XML namespace errors

[woutdenolf]

I'm using the XML language plugin by Red Hat in VScode

I'm getting these errors:

I'm not an XML expert but the file http://definition.nexusformat.org/nxdl/nxdlTypes.xsd is missing. Perhaps that causes some of the errors?

[prjemian]

It's here:

definitions/nxdl.xsd

Lines 35 to 42 in 0592a98

	<xs:include schemaLocation="nxdlTypes.xsd">
	<xs:annotation>
	<xs:documentation>
	Definitions of the basic data types and unit types
	allowed in NXDL instance files.
	</xs:documentation>
	</xs:annotation>
	</xs:include>

How is this tool trying to find it? Perhaps assuming the targetNamespace URI is a valid URL?

definitions/nxdl.xsd

Line 4 in 0592a98

targetNamespace="http://definition.nexusformat.org/nxdl/3.1"

It is not required for the targetNamespace to be a valid web address, or even formatted as such, but it is customary for the formatting. I'm guessing this tool makes the assumption that the nxdlTypes.xsd file will be served from this web address. In our case, targetNamespace is a URI that is not a URL.

For reference about targetNameSpace, this SO post has helpful explanations. The W3schools has reference documentation on [targetNamespace(https://www.w3schools.com/xml/el_schema.asp) and the related xmlns.

[prjemian]

W3schools provides documentation for the XML <xs:include> element (where xs is the namespace of the XML Schema for XSD) and the xs symbol is declared here:

definitions/nxdl.xsd

Line 3 in 0592a98

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"

Note: The re-use of terms here is really mind numbing.

[woutdenolf]

The tool gets the namespace information from http://definition.nexusformat.org/nxdl/nxdl.xsd but the file nxdlTypes.xsd does not exist there...

[prjemian]

Note that since targetNamespace is not a URL (in our case), then attempts to access URL http://definition.nexusformat.org/nxdl/nxdlTypes.xsd give a 404 (not found) error, as expected. Nothing to fix here other than the assumption that a URI must always be a working URL.

[prjemian]

As discussed in #92 and answered in #835. Also referenced in #212.

[woutdenolf]

So this means I can only work on new nxdl.xml files inside the definitions repo and not anywhere else?

[woutdenolf]

The tool gets the namespace from

xsi:schemaLocation="http://definition.nexusformat.org/nxdl/3.1 ../nxdl.xsd"

which I had to change to this to work

xsi:schemaLocation="http://definition.nexusformat.org/nxdl/3.1 http://definition.nexusformat.org/nxdl/nxdl.xsd"

It finds it but gives lots of errors because "nxdlTypes.xsd" is not available in "http://definition.nexusformat.org/nxdl/" I presume.

[woutdenolf]

So this means I can only work on new nxdl.xml files inside the definitions repo and not anywhere else?

Isn't the idea of publishing an xml namespace that it can be used by validation tools everywhere?

[prjemian]

So this means I can only work on new nxdl.xml files inside the definitions repo and not anywhere else?

If you want to use such automation tools that assist you in editing and checking validity of NXDL (.nxdl.xml) files, then the answer is Yes. Inside a branch or fork.

[prjemian]

Isn't the idea of publishing an xml namespace that it can be used by validation tools everywhere?

Pick up the previous discussion: #835 (comment)

Propose the publishing of this URI as an actual URL in a new issue.

[woutdenolf]

Having a URL for nxdl.xsd but not for nxdlTypes.xsd makes no sense imo. Either you have a URL for all .xsd files or for none.

So yes I could propose that but the .xsd files refer to each other with URI's:

definitions/nxdl.xsd

Line 35 in 0592a98

<xs:include schemaLocation="nxdlTypes.xsd">

So I'm not sure this is even going to solve the problem.

[woutdenolf]

definitions/nxdl.xsd

Line 3 in 0592a98

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"

xs is the namespace of the XML Schema for XSD

From this and this description it seems that xs is the prefix of the "http://www.w3.org/2001/XMLSchema" namespace (a.k.a. the XML Schema, XML Schema Definition or XDS namespace). The name of an XML namespace is often a URL to avoid global collisions.

The re-use of terms here is really mind numbing.

Yes I'm losing my mind over here. For example XML Schema is apparently one of the several XML schema languages. That's like having a car brand called Car. Do you have a car, a Car or both?

[prjemian]

RIght: xs is the prefix we define for use in the nxdl.xsd file. The choice of xs follows a convention.

clarify: The http://www.w3.org/2001/XMLSchema namespace is a URI (a formatted string) that just happens to also be a URL (a page available from a web server).

Right: XML Schema is one of several (perhaps ~6 in common use?). They have different strengths. I believe we experimented with schematron as an alternative to better express differences between rules for base classes and application definitions.

Right: If we publish our XML Schema as a URL, we could publish both files (nxdl.xsd and nxdlTypes.xsd).

[woutdenolf]

So for XML validation to work for NXDL files located anywhere we would have the rely on schemaLocation being a URL which means

1. In all XML files replaces this

"xsi:schemaLocation="http://definition.nexusformat.org/nxdl/3.1 ../nxdl.xsd"

by this

xsi:schemaLocation="http://definition.nexusformat.org/nxdl/3.1 http://definition.nexusformat.org/nxdl/nxdl.xsd"

2. In nxdl.xsd replace this

<xs:include schemaLocation="nxdlTypes.xsd"> 

by this

<xs:include schemaLocation="http://definition.nexusformat.org/nxdl/nxdlTypes.xsd"> 

3. Deploy nxdlTypes.xsd to http://definition.nexusformat.org/nxdl/nxdlTypes.xsd (separate issue http://definition.nexusformat.org/nxdl/nxdlTypes.xsd is missing  #1032)

How does the content of http://definition.nexusformat.org/nxdl/ get build and deployed? Perhaps URI to URL substitution can be done in that process? We obviously don't want to do it in the .xsd and .xml files in this repository.

[woutdenolf]

Additional remarks:

• http://definition.nexusformat.org/nxdl/ contains deployments of the Nexus standard.
• The version of the Nexus Definition Language (i.e. the .xsd files) is the same as the version of the Nexus standard (i.e. the nxdl.xml files)
• http://definition.nexusformat.org/nxdl/ only contains version 3.1 (we are current at v2020.10)

So there are some inconsistencies:

The http://definition.nexusformat.org/nxdl/ structure should be
http://definition.nexusformat.org/nxdl/{version}/nxdl.xsd # the Nexus definition language
http://definition.nexusformat.org/nxdl/{version}/nxdlTypes.xsd # the Nexus definition language
http://definition.nexusformat.org/nxdl/{version}/definitions/*.nxdl.xml # the Nexus Standard
http://definition.nexusformat.org/nxdl/{version}/manual # the documentation

Edit: the NXDL source links in the manual could then also points to the deployed sources

[woutdenolf]

@FreddieAkeroyd Could you comment on how to deploy to http://definition.nexusformat.org/nxdl/ from github actions (if possible)?

[prjemian]

No work on this issue at 2022-06 Code Camp. Is it necessary to resolve this for release of NXDL now?

[woutdenolf]

We can keep it for the next release