nxdlTypes: invalid XML schema

[woutdenolf]

import xmlschema
xmlschema.XMLSchema("nxdl.xsd")

Traceback (most recent call last):
  File "/home/denolf/virtualenvs/nexus/lib/python3.10/site-packages/xmlschema/validators/schemas.py", line 1197, in _parse_inclusions
    self.include_schema(location, self.base_url)
  File "/home/denolf/virtualenvs/nexus/lib/python3.10/site-packages/xmlschema/validators/schemas.py", line 1264, in include_schema
    schema = type(self)(
  File "/home/denolf/virtualenvs/nexus/lib/python3.10/site-packages/xmlschema/validators/schemas.py", line 482, in __init__
    self.parse_error(e.reason or e, elem=e.elem)
  File "/home/denolf/virtualenvs/nexus/lib/python3.10/site-packages/xmlschema/validators/xsdbase.py", line 196, in parse_error
    raise error
xmlschema.validators.exceptions.XMLSchemaParseError: character data between child elements not allowed:

Schema component:

  <xs:element xmlns:xs="http://www.w3.org/2001/XMLSchema" name="example">m^2</xs:element>

Path: /xs:schema/xs:simpleType[4]/xs:annotation/xs:documentation/xs:element[1]

Schema URL: file:///tmp/nexus_definitions/nxdlTypes.xsd

Origin URL: file:///tmp/nexus_definitions/nxdl.xsd

[woutdenolf]

This was created in #592 to make the unit examples machine readable. Unfortunately this is not a valid XML schema: https://www.w3schools.com/xml/el_documentation.asp

[prjemian]

Thanks. Mea culpa. I'll look at it later today.

…

On Sun, Mar 3, 2024, 8:49 AM Wout De Nolf ***@***.***> wrote: This was create in #592 <#592> to make the unit example machine readable. Unfortunately this is not a valid XML schema: https://www.w3schools.com/xml/el_documentation.asp — Reply to this email directly, view it on GitHub <#1368 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AARMUMHN6DJOPZX22ZGW3ZLYWM2ALAVCNFSM6AAAAABED7TLG2VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMYTSNZVGE4DMNZZHE> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[prjemian]

At issue here is the use of xs:element element(s) within an xs:documentation element. The error is due to the presence of text content in the xs:element element:

definitions/nxdlTypes.xsd

Lines 87 to 95 in 4c09c77

	<xs:simpleType name="NX_ANGLE">
	<xs:annotation>
	<xs:documentation>
	units of angle
	<xs:element name="example">rad</xs:element>
	</xs:documentation>
	</xs:annotation>
	<xs:restriction base="xs:string" />
	</xs:simpleType>

The intent of PR #592:

makes the examples machine-readable

The examples should be re-factored to make the XML Schema file valid, yet allow the units to be machine-readable.

[prjemian]

@woutdenolf : Why are you convinced the XML Schema file nxdlTypes.xsd is not a valid XML Schema file?

The XML Schema files (nxdl.xsd and nxdlTypes.xsd) are checked (by the lxml package) each time they are loaded in the current unit testing:

definitions/dev_tools/tests/test_nxdl.py

Line 30 in 4c09c77

validate_definition(nxdl_file, xml_schema)

definitions/dev_tools/nxdl/syntax.py

Line 23 in 4c09c77

xml_schema = nxdl_schema()

definitions/dev_tools/nxdl/syntax.py

Line 12 in 4c09c77

return lxml.etree.XMLSchema(lxml.etree.parse(get_xsd_file()))

https://github.com/nexusformat/definitions/blob/4c09c7718c41dc90eb996475efdf1c0d30fb1d5d/dev_tools/globals/directories.py#L40C30-L40C44

definitions/dev_tools/globals/directories.py

Line 116 in 4c09c77

_XSD_FILE_NAME = "nxdl.xsd"

When I load this file into a XML Schema editor in a new installation of the eclipse IDE (eclipse.org), the validator for such XML Schemas does not show any errors on these xs:element elements within a xs:document element. (Errors would be flagged by a red icon, all the icons are green)

The W3Schools page you referenced state that a xs:documentation element can contain

Any well-formed XML content

[prjemian]

On the xmlschema page on PyPI, there is an example using XSD 1.1. It shows the exact same error as you described above. According to the docs, you are using the XSD 1.0 support.

Would it help to add an additional attribute of type="xs:string" to each of the xs:elements elements?

				<xs:element name="example">m^2</xs:element>
				<xs:element name="example">barns</xs:element>

would change to

				<xs:element name="example" type="xs:string">m^2</xs:element>
				<xs:element name="example" type="xs:string">barns</xs:element>

[woutdenolf]

Adding type="xs:string" does not help

Traceback (most recent call last):
  File "/home/denolf/virtualenvs/nexus/lib/python3.10/site-packages/xmlschema/validators/schemas.py", line 1197, in _parse_inclusions
    self.include_schema(location, self.base_url)
  File "/home/denolf/virtualenvs/nexus/lib/python3.10/site-packages/xmlschema/validators/schemas.py", line 1264, in include_schema
    schema = type(self)(
  File "/home/denolf/virtualenvs/nexus/lib/python3.10/site-packages/xmlschema/validators/schemas.py", line 482, in __init__
    self.parse_error(e.reason or e, elem=e.elem)
  File "/home/denolf/virtualenvs/nexus/lib/python3.10/site-packages/xmlschema/validators/xsdbase.py", line 196, in parse_error
    raise error
xmlschema.validators.exceptions.XMLSchemaParseError: character data between child elements not allowed:

Schema component:

  <xs:element xmlns:xs="http://www.w3.org/2001/XMLSchema" name="example" type="xs:string">rad</xs:element>

Path: /xs:schema/xs:simpleType[2]/xs:annotation/xs:documentation/xs:element

Schema URL: file:///tmp/nexus_definitions/nxdlTypes.xsd

Origin URL: file:///tmp/nexus_definitions/nxdl.xsd

Also using XMLSchema11 does not change anything

import xmlschema
xmlschema.XMLSchema11("nxdl.xsd")

I believe we are using "1.0" anyway

<?xml version="1.0" encoding="UTF-8"?>

Why are you convinced the XML Schema file nxdlTypes.xsd is not a valid XML Schema file?

"Convinced" is a strong word. The validator I used said character data between child elements not allowed so I thought there was an issue. But maybe there is an issue with the validator. I'll investigate.

Any well-formed XML content

I did not understand what that meant.

[prjemian]

What about xmlschema.XMLSchema("nxdl.xsd", validation="lax")? The default is strict. I'm thinking the xmlparser package is different (and more strict) than the other two tools I showed above.

Well-formed XML content adheres to the XML standard:

• XML documents must have a root element
• XML elements must have a closing tag
• XML tags are case sensitive
• XML elements must be properly nested
• XML attribute values must be quoted

Valid XML means additional rules must be met. Valid XML must adhere to the DTD or schema. In this case, it is the schema for XML Schema files.

[woutdenolf]

With validation="lax" the exception is indeed not raised. I asked the xmlschema developers what rule character data between child elements not allowed refers too.

Thanks for looking into this @prjemian !

[prjemian]

Their example suggested the root cause to me. In their example, which produced the same error message, the problem was produced from the xs:element when the type was not specified.

As I understand it, type defaults to xs:string. Perhaps the strict mode (in xmlparser) does not assume this default? Defining the type did not solve the problem but dropping the mode to lax ignores this problem.

[woutdenolf]

It turns out to be an error in the validator (mixed vs. element-only). Sorry for the noise!

[prjemian]

Thanks for testing our foundation structures!

[woutdenolf]

In fact there is a problem as pointed out here: sissaschool/xmlschema#390 (comment)

It is not xs:documentation which is wrong (it can have elements) but it is xs:element itself (cannot have text).