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 > > > > > > > > > > > > > > > _________________________________________________________________ > > > > > New Windows 7: Find the right PC for you. 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