Add an XSD

.gitmodules

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+[submodule "xml-schemas/ebu-tt-m-xsd"]
+	path = xml-schemas/ebu-tt-m-xsd
+	url = https://github.com/ebu/ebu-tt-m-xsd.git

schema-validator/README.md

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+# DAPT XSD Validator
+
+Basic command line utility for validating DAPT documents using
+the XML Schema Definition in the w3c/dapt repository.
+
+This script uses the MIT licensed [`xmlschema`](https://github.com/sissaschool/xmlschema) library.
+
+This script is provided as-is with no warranties of any kind.
+The repository's `LICENSE.md` applies, with the contents of this folder
+being considered a _code example_.
+
+## Build
+
+1. Install poetry - [installation instructions](https://python-poetry.org/docs/#installing-with-the-official-installer)
+2. Ensure you have a version of Python greater than or equal to 3.11 available
+for example with the command `poetry env use 3.11`
+3. Install the dependencies by running `poetry install`
+
+## Usage
+
+```sh
+poetry run validate -dapt_in path/to/dapt_file.ttml
+```
+
+or pass the document for validating in via stdin, e.g.:
+
+```sh
+poetry run validate < path/to/dapt_file.ttml
+```
+
+## Tests
+
+```sh
+poetry run python -m unittest
+```

schema-validator/pyproject.toml

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+[tool.poetry]
+name = "dapt-xsd-val"
+version = "0.1.0"
+description = "Thin wrapper around xmlschema to support XSD validation using the supplied DAPT XSD"
+authors = ["Nigel Megitt <[email protected]>"]
+readme = "README.md"
+packages = [
+    { include = "src" },
+    { include = "test" },
+]
+
+[tool.poetry.dependencies]
+python = ">=3.11"
+xmlschema = "^3.4.3"
+
+[tool.poetry.group.dev.dependencies]
+flake8 = "^7.1.2"
+
+[build-system]
+requires = ["poetry-core"]
+build-backend = "poetry.core.masonry.api"
+
+[tool.poetry.scripts]
+validate = "src.validate:main"

schema-validator/src/validate.py

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+import os
+import sys
+import argparse
+import xmlschema
+import logging
+
+logging.getLogger().setLevel(logging.INFO)
+
+
+schema_path = os.path.normpath(
+    os.path.join(
+        os.path.dirname(__file__),
+        '../../xml-schemas/dapt.xsd')
+)
+metadata_items_schema_path = os.path.normpath(
+    os.path.join(
+        os.path.dirname(__file__),
+        '../../xml-schemas/ttml2-metadata-items.xsd')
+)
+
+
+def validate_dapt(args):
+    # xmlschema gets baffled following the import of metadata_items,
+    # so make it load it explicitly instead, which seems to work.
+    schema_paths = [schema_path, metadata_items_schema_path]
+    logging.info('Creating schema from XSDs at {}'.format(schema_paths))
+    schema = xmlschema.XMLSchema(schema_paths)
+    schema.build()
+    if schema.validity:
+        logging.info('Schemas are valid')
+    else:
+        logging.error('Schemas are not valid, exiting early')
+        return -1
+
+    try:
+        logging.info('Validating document at {}'.format(args.dapt_in.name))
+        schema.validate(args.dapt_in)
+    except xmlschema.XMLSchemaValidationError as valex:
+        logging.error(str(valex))
+        logging.error('Document is not valid.')
+        return -1
+
+    logging.info(
+        'Document is syntactically valid with respect to the '
+        'DAPT XML Schema Definition; '
+        'this does not check all semantic requirements of the '
+        'DAPT specification.')
+    return 0
+
+
+def main():
+    parser = argparse.ArgumentParser()
+
+    parser.add_argument(
+        '-dapt_in',
+        type=argparse.FileType('rb'),
+        default=sys.stdin, nargs='?',
+        help='Input DAPT file to validate',
+        action='store')
+    parser.set_defaults(func=validate_dapt)
+
+    args = parser.parse_args()
+    return args.func(args)
+
+
+if __name__ == "__main__":
+    # execute only if run as a script
+    sys.exit(main())

schema-validator/test/fixtures/valid_dapt.ttml

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+<?xml version="1.0" encoding="UTF-8"?>
+<tt xmlns="http://www.w3.org/ns/ttml"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xmlns:tta="http://www.w3.org/ns/ttml#audio"
+    xmlns:ttm="http://www.w3.org/ns/ttml#metadata"
+    xmlns:ttp="http://www.w3.org/ns/ttml#parameter"
+    xmlns:daptm="http://www.w3.org/ns/ttml/profile/dapt#metadata"
+    xmlns:ebuttm="urn:ebu:tt:metadata"
+    ttp:contentProfiles="http://www.w3.org/ns/ttml/profile/dapt1.0/content"
+    daptm:scriptRepresents="audio"
+    daptm:scriptType="originalTranscript"
+    xml:lang="en">
+    <head>
+        <metadata>
+            <ttm:agent  type="person" xml:id="actor_A">
+                <ttm:name type="full">Matthias Schoenaerts</ttm:name>
+            </ttm:agent>
+            <ttm:agent type="character" xml:id="character_2">
+                <ttm:name type="alias">BOOKER</ttm:name>
+                <ttm:actor agent="actor_A"/>
+            </ttm:agent>
+        </metadata>
+    </head>
+    <body>
+        <div xml:id="se1" begin="3s" end="10s" ttm:agent="character_2" daptm:represents="audio.dialogue" daptm:onScreen="ON">
+            <ttm:desc daptm:descType="scene">high mountain valley</ttm:desc>
+            <metadata></metadata>
+            <p daptm:langSrc="en"><span>Look at this beautiful valley.</span></p>
+        </div>
+    </body>
+</tt>

schema-validator/test/test_validate.py

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+import os
+import unittest
+from argparse import Namespace
+from src.validate import validate_dapt
+
+fixture_dur = \
+    os.path.join(
+        os.path.dirname(__file__),
+        'fixtures')
+
+
+class testValidate(unittest.TestCase):
+    maxDiff = None
+
+    def testValidFile(self):
+        with open(
+            os.path.join(fixture_dur, 'valid_dapt.ttml'), newline='') \
+                as dapt_file:
+            result = validate_dapt(args=Namespace(dapt_in=dapt_file))
+
+        self.assertEqual(result, 0)

xml-schemas/README.md

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+# DAPT XSD Readme
+
+The [DAPT](https://www.w3.org/TR/dapt/) XML Schema is provided as an informative (i.e. non-normative) addition
+to the specification as an aid to implementers.
+
+The XML Schema is provided as an [XSD 1](https://www.w3.org/TR/xmlschema-1/) (XML Schema definition language) document.
+
+## Usage
+
+An XSD 1 conformant XML validator should be able to validate a DAPT document against the top level [`dapt.xsd`](dapt.xsd)
+schema document.
+
+As a convenience, a Python script is provided to allow use of the XSDs to validate
+a DAPT document using only open source libraries.
+
+## Design
+
+The DAPT XSD is designed to be inclusive of all content predicted from the DAPT specification,
+rather than defining attributes and elements from the DAPT specification
+and relying on external XSDs for other namespace vocabulary.
+This also permits DAPT-specific constraints, such as the prohibition of the `<animation>` element,
+or the requirement for the `daptm:scriptRepresents` attribute on the root `<tt>` element,
+can be applied.
+
+### Sources
+
+Structurally, much of the XSD consists of a copy of the [TTML2 XSD](https://github.com/w3c/ttml2/tree/main/spec/xsd), though in some cases changes have been
+made to represent those additional DAPT constraints.
+This means that if the TTML2 XSD changes, there could be a maintenance task to update the DAPT XSD.
+However it also simplifies usage.
+
+Additionally, DAPT namespaces and DAPT-specific data types are defined in imported files whose name is prefixed `dapt-`.
+
+EBU-TT Metadata is imported via a git submodule pointed at the XSD 1 version of the
+[EBU-TT Metadata schema](https://github.com/ebu/ebu-tt-m-xsd/tree/issue-0030-schema-v1).
+
+### Type restrictions
+
+Two mechanisms are used to enforce DAPT-specific type restrictions:
+
+1. DAPT-specific complex type definitions with `xs:complexContent` containing `xs:restriction` based on the TTML2 type.
+This method is used where attributes permitted on the TTML2 type are prohibited in DAPT, and/or when additional
+DAPT-specific attributes need to be permitted as extensions to the TTML2 element.
+The relevant element definitions then point to the restricted DAPT type rather than the base TTML2 type.
+2. Edits to remove DAPT-prohibited elements or attribute groups from TTML2 types - where this
+pattern is used, XML comments highlight the change in the XSD file.
+

xml-schemas/dapt-datatypes.xsd

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+<?xml version="1.0" encoding="UTF-8"?>
+<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
+    targetNamespace="http://www.w3.org/ns/ttml/profile/dapt#datatype"
+    xmlns:daptd="http://www.w3.org/ns/ttml/profile/dapt#datatype">
+    <xs:simpleType name="contentDescriptorType">
+        <xs:annotation>
+            <xs:documentation>
+                    descriptor-token ( descriptor-delimiter descriptor-token )*
+
+                    descriptor-token
+                        : (descriptorTokenChar)+
+
+                    descriptorTokenChar  # xsd:NMtoken without the "."
+                    : NameStartChar | "-" | [0-9] | #xB7 | [#x0300-#x036F] | [#x203F-#x2040]
+
+                    descriptor-delimiter
+                        : "."  # FULL STOP U+002E
+            </xs:documentation>
+        </xs:annotation>
+        <xs:restriction base="xs:string"/>
+    </xs:simpleType>
+
+</xs:schema>