I think the best solution here is to have an instance enumeration on MetaModelClass. Singletons are special case of an enumeration.
See: http://www.w3.org/TR/2002/WD-owl-ref-20021112/#Enumerated http://owl.cs.manchester.ac.uk/2007/05/api/javadoc/org/semanticweb/owl/model/OWLObjectOneOf.html > Date: Thu, 8 Apr 2010 22:33:11 +0200 > From: matt...@neotechnology.com > To: user@lists.neo4j.org > Subject: Re: [Neo] meta meta classes > > Ok now I get your point! Thank you for clarifying. > > Your singleton proposal could be a good idea then. Could it > potentially be a hindrance in some scenario? I mean should we have a > MetaModelClass#setSingleton(boolean) or something so that this > behaviour can be controlled? > > 2010/4/8, Niels Hoogeveen <pd_aficion...@hotmail.com>: > > > > Each country needs to be modeled as classes, because I want to set the > > restriction that French regions (which can have different properties from > > Canadian provinces) can only have a relationship with the country France, > > and Canadian provinces can only have a relationship with the country Canada. > > The domain and the range of a PropertyType are classes not instances. If > > countries were simply instances of the "country" class, it would be > > possible to say that an instance of a Canadian province is a subdivision of > > France. > > > > I'd like to be able to iterate over the subdivision of France and have > > guaranteed that each instance has the property "region code", a property > > unknown to Canadian provinces. Without having a restriction stating that a > > specific sub-division belongs to a specific country, any sub-division can be > > related to any country, so a user may erroneously say that Alberta is a > > French region. Not only is this factually incorrect, but structurally too. > > Alberta, being a Canadian province, doesn't have the "region code" property, > > which I want French regions to have. > > > > > >> Date: Thu, 8 Apr 2010 20:06:32 +0200 > >> From: matt...@neotechnology.com > >> To: user@lists.neo4j.org > >> Subject: Re: [Neo] meta meta classes > >> > >> 2010/4/8 Niels Hoogeveen <pd_aficion...@hotmail.com> > >> > >> > > >> > Your point about the cardinality restriction is a correct observation. > >> > > >> > In fact it would be better to create a "is-subdivision-of" PropertyType > >> > on > >> > "sub-division" and give that a range "country" with a cardinality of 1. > >> > Then > >> > for each subclass of "sub-division" a restriction should be set, naming > >> > the > >> > "country" class this specific "sub-division" class applies to. > >> > > >> > Still, it requires each country to be defined as both a class and an > >> > instance. > >> > > >> Why just countries as classes? why not each subdivision as classes as > >> well? > >> Why countries as classes at all? > >> > >> > > >> > > Date: Thu, 8 Apr 2010 19:15:30 +0200 > >> > > From: matt...@neotechnology.com > >> > > To: user@lists.neo4j.org > >> > > Subject: Re: [Neo] meta meta classes > >> > > > >> > > So, you describe the model (with "country", "sub-division" and > >> > > "has-sub-division") which is OK! Then you not just want to add data > >> > > which > >> > > would conform to it, you also describe the highest level of that data > >> > > in > >> > the > >> > > meta model itself with cardinality for how many sub-divisions each > >> > > such > >> > > level must contain. > >> > > > >> > > My first though here is: why put actual data into the meta model (the > >> > design > >> > > isn't intended for that)? > >> > > The second is: why (since you put actual data into the meta model) > >> > > would > >> > you > >> > > stop there? why only say that "France" have 10 subdivisions? You don't > >> > say > >> > > exactly which subdivisions or how many/which subdivisions each > >> > subdivision > >> > > has, a.s.o. Which benefits would modeling only the highest level of > >> > > data > >> > get > >> > > you? And if you could describe the entire data in the meta model, you > >> > > end > >> > up > >> > > with a meta model which describes the entire data and then, in > >> > > addition, > >> > the > >> > > data which is exactly the same as the meta model... what benefits does > >> > that > >> > > give you? > >> > > > >> > > I'm just confused about the fact that you want to have the meta model > >> > > (classes, properties, restrictions) and (some of) the actual data > >> > > modeled > >> > in > >> > > the meta model, whereas the meta model was intended to model the meta > >> > model > >> > > (the UML diagram, so to speak) and not the actual data it would have > >> > conform > >> > > to it. > >> > > > >> > > Help me understand which benefits you're after by modeling the "top > >> > level" > >> > > of your actual data into the meta model itself. > >> > > > >> > > > >> > > Best, > >> > > Mattias > >> > > > >> > > 2010/4/8 Niels Hoogeveen <pd_aficion...@hotmail.com> > >> > > > >> > > > > >> > > > The example of the tag library and countries/sub-divisions are not > >> > > > necessarily similar. The first shows the need to model the > >> > > > properties > >> > of a > >> > > > class. > >> > > > > >> > > > The second example shows the need to have singleton classes, which > >> > > > is a > >> > > > different concept, and something that cannot be done out of the box, > >> > but I > >> > > > will show a solution that requires minimal modifications to the > >> > > > current > >> > > > software. > >> > > > > >> > > > Suppose we want to model "countries" and their "sub-divisions". > >> > > > > >> > > > We do the following: > >> > > > > >> > > > create class "country" > >> > > > create class "sub-division" > >> > > > create property "has-sub-division" > >> > > > make "has-subdivision" a property of "country" > >> > > > > >> > > > Now we like to populate the database, since all countries have > >> > different > >> > > > types of sub-divisions we need to create those: > >> > > > > >> > > > create class "french_region" > >> > > > create class "canadian_province" > >> > > > create class "canadian_territory" > >> > > > create class "US_state" > >> > > > etc. > >> > > > > >> > > > Populate the various classes with instances: > >> > > > > >> > > > create node for "Alsace" and make it an instance of "french_region" > >> > > > create node for "Aquitaine" and make it an instance of > >> > > > "french_region" > >> > > > create node for "Alberta" and make it an instance of > >> > > > "Canadian_province" > >> > > > create node for "Nanavut" and make it an instance of > >> > > > "Canadian_territory" > >> > > > create node for "British Columbia" and make it an instance of > >> > > > "Canadian_province" > >> > > > create node for "Alabama" and make it an instance of > >> > > > "US_State" > >> > > > create node for "Alaska" and make it an instance of > >> > > > "US_State" > >> > > > etc. > >> > > > > >> > > > We'd like to state that each country has its own restriction on the > >> > type of > >> > > > subdivision. To do that we need to create classes for each country. > >> > > > > >> > > > create class "France" > >> > > > create class "Canada" > >> > > > create class "United_States_of_America" > >> > > > etc. > >> > > > > >> > > > make class "France" a subclass of "Country" > >> > > > make class "Canada" a subclass of "Country" > >> > > > make class "United_States_of_America" a subclass of "Country" > >> > > > etc. > >> > > > > >> > > > create restriction for "France" on "has-sub-division" with range > >> > > > "french_province" and cardinality = 26 > >> > > > create restriction for "Canada" on "has-sub-division" with range > >> > > > "canadian_province" and cardinality = 10 > >> > > > create restriction for "Canada" on "has-sub-division" with range > >> > > > "canadian_territory" and cardinality = 3 > >> > > > create restriction for "United_States_of_America" on > >> > > > "has-sub-division" > >> > > > with range "US_State" and cardinality = 50 > >> > > > etc. > >> > > > > >> > > > Now we have classes for each country, but no instances. > >> > > > Unfortunately > >> > we > >> > > > cannot say that a class is an instance of itself, that would require > >> > > > a > >> > > > relationsship where the endnode equals the startnode, which Neo4J > >> > doesn't > >> > > > allow. So we have to create separate instances for each country. > >> > > > > >> > > > create node for "France" > >> > > > create node for "Canada" > >> > > > create node for "United_States_Of_America" > >> > > > etc. > >> > > > > >> > > > make node "France" an instance of class "France" > >> > > > make node "Canada" an instance of class "Canada" > >> > > > make node "United_States_of_America" an instance of class > >> > > > "United_States_of_America" > >> > > > > >> > > > And finally link the subdivisions to their countries: > >> > > > > >> > > > "France" "has-sub-division" "Alsace" > >> > > > "France" "has-sub-division" "Aquitaine" > >> > > > "Canada" "has-sub-division-of" "Alberta" > >> > > > "Canada" "has-subdivision" "British Columbia" > >> > > > "Canada" "has-subdivision" "Nanavut" > >> > > > "United_States_of_America" "has-sub-division" "Alabama" > >> > > > "United_States_of_America" "has-sub-division" "Alaska" > >> > > > > >> > > > So we end up having a class for each country and an instance for > >> > > > each > >> > > > country. > >> > > > > >> > > > Writing this down, I realize the patch I sent you a few days ago, > >> > contains > >> > > > a minor flaw, that needs to be fixed. In that patch I added an > >> > > > indexed > >> > > > property "uri" to the meta model, to bring it in line with what is > >> > being > >> > > > done in the RDF module, and to make certain that the same URI is not > >> > used > >> > > > for two different properties. Without unicity a class can have > >> > > > several > >> > > > different ProperyTypes with the same name. In that situation the > >> > > > lookup > >> > of > >> > > > the PropertyType of a property or relationship becomes impossible. > >> > > > > >> > > > The flaw in my patch is the name of the "uri" property, which should > >> > > > be > >> > > > something like "class_uri". That way the class of each country can > >> > > > be > >> > given > >> > > > the same URI as the instance of each country, because they live in > >> > different > >> > > > name spaces. > >> > > > > >> > > > This same technique is used in OWL to provide "punning". An instance > >> > and a > >> > > > class can have the same URI, because instances in OWL live in a > >> > different > >> > > > namespaces from classes. > >> > > > > >> > > > Through the use of the "uri" property and the "class_uri" property > >> > > > we > >> > can > >> > > > also distill that each country class is a singleton class, because > >> > there > >> > > > exists an instance with the same URI. That way we can work around > >> > > > the > >> > > > limitation that relationships cannot have the same start and end > >> > > > node. > >> > > > > >> > > > Furthermore, it allows for some extra restrictions to MetaModelClass > >> > with > >> > > > the following logic: If a class has exactly one instance where the > >> > "uri" of > >> > > > that instance equals the "class_uri" of the class, no more instances > >> > can be > >> > > > added And if there is an instance of a class without a "uri" that > >> > equals the > >> > > > "class_uri", no instances can be added where the "uri" of the > >> > > > instance > >> > > > equals the "class_uri" of the class. With that logic, we have proper > >> > > > singleton classes in the meta model of Neo4J. > >> > > > > >> > > > Kind regards, > >> > > > Niels Hoogeveen > >> > > > > >> > > > > Date: Thu, 8 Apr 2010 11:37:37 +0200 > >> > > > > From: matt...@neotechnology.com > >> > > > > To: user@lists.neo4j.org > >> > > > > Subject: Re: [Neo] meta meta classes > >> > > > > > >> > > > > 2010/3/30 Niels Hoogeveen <pd_aficion...@hotmail.com> > >> > > > > > >> > > > > > > >> > > > > > MetaModelObject already has a getter (without using the word > >> > > > > > "get") > >> > to > >> > > > > > access the node. > >> > > > > > > >> > > > > > Wrapping MetaModelObject to give it a Node-interface makes it > >> > possible > >> > > > to > >> > > > > > directly write: > >> > > > > > > >> > > > > > metalObject.setProperty("a", b) > >> > > > > > > >> > > > > > instead of > >> > > > > > > >> > > > > > metaobject.node.setPropert("a", b) > >> > > > > > > >> > > > > > If that were all, I wouldn't make a post about it. The more > >> > interesting > >> > > > > > part is the meta modeling of the node gotten from a > >> > MetaModelObject. > >> > > > This > >> > > > > > node represents the class, but it is not an instance of any > >> > > > > > class > >> > > > itself. > >> > > > > > That's where the reify method comes into play, which takes the > >> > > > > > node > >> > > > from a > >> > > > > > MetaModelObject and creates a class with the same name, but in a > >> > > > different > >> > > > > > namespace, and makes the node an instance of this new class. > >> > > > > > > >> > > > > > With that construction it becomes possible to model the > >> > > > > > relationships/properties of a class. > >> > > > > > > >> > > > > > There are many examples where this can be handy. > >> > > > > > > >> > > > > > I already gave the example of HTML tags, where the attributes > >> > > > > > can > >> > be > >> > > > > > modeled as properties and the tagname as a property of the meta > >> > class. > >> > > > > > > >> > > > > > Another example is: > >> > > > > > > >> > > > > > All countries have subdivision. Countries and their subdivisions > >> > all > >> > > > are > >> > > > > > instances of a certain class. There is one class for country, > >> > > > > > but > >> > there > >> > > > is a > >> > > > > > set of classes for subdivisions. In some countries, a > >> > > > > > subdivision > >> > is > >> > > > called > >> > > > > > "province", in others it's a "state" or a "district". > >> > > > > > Subdivision > >> > of > >> > > > various > >> > > > > > countries can have different sets of properties and relations. > >> > > > > > > >> > > > > > How to model the fact that the instance "United States of > >> > > > > > America" > >> > has > >> > > > > > subdivisions of the class "State_(US)"? Using the reify method > >> > > > > > we > >> > can > >> > > > make a > >> > > > > > class "United States of America", where we can model that the > >> > > > ClassRange of > >> > > > > > "State_(US)" is "United States of America". Or if we want the > >> > > > relationship > >> > > > > > to point the other way, that the "United States of America" has > >> > > > > > 50 > >> > (use > >> > > > of > >> > > > > > cardinality) subdivisions of the class "State_(US)". > >> > > > > > > >> > > > > Here you take a step into modeling the actual data into the meta > >> > model > >> > > > which > >> > > > > describes the data. Is it desirable to first model exactly how the > >> > data > >> > > > will > >> > > > > look, and then add data so that it looks like that? I get a > >> > > > > feeling > >> > that > >> > > > the > >> > > > > data is described twice here... > >> > > > > > >> > > > > > > >> > > > > > Of course all this can directly be expressed with nodes and > >> > > > relationships, > >> > > > > > but that's what the meta model does anyway. > >> > > > > > > >> > > > > > I do have one peeve with the meta model API. The class DataRange > >> > has a > >> > > > > > constructor: > >> > > > > > > >> > > > > > DataRange(String datatype, Object... values) > >> > > > > > > >> > > > > > I'd much rather see a new Restrictable class Datavalue, and see > >> > > > > > a > >> > > > > > constructor: > >> > > > > > > >> > > > > > DataRange(String datatype, Datavalue... values) > >> > > > > > > >> > > > > > That way the possible values a property can have additional > >> > properties > >> > > > and > >> > > > > > relationships (eg. link to Wordnet definition or Wikipedia > >> > > > > > entry). > >> > > > > > > >> > > > > > Kind regards, > >> > > > > > Niels Hoogeveen > >> > > > > > > >> > > > > > > >> > > > > > > >> > > > > > > >> > > > > > > >> > > > > > > >> > > > > > > Date: Tue, 30 Mar 2010 09:30:10 +0200 > >> > > > > > > From: matt...@neotechnology.com > >> > > > > > > To: user@lists.neo4j.org > >> > > > > > > Subject: Re: [Neo] meta meta classes > >> > > > > > > > >> > > > > > > Would making the underlying Node publically available (via a > >> > getter) > >> > > > be > >> > > > > > > virtually the same thing? In that case the meta model classes > >> > could > >> > > > have > >> > > > > > > such a getter. > >> > > > > > > > >> > > > > > > 2010/3/26 Niels Hoogeveen <pd_aficion...@hotmail.com> > >> > > > > > > > >> > > > > > > > > >> > > > > > > > Hi Peter, > >> > > > > > > > > >> > > > > > > > I added a Wiki entry in my github repo called "Reification > >> > > > > > > > of > >> > meta > >> > > > > > classes > >> > > > > > > > and meta properties": > >> > > > > > > > > >> > > > > > > > > >> > > > > > > > > >> > > > > > > >> > > > > >> > http://wiki.github.com/NielsHoogeveen/Scala-Neo4j-utils/reification-of-meta-classes-and-meta-properties > >> > > > > > > > > >> > > > > > > > The source code for the Scala wrappers can be found found in > >> > > > > > > > my > >> > > > repo: > >> > > > > > > > > >> > > > > > > > http://github.com/NielsHoogeveen/Scala-Neo4j-utils > >> > > > > > > > > >> > > > > > > > Kind regards, > >> > > > > > > > Niels Hoogeveen > >> > > > > > > > > >> > > > > > > > > From: neubauer.pe...@gmail.com > >> > > > > > > > > Date: Fri, 26 Mar 2010 17:25:01 +0100 > >> > > > > > > > > To: user@lists.neo4j.org > >> > > > > > > > > Subject: Re: [Neo] meta meta classes > >> > > > > > > > > > >> > > > > > > > > Awesome Niels! > >> > > > > > > > > > >> > > > > > > > > maybe you could blog or document some cool example on > >> > > > > > > > > this? > >> > > > > > > > > > >> > > > > > > > > Cheers, > >> > > > > > > > > > >> > > > > > > > > /peter neubauer > >> > > > > > > > > > >> > > > > > > > > COO and Sales, Neo Technology > >> > > > > > > > > > >> > > > > > > > > GTalk: neubauer.peter > >> > > > > > > > > Skype peter.neubauer > >> > > > > > > > > Phone +46 704 106975 > >> > > > > > > > > LinkedIn http://www.linkedin.com/in/neubauer > >> > > > > > > > > Twitter http://twitter.com/peterneubauer > >> > > > > > > > > > >> > > > > > > > > http://www.neo4j.org - Your high performance > >> > graph > >> > > > > > database. > >> > > > > > > > > http://www.tinkerpop.com - Processing for > >> > Internet-scale > >> > > > > > graphs. > >> > > > > > > > > http://www.thoughtmade.com - Scandinavias coolest > >> > Bring-a-Thing > >> > > > > > party. > >> > > > > > > > > > >> > > > > > > > > > >> > > > > > > > > > >> > > > > > > > > On Fri, Mar 26, 2010 at 5:22 PM, Niels Hoogeveen > >> > > > > > > > > <pd_aficion...@hotmail.com> wrote: > >> > > > > > > > > > > >> > > > > > > > > > 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. Learn > >> > more. > >> > > > > > > > > >> > > > > http://windows.microsoft.com/shop > >> > > > > > > > > >> > > > > _______________________________________________ > >> > > > > > > > > >> > > > > Neo mailing list > >> > > > > > > > > >> > > > > User@lists.neo4j.org > >> > > > > > > > > >> > > > > https://lists.neo4j.org/mailman/listinfo/user > >> > > > > > > > > >> > > > > > >> > > > > > > > > >> > > > > >> > > > > > > > > >> > > > > >> > > > > > > > > >> > > > > >> > > > > > > > > >> > > > -- > >> > > > > > > > > >> > > > Mattias Persson, [matt...@neotechnology.com] > >> > > > > > > > > >> > > > Neo Technology, www.neotechnology.com > >> > > > > > > > > >> > > > _______________________________________________ > >> > > > > > > > > >> > > > Neo mailing list > >> > > > > > > > > >> > > > User@lists.neo4j.org > >> > > > > > > > > >> > > > https://lists.neo4j.org/mailman/listinfo/user > >> > > > > > > > > >> > > > >> > > > > > > > > >> > > > >> > > > > > _________________________________________________________________ > >> > > > > > > > > >> > > Express yourself instantly with MSN Messenger! > >> > Download > >> > > > today > >> > > > > > it's > >> > > > > > > > FREE! > >> > > > > > > > > >> > > > >> > > > > > http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/ > >> > > > > > > > > >> > > _______________________________________________ > >> > > > > > > > > >> > > Neo mailing list > >> > > > > > > > > >> > > User@lists.neo4j.org > >> > > > > > > > > >> > > https://lists.neo4j.org/mailman/listinfo/user > >> > > > > > > > > >> > > >> > > > > > > > > >> > > >> > > > > > _________________________________________________________________ > >> > > > > > > > > >> > New Windows 7: Find the right PC for you. Learn more. > >> > > > > > > > > >> > http://windows.microsoft.com/shop > >> > > > > > > > > >> > _______________________________________________ > >> > > > > > > > > >> > Neo mailing list > >> > > > > > > > > >> > User@lists.neo4j.org > >> > > > > > > > > >> > https://lists.neo4j.org/mailman/listinfo/user > >> > > > > > > > > >> > >> > > > > > > > > >> > >> > > > _________________________________________________________________ > >> > > > > > > > > >> New Windows 7: Find the right PC for you. Learn more. > >> > > > > > > > > >> http://windows.microsoft.com/shop > >> > > > > > > > > >> _______________________________________________ > >> > > > > > > > > >> Neo mailing list > >> > > > > > > > > >> User@lists.neo4j.org > >> > > > > > > > > >> https://lists.neo4j.org/mailman/listinfo/user > >> > > > > > > > > >> _______________________________________________ > >> > > > > > > > > >> Neo mailing list > >> > > > > > > > > >> User@lists.neo4j.org > >> > > > > > > > > >> https://lists.neo4j.org/mailman/listinfo/user > >> > > > > > > > > > > >> > > > > > > > > > > >> > > > _________________________________________________________________ > >> > > > > > > > > > New Windows 7: Find the right PC for you. Learn more. > >> > > > > > > > > > http://windows.microsoft.com/shop > >> > > > > > > > > > _______________________________________________ > >> > > > > > > > > > Neo mailing list > >> > > > > > > > > > User@lists.neo4j.org > >> > > > > > > > > > https://lists.neo4j.org/mailman/listinfo/user > >> > > > > > > > > > > >> > > > > > > > > _______________________________________________ > >> > > > > > > > > Neo mailing list > >> > > > > > > > > User@lists.neo4j.org > >> > > > > > > > > https://lists.neo4j.org/mailman/listinfo/user > >> > > > > > > > > >> > > > > > > > > >> > _________________________________________________________________ > >> > > > > > > > Express yourself instantly with MSN Messenger! Download > >> > > > > > > > today > >> > it's > >> > > > > > FREE! > >> > > > > > > > > >> > http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/ > >> > > > > > > > _______________________________________________ > >> > > > > > > > Neo mailing list > >> > > > > > > > User@lists.neo4j.org > >> > > > > > > > https://lists.neo4j.org/mailman/listinfo/user > >> > > > > > > > > >> > > > > > > > >> > > > > > > > >> > > > > > > > >> > > > > > > -- > >> > > > > > > Mattias Persson, [matt...@neotechnology.com] > >> > > > > > > Neo Technology, www.neotechnology.com > >> > > > > > > _______________________________________________ > >> > > > > > > Neo mailing list > >> > > > > > > User@lists.neo4j.org > >> > > > > > > https://lists.neo4j.org/mailman/listinfo/user > >> > > > > > > >> > > > > > _________________________________________________________________ > >> > > > > > Express yourself instantly with MSN Messenger! Download today > >> > > > > > it's > >> > > > FREE! > >> > > > > > http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/ > >> > > > > > _______________________________________________ > >> > > > > > Neo mailing list > >> > > > > > User@lists.neo4j.org > >> > > > > > https://lists.neo4j.org/mailman/listinfo/user > >> > > > > > > >> > > > > > >> > > > > > >> > > > > > >> > > > > -- > >> > > > > Mattias Persson, [matt...@neotechnology.com] > >> > > > > Hacker, Neo Technology > >> > > > > www.neotechnology.com > >> > > > > _______________________________________________ > >> > > > > Neo mailing list > >> > > > > User@lists.neo4j.org > >> > > > > https://lists.neo4j.org/mailman/listinfo/user > >> > > > > >> > > > _________________________________________________________________ > >> > > > Express yourself instantly with MSN Messenger! Download today it's > >> > FREE! > >> > > > http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/ > >> > > > _______________________________________________ > >> > > > Neo mailing list > >> > > > User@lists.neo4j.org > >> > > > https://lists.neo4j.org/mailman/listinfo/user > >> > > > > >> > > > >> > > > >> > > > >> > > -- > >> > > Mattias Persson, [matt...@neotechnology.com] > >> > > Hacker, Neo Technology > >> > > www.neotechnology.com > >> > > _______________________________________________ > >> > > Neo mailing list > >> > > User@lists.neo4j.org > >> > > https://lists.neo4j.org/mailman/listinfo/user > >> > > >> > _________________________________________________________________ > >> > New Windows 7: Find the right PC for you. Learn more. > >> > http://windows.microsoft.com/shop > >> > _______________________________________________ > >> > Neo mailing list > >> > User@lists.neo4j.org > >> > https://lists.neo4j.org/mailman/listinfo/user > >> > > >> > >> > >> > >> -- > >> Mattias Persson, [matt...@neotechnology.com] > >> Hacker, Neo Technology > >> www.neotechnology.com > >> _______________________________________________ > >> Neo mailing list > >> User@lists.neo4j.org > >> https://lists.neo4j.org/mailman/listinfo/user > > > > _________________________________________________________________ > > Express yourself instantly with MSN Messenger! Download today it's FREE! > > http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/ > > _______________________________________________ > > Neo mailing list > > User@lists.neo4j.org > > https://lists.neo4j.org/mailman/listinfo/user > > > > > -- > Mattias Persson, [matt...@neotechnology.com] > Hacker, Neo Technology > www.neotechnology.com > _______________________________________________ > Neo mailing list > User@lists.neo4j.org > https://lists.neo4j.org/mailman/listinfo/user _________________________________________________________________ Express yourself instantly with MSN Messenger! Download today it's FREE! http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/ _______________________________________________ Neo mailing list User@lists.neo4j.org https://lists.neo4j.org/mailman/listinfo/user
