[dna-dev] Re: JBoss DNA 0.4 planning
Sergey Litsenko
litsenko_sergey at yahoo.com
Tue Nov 18 18:03:39 EST 2008
>FLEX can be driven entirely
from data. Could Seam and Rich Faces be
used this way?
Sure. Did you have any chance to look at https://www.jboss.org/community/docs/DOC-12952 (especially RichFaces live demo links and RichFaces UI components - http://www.jboss.org/file-access/default/members/jbossrichfaces/freezone/docs/devguide/en/html/RichFacesComponentsLibrary.html )?
Seam + JSF API + Facelets (XHTML templating)+ RichFaces (JSF
impl) are very flexible, have extension points and can implement majority of
RIA use cases (including an integration with plenty of other frameworks that
I’ve mentioned on the wiki page).
Seam/JSF/RichFaces integrated with other RIA frameworks like JQuery - http://jquery.com. Exadel proved that it is possible to integrate Flex and JavaFX with JBoss Seam (Exadel Flamingo and Exadel Fiji) - this addresses your concerns about "allowing graphical navigation".
However some “glue” code might be needed
depending of specific use case(s) – or we can make it generic.
In fact, Seam/JSF/RichFaces frameworks are very similar to Flex by
functionality but RichFaces/JSF relying on more generic, widely sources like
(X)HTML, JS, AJAX,
CSS. For example, both frameworks using
view described in XML; data binding in Flex (http://www.adobe.com/devnet/flex/quickstart/using_data_binding/)
is almost identical to JSF. For example, an input text UI control described as following:
FLEX: <mx:Text text="{myData.value}"/>
Pure JSF: <h:inputText value="#{myData.value}"/>
RichFaces: <rich:inplaceInput value="#{myData.value}"/>
Plus we can combine Flex + JSF too if needed.
IMO, what we should do first – regardless of preferred UI
choice - is that we would need to define
few critical/major use cases in
details in terms of pure
requirements (e.g. using language not specific to view frameworks) and
generic UI controls. And then see how it fits onto features of available
frameworks. This would help to understand what is really needed and jumpstart
on development of web app infrastructure.
>What if we put the REST service
on top of the Graph API (new to 0.3), which operates on top of a connector?
I agree that we need to consider both approaches side by
side and they impact on REST service implementation, and agree that both
mapping types might be twin brothers. So why don't we have core semi abstract class(es) that handles REST requiests based of http://jcp.org/en/jsr/detail?id=311 annotations and JBoss RestEasy implementation. And then two direct implementations based on Graph API (preffered?) and on JNDI/JCR API.
Basic question #1 to
answer: is REST service shall be considered an external component of
JBoss DNA that threat it as another JCR repository (black box), or is it
integrated part of DNA with some knowledge of internal processing/model?
BTW, same question is valid for other services (reporting,
analysis, etc), Web UI application.
Basic question #2 to
answer: shall we consider using Graph API for REST service, where we’ll
stop? In other words, do we need to use JCR API at all for components? What the boundaries between internal engine’s
code, and services.
IMO, we could use Graph API if it covers all traversal
access provided by JCR API + Query API (provided by JCR)? IMO, this bit is as much as important as federated tree of
nodes + traversal. It helps client to quickly find an important metadata in a
same way like Google does for internet search.
The clear advantage of using Graph API is that it can
provide some functionality behind the JCR API coverage.
On the other hand, considering that Graph API is the “core engine”
of JCR implementation, I doubt that using JCR API on top of Graph API will have
any visible impact on a performance (since JCR layer is extra thin and just
converts JCR call to Graph API call(s)).
I like an idea using Graph API but worrying about question
#2.
________________________________
From: Randall Hauch <rhauch at redhat.com>
To: Sergey Litsenko <litsenko_sergey at yahoo.com>; JBoss DNA <dna-dev at lists.jboss.org>
Sent: Monday, 17 November, 2008 4:24:48 AM
Subject: Re: [dna-dev] Re: JBoss DNA 0.4 planning
On Nov 16, 2008, at 4:25 AM, Sergey Litsenko wrote:
Regarding JDBC metadata.
...
1) I'll review new chapter "how to write custom connectors"and use the dna-connector-svn as a reference to implement the dna-connector-jdbc in extensions. It will accept two configuration styles to specify JDBC configuration - javax.sql.DataSource and more generic java.sql.Driver (connection URL, username/password, etc).
Maybe this would help or give you some ideas: this weekend I've created a prototype connector that uses Hibernate for persistent storage. (Not quite ready for committing to SVN, but should be this week). The RepositorySource implementation just has JavaBean properties for the regular connection properties for Driver-based connection, and another JavaBean property for the JNDI name of the DataSource. The RepositorySource has a transient Hibernate Ejb3Configuration, which it creates lazily (and stores as a transient attribute) before creating a RepositoryConnection. The Ejb3Configuration is created programmatically, so the Driver properties are set as properties, but the DataSource has to be set as a reference. (Yeah, the JNDI name could be set as a Ejb3Configuration property, but in order to support the XAResource, I need to get the DataSource object in the RepositorySource, which holds onto it via a transient attribute. This works with Hibernate,
since the config also has a setDataSource(DataSource) method. Oh, and to make testing easier (by eliminating requirement for JNDI), I also added a package-level setter for a DataSource object, which sets the transient attribute value. Let me know if you want to see code.
2) create dna-sequencer-jdbc-metadata subproject in extensions that will implement an interface similar to org.jboss.dna.graph.sequencers.StreamSequencer except for the “stream” input parameter because it is irrelevant for JDBC based conversations:
package org.jboss.dna.graph.sequencers;
public interface JdbcSequencer {
void sequence(java.sql.Connection jdbcConnection,
SequencerOutput output,
SequencerContext context);
}
The main purpose – is to make it generic enough to allow implementing different JDBC sequencers.
How it sounds?
Basically, what I need to do is to port my DatabaseMetadata Extractor (I did it few years ago, and tested against Oracle9i, MS SQL Server 2005, and MySQL) into org.jboss.dna space. The extractor as whole package is a bit too heavy to just simply copy it – it is relying on several Apache\Jacarta libraries (notably on Jacarta commons Chain (Chain of Responsibility" pattern) + generates JDBC drivers comparison reports in XML and HTML. So, I’m trying to refactor it in the same time.
Okay, I think I see what you're trying to do. Very interesting idea. This would all be in the connector, then? And the connector would essentially cache the metadata graph extracted from the database metadata, so it could respond to the different ReadNodeRequest (or other requests) coming into the connector? (If I don't have this right, please let me know.) Also, if you're refactoring the extractor, would it be possible for the extractor to be used directly the connector to obtain only part of the metadata?
BTW, the musings I've had in the past about this connector is that it might use Hibernate (to automatically get support for the many database management systems that Hibernate already supports; see http://www.hibernate.org/80.html). Hibernate Tool's DatabaseMetadata class works on top of the many dialects that Hibernate has (http://www.hibernate.org/hib_docs/v3/api/org/hibernate/tool/hbm2ddl/DatabaseMetadata.html). Again, not sure if this would even work or provide everything we'd want. For example, it may not provide much (if any) of the database-specific metadata.
Regarding REST mapping. My intention was to just describe “prior art” for reference purposes only – let others to they work - while it sounds like Jerome K. Jerome’s famous quote about his addiction to work ;) - we may save more time on analysis of possible REST mapping strategies.
My point is simple (and btw, it didn’t changed for years) – “program to interfaces”, likely standards based and setup transparent links (inject, configure, etc) to open source software implementations (preferably) of those interfaces where appropriate and possible.
I’m completely agree with your comments on that, and even more – inspired by your feeling towards choosing right balance between writing own code and reusing available libraries and frameworks I decided to spend some time analysing possible choices and wrote a wiki page about prospective ways to integrate/implement various JBoss DNA components in the future. Basically its small review of technologies available in OSS community (especially in JBOSS community) that might be related to JBoss DNA concept and might be reused in its implementation – have a look at it here https://www.jboss.org/community/docs/DOC-12952 – your comments are greatly appreciated. The main purpose of that review was to make the DNA implementation technology(s) / framework(s) choices broader and to address time to market requirement (while I love those frameworks and JEE in particular - I don’t want to push it too hard). The bottom line is that one of the main JBoss
DNA/JCR and JBoss DNA/Web purposes shall be to simplify metadata management things, not to complicate them – from client prospective. Plus (I guess) serve as JBoss technology stack show case (to some reasonable degree).
So, basically we will stick with JCR API for traversal, search, update nodes and map it onto URL, right?
The beauty of JCR API is that we don’t need to wait till our JCR implementation will be ready to integrate with other frameworks or services. As long as all components will rely strictly on JCR API interfaces and access it through standard way (e.g. JNDI lookup, dependency injection, etc) – we can easily use JackRabbit embedded in a meantime, and then substitute it with our JCR implementation when it became ready. We would need to address performance limitations of JackRabbit in our implementation of JCR API – in order to make it better (since it mean to be enterprise wide repository – e.g. thousands of nodes, subnodes, properties).
Yes, that is an entirely valid, and maybe preferred approach. Yes, we could start working on the REST service today. But a disadvantage is that we couldn't use the REST API on top of DNA repositories until our JCR API was finished (or at least those parts that the REST service would use).
Also, it doesn't seem like the REST service would use much of the JCR API. (Yes, this may make it easier to get our JCR implementation complete enough to put the REST service on top of DNA repositories.) But are we making it more complicated than it needs to be? What if we put the REST service on top of the Graph API (new to 0.3), which operates on top of a connector. This is essentially all that our JCR implementation is doing. The Graph API can read and write today, and it basically just consists of nodes with properties and children. And my intuition (nothing more than that!) is that the REST mapping to JCR would also map similarly/identically to the Graph API. The benefit is that this would be more efficient, since the extra JCR layer is eliminated.
I'm not sure what my preference would be. Both have advantages and disadvantages. But maybe we could consider both before we decide. Anyone have thoughts here?
I have the same opinion like you that RESTful service in not the equal to web app UI. We need separate JIRA ticket(s) for Web UI app, each panned/proposed WS (e.g. REST-based API for remote access and usage).
Also, we would need to clarify deployment scenarios of JBoss DNA stack in detail (like JackRabbit’s team did) – also highlighted on my wiki page.
Regarding Web application UI. I’m not against Flex as one of possible UI rendering but I’m just not sold on the fact that Flex is the first or preferable choice for DNA UI. Reasons explained in more detail on the same wiki page – but basically it is all about infrastructure and technology/feature enablers that btw already part of JBoss stack. For instance, thin and rich JSF framework like RichFaces that nicely integrates with JBoss Seam as a web infrastructural component might implement all required UI functionality. It is easy to use, understand how it works (both projects have comprehensive documentation) + my past experience with both frameworks might help in setting up quickly web infrastructure for JBoss DNA web.
I would agree that it's very important for other technologies (like Seam, RichFaces, GWT, even plain-old JSPs) to use JBoss DNA, because people writing web applications should be able to use JBoss DNA. However, I believe that we also need to provide an out-of-the-box ready-to-use metadata management repository web application, and that this will likely need to be offer rich interaction model (maybe even allowing graphical navigation). But perhaps the most critical need is for the application to over ways of customizing and extending how it views information, by not changing the application but by adding/changing data. This is content-driven, and not many frameworks make this possible. For example, GWT does not, since everything must be coded in Java and then compiled into the application. FLEX can be driven entirely from data. Could Seam and Rich Faces be used this way?
Best regards,
Sergiy
________________________________
From: Randall Hauch <rhauch at redhat.com>
To: Sergey Litsenko <litsenko_sergey at yahoo.com>; JBoss DNA <dna-dev at lists.jboss.org>
Sent: Tuesday, 11 November, 2008 2:57:38 AM
Subject: Re: [dna-dev] Re: JBoss DNA 0.4 planning
Excellent! Can't wait to see what you have. You're right that we could code to JSR 311 and use any valid implementation, but I have no problem relying upon RESTeasy, since we could leverage new features (e.g., http://bill.burkecentral.com/2008/11/10/jax-rs-atom-support-with-resteasy/), and since the RESTful service would certainly be packaged to run in a servlet container and thus shouldn't have any problems with clashes in dependencies. Plus, RESTeasy is another JBoss technology.
I'm wondering if you meant to say a JDBC Metadata "connector" (rather than "sequencer"). If you did mean "sequencer", I'd be interested in hearing about how that might work (what might be sequenced so the sequencer knows how to establish the connection and retrieve the metadata).
Now, regarding a REST mapping. I've looked at Sling (which has other features besides just a REST service), and based upon the documentation (which may very well be out of date), the client specifies the content type in the URL - that's not very appealing. I would much rather see standard content negotiation via the standard accept header. Now, the other two examples don't always look very RESTful (or at least "resource oriented"). For example, Alfresco's REST API's login method (http://wiki.alfresco.com/wiki/Repository_RESTful_API_Reference#Login) uses GET even though it's not idempotent. POST would seem to be better here. I would love to see a more detailed discussion on the REST mapping. Perhaps you could start off with what you've used in your prototype?
Another important topic is this: will we want to build a content-driven application framework or will we want to use Sling or Alfresco's WebScripts (or other)? Some advantages of reusing an existing system are:
* more functionality out of the box (i.e., we're not 1+ years behind)
* reuse existing technology
* leveraging existing community and possibly expand DNA community via participation in the other community
There are probably others, too. Some disadvantages are:
* must choose a technology
* must live with their interface and design
* little or no value-add over the existing technology
* our JCR support must be close-to-complete before we can do this
I'm a bit conflicted: I think we could do better, but just because we can doesn't mean we should. There's something to be said about focusing on what makes DNA unique and advantageous (primarily federation and sequencing), and just using Sling or Alfresco to build out some great useable applications. In fact, I think that a really usable and really useful content-driven rich internet application (perhaps using Flex) is another potential focus area for DNA.
So, as long as as have a correct and complete (enough) JCR implementation, then we (or anyone else) should be able to use DNA in combination with Sling and/or Alfresco. We may even win over the Alfresco community, if DNA's repository implementation is better than Jackrabbit. (Jackrabbit does a lot of things well, but there are some things it doesn't do well. All we need to do is be better at how Alfresco uses JCR.)
Now, having said that, I think that a RESTful service is not the same as a content-driven application framework. I think DNA should offer a lightweight, full-functioning RESTful service that doesn't depend on the larger content-driven applications. After all, I think many embedded use cases will simply want a deployable RESTful service so that client apps can work with a remote (federated) repository. And I think we can achieve this with very little code using RESTeasy (or maybe even other JSR-311 implementations). So we definitely need to do this.
Best regards,
Randall
On Nov 10, 2008, at 6:04 AM, Sergey Litsenko wrote:
Hi All,
I've already started working on (not yet in SVN - will wait till 0.3 release):
1) JDBC Metadata sequencer (POJO model is ready, working on extraction of metadata)
2) JAX-RS prototype.
IMO, we would need to start working on REST mapping for JCR resources. Basicaly, any implementation of http://jcp.org/en/jsr/summary?id=311 may be used as a core of the REST-JCR integration (RestEasy?)
There are at least few available implementations exists that we may review:
1) Sling project http://incubator.apache.org/sling/site/resources.html#Resources-JCRbasedResources)
2) Alfresco REST API for JCR at http://wiki.alfresco.com/wiki/HTTP_API#Alfresco_RESTful_API_Reference
3) Alfresco Content Management Interoperability Services (CMIS) API http://wiki.alfresco.com/wiki/CMIS_Web_Scripts_Reference
It would be nice to see as one of future features of DNA auto-discovery (zeroconf) of some resources as well as DNA repository self advertizing (for example - http://activemq.apache.org/zeroconf.html).
Best regards,
Sergiy
________________________________
From: "dna-dev-request at lists.jboss.org" <dna-dev-request at lists.jboss.org>
To: dna-dev at lists.jboss.org
Sent: Thursday, 6 November, 2008 4:00:27 AM
Subject: dna-dev Digest, Vol 8, Issue 3
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Today's Topics:
1. Preparing for the 0.3 release (Randall Hauch)
2. JBoss DNA 0.4 planning (Randall Hauch)
----------------------------------------------------------------------
Message: 1
Date: Tue, 4 Nov 2008 12:18:59 -0600
From: Randall Hauch <rhauch at redhat.com>
Subject: [dna-dev] Preparing for the 0.3 release
To: JBoss DNA <dna-dev at lists.jboss.org>
Message-ID: <92A505A6-0D05-47BF-813B-438181005D27 at redhat.com>
Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes
We're down to just a handful of outstanding issues targeted to 0.3,
and all of the big fish issues were completed. I'll be working my two
issues over the next few days, but I should be ready for releasing as
early as this week. Serge has the other outstanding issues, which are
all regarding the SVN connector. Serge, where do we stand on this?
Do you want more time to get some functionality finished, or is the
connector fairly close?
Anybody else have anything to discuss?
Best regards,
Randall
------------------------------
Message: 2
Date: Tue, 4 Nov 2008 12:37:05 -0600
From: Randall Hauch <rhauch at redhat.com>
Subject: [dna-dev] JBoss DNA 0.4 planning
To: JBoss DNA <dna-dev at lists.jboss.org>
Message-ID: <9643F3D3-5E3F-4219-A492-6BC1F6196C73 at redhat.com>
Content-Type: text/plain; charset="us-ascii"
Now that 0.3 is almost out the door, I'd like to start discussing the
goals for the next release.
I'd love to see the JCR implementation take more shape. Right now
it's read-only, so getting that much farther along would be
outstanding. Anybody interested? I think we could easily put several
people to work here. The graph API is pretty good, and should make
implementing JCR relatively straightforward. Any interest, Michael
Trezzi and Alexandre and Serge?
We need to add events to the connector framework. That should be
pretty straightforward. Also versioning, which will require a bit
more work. Plus, there are a couple of connectors that we may want to
start working on. This is something I'd be happy to continue with.
Serge P. also has expressed interest in working on some connectors (in
fact his SVN connector is coming along great!).
The CND sequencer could use some love and attention. Dan was stuck in
some ANLTR hell, and got pulled off onto a different project. Since
it uses ANTLR, maybe you might be interested in it, Alexandre?
We also have a need to start working on a REST/WebDAV layer that
allows other client apps to access a DNA repository. There's a couple
of things we can do, including looking at Apache Sling, or using
RESTeasy for a more simple implementation, or something else. Sergiy
and John both expressed interest in this.
Anything else?
We can either tackle several things at once and move them all
incrementally, or we can do more in just a few areas. Ideally, we're
looking at a 4-5 week cycle (finishing before the year-end holidays.)
A lot will depend on how much effort people might be able to dedicate
to the project.
Please respond with your thoughts and comments!
Best regards,
Randall
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