Very cool.
-----Original Message-----
From: Niels Hoogeveen <pd_aficion...@hotmail.com>
Date: Fri, 26 Mar 2010 17:22:41
To: <user@lists.neo4j.org>
Subject: Re: [Neo] meta meta classes
Using Scala, I was actually able to extend MetaModelThing to act as a Node and
MetaModelClass to have shadowing functionality for both MetaModelClasses and
for MetaModelProperties, without touching the original source code.
> To: user@lists.neo4j.org
> From: rick.bullo...@burningskysoftware.com
> Date: Fri, 26 Mar 2010 14:29:03 +0000
> Subject: Re: [Neo] meta meta classes
>
> Such are the joys and challenges of frameworks and abstractions. Sometimes
> you do need to get "close to the metal" though, to achieve specific
> functional and performance requirements. Thus the reason open source
> frameworks are awesome. At least we can change and extend them more easily!
>
>
>
> -----Original Message-----
> From: Niels Hoogeveen <pd_aficion...@hotmail.com>
> Date: Fri, 26 Mar 2010 15:20:15
> To: <user@lists.neo4j.org>
> Subject: Re: [Neo] meta meta classes
>
>
> Making MetaModelThing implement the Node interface is actually orthogonal to
> the creation of Shadow objects. Though it does make code using classes as
> objects cleaner, and allows the node property of MetaModelThing to become
> private.
>
> > From: pd_aficion...@hotmail.com
> > To: user@lists.neo4j.org
> > Date: Fri, 26 Mar 2010 14:38:08 +0100
> > Subject: Re: [Neo] meta meta classes
> >
> >
> > Or, and this probably the simplest solution. Let a MetaModelThing implement
> > the Node interface. This allows a class to be an instance of another class
> > and/or a SubType of another class.
> >
> >
> > > From: pd_aficion...@hotmail.com
> > > To: user@lists.neo4j.org
> > > Date: Fri, 26 Mar 2010 14:20:07 +0100
> > > Subject: Re: [Neo] meta meta classes
> > >
> > >
> > > The class as object phenomenon is actually quite pervasive, and I think
> > > it is possible to have a generalized solution for it.
> > >
> > > After sending this email yesterday, I came up with a slightly different
> > > solution.
> > >
> > > val taggable = namespace.getMetaClass("taggable", true)
> > >
> > > val tagName = metaModelNamespace.getMetaProperty("tagname", true)
> > > tagName.setCardinality(1)
> > >
> > > val metaTaggable = metaModelNamespace.getMetaClass("taggable", true)
> > > metaTaggable.getDirectProperties.add(tagName)
> > > metaTaggable.getDirectInstances.add(taggable.node)
> > >
> > > val body = namespace.getMetaClass("body", true)
> > > taggable.getDirectSubs.add(body)
> > >
> > > Instead of directly relating the class "body" to the meta class
> > > "taggable", I create a shadow of the meta class "taggable" with the same
> > > name in the namespace of the class "body", and make "body" a subclass of
> > > this shadow. That way the sub classing relationship remains nicely in one
> > > name space, while the instance relationship transcends name spaces, as it
> > > should.
> > >
> > > This could in principle be generalized by adding a methods to
> > > MetaModelClass:
> > >
> > > public MetaModelClass createShadowClass(NameSpace ns){
> > >
> > > MetaModelClass mc = ns.getMetaClass(this.getName(), true);
> > > this.getDirectInstances.add(mc.node);
> > > return mc;
> > > }
> > >
> > > This returns a shadow of a given MetaModelClass in a given namespace and
> > > adds it as a an instance of this.
> > >
> > > It would of course be nicer to have a method with the signature:
> > >
> > > public MetaModelClass getShadow(NameSpace ns, Boolean create)
> > >
> > > This is much more in line with the rest of the API, but requires a way to
> > > find out the namespace a given MetaModelClass is defined in. I didn't see
> > > a method getNamespace() for a given class, and didn't delve deeply enough
> > > in the source code to figure out how to do that.
> > >
> > > A similar approach can of course also be applied to MetaModelProperties,
> > > by adding the following method to MetaModelClass:
> > >
> > > public MetaModelProperty
> > > createShadowProperty(NameSpace ns){
> > >
> > >
> > >
> > > MetaModelProperty mp =
> > > ns.getMetaProperty(this.getName(), true);
> > >
> > >
> > > this.getDirectInstances.add(mp.node);
> > >
> > > return mp;
> > >
> > > }
> > >
> > >
> > > This way the underlying node of a MetaModelProperty can properly be used
> > > as a class of its own and have properties, relationships, that can be
> > > further modeled in the meta layer. This e.q. allows to set a default
> > > rendering format for a given property class.
> > >
> > > I don't see a MetaModelRelationships, which is unfortunate, since that
> > > would allow the modeling of the properties of a Relationship.
> > >
> > >
> > > Kind regards,
> > > Niels Hoogeveen
> > >
> > >
> > > > Date: Fri, 26 Mar 2010 11:26:29 +0100
> > > > From: matt...@neotechnology.com
> > > > To: user@lists.neo4j.org
> > > > Subject: Re: [Neo] meta meta classes
> > > >
> > > > That's an interresting case you've got here and it looks to me like it's
> > > > probably the best way to model it in the meta model.
> > > >
> > > > 2010/3/25 Niels Hoogeveen <pd_aficion...@hotmail.com>
> > > >
> > > > >
> > > > > For my application, I want to model an HTML template in Neo4J, using
> > > > > the
> > > > > MetaModel api.
> > > > >
> > > > > So I started setting up MetaModelClasses for the various HTML
> > > > > entities.
> > > > >
> > > > > e.g. (code in Scala)
> > > > >
> > > > > val classProp = namespace.getMetaProperty("class", true)
> > > > > val idProp =
> > > > > namespace.getMetaProperty("id", true)
> > > > > idProp.setCardinality(1)
> > > > >
> > > > >
> > > > > val body = namespace.getMetaClass("body", true)
> > > > > body.getDirectProperties(classProp)
> > > > > body.getDirectProperties(idProp)
> > > > >
> > > > >
> > > > > Which creates a class named "body" which has a property named "class"
> > > > > without a cardinality restriction and a property named "id" with a
> > > > > cardinality restriction of 1.
> > > > >
> > > > > Now I can create nodes of class "body" with various values for
> > > > > "class" and
> > > > > for "id".
> > > > >
> > > > > So far so good, but now I want to say that the class body has a
> > > > > property
> > > > > "tagname" which should get the value "body".
> > > > >
> > > > > The meta model itself doesn't allow classes to have properties, but it
> > > > > allows access to the underlying node of the class.
> > > > >
> > > > > So I created a separate namespace for the meta meta classes and added
> > > > > the
> > > > > following three definitions:
> > > > >
> > > > > val tagName = metaNamespace.getMetaProperty("tagname", true)
> > > > > tagName.setCardinality(1)
> > > > > val taggable = metaNamespace.getMetaClass("taggable", true)
> > > > >
> > > > > body.node.setProperty("tagname", "body")
> > > > >
> > > > > This creates a property "tagname" with the value "body" for the class
> > > > > named
> > > > > "body".
> > > > >
> > > > > Now comes the more ambiguous part, how to link "body" to "taggable".
> > > > >
> > > > > I can make body.node an instance of taggable. Once there is a
> > > > > validator,
> > > > > the existence of a "tagname" property with cardinality 1 should be
> > > > > checked,
> > > > > so it is reasonable to make body.node an instance of taggable.
> > > > >
> > > > > At the same time the class body is actually a subclass of taggable,
> > > > > so I am
> > > > > inclined to define that as well.
> > > > >
> > > > > So I end up doing the following:
> > > > >
> > > > > taggable.getDirectInstances.add(body.node)
> > > > > taggable.getDirectSubs.add(body)
> > > > >
> > > > > I would like to know if this is the correct approach to this
> > > > > situation, or
> > > > > whether there are better alternatives.
> > > > >
> > > > > Kind regards,
> > > > > Niels Hoogeveen
> > > > >
> > > > >
> > > > > _________________________________________________________________
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> > > >
> > > >
> > > >
> > > > --
> > > > Mattias Persson, [matt...@neotechnology.com]
> > > > Neo Technology, www.neotechnology.com
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