doubletype-dev-en

[DoubleType-dev-en] Question Relaxer

[Yannik De V. <Yan...@vu...>]

Hello,

As you said, I subscribed myself to the mailinglist, this will be a lot easier to communicate. Thanks a lot for wanting to help me in the first place!
As I said, I'm trying to make an application just like yours, and during a little search on the web, I stumbled across your program. I instantly installed it, and found it to be great!
So I downloaded the source-code to try to understand you ways of thinking, of getting it all together. I think i kinda understand the most of it, but I can't seem to understand what the Relaxer-part is all about. I can find it's a tool to put XML-code into java-code, and so it generates the whole xml-package, but i don't understand the meaning of it within the program...
I'm sorry if I'm being stupid and this is obvious :(
Many thanks in advance,

Kind regards,

Nemesis

Re: [DoubleType-dev-en] Question Relaxer

[e.e <eed...@us...>]

Hi Nemesis,

 > I think i kinda understand the most of it, but
 > I can't seem to understand what the Relaxer-part is all about.
 > I can find it's a tool to put XML-code into java-code,
 > and so it generates the whole xml-package, but i don't understand the
 > meaning of it within the program...

You've mentioned you wanted to know the thinking process behind
DoubleType so I'll try to explain that.

When I started designing the program I knew XML would be used.
XML is simple but deep. From simple point of view, XML is just
HTML look-alike. Bunch of tags.
More modern way of looking as XML is XML as a meta-language:
a language that lets you define your own language.
For example, we can define a language where you have a <root> tag,
and within the <root> tag, you have zero or more <employee> tags,
and within each <employee> tag you have a <lastname> tag.

A sample document in the language would look like this:
<root>
	<employee><lastname>Smith</lastname></employee>
	<employee><lastname>Brown</lastname></employee>
</root>

It would be useful if we can describe the grammer in some way.
A language that let's you describe the grammer of XML-derived language
is called schema language. The most standard schema language is
W3C XML Schema (.xsd file) but it is too difficult for human to use it.
As an alternative schema language, there is RELAX NG.
There are two notations for RELAX NG, the original XML syntax (.rng) and
compact syntax (.rnc). I personally prefer compact syntax now,
but for DoubleType XML syntax is used.
- http://www.oasis-open.org/committees/relax-ng/tutorial.html
- http://relaxng.org/compact-tutorial-20030326.html

Let's describe our sample language using RELAX NG compact syntax:
element root {
	element employee {
		element lastname { text }
	}*
}

One of the benefit to define the grammar of your language using
using a schema language is that there are tools that lets you
parse the XML document into object automatically.
Without those tools, you would have to manually parse/generate XML 
documents, which people used to do.
Since we defined <root> tag and <employee> tag, it would be convenient
if a tool can generate root class and employee class so you can just
use it in code like

m_root.getEmployee(0).lastname = "smith";

This idea of mapping XML document and object is called XML data binding.
Relaxer is a XML data binding tool that uses RELAX NG as input.
# There are other tools that does XML data binding.
# Castor is more popular, I think. Other platforms have their own stuff.
X-prefixed classes in org.doubletype.ossa.xml package generated by Relaxer.

I put anything that needs to be saved into the file into my glyph
language. This saves a lot of work because I only need to define it once
in the schema and it would be in both Java object and XML.

It's kind of getting long, so I'll send it here and continue.

Thanks,
e.e

Re: [DoubleType-dev-en] Question Relaxer

[e.e <eed...@us...>]

Hello,

e.e wrote:
> This idea of mapping XML document and object is called XML data binding.
> Relaxer is a XML data binding tool that uses RELAX NG as input.
> # There are other tools that does XML data binding.
> # Castor is more popular, I think. Other platforms have their own stuff.
> X-prefixed classes in org.doubletype.ossa.xml package generated by Relaxer.
> 
> I put anything that needs to be saved into the file into my glyph
> language. This saves a lot of work because I only need to define it once
> in the schema and it would be in both Java object and XML.

So X-prefixed classes such as XContour would take care of saving and
loading data from .glyph file.
But from object-oriented perspective these classes are pretty "dumb",
because they only store the data and it doesn't have any behavior
associated with them.
To overcome this issue, Relaxer has a facility called abstract factory
to let me extend the X-prefixed classes. When Relaxer finds a
<contour> tag, it creates EContour object instead of XContour object.
# E is for extend, not Emulator
EContour defines methods such as display() and move(), so it's more
smarter because it knows what to do with the data.

As it turns out, most of the objects in DoubleType requires similar
operation such as displaying and moving. In that case, it would be
useful to define an interface so I can treat them the same way.
This way, I can put whatever objects in a list and let each object
decide how to display or move itself.
For example, take a look at GlyphFile class's display method:

	public void display(Graphics2D g, AffineTransform a_trans)
	{			
		Iterator i = createIterator();
		while (i.hasNext()) {
			GlyphObject object = (GlyphObject) i.next();
			object.display(g, a_trans);
		} // while
	}

A point and a contour would have totally different logic for displaying
but GlyphFile doesn't have to know about it.
In other words, E-prefixed classes are acting as an adapter from
X-prefixed classes to GlyphObject based classes.

Design architecture such as abstract factory and adapter are called
Design Patterns. The following page lists some of the patterns that's
used in my code:
- http://doubletype.sourceforge.net/?DesignPatterns

Thanks,
e.e