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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