Re: Ada Advocacy - WPG (Web Page Generation) scheme

[Pascal Obry <p.obry@wanadoo.fr>]

"Nick Roberts" <nickroberts@blueyonder.co.uk> writes:

> I've had an idea (not a blindingly original one) which might be a way to
> help promote Ada. Dynamic web content is all the rage these days; there are
> dozens of techniques used by millions of people to achieve it, including but
> not limited to SSI, ASP, JSP, PHP, CGI, and many other acronyms.
> 
> How to get Ada into this picture?

By looking at AWS :)

> I think one of the big attractions of schemes like ASP, JSP, and PHP (to
> name but three) is that to use them you merely have to embed a few special
> directives into an otherwise ordinary HTML file, and often the directives
> are very simple.

Yep, but in many places you have scripts and this is plain wrong. Having
script into a Web page is mixing layout (HTML) and code. Both must really be
separated, one of the reason is that they are done by differents peoples.

> So, it seems to me, an attractive scheme would be to allow Ada code to be
> embedded into an HTML file.

No, I don't think this is right. Note that Java is moving on the opposite side
just because of this problem. A script in a page means bugs in Web document,
this is wrong. Look at the Java struts.

In AWS we have a Templates_Parser engine which can compile on-the-fly
templates file and interpret them. This is really quick and only some "tags"
needs to be added into the HTML (or whatever) document.

> A special program would transform this file into
> a complete Ada program (procedure Main is ...) in a .adb file. The Ada
> program would be a complete CGI program: you upload it, and compile it into
> your cgi-bin directory.

This is again the wrong way. CGI (Common Gateway Interface) is the old way to
develop Web apllications. A CGI have to be spawned, this is a new process on
the server side. This scheme has been dropped long time ago for the
Application Server framework (JSP, ASP, PHP...).

> It could 'with' a simple package providing support
> for the CGI protocol (and HTTP/HTML web page generation); I'm aware of an
> existing AdaCGI package that might suit this.

Which must be history now :)

> Since a TLA (three-letter acronym) seems to be obligatory for these things,

Good, lets go with AWS :)

> we might call it 'WPG' for Web Page Generation. The source file containing
> the HTML with embedded Ada could then have the .wpg extension. Other
> possibilities that occur to me are: DWP (Dynamic Web Pages); HRA (Hypertext
> Response with Ada). The sillier the better, really.
> 
> The special program doing the translation (from WPG to Ada) - let's call it
> the WPGT - would (naturally!) be written in Ada, and I think it should be
> quite simple to write. Obviously I'm volunteering, if nobody else makes a
> claim.

Ok, this is Templates_Parser (see AWS.Templates). BTW, AWS's templates engine
is very fast. Lot faster than JSP, PHP or ASP.

> I propose the following embedding syntax.

[example removed]

BTW, I found it quite unreadable.

> One big selling point would be that your dynamic web pages are generated by
> a native code compiled program; a bit more efficient than a script. Another
> point is that you have the full facilities of Ada programming available to
> you (utility packages, bindings, and so on).

In AWS, the "scripts" are compiled into your main application.

> Other possibilities include: allow the name of a package to be 'withed'
> between [+ +] brackets; provide some handy translation-time values, e.g.
> [?UPDATE?] to be replaced by the date and time the translation is executed.
> 
> Some issues I can see are:
> 
> (1) HTTP headers. You'll see my example program above generates one HTTP
> header line. I get the impression that the headers a CGI program is supposed
> to generate are not very well defined anywhere. I think AdaCGI has a
> procedure to generate CGI headers; handy, but correct?

Supported in AWS.

> (2) Conversion of < > and & characters into escaped forms in fields. I think
> AdaCGI has a function to do this; could it be done automatically?

Supported in AWS.

> (3) Access to databases. Most CGI programs and web scripts need to get their
> information from a database, and some update databases too. I'm aware of a
> project to produce a binding to PostgreSQL and MySQL; might this be what is
> needed?

Supported in AWS, just use GNADE or whatever binding to ODBC, MySQL...

> (4) Most hosting companies don't allow binary CGI programs, for "security
> reasons" (i.e. their own stupidity). Of those which do, many refuse to
> install GNAT (despite providing GCC C++). Outrageous. However, I know at
> least one hosting company (Liquid Web, http://www.liquidweb.com/ ) who is
> willing to install GNAT, so maybe this isn't a hopeless problem.

This is a real problem. Not solved, you need to use PHP...

> Comments?

Please have a look at AWS before doing this. As I said most of the ideas here
are old-fashioned way to build Web applications.

Also note that a Web server is only a start. You'll need to support SOAP,
WSDL, SMTP, LDAP... to build real Web applications... All these standard are
supported by AWS.

Just in case : http://libre.act-europe.fr/aws

Pascal.

-- 

--|------------------------------------------------------
--| Pascal Obry                           Team-Ada Member
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