topic Re: Reference Library for Converting Between LabVIEW and XML Data (GXML) in Components

Reference Library for Converting Between LabVIEW and XML Data (GXML)

ninjaphil — Thu, 29 Feb 2024 21:11:20 GMT

Please provide feedback, comments and questions on the Reference Library for Converting Between LabVIEW and XML Data (GXML) in this thread.

The latest version of the NI GXML Library is availble in VIPM on the NI LabVIEW Tools Network repository.

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

dotan — Thu, 17 Dec 2009 14:31:45 GMT

I am unable to parse a simple xml file:

<?xml version="1.0" encoding="utf-8"?>
<Timerscript>
<Options Units="Ticks" MaskHex="F" FlickerHex="F" SaveLastFew="F" />
<Revisions>
    <R0>Revision: 0, 3/27/2006 1:58:21 PM: Initial</R0>
    <R1>Revision: 1, 3/27/2006 2:04:28 PM: Pruned out some junk</R1>
    <R2>Revision: 2, 3/27/2006 2:06:58 PM: Added a GO command</R2>
    <R3>Revision: 3, 3/27/2006 2:18:26 PM: Fixed GO</R3>
    <R4>Revision: 4, 3/27/2006 2:20:14 PM: add sched4 freerun</R4>
    <R5>Revision: 5, 3/27/2006 8:57:55 PM: Added CONTINUOUS task</R5>
    <R6>Revision: 6, 3/28/2006 5:31:06 PM: First whack at series task</R6>
    <R7>Revision: 7, 3/28/2006 5:34:15 PM: some tweaks</R7>
    <R8>Revision: 8, 3/28/2006 5:45:15 PM: Added flicker</R8>
    <R9>Revision: 9, 3/28/2006 7:54:06 PM: MaskFix</R9>
</Revisions>
</Timerscript>

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

Jeff_T. — Thu, 17 Dec 2009 15:45:21 GMT

Hello dotan,

GXML will not parse any XML string, pretty much only XML strings created by GXML. The purpose is to encode arbitrarily complex LabVIEW data structures into a human readible format that can be parsed and brought back into LabVIEW as a user-defined data structure. If you can represent this data as a LabVIEW cluster then GXML could be used to encode and parse that data. Sorry for the confusion.

Regards,

Jeff Tipps

NI Systems Engineer

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

Řeřicha — Fri, 22 Jan 2010 09:01:02 GMT

GXML parse "LabView"XML. It is nice, but is any easy solution, how parse (read and write) common XML via LabVIEW?

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

Christian_L — Fri, 22 Jan 2010 15:50:51 GMT

You can use the XML Parser VIs and functions available in LabVIEW to parse any generic XML.

With XML able to represent any generic data, which may not be easily represented by standard LabVIEW data types, it generally is not a trivial matter to parse any XML that you may encounter. It is much more common to use a predefined XML schema as part of your application and build a parser using these functions for your specific needs.

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

Brad_B. — Sat, 06 Feb 2010 12:36:06 GMT

Does the GXML reference library handle units that are used with numerical indicators? If so, are they output as XML attributes or elements?

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

Jeff_T. — Sun, 07 Feb 2010 19:29:47 GMT

Hello Brad,

No currently it does not generate XML for the numerical units. If I were to add it though I would prefer to do it as an attribute, perhaps right after the datatype attribte.

The VI which decodes the type descriptors from the variant data type is:

vi.lib\Utility\VariantDataType\GetNumericInfo.vi

It appears there is an output for units though I haven't played with it yet. I would experiment with this output and see if it supports custom units. If it did work then it would go in the "gxml_UnflattenandScanItem" subVI in the cases that handle numeric datatypes. It would be a pretty simple modification. If you invest any time in it let me know and I may add it to a future release of the reference library. I'll look into it myself when I get some time.

Best Regards,

Jeff Tipps

Systems Engineer - Sound and Vibration

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

Brad_B. — Mon, 08 Feb 2010 07:16:38 GMT

Hi Jeff,

Thanks for the reply.

I've fired up an evaluation version of LabVIEW 2009 and provided the GXML VI with a cluster with a numerical control and units as a quick test. An error exception is thrown from the "gxml_builder.vi" with possible reason "Item has an unsupported datatype (Double float with unit). I tried to dive down in to the library you mention but can't get inside as it is password locked.

We're quite interested in passing the numerical units to the XML file, but are still weighing up the implications of storage as an attribute vs. an element. It certainly seems to be a case you can argue either way!

We'd certainly be interested in seeing the handling of units addressed in a future release as we have an immediate need to do such.

Regards,

Brad

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

Jeff_T. — Mon, 08 Feb 2010 16:55:32 GMT

Ah LabVIEW treats it is its own data type. So we would simply need to add a case to accept this new data type.

Initial tests looks promising. One question though. In the example I attached I use a unit of "Pascals". The GetNumericInfo.vi treats that as kg/(ms^2) so I would be inclined to encode the attribute that way. Would you consider this expected or would you expect the XML string to report Pascals?

Regards,

Jeff Tipps

Systems Engneer - Sound and Vibration

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

Brad_B. — Tue, 09 Feb 2010 04:11:16 GMT

I'd expect the XML string to be consistent with the input units rather than expressing in what looks to be like the 7 base SI units. Probably makes things a little bit more complex on your end unfortunately.

Is there any chance of swaying you to use an XML element instead of an attribute?

Cheers,

Brad

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

Jeff_T. — Tue, 09 Feb 2010 15:42:51 GMT

I would encourage you to make the modifications yourself. My intention was to give the reference library enough framework and documentation that an end user could add features like this with minimal effort.

I am not in a position to develop new features in the near future but I am happy to answer any questions you may have about modifying the library. The generation side of things would be pretty simple (like you pointed out though we would need some kind of look up table to preserve the input units in the XML string).

FYI I also looked at the LabVIEW flatten to XML and EasyXML but neither of them support numeric with units either.

Best Regards,

Jeff Tipps

Systems Engineer - Sound and Vibration

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

J.M.N. — Mon, 01 Mar 2010 20:06:14 GMT

Does the Reference Library for Converting Between LabVIEW and XML Data (GXML) work under Linux?

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

Jeff_T. — Mon, 01 Mar 2010 22:36:47 GMT

Hello,

I have not tested this on LabVIEW for Linux but the entire reference library is written in LabVIEW code. The reference library uses native recursion (supported only on LV 2009) and leans very heavily on the library VariantType.lvlib found at \LabVIEW 2009\vi.lib\Utility\VariantDataType. If this library exists then you should be in good shape.

Best Regards,

Jeff Tipps

Systems Engineer - Sound and Vibration

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

Francesco_P. — Wed, 21 Apr 2010 08:24:56 GMT

Hi,

I'm exploring options to share data via XML between LabVIEW and other components for a new project. I'm experimenting with both the standard 'Flatten to XML' function and GXML.

The GXML-generated XML is more terse, and would be practically preferable, but I fail to understand two points:

The statement made above in this thread, that "GXML will not parse any XML string, pretty much only XML strings created by GXML". It does seem that the GXML parser refuses to parse attributes that are not separated by CRLF (as such it is not an XML 1.0 compliant processor, see http://www.w3.org/TR/2008/REC-xml-20081126/#sec-line-ends), but why would one then choose XML at all to share data between LabVIEW and LabVIEW? There are plenty of (possibly more efficient) data serialization alternatives within LabVIEW.

Probably a consequence of (1): why, unlike the case of 'Flatten to XML', is the XML schema for GXML not published?
LVXMLSchema.xsd does specify all data just as plain xsd:strings, but at least provides the list of allowable data types and structures.

I'd vastly prefer not having to develop yet another custom VI to serialize LabVIEW data over XML, but the downsides of both "Flatten to XML" and GXML may leave no other viable option.

Francesco Prelz

INFN - Milan, Italy

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

Jeff_T. — Wed, 21 Apr 2010 15:09:12 GMT

Francesco,

Thank you for the feedback. With this component it was my intention to make a more "terse" version of the LabVIEW Flatten to XML VI that was also supported on RT and that gave the user more flexbility regarding the structure of the parsing type definition.

I think you are right that the XML parser is not compliant to section 2.11 of the XML spec. The parser does specifically looking for a #D#A and this appears to be an oversight on my part. Please confirm for me, the specifcation is saying that the XML parser should be able to recognize three possibilities as an "end of line" character: #D#A, #D, or #A. Am I reading this right?

There are more efficient (and in some cases much more efficient) ways of sharing data between LabVIEW and LabVIEW: some examples are flattened binary strings and the datalog binary format. XML is slower than these optons but the upside is that it is human readable. Furthermore XML is inherently hierarchical which is convenient for complex data structures like clusters of arrays of clusters, etc. If you don't care about human readability then you are correct XML doesn't make as much sense.

I will return to the GXML source code and try to fix this in the near future but I would hope that instead of creating yet another custom VI from scratch that you could reuse what I have provided for you. I included enough documentation in the source code so that users could make some modificiations themselves.

The target application for this reference library was LabVIEW to LabVIEW communication. As such I documented the schema on the dev zone document from a LabVIEW perspective. It includes all the supported datatypes and all the supported data structures (cluters, arrays, multidimensional arrays, clusters of multidimensional arrays, etc.) I do see some value in making a more conventional XML spec but the time investment required didn't really line up with my intended use case.

Were there any other downsides to GXML that I have missed?

Best Regards,

Jeff Tipps

Systems Engineer - Sound and Vibration

Message Edited by Jeff T. on 04-21-2010 10:09 AM

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

Francesco_P. — Wed, 21 Apr 2010 16:13:21 GMT

Please confirm for me, the specifcation is saying that the XML parser should be able to recognize three possibilities
as an "end of line" character: #D#A, #D, or #A. Am I reading this right?

The spec says that all combinations should be converted to linefeed (#A), which is in practice the same as saying that all those combinations represent valid end-of-line sequences.

This said, always according to the same spec (http://www.w3.org/TR/2008/REC-xml-20081126/#sec-element-content) the use of any whitespace in XML nodes that have 'element content' (i.e. they only contain other XML elements) is optional. So I believe that the parser should discard any particular combination of whitespace (including line feeds) when parsing the contained elements.

In other words, there should be no -required- line feeds separating the various attributes.

I'll take your suggestion to look at the source and see if it can be adapted as needed.

Thank you for your attention.

Francesco Prelz

INFN - Milan, Italy

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

Yee — Fri, 11 Jun 2010 00:40:10 GMT

How do I use GXML to convert clusters that are bundled up programmatically?

That is, I have a large amount of clusters that get bundled up during runtime and later bundled together. Is there a nice way to use GXML to convert them? Unfortunately because they are bundled at runtime, the clusters do not have names and I get the error:

gxml_Builder.vi <ERR>Cluster item '' has an invalid name. Each name must begin with a letter and subsequent characters may be letters, digits, a period, a dash, or an underscore.

See the attached for some sample code. I would love to change the cluster name during runtime, but that's not allowed either. I suppose I could set up individual cluster structures that I could later stuff as I get values, but that's a lot of work.

Any nice way to get this to work? Example code would be great, as I'm still new at this.

Thanks

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

Jeff_T. — Fri, 11 Jun 2010 16:37:09 GMT

I recommend making a type definition cluster and bundling your elements by name:

This way you have the ability to name the encapsulating datatypes. You will need a typedef anyway to parse the data in LabVIEW.

Regards,

Jeff Tipps

S&V Systems Engineer

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

Yee — Fri, 11 Jun 2010 17:49:32 GMT

Hi Jeff!

Thanks for the solution! Yes, I'll do that. I was hoping GXML could typedef and name everything itself (and be more flexible) but this certainly will work.

Thanks again,

Re: Reference Library for Converting Between LabVIEW and XML Data (GXML)

Yee — Fri, 11 Jun 2010 18:09:26 GMT

Is there a nice way to hack the VI gxml_NameFilter to assign unique XML member names to unnamed LabView items?

For example, attached is my attempt to assign a unique name based on the time stamp that the subVI is called. Unfortunately LabView seems to call this VI simultaneously for different items, giving the XML items non-unique names.

<Item0634.7842 mems='2'>
<Item0634.7842 mems='2'>
    <Transmit_High_Voltage type='U16'>140</Transmit_High_Voltage>
    <Verilog_Var type='String'>pioBurst</Verilog_Var>
</Item0634.7842>
<Item0634.7842 mems='3'>
    <Burst_Number_of_Pulses type='U8'>1</Burst_Number_of_Pulses>
    <Verilog_Var2 type='String'>pioBurst</Verilog_Var2>
    <Boolean type='Bool'>FALSE</Boolean>
</Item0634.7842>
</Item0634.7842>

Thanks again,