Re: Framework for StAX-based model loading

[Jim Marino]

Thanks Frank for answering these questions.  I have a few more that  
maybe you or others could offer opinions on.

On Mar 24, 2006, at 12:10 PM, Frank Budinsky wrote:
I don't know much about how the sca properties are configured, but  
I'll
try to answer your questions anyway.


- As a user what steps do I need to take to provide custom data
values for config properties? In a previous post, I listed an example
of a concrete "Foo" class


Option 1)

Provide an XML schema completxType definition for the Type and let the
generator gen the impl including the deserialization support. In the
future, we plan to also let you provide a Java interface (with
annotations, if necessary) to define the type, and then have the
implementation class generated for you.

The SDO generator will essentially generate the same Foo class that  
you
showed in the other thread, just with the addition of a base class
(DataObjectBase), and some get/set method overrides that implement
efficient switch-based reflective accessors - used by the generic XML
serializer/deserializer. If we also provide an option to generated a
loader, in the future, we could also provide an option to supress the
generation of the reflective accessors. The resulting class would no
longer be an SDO object in this case - but it would be easy to do as a
value-add feature in our generator (i.e., a -generateSimpleBean  
option).

Option 2)

Write the Foo implementation class yourself (or maybe generate it with
some other technology - like JAXB) and then simply register it as a
DataType with SDO. Remember that not all objects in an SDO model  
need to
be DataObjects. If you want non-DataObjects, they're modeled as  
DataTypes,
and you need to provide create from and convert to String methods for
them.
I think option two is the more appealing one for applications  
developers. I read option 1 to require a schema, which we may be able  
to do for extensions, but is a bit much to ask application developers  
to produce.  So, I'm curious as to how the conversion methods you  
mentioned look like.  Assume I have the following Java implementation  
and configuration class:

public class MyComponent{

    @Property
    private Foo; myFoo;

}


public class Foo{

    public Foo(){}

    private String name;

    public setName(String val){
        name = val;
    }

    private Foo foo;

    public void setFoo(Foo val){
        foo = val;

    }

    private MyJaxBThing jaxBThing;

    public void setMyJaxBThing(MyJaxBThing thing){
        jaxBthing = thing;
    }
}



And I want to use the following configuration:

    <component name="myComp>
        <implementation.java class="MyComponent/>
        <properties>
            <v:myFoo>
                    <v:name>my name</v:name>
                    <v:foo>
                            <v:name>my sub name</v:name>
                    </v:foo>
                    <jaxb:jaxBThing>
                            <!-- other configuration according to  
JAX-B--->
                    <jaxb:jaxBThing>
            <v:myFoo>
        </properties>
    </component>

I'm assuming I would have to register Foo and MyJaxBThing with SDO?   
Could someone walk through the steps I would need to do to tell the  
runtime how to take the particular configuration and deserialize it?  
Also, what would the string transformation methods look like in this  
case? I'm also having difficulty pinning down how the JAXB class is  
instantiated (I'm assuming something needs to access a JAXB factory  
at some point).

Another really common use case (sorry to keep harping on this one,  
but I see it all of the time) is support for List and Map. I should  
be able to specify some type of XML serialized form and have property  
configuration injected on a component as a List or Map.  I'm assuming  
based on your comments below this can be done to the SDO  
implementation and we could provide this to end-users without them  
having to configure something?

One final scenario, related to this, is support for factories for  
property instantiation. IoC containers such as Spring have a way to  
pass a factory in to the injection engine to delegate to for creating  
property instances.  Could this be done with SDO?


- What steps do I need to extend the current model? What dependencies
are there?


I'm not sure about this, it depends on the model. Is there a base  
type in
the XSD for these properties. If so, then I suspect that you need to
define the schema for your extension. If you go with option 1,  
above, that
comes for free. If you want to do things by hand, then I think you  
could
just treat your extension as unstructured XML (in the open content
extension points in the model). Maybe someone else understands the  
model
here better than I do?


- Can I use a custom binding technology to produce my model object?



I think I answered this in the option 2) section, above.


- Is it easy to support isolation between classloaders in managed
environments? My impression is that this is extremely problematic due
to required support of .INSTANCE.  If that is the case, what is the
likelihood that the spec can be changed in a timely manner to improve
this?


I don't think I understand where this problem will come up. In the  
static
generated class scenarios that we're talking about, there really  
shouldn't
be any access to .INSTANCE variables. Maybe someone can give a  
concrete
example where this might be a problem, and we can try to figure out  
the
solution from there.

I have two concrete examples here where I have seen problems in other  
projects:


1. Assume there are two nested components whose implementation types  
are loaded by different classloaders. These two nested components  
have a property that takes a "Foo". The configuration schema is the  
same but the "Foo" classes are different because they are loaded by  
different classloaders. Do you think we will run into any issues here?

2. Another concern is around application reloadability. If I have a  
registered type of "Foo" and the application it was registered by  
needs to be reloaded, how is it flushed from SDO? Does the container  
have to call a flush method somewhere?


I think we need to be clear that any shortcomings in the SDO spec  
should
not be a problem in generated scenarios. Other than saying that the
generated interfaces for SDO types are bean-like, the SDO spec  
dictates
very little about the nature of the generated code. We can fix  
whatever we
need to.

I appreciate that and you taking the time to help explain this stuff  
to me. I guess I'm going to be a typical example of someone who wants  
to extend the container and has a bunch of questions :-)

We really are just trying to leverage the Tuscany generator to do
XML binding here ... our config loader does not need to be a fully
compliant SDO application.

Thanks,
Frank.


Jim Marino <[EMAIL PROTECTED]> wrote on 03/24/2006 01:31:20 PM:


I think there may be some issues uncovered with the requirements and
I'm not sure we all understand the advantages/disadvantages of each
approach.  We may be over-analyzing this but the discussion was
getting very heated, there was a lot of disagreement over what the
actual (dis)advantages were, and I wanted to understand (at least for
myself) the broader implications.  I thought stepping back a bit what
help clarify these things. For example, I am personally unclear on
how to do the following with SDO:

- As a user what steps do I need to take to provide custom data
values for config properties? In a previous post, I listed an example
of a concrete "Foo" class

- What steps do I need to extend the current model? What dependencies
are there?

- Can I use a custom binding technology to produce my model object?

- Is it easy to support isolation between classloaders in managed
environments? My impression is that this is extremely problematic due
to required support of .INSTANCE.  If that is the case, what is the
likelihood that the spec can be changed in a timely manner to improve
this?

I thought Jeremy's list was good and would provide a way to "weight"
answers to these and other questions.

Jim

On Mar 24, 2006, at 6:10 AM, Frank Budinsky wrote:


Jim, looking at your requirements (which I don't disagree with), I
think
that both approaches, if not already, can be made to meet them.

Personally I think that we're over analyzing this. Both approaches
have
some advantages and disadvantages, but both will work. Whichever
approach
we take, I suspect that some people will like it and others won't .
For
example, people that know how to program with StAX will say it's
easy to
use ... people who don't will say the opposite. If we can get to
the point
that we effectively generate the logical model (so the user has to
write
no code), I think everyone will agree it's easy to use, since doing
nothing is easy by definition :-) Of course we need to take a  
leap of
faith that the current painful SDO codegen will evolve to that in
the end.

Having a vested interest to make the SDO binding technology as  
good as
possible, I would support, and obviously love to see the decision
go that
way, That said, I think it's got to be about time to just make a
decision
and run with it. If this much discussion went into every design
decision,
we'd still be sharpening our chisels and working on carving the
wheel :-)

Thanks,
Frank




Jim Marino <[EMAIL PROTECTED]>
03/23/2006 02:53 PM
Please respond to
tuscany-dev


To
tuscany-dev@ws.apache.org
cc

Subject
Re: Framework for StAX-based model loading






There has been a lot of discussion on this topic and Jeremy's point
brings up an issue I think needs to be fleshed out. Specifically,
what are the requirements and priorities for loading configuration.
Could we perhaps take the following approach?

1. Agree on the requirements and their priorities without getting
into a technical discussion. I would suggest we rank requirements by
absolute priority, i.e. the most important first, the next  
important,
etc. rather than "requirements A and B are p1, requirements  X and
Y p2"

2. Based on the requirements and priorities, compare the StAX and  
SDO
approaches for each

3. Agree on one approach moving forward for configuration

If this acceptable, my opinion on requirements in priority order  
are:

1. The configuration mechanism must be easy for end-users to use to
promote widespread adoption of Tuscany

     - For example, basic types defined by the spec should be a
given, but it should also be easy for someone to add a custom type.
For instance, my Foo component may take a Bar type as configuration.
Based on past experience with IoC containers, I have found this  
to be
a very common situation.

     -I assume this would have to involve describing the type and
registering some kind of custom handler with the runtime

2. The configuration mechanism must be easy for container extenders
to promote widespread adoption of Tuscany in the developer community

     - Similar to point 1, although I think the requirements on  
ease-
of-use may be slightly different.
     - One additional item here is the configuration mechanism  
should
follow Java idioms as closely as possible. Manipulating the model
should not be foreign to Java developers
     - As a side note, I think items 1 and 2 are intimately related,
but 1 is slightly more important since Tuscany developers will  
have a
higher pain threshold than end-users

3. Operation in a variety of deployment environments. For example,
how does each approach handle different classloader hierarchy
scenarios?

4. Ability to handle serializations other than XML. This was one of
the reasons why we went to a separate logical model. It's also not
just related to testing although that is one use case. For example,
configuration may be pulled from sources other than XML such as a
registry.

5. Maintenance

     - There are probably two considerations here. First, what we  
use
should be easily understood and used by Java developers wanting to
contribute to Tuscany. A second consideration is as the spec XML
changes, is it easy for us to evolve the code. Here, I would say we
concentrate on the first. The second use case has a lower priority I
have put to item 8.

6. Versioning

     - We need a mechanism that easily supports versioning. In the
future, we will need to support multiple configuration format  
versions

7. Performance

     - We need something that will be performant. On at least two
separate occasions, I have seen IoC container start-up brought to  
its
knees handling configuration processing.  This may not seem like a
big deal but when there are 1,000s (or even a couple hundred) of
components, it rears its head.

8. Ease on "us", the commiters (the second maintenance  
consideration)

     - This is where I would say how easy is it to accommodate spec
changes comes in. Either approach can handle changes so the question
becomes which alternative offers a better solution for commiters.

Perhaps we could come up with a set of objective criteria to  
judge by
and then move to a technical discussion of each approach?
Jim

On Mar 23, 2006, at 11:02 AM, Jeremy Boynes wrote:



I think we need to be careful to distinguish the needs we have for
loading our configurations from the needs users have of SDO in
general. I think the SCA schemas have things in them that are
atypical: lots of extensibility, many namespaces, custom data
types, few attributes/properties and so forth. On the other hand,
our use case doesn't need things like change tracking or streaming
that SDO provides.

We need a good SDO implementation, we need a loading mechanism that
can handle our configurations; the two don't have to be the same.
If they are, that is good; if they aren't, that's not bad.

--
Jeremy

Jean-Sebastien Delfino wrote:



Raymond Feng wrote:



Hi, Frank.

I think I fully agree with you. An efficient databinding is what
we're looking for.

Ideally, if SDO later on supports lazy-loading (create the
DataObject skeleton first and pull in properties as they're
assessed) from XMLStreamReader, I assume we'll take advantage of
the benifits advocated by both camps (Databinding vs. StAX).

Raymond

----- Original Message ----- From: "Frank Budinsky"
<[EMAIL PROTECTED]>
To: <tuscany-dev@ws.apache.org>
Sent: Thursday, March 23, 2006 9:37 AM
Subject: Re: Framework for StAX-based model loading





I stand by my statement that the EMF problem is short term pain
for long
term gain :-) I think that in the long term using the SDO
generator will
be the best and easiest way to do this. Yes I am biased, but
I've seen it
before - avoiding reuse/dependencies works nicely at first, but
as things
grow/change and get more comlicated, the amount of reworking/
reinventing
becomes quite a nightmare. The opposite problem, which I think
we're
suffering from here, is that the reusable component that we are
trying to
leverage isn't as nice and clean and a perfect fit as we'd like,
so it
really looks undesirable. Since we have control of all the
pieces, in this
case, I think we have a great opportunity to make it a clean
fit. And like
I said in my reply to Jeremy, earlier, I really strongly feel
that the
problems that we're identifying here are not unique to SCA, so
fixing them
is really in our best interest.

Frank.

"ant elder" <[EMAIL PROTECTED]> wrote on 03/23/2006  
10:13:24 AM:




On 3/23/06, Guillaume Nodet <[EMAIL PROTECTED]> wrote:

<snip/>

 As the binding itself uses JAXB2 (though it may change in


the future), I have to include all eclipse dependencies and


SDO stuff,


just to load the system configuration files :(




From the discussion I'm starting to be persuaded by some of the



arguments



for the SDO approach, but this EMF dependency seems a draw
back. If



we're



going to support alternate data bindings for the WS binding its
not



great to



still be dragging in EMF to run the thing. And I'd guess it
would be



much



easier to sell SDO to say the Axis2 guys to use instead of
XmlBeans if



there



was a pure Java SDO impl. Any Axis2 guys listening who'd
comment on



this?




As another comparison look at Axis2, they have their own very
simple



Axis



Data Binding (ADB) which supports simple XSDs, and they use
XmlBeans for



all



the complicated stuff. They don't use XmlBeans all the time
because lots



of



things don't need the complexity a full blown data binding
brings. And



as



Guillaume points out, the SCA binding schema are usually pretty
simple.

   ...ant












Raymond,
That's a very good point, I agree.
I think that this whole discussion thread is very useful as it
helps us identify requirements and areas of improvement for our
SDO databinding and codegen story. For example, Guillaume
mentioned that it would be great to have a Maven 1 SDO codegen
plugin, as ServiceMix is still built with Maven 1 at the moment
(and I guess a number of other projects out there still use Maven
1 as well). I can spend some time in the next few days and work
with anybody who would like to volunteer and try to wrap the code
generator in a Maven 1 plugin, if it helps. Guillaume, are you
using Ant at all? or just Maven 1?