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After the release of a set of Azure Functions that will help us minimize or completely remove the need for an Integration Account:

Today, I’m going to release a new function – validate XML against DTD – that will bring additional capabilities to Logic App Consumption and Standard since this functionality is not currently supported in either of the tiers nor with the support of the Integration Account.

DTD? What is a DTD?

Yes, this is probably old school, which is not often used nowadays. But DTD, which stands for Document Type Definition, allows you to define the structure and the legal elements and attributes of an XML document.

This is a sample of a DTD file:

And this is a sample of an XML message with a reference to a DTD:

   My stock
   (099) 999-9999

The DOCTYPE declaration above contains a reference to a DTD file.

Although the use of DTDs is not very frequent to see these days, it is still very common to encounter this in RosettaNet PIPs.

Validate XML against DTD

A Document Type Definition (DTD) is a document that describes the structure of an XML document, what elements and attributes it contains, and what values it may have. DTDs form part of the W3C’s XML Standard but are typically considered to be a separate schema technology and are not typically used in conjunction with other schema formats like XSD and so on.

A DTD document can be embedded within an XML file or can exist on its own. When it is not embedded, normally, there are two ways to reference the DTD:

  • Using the PUBLIC keyword: This format is generally used to declare publicly available DTDs, standard character sets, and commonly used notations

  • Or using the SYSTEM keyword: These entities are not assumed to be known to a receiving system. Thus, such entities require a full declaration of system identification (path, etc.) when they are exchanged.
    • The SYSTEM identifier specifies the location of the DTD file. Since it does not
      start with a prefix like http:/or file:/, the path is relative to the location of
      the XML document.

This Azure Function allows you to perform XML validations against a DTD file. The function only accepts DTDs defined using the SYSTEM keyword.

To trigger this function, you need to:

  • In the Body, the XML payload that you want to be validated.
  • You should specify the following mandatory headers:
    • Content-Type as text/xml (or application/xml).
    • DTDFileName with the name of the DTD file present in the storage account.

The response will be a:

  • 200 OK – Validation successful. If it’s a valid message.
  • Or 400 Bad Request with a list of errors if there is something invalid.

Where can I download it?

You can download the complete Azure Functions source code here:

Hope you find this helpful! So, if you liked the content or found it useful and want to help me write more, you can buy (or help me buy) my son a Star Wars Lego! 

Author: Sandro Pereira

Sandro Pereira lives in Portugal and works as a consultant at DevScope. In the past years, he has been working on implementing Integration scenarios both on-premises and cloud for various clients, each with different scenarios from a technical point of view, size, and criticality, using Microsoft Azure, Microsoft BizTalk Server and different technologies like AS2, EDI, RosettaNet, SAP, TIBCO etc.

He is a regular blogger, international speaker, and technical reviewer of several BizTalk books all focused on Integration. He is also the author of the book “BizTalk Mapping Patterns & Best Practices”. He has been awarded MVP since 2011 for his contributions to the integration community.
View all posts by Sandro Pereira