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Comment by m3nu | Hacker News Reader

Earlier this year I was working on hybrid PDFs[1] that embed a full XML invoice. Standardized and promoted by the German and French.[2] One more thing to hide.

1: https://github.com/invoice-x/factur-x-ng 2: http://fnfe-mpe.org/factur-x/factur-x_en/

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This is actually pretty cool. I'v been working in an accounting company and i'v been thinking about such thing a lot lately. Is Factur-X used in practice in Germany and France? Do you know about some other similar things?

The lower-level library is used in Odoo ERP for example. Possibly others, as there are a few implementations[1] (mostly Java). This is lots of work because you need to create the XML yourself. I tried to make mappings between simple keywords and the XPaths of different XML standards (there are a bunch)[2]

So in theory you could just give a few keywords and get the full XML. Currently this is on hold, but if someone has a use case and wants to contribute, I'd be happy to continue working on it. I also provide this other library[3] that extracts some essential data from PDFs. The plan is to use them together to automatically build the XML from just the PDF.

1: https://www.invoice-x.org/related/

2: https://www.invoice-x.org/standards/

3: https://github.com/invoice-x/invoice2data

Thank you! I will look into these. I know the problems. As i was working in the accounting firm i was dealing with imports/exports from various accounting softwares a lot. In fact i'm currently working on an app which can convert between them as my side project.

As far as I understand this the "standard" is the XML that is being embedded inside PDF, so you need a small tool to extract the XML from the PDF and then you've got the standard XML invoice. The PDF is just for nice presentation.

I did a similar approach of using XML Stylesheets (XSL) to render the standard invoice as HTML when opened, this also looked nice.

Is the PDF rendered from the XML? If not that sounds mad.

Mad how? PDF is a notoriously bad format to extract data from, but great for visually representing the data to humans. XML is human unfriendly but good for structuring data so that software can read it. Embedding the machine readable XML representation of the data in the PDF ensures that both representations of the data are available always.

I think OP is concerned about conflicting data - the visual representation may not match the XML data.

...the visual representation may not match the XML data

Hopefully OP doesn't learn about how his medical history is possibly passed around.

https://en.wikipedia.org/wiki/Continuity_of_Care_Document

Given that it's possible to have javascript in a PDF as well, it wouldn't be too hard to have a bit of code that verifies the XML matches the human-readable version. Or, failing that, some sort of crypto signature to check both to see things haven't been tampered with.

As far as I can tell the standard prohibits PDF files with any dynamic content, including javascript. Also there is no point in embedding the verification code in the PDF if you don't trust its contents.

Because it will be easy to accidentally make the invoice say something different to the XML. Imagine a company accepts and pays out invoices via this PDF format...

It doesn't sound very safe and the draft I found online only describes various restrictions on the PDF and the expectation that the XML is to be seen as an alternative representation for processing. Nothing to enforce that the contents of both are identical or tamper proof. At best you could claim that an invoice were both don't match is invalid, however that would require manual verification.

Meanwhile I write the documentation of my xml configuration files in xsd and convert them to something readable using xslt. One set of data for processing and display everywhere and one less headache about duplicated and badly maintained data.

No, but it does include validation. I agree that it's mad for a person to use this, but having a machine use the API can help ensure that the PDF and XML always match

Mostly the other way round. There are 2 use cases I know of:

1. You generate invoices in your ERP and have all the info. To make your client's life easier, you embed the info as XML, so he doesn't need to type it from the PDF.

2. You get invoices without XML and use e.g. invoice2data[1] to extract key fields and then add them as XML for later.

1: https://github.com/invoice-x/invoice2data

I seem to remember JDEdwards marked up their PDF output in a way that made it easy to parse out the data.

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