Diff tool for XML Schema file?

Question

I was tasked with migrating an xsd generation tool to something new. But since the XSD's are part of a publicly published interface they should not change.
The new tool does things a bit differently, so when comparing the xsd's with a text diff tool I get a lot of differences, for example the order of global elements is different, order of enumeration tags is different, etc...

Anyone know a tool (or a method -> I do write code) that can compare XSD's functionally, ignoring changes that do not change the content of the XSD?

And since I have a lot of XSD's to compare (about 740 in total) I would prefer a tool that could do them all at once and then give me some kind of report with the details.

Answer 1

To summarise, addressing your requirements:

1. Comparison tool that can compare XSD files: Yes
2. Can identify changes in structure, not just content of XSD files: Yes
3. Can ignore expected changes: Yes
4. Orderless comparisons; avoiding false positives from moved elements: Yes
5. Compare all files at once: Yes, through batch processing
6. Produce a report with the details: Unclear what is needed here

XML Compare, developed by DeltaXML, is a structurally aware XML comparison tool that is able to identify change in both the structure and the content of XML files, including XSD.

In instances where elements have moved in the file but the order of said elements is not significant to the comparison, XML Compare has built in functionality for Comparing Orderless Elements. This can be customised extensively using XSLT as needed.

When you are expecting changes that do not need to be identified as change, you can use XML Compare's built in Ignoring Changes functionality which can again be customised using XSLT.

For bulk processing of your files, although XML Compare only compares files 1-to-1, it can be run via the command line, REST API and Java API. This means that by writing a batch file to queue up comparison operations, or if you use the REST API the comparison operations will be queued automatically.

Finally, to address your need for a report summarising the results, this depends on what you mean. XML Compare is capable of producing HTML reports from diff outputs that highlight changes in-line or side-by-side. It sounds however like you may be looking for a more statistical report on the results of the comparisons, for which XML Compare does not currently have a facility. It is worth noting however that the diff outputs produced by XML Compare are valid XML, and can be readily processed to identify the change attributes in the file.

Disclosure: I am an employee of DeltaXML.

Answer 2

That's quite a challenge, because so many differences are possible: you may have to make compromises depending on what you actually encounter. (For example, you may or may not need to bother with named model groups, depending on whether either of the schemas you are comparing actually uses them. Most schemas don't.)

If I were doing this (and of course I'm biased towards using my own tools) I would start by using Saxon's schema validator to generate SCM (schema component model) files for both schemas. This will do a fair bit of normalization, e.g. handling the difference between inline types and references to named global types. I would then write an XSLT stylesheet to do further normalization on the SCM files, for example sorting components into a canonical order, sorting enumeration values, and so on; also, eliminating the parts of the SCM files that aren't relevant, such as finite state machine details. I would then probably write a custom XSLT comparison module to compare the two normalized SCM files (along the lines of https://dvcs.w3.org/hg/xslt30-test/file/tip/runner/compare.xsl which is used for comparing XSLT test results) - the key being that you don't just want a boolean answer saying whether they are the same or different, you want to highlight the differences. Alternatively you could use fn:deep-equal to test whether they are the same, and then using a visual diff tool to examine them side-by-side if not.