[Neo] meta meta classes

Niels Hoogeveen pd_aficionado at hotmail.com
Thu Apr 8 23:52:02 CEST 2010


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: mattias at neotechnology.com
> To: user at 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_aficionado at 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: mattias at neotechnology.com
> >> To: user at lists.neo4j.org
> >> Subject: Re: [Neo] meta meta classes
> >>
> >> 2010/4/8 Niels Hoogeveen <pd_aficionado at 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: mattias at neotechnology.com
> >> > > To: user at 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_aficionado at 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: mattias at neotechnology.com
> >> > > > > To: user at lists.neo4j.org
> >> > > > > Subject: Re: [Neo] meta meta classes
> >> > > > >
> >> > > > > 2010/3/30 Niels Hoogeveen <pd_aficionado at 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: mattias at neotechnology.com
> >> > > > > > > To: user at 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_aficionado at 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.peter at gmail.com
> >> > > > > > > > > Date: Fri, 26 Mar 2010 17:25:01 +0100
> >> > > > > > > > > To: user at 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_aficionado at 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 at lists.neo4j.org
> >> > > > > > > > > >> From: rick.bullotta at 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_aficionado at hotmail.com>
> >> > > > > > > > > >> Date: Fri, 26 Mar 2010 15:20:15
> >> > > > > > > > > >> To: <user at 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_aficionado at hotmail.com
> >> > > > > > > > > >> > To: user at 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_aficionado at hotmail.com
> >> > > > > > > > > >> > > To: user at 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: mattias at neotechnology.com
> >> > > > > > > > > >> > > > To: user at 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_aficionado at 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 at lists.neo4j.org
> >> > > > > > > > > >> > > > > https://lists.neo4j.org/mailman/listinfo/user
> >> > > > > > > > > >> > > > >
> >> > > > > > > > > >> > > >
> >> > > > > > > > > >> > > >
> >> > > > > > > > > >> > > >
> >> > > > > > > > > >> > > > --
> >> > > > > > > > > >> > > > Mattias Persson, [mattias at neotechnology.com]
> >> > > > > > > > > >> > > > Neo Technology, www.neotechnology.com
> >> > > > > > > > > >> > > > _______________________________________________
> >> > > > > > > > > >> > > > Neo mailing list
> >> > > > > > > > > >> > > > User at lists.neo4j.org
> >> > > > > > > > > >> > > > https://lists.neo4j.org/mailman/listinfo/user
> >> > > > > > > > > >> > >
> >> > > > > > > > > >> > >
> >> > > > > > _________________________________________________________________
> >> > > > > > > > > >> > > Express yourself instantly with MSN Messenger!
> >> > Download
> >> > > > today
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> >> > > > > > > > FREE!
> >> > > > > > > > > >> > >
> >> > > > > > http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/
> >> > > > > > > > > >> > > _______________________________________________
> >> > > > > > > > > >> > > Neo mailing list
> >> > > > > > > > > >> > > User at 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 at 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 at lists.neo4j.org
> >> > > > > > > > > >> https://lists.neo4j.org/mailman/listinfo/user
> >> > > > > > > > > >> _______________________________________________
> >> > > > > > > > > >> Neo mailing list
> >> > > > > > > > > >> User at 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 at lists.neo4j.org
> >> > > > > > > > > > https://lists.neo4j.org/mailman/listinfo/user
> >> > > > > > > > > >
> >> > > > > > > > > _______________________________________________
> >> > > > > > > > > Neo mailing list
> >> > > > > > > > > User at 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 at lists.neo4j.org
> >> > > > > > > > https://lists.neo4j.org/mailman/listinfo/user
> >> > > > > > > >
> >> > > > > > >
> >> > > > > > >
> >> > > > > > >
> >> > > > > > > --
> >> > > > > > > Mattias Persson, [mattias at neotechnology.com]
> >> > > > > > > Neo Technology, www.neotechnology.com
> >> > > > > > > _______________________________________________
> >> > > > > > > Neo mailing list
> >> > > > > > > User at 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 at lists.neo4j.org
> >> > > > > > https://lists.neo4j.org/mailman/listinfo/user
> >> > > > > >
> >> > > > >
> >> > > > >
> >> > > > >
> >> > > > > --
> >> > > > > Mattias Persson, [mattias at neotechnology.com]
> >> > > > > Hacker, Neo Technology
> >> > > > > www.neotechnology.com
> >> > > > > _______________________________________________
> >> > > > > Neo mailing list
> >> > > > > User at 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 at lists.neo4j.org
> >> > > > https://lists.neo4j.org/mailman/listinfo/user
> >> > > >
> >> > >
> >> > >
> >> > >
> >> > > --
> >> > > Mattias Persson, [mattias at neotechnology.com]
> >> > > Hacker, Neo Technology
> >> > > www.neotechnology.com
> >> > > _______________________________________________
> >> > > Neo mailing list
> >> > > User at 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 at lists.neo4j.org
> >> > https://lists.neo4j.org/mailman/listinfo/user
> >> >
> >>
> >>
> >>
> >> --
> >> Mattias Persson, [mattias at neotechnology.com]
> >> Hacker, Neo Technology
> >> www.neotechnology.com
> >> _______________________________________________
> >> Neo mailing list
> >> User at 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/
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> > Neo mailing list
> > User at lists.neo4j.org
> > https://lists.neo4j.org/mailman/listinfo/user
> >
> 
> 
> -- 
> Mattias Persson, [mattias at neotechnology.com]
> Hacker, Neo Technology
> www.neotechnology.com
> _______________________________________________
> Neo mailing list
> User at lists.neo4j.org
> https://lists.neo4j.org/mailman/listinfo/user
 		 	   		  
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