Jim Marino <[EMAIL PROTECTED]> wrote on 03/24/2006 05:53:46 PM:
> 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:
I wouldn't write off option 1 so quickly. For your example, a schema (or
equivalent SDO metadata) something like this is all that one needs:
<element name="myFoo" type="Foo"/>
<complexType name="Foo">
<sequence>
<element name="name" type="xsd:int"/>
<element name="foo" type="Foo"/>
<element name="myJaxBThing" type="jaxb:jaxBThing"/>
</sequence>
</complexType>
This schema could be deduced (under the covers) from the Java classes you
show below, so you wouldn't need to actually write it (once we get the
Java import support working, of course).
>
> 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?
Assuming, however, that we don't have metadata, but just want to
deserialize by hand. I don't think the SDO approach is any easier or more
difficult than the StAX approach. By default the SDO deserializer will
represent the "untyped" properties section of the model as a Sequence
(i.e., an unstructured representation of the "xsd:any" contents). We'll
need some way to plug-in a converter, maybe something like a FooFactory,
similar to what Jeremy described for the StAX approach. Btw, SDO has
createFromString methods for all the standard basic types plus a generic
createFromString method that work like Jeremy described (i.e., try
valueOf, constructors, etc.).
> 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).
I don't know enough about JAXB to say. Maybe someone else knows?
>
> 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?
Yes ... the Sequence (DOM-like) view of the properties is there by
default.
>
> 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?
I think we could provide something like this in Tuscany ... a
Tuscany-specific extension SPI.
> >
> >
> >> - 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?
Not unless the first Foo instance is passed to the second component
(that's expecting the second Foo). But this doesn't strike me as an SDO
issue, it would be a problem even if the Foo class was hand coded, don't
you think?
>
> 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?
This depends on how we handle the scoping. If the TypeHelper that knows
about Foo is in a private application scope then it should go away with
the application.
>
>
> > 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 :-)
This is a good excersize for me as well. Regardless of the actual decision
of whether or not to use SDO for this particular purpose in SCA, it will
help to clarify the issues and what parts of the SDO impl need attention.
Thanks, Frank.
>
> > 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
> >>> [email protected]
> >>> 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: <[email protected]>
> >>>>>> 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?
> >>>>>
> >>>>>
> >>>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>
> >>
> >
> >
>
