From: Robert Klemme <bob.news@...>
Date: 2005-11-22T00:32:24+09:00
Subject: Re: [ANN] xampl 0.1.0

Bob Hutchison wrote:
> On Nov 21, 2005, at 9:47 AM, Robert Klemme wrote:
>
>>
>> Some questions just out of curiosity.  No offense intended.
>
> No problem. You've asked a couple of interesting questions.
>
>>
>> Bob Hutchison wrote:
>>
>> <snip/>
>>
>>> Xampl is a tool for developing Ruby programs. It facilitates the 'M'
>>> part
>>> of an MVC architecture. It is meant to be very easy to use,
>>> supportive of
>>> idiomatic Ruby usage, and mostly invisible.
>>>
>>> Features:
>>>    - pure Ruby, no libraries required except those shipped with Ruby
>>> 1.8.2
>>>    - uses XML to declaratively describe a object structures
>>>      - uses a collection of example XML documents, no schema are
>>> required
>>
>> Interestingly some days ago I thought about how J2EE is really two
>> languages (Java for implementation, XML for configuration) and how
>> Ruby
>> can do both very neatly because of its clean syntax.  From your
>> experience, does it really pay off to use XML here?  Or is ist just
>> because you want to be able to read in arbitrary files and use the
>> content
>> as Ruby objects?
>
> Yes it does make sense I think. How do you express succinctly the
> relationship between a bunch of live objects? Amusingly, the hyper-
> verbose XML can actually do that :-) It all depends on how you
> interpret the XML. XML can reflect a containment/composition/
> aggregation relationship about as tersely as you can get in text.

Well, you can describe those relationships in Ruby, too.  In fact, nearly
every Ruby program does it by creating / assigning member variables. :-)

> Xampl is not about using XML for configuration, but for 1) describing
> dynamic relationships between objects; and 2) persistence.

"describe" persistence or "implement" persistence?  It seems rather the
latter.

> I agree with you that much of what XML, or YAML for that matter, is
> used for can be better done in Ruby (or Python, or any other dynamic
> language), certainly the way XML is used conventionally. Though xampl
> changes the picture a bit.
>
> The other thing xampl does is makes it a lot easier to deal with XML
> based protocols. I've provided an example with the distribution (and
> discussed in the documentation) of how to use xampl to read an Atom
> 1.0 or 0.3 feed over the internet, cache the feeds, extract the
> entries, convert 0.3 entries to 1.0, aggregate in a new 1.0 feed
> paying attention to ordering, and serve it up via WEBrick. Xampl
> really helps in this kind of thing.
>
> This is actually a really good question and I should prepare a better
> answer. The background for what I'll say is documented in the
> download file, but there is no direct answer to this question there.

So one of the strengths of xampl is to deal with existing XML data.

>> <snip/>
>>
>>>      - XML, Ruby, and YAML persistence mechanism (purposely no
>>> Marshal support)
>>
>> Why is that?  What's the reasoning behind this?
>
> 1) Upgrades of marshalled objects can be really nasty, using a text
> form that xampl has control over while parsing, you have a chance of
> intervening at an opportune time, making your life a lot easier.
> 2) You can read XML, Ruby and YAML.
> 3) You can use the data easily independently of any xampl program
> (e.g. in a text editor :-)
> 4) You cannot control how much of the network of reachable objects is
> written to one file (this is very important in xampl because of its
> clustering capabilities).
>
> There are more reasons that I've forgotten, these are enough for me.

Well, that's quite comprehensive!  Thanks for the quick and exhaustive
answer!

Kind regards

    robert