From: Richard Kilmer <rich@...>
Date: 2003-03-19T16:01:53+09:00
Subject: Re: XML too hard (YAML opportunity?)


On Wednesday, March 19, 2003, at 01:27  AM, <jbritt@ruby-doc.org> wrote:

>> jbritt@ruby-doc.org wrote:
>>
>>> YAML has its place, though personally I haven't had a need for
>> a statically-typed markup language (and I admit I still haven't
>>> managed to finish reading the spec). But it can't (so far, at
>> least) stand in for XML; comparisons between the two are apples and
>>> oranges.
>>
>> What does statically typed mean here?
>
> I mean the data carries with it instructions on how it is to be 
> processed.
> It says "Process me as a String," or, "Process me as a Hash."
>
> I don't usually want that in my data files.  It tends towards 
> application
> logic.
>

So the fact is the parser of YAML infers (through rules) the types of 
the elements it parses is bad from your perspective?  The issue is 
SOMETHING has to know this.  Its either written in some parser function 
and mapped (from XML) into your internal object structure, or read in 
directly from YAML.  As we did with FreeRIDE, the classes that are 
serialized to YAML are, in fact, utility classes that YAML is 
serializing for us.  We just maintain those files (in Ruby).  This is 
far better than writing an emitter/parser pair for an XML format. I get 
to code in my language...and don't worry about the data format.

Think of it this way:

class Person
   attr_accessor :firstname, :lastname
end

p = Person.new
p.firstname = "Richard"
p.lastname = "Kilmer"

=== Output ===

XML:
#BUILD EMITTER
class Person
   def to_xml
     "<Person firstname='#{@firstname}' lastname='#{@lastname}'/>"
   end
end

xml = person.to_xml
puts xml
<Person firstname='Richard' lastname='Kilmer'/>

YAML:
yaml = person.to_yaml
puts yaml
--- !ruby/object:Person
firstname: Richard
lastname: Kilmer

=== Input ===

XML:
# BUILD PARSER
class Person
   def Person.from_xml(xml)
     doc = REXML::Document.new(xml)
     p = Person.new
     p.firstname = doc.root.attribute['firstname']
     p.lastname = doc.root.attribute['lastname']
     return p
   end
end
p = Person.from_xml(xml)

YAML:
p = YAML.load(yaml)

........

And now, add some new properties:

class Person
   attr_accessor :firstname, :lastname, :middle, :age, :hair_color, 
:eye_color
end

Here is what you do with YAML:

p = Person.new
p.firstname = "Richard"
p.lastname = "Kilmer
p.hair_color = "Brown"
yaml = p.to_yaml

p2 = YAML.load(yaml)

In XML we have to update our emitter and parser.


.......

-rich