmp_example stix2/test/v21/test_observed_data.py::test_network_traffic_socket_example stix2/test/v21/test_observed_data.py::test_correct_socket_options stix2/test/v21/test_observed_data.py::test_incorrect_socket_options stix2/test/v21/test_observed_data.py::test_network_traffic_tcp_example stix2/test/v21/test_observed_data.py::test_mutex_example stix2/test/v21/test_observed_data.py::test_process_example stix2/test/v21/test_observed_data.py::test_process_example_empty_error stix2/test/v21/test_observed_data.py::test_process_example_empty_with_extensions stix2/test/v21/test_observed_data.py::test_process_example_windows_process_ext stix2/test/v21/test_observed_data.py::test_process_example_windows_process_ext_empty stix2/test/v21/test_observed_data.py::test_process_example_extensions_empty stix2/test/v21/test_observed_data.py::test_process_example_with_WindowsProcessExt_Object stix2/test/v21/test_observed_data.py::test_process_example_with_WindowsServiceExt stix2/test/v21/test_observed_data.py::test_process_example_with_WindowsProcessServiceExt stix2/test/v21/test_observed_data.py::test_url_example stix2/test/v21/test_observed_data.py::test_user_account_example stix2/test/v21/test_observed_data.py::test_user_account_unix_account_ext_example stix2/test/v21/test_observed_data.py::test_windows_registry_key_example stix2/test/v21/test_observed_data.py::test_x509_certificate_example stix2/test/v21/test_observed_data.py::test_x509_certificate_error stix2/test/v21/test_observed_data.py::test_new_version_with_related_objects stix2/test/v21/test_observed_data.py::test_objects_deprecation stix2/test/v21/test_observed_data.py::test_deterministic_id_same_extra_prop_vals stix2/test/v21/test_observed_data.py::test_deterministic_id_diff_extra_prop_vals stix2/test/v21/test_observed_data.py::test_deterministic_id_diff_contributing_prop_vals stix2/test/v21/test_observed_data.py::test_deterministic_id_no_contributing_props stix2/test/v21/test_observed_data.py::test_id_gen_recursive_dict_conversion_1 stix2/test/v21/test_observed_data.py::test_id_gen_recursive_dict_conversion_2
stix2/v21/observables.py
stix2/v21/observables.py