Trying to make XMLada use a validating SAX Parser

Trying to make XMLada use a validating SAX Parser

[Serge Robyns]

Being very new to the Ada object programming and desiring to write an application in Ada that is capable of reading XML data I'm fighting to use XMLada.  The AdaCore documentation and Google isn't providing much help.

I've managed to do some stuff in Ada in the past (booting a full native gnat kernel attempt, back in 2001).

So far I managed to:
  1) use a SAX parser to read the file and create ADA objects. (SAX.Readers.Reader)
  2) use the DOM reader to read an XML file and and walk the tree.
  3) use the DOM reader and have the file validated by the XSD. (Schema.Dom_Readers.Tree_Reader) and walk the tree.
  4) use the SAX validating parser to validate the XML file. (Schema.Readers.Validating_Reader) but without creating Ada objects.

But what doesn't work is to use the SAX validating parser to validate and call the callbacks to build my objects.

Below is the code I'm trying to compile:

with Unicode.CES;
with Sax.Readers;
with Sax.Attributes;
with Schema.Readers;

package MyXML is
      -- type MyReader is new SAX.Readers.Reader with null record;
      type MyReader is new Schema.Readers.Validating_Reader with null record;

      overriding procedure Start_Element (
                               Handler           : in out MyReader;
                               The_Namespace_URI : Unicode.CES.Byte_Sequence := "";
                               The_Local_Name    : Unicode.CES.Byte_Sequence := "";
                               Qname             : Unicode.CES.Byte_Sequence := "";
                               Atts              : Sax.Attributes.Attributes'Class
                              );
end MyXML;

When I try to compile the compiler complains that the subprogram "Start_Element" is not overriding.  However, according to the adacore documentation for xmlada it does say in section 6.4 that "As usual, you can still override the predefined ....".

Does anyone have an explanation for my error?

Thanks you.

Serge

Re: Trying to make XMLada use a validating SAX Parser

[Simon Wright]

Serge Robyns <serge.robyns@gmail.com> writes:

> package MyXML is
>       -- type MyReader is new SAX.Readers.Reader with null record;
>       type MyReader is new Schema.Readers.Validating_Reader with null record;
>
>       overriding procedure Start_Element (
>                                Handler           : in out MyReader;
>                                The_Namespace_URI : Unicode.CES.Byte_Sequence := "";
>                                The_Local_Name    : Unicode.CES.Byte_Sequence := "";
>                                Qname             : Unicode.CES.Byte_Sequence := "";
>                                Atts              : Sax.Attributes.Attributes'Class
>                               );
> end MyXML;
>
> When I try to compile the compiler complains that the subprogram
> "Start_Element" is not overriding.  However, according to the adacore
> documentation for xmlada it does say in section 6.4 that "As usual,
> you can still override the predefined ....".

Validating_Reader isn't (now?) derived from SAX.Readers.Reader but
instead from SAX.Readers.SAX_Reader, & the subprogram profile has
changed.

There's a comment in SAX.Readers recommending to upgrade to the new
forms.

Re: Trying to make XMLada use a validating SAX Parser

[Serge Robyns]

Dear Simon,

Thank you very much for the hint.  It does indeed work as suggested.

It is very disappointing that the "official" documentation of Ada Core does described "legacy". Going through almost 200 sources files is not the ideal way to achieve success.  I've been wasting many evening hours trying to figure out this issue.  Such hurdles will certainly not help attracting people to Ada.  If I wasn't convinced about code and language quality I would have given up and used more hype languages.

Below the code that does do all what I want (well here only debugging as creating objects from XML will be fine).  I share this so others could stumble on it when Google-ing.

=== MyXML.ads ===
with Sax.Readers;
with Sax.Utils;
with Sax.Symbols;
with Schema.Readers;

package MyXML is
   -- type MyReader is new Sax.Readers.Sax_Reader with null record;
   type MyReader is new Schema.Readers.Validating_Reader with null record;

   overriding procedure Start_Element
     (Handler    : in out MyReader;
      NS         : Sax.Utils.XML_NS;
      Local_Name : Sax.Symbols.Symbol;
      Atts       : Sax.Readers.Sax_Attribute_List);

end MyXML;

=== MyXML.adb ==
with Ada.Text_IO; use Ada.Text_IO;

package body MyXML is

   procedure Start_Element
     (Handler    : in out MyReader;
      NS         : Sax.Utils.XML_NS;
      Local_Name : Sax.Symbols.Symbol;
      Atts       : Sax.Readers.Sax_Attribute_List) is
   begin
      Put_Line (Sax.Symbols.Debug_Print (Local_Name));
      for I in 1 .. Sax.Readers.Get_Length (Atts) loop
         Put_Line (Sax.Symbols.Debug_Print (Sax.Readers.Get_Value (Atts, I)));
      end loop;
   end Start_Element;

end MyXML;


=== SaxTester.adb ===
with Ada.Text_IO; use Ada.Text_IO;
with Ada.Exceptions;

with Input_Sources.File;
with Sax;
with Sax.Readers;
with Schema.Validators;

with MyXML; use MyXML;

procedure SaxTester is
   Input     : Input_Sources.File.File_Input;
   My_Reader : MyReader;
begin
   Put_Line ("Start");

   Input_Sources.File.Open ("transactions.xml", Input);
   My_Reader.Set_Feature (SAX.Readers.Schema_Validation_Feature, True);
   My_Reader.Parse (Input);
   Input.Close;

exception
   when Schema.Validators.XML_Validation_Error
      => Put_Line ("Invalid transaction file!");
      raise;
   when Except_ID : others
      => Put_Line ("Got Exception");
      Put_Line (Ada.Exceptions.Exception_Information (Except_ID));

end SaxTester;

Re: Trying to make XMLada use a validating SAX Parser

[David Botton]

> Such hurdles will certainly not help attracting people to Ada.

AdaCore has little interest in community use of Ada or popularizing it beyond its customer niche, it runs contrary to their business model. What is important is that there is a community and when you reached out you got an answer. So don't focus on what AdaCore did wrong (since they will tell you they did "right" while everyone else sees the problem). Very few languages have as strong a community or ones filled with as much expertise.


Perhaps consider writing a new Ada XML parser or binding to an existing C one to help improve the image? I wish I could say to help document XMLAda but its license restrictions make that effort wasteful.

David Botton

Re: Trying to make XMLada use a validating SAX Parser

[Vadim Godunko]

On Friday, June 5, 2015 at 1:50:30 PM UTC-4, David Botton wrote:
> 
> Perhaps consider writing a new Ada XML parser or binding to an existing C one to help improve the image? I wish I could say to help document XMLAda but its license restrictions make that effort wasteful.
> 
Another XML parser is provided by Matreshka.

http://forge.ada-ru.org/matreshka

Re: Trying to make XMLada use a validating SAX Parser

[Pascal Obry]

Le vendredi 05 juin 2015 à 10:50 -0700, David Botton a écrit : 
> AdaCore has little interest in community use of Ada or popularizing it beyond its customer niche

Sure:
- GNAT GPL
- AdaCore University
- GEMS
- Contributing to FSF/GCC

All this for free (as in free speech and in free beer).

From there I think the community should be able to contribute good
libraries, no?

You're probably kidding or letting your current mood controlling your
keyboard :)

-- 
  Pascal Obry /  Magny Les Hameaux (78)

  The best way to travel is by means of imagination

  http://v2p.fr.eu.org
  http://www.obry.net

  gpg --keyserver keys.gnupg.net --recv-key F949BD3B

Re: Trying to make XMLada use a validating SAX Parser

[Serge Robyns]

On Saturday, 6 June 2015 10:22:35 UTC+2, Pascal Obry  wrote:
> Sure:
> - GNAT GPL
> - AdaCore University
> - GEMS
> - Contributing to FSF/GCC
> 
> All this for free (as in free speech and in free beer).
> 
> From there I think the community should be able to contribute good
> libraries, no?
> 

Hmmm ... I didn't want to start a flame war.   It was just a genuine disappointment.  I agree that they do deliver their tools as for free in beer.  And I'm even thinking about returning some contribution by adding Oracle support in their gnatcoll SQL library, once I got my head around this library too.

And I don't mind they have a business model with professional support, we all have to have a revenue.

Re: Trying to make XMLada use a validating SAX Parser

[David Botton]

> Sure:
> - GNAT GPL

Shareware (see shareware thread) - Damaging to Ada and community because of GPL encumbered runtime

> - AdaCore University

Not community oriented, but not a bad corporate move and is beneficial to Ada. 

GAP program suffers same issues as GNAT GPL however.

> - GEMS
No longer in progress, but was same as any other corporate blog to use their product. Beneficial to the GNAT compiler specifically but not about community.

> - Contributing to FSF/GCC
Yes, it is the one saving grace that their some of their work is contributed back to the FSF with a proper license on the run time.

However statements on the AdaCore websites have implied there are potential IP violations to use it and the build tools needed are not sent to the FSF making it more and more complicated to make actual truly Free and in speech versions available. (gnatmake is now deprecated further complicating things). If there was a community "angle" to the FSF contributions there would be a complete upstream of the needed tools along with actual build releases. Doing your "duty" to contribute to the FSF is a discharge of obligations not a care for the Ada community.

BTW, AdaCore has never announced contributions to the FSF to the community nor encouraged the FSF versions development for community use (only stated - that the FSF version is sufficient for quality use by the public when asked). Even the GPL versions are not announced at community forums for years. Oh ya.. don't forget the fiasco of make believe that GPL can be passed through site downloads or checkouts from public repos...

> All this for free (as in free speech and in free beer).
Not true, the GPL on runtimes limits ones ability to speech. AdaCore is not helping the community by flooding it with runtimes and libraries that encumber and restrict peoples "speech" or ridiculous statements about the potential IP harm they could be in from using non-AdaCore compilers.

AdaCore should be acting as leaders and stewards for the community and Ada's proliferation as a general purpose language (especially now that they are the defacto monopoly in the business world for new projects) in addition to their niche markets.

Their company was built on contributions that were intended to encourage that direction not corporate control of a language with GPL virused runtime version distribution to make pretend there is a community "concern".

* Usual legal disclaimer and self protection - there is no legal violations by AdaCore to my knowledge, they have the legal right to remove the runtime exception clauses of the run-time causing them to be GPL virused and can restrict their direct contribution of code back to the FSF archives as they see fit.

> From there I think the community should be able to contribute good
> libraries, no?

Not possible

The community can not build on AdaCore's GPL encumbered libraries (tools yes but not libraries) if they want true free speech (outside the FSF versions) and Ada as a whole is harmed by license abuse of the GPL on runtimes.

My campaign has been and is to make as clear as possible the GPL runtime abuses and the harm they cause and to offer what solution we have now:

GetAdaNow.com - there is a true free version available with out GPL virused runtimes in the spirit of the FSF itself.

Ada logo contests, work towards a new LearnAdaNow.com site, I'm working on a revamp soon of AdaPower to allow for direct community control and public repo of available project, so that people should take serious that there is an Ada community.

I wish I had more time and money to put in, but doing what I can on my time and money budget.

> You're probably kidding or letting your current mood controlling your
> keyboard :)

I am not kidding and everyone here knows it. My words have been clear and consistent in every post concerning these issues.

I speak out because I afford to do so (many others can not) and because I care about having a language like Ada to express my "art" in. Ada ain't perfect but it's the best available.

Bottom line time has proven that AdaCore's releasing of GPL virused runtimes has harmed the overall community, reduce contributions of open source projects and in the eyes of non-AdaCore associates reduced its viability as a platform for long term contribution and development.

I have little interest in trying to change AdaCore's mind (that was never my intention from the start this time around, I gave that up 10 years ago), the humility needed to pursue business models beyond the current one is just not there and sadly so because the current model has hard limits. What I'm hoping for is enough people to wake to the issue to consider rallying around FSF-GNAT and a new Ada revival (before one is really needed from its death). 

David Botton

Re: Trying to make XMLada use a validating SAX Parser

[David Botton]

>And I'm even thinking about returning some contribution by adding Oracle support in their gnatcoll SQL library, once I got my head around this library too.

I hope you would consider releasing that as a separate project from GnatCOLL do to its license issues. 

 
> And I don't mind they have a business model with professional support, we all have to have a revenue.

Everyone agrees with and I am the first one to talk about AdaCore's professional top notch support product. The problem is using the GPL run time as a negative lever to encourage business instead of the playing up the true value they have as an awesome support company, taking a leadership role, etc.

It's a funny position for me to be in, I like them genuinely as people, believe in their support product (been on both sides of the table and can say wonderful at both ends) but am ashamed at the negative end of the business model that was taken in desperation and lacking creativity with the belief it would hold in more customers instead of taking a positive directions.

I often regret that 11 years ago I didn't made a bigger deal about it instead of just walking away from Ada and my one projects in it. So I take some blame for taking the easy way out myself then, but doing what I can now.

David Botton

Re: Trying to make XMLada use a validating SAX Parser

[Simon Wright]

David Botton <david@botton.com> writes:

> I hope you would consider releasing that as a separate project from
> GnatCOLL do to its license issues.

Not sure what your view of this will be - but - the GNATColl sources,
*with* the GCC Runtime Library Exception, are available for read-only
access at [1]. The last update was 9 months ago, though.

[1] http://viewvc.libre.adacore.com/viewvc.cgi/Public/trunk/gps/gnatlib/

Re: Trying to make XMLada use a validating SAX Parser

[David Botton]

> Not sure what your view of this will be - but - the GNATColl sources,
> *with* the GCC Runtime Library Exception, are available for read-only
> access at [1]. The last update was 9 months ago, though.
> 
> [1] http://viewvc.libre.adacore.com/viewvc.cgi/Public/trunk/gps/gnatlib/

I drudged up a number of links at one point if you recall to repos. There is muddy waters as to if source from the repos can be considered per the license in the repo or per statements else wise from AdaCore (and there are contradictory statements there as well).

The only exception could be AWS where the repo is external to the regular AdaCore repos so it would be difficult (but not impossible) to say the stated runtime exceptions are not intentional.

In all cases it doesn't change my statement regarding AdaCore's lack of interest in community use (which includes pro work) of Ada. An interest would be demonstrated with clarity and encouragement not threats of possible IP / License honey pots (regardless if it held up in court or not no one wants that mess around them). There is no reason that a mutually beneficial relationship could have existed all these years with the community as there once was.

Again, I'm not making pleas for AdaCore to change policy (and never have, my proposals last year were for a different type of release) but rather that we as a community understand with clarity what we have in our hands and the relationship that _really_ exists in fact.

My grandfather used to say "free is the most expensive" that can be taken in many ways and from the perspective of the giver or the receiver.

The "freebies" from AdaCore come with a big price tag, your use of their "free" means the removal of your rights. That is a trade off that makes sense for many projects, but not for a language community in an Open Source world with many really "free" options. As I said many times to their credit they do contribute a truly free subset of sources _back_ to the FSF that so far has allowed the community to create a free version.

So, my point of emphasizing the importance of using and promoting the FSF GNAT version and making sure that people look at those versions and not GPL runtime virused versions that are harmful for Ada and the community.

The long term importance of community support, marketing and encouragement of FSF GNAT can not be understated. Tying the future of Ada to a single company and its maintenance of the only existing viable libre compiler is a huge mistake when that company treats the greater community as a leach instead of a marketing arm for future potentials.

I wish only good to AdaCore and give credit where credit is do, and my consistent message is always that their support product is worth the money, because it is. However, AdaCore can not be "Ada" or Ada is forever banished to a few niche markets and academia both of which are not long term guarantees of Ada interest.

David Botton

Re: Trying to make XMLada use a validating SAX Parser

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