[I think this thread is getting further away from BaseX, and might belong on query-talk instead, but on the other hand the use of XQuery as a back-end for Web Apps is definitely on the increase]
On Tue, 2013-05-14 at 11:14 -0600, James Wright wrote:
Hello Again, If this is the wrong forum for these type of questions let me know. By the way Liam I picked up your book last night, I like the flavor as it differs from my other reads such as those from Kay. Although I have been using XML for years and understand the core concepts it should be a great refresher.
Thanks, I wrote the boring chapters :-)
The Organizational Overall Problem: There aren't many people in my industry that use XQuery and xml in the way it was intended (IMHO). In fact most developers in my organization are rather uneducated in it and as you know there is some un-rational backlash as many correlate XML to the DOM and XPath/XSLT 1.0 and as a competitor to JSON which is ludicrous.
You're right, it's crazy and unfortunate.
XML was originally designed as an interoperable way to put SGML technical documentation on the Web in Netscape plugins!
The DOM has its issues of scale-ability which our products are currently running into. This isn't really xml's or the DOM's problem but simply poor implementation. As you know though, all that matters is perception.
If it helps, XQuery, Xpath 2 and later, XSLT 2 and later, are not DOM-based, but have an abstract data model, and are designed with performance very much in mind.
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we are stuck with a .NET XSLT 1.0 processor.
There's at least two .net-based XSLT 2 processors, and another in development. But I think that's maybe off-topic for this list ;)
We have two primary use cases:
- as a local db to replace the context DOM for our 'documents' which
in our case relates to Utilitiy GIS Designs of circuit, subdivisions, fiber, etc... I am thinking BaseX coupled with RestXQ could replace our DOM for local installs and allow ourselves to decouple from the Geodatabase and provide a browser based UI.
Yes, that will likely make sense.
- as a service for hosting uploading and allowing users/delivery and
support to view, query and modify complex sets of interrelated XML configuration files. Some of our applications have hundreds. Again all these documents follow a similar semantics however their is no defined schema for any of them.
You might want to look at W3C SML as a way of orchestrating validation for configuration management.
I think we can accomplish both of the above tasks using a single codebase and restXQ
it's likely although obviously you'll want separate database instances. Note also that there are size/performance issues with BaseX today if you have a lot of data - "a lot" is subjective but if it's multiple terabytes you'll probably need multiple database instances. The good news is that it's relatively easy to move to different XQuery engines if needed, and also that BaseX keeps improving so you might well not need to move :-) I do know of people with petabyte XQuery databases.
I have written an XQuery expression which using our 'common' xml semantics can ascertain entities/properties/relationships and distill this in the form of metadata which then using RestXQ is distilled into a metadata driven api for manipulated data centric xml documents.
This pattern is rather like creating a persistent "view" in SQL.
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The XML/BaseX Question:We need to be able to query effectively across relationships. Are there any facilities in XML/XQuery/3rd party that do this? I was hoping Id and IDref could accomplish this but as you stated that is not the case....
ID and IDREF support is almost certainly irrelevant here.
given $doc1 with <student sn="3016"><name>Simon</name></student> and $doc2 with <course><enrolled>3016</enrolled>.... you can easily do for $student in $doc1//student return $doc2//course[enrolled = $student/@sn] to get a list of courses with students from $doc1.
Basically I won't know before hand whether a child node is inline or a reference but would like to be able to query both as those they were the same.. If I had two nodes (I will call them parents) both with the same child. One has the actual inline child node and the other has just a reference to it. Lets say the child's attribute name is 'Tom'. I would like to be able to query like this and return both parents nodes: //parents[child/@name = 'Tom']
Write a function to do it. declare function local:get-children($input as element(*)) as element(*)* { for $child in $input/node() return if (local:isreferences($child)) then local:getreference($child) else $child }
and maybe declare function local:get-reference($input as element(*)) as element(*)* { return /documents[@id eq $input/@doc]//*[@id eq $input/ref] }
Anything? If not, is this a weird use case? I wouldn't think so.
I haven't encountered it, but RDF people often want something similar.
After this you can write e.g. /documents[@id = "36"]//parents[local:get-children()/@name = 'Tom']
I could imagine however that this use case may be hard to 'generally' support in xml given referential loops etc especially in a non schemed/validated document.
The nature of XML is that you don't necessarily know what's a reference when you create a document.
Liam