Hi Michael, I do not share the type mapping code I just described, at least not yet. I'd like to launch a product using these techniques first and maybe somewhere down the line decide to make it open source, but for now I am keeping this work to myself, to at least have some competitive edge.
> From: michael.hun...@neotechnology.com > Date: Thu, 5 May 2011 22:37:19 +0200 > To: user@lists.neo4j.org > Subject: Re: [Neo4j] First-class "type" property on relationships but not > nodes; why? > > Sorry meant Niels of course ;) > > Sent from my iBrick4 > > > Am 05.05.2011 um 22:35 schrieb Michael Hunger > <michael.hun...@neotechnology.com>: > > > Nils that sounds interesting do you share the type mapping code for scala > > somewhere? > > > > Michael > > > > Sent from my iBrick4 > > > > > > Am 05.05.2011 um 22:22 schrieb Niels Hoogeveen <pd_aficion...@hotmail.com>: > > > >> > >> I agree it can be valuable to assign a type to a node. In my own work I do > >> that, but we may have very different needs with regards to typing. In the > >> application I have built, I use relationships to make nodes an instance of > >> one or more types, while node types can be subtype of one or more other > >> node type. This does not lead to a singular type, but in fact to a > >> type-forest. Each type can have an associated trait (I am working in > >> Scala) that will be mixed in when creating an instance. > >> On runtime the type-forest is flattened and a signature for the instance > >> is generated based on this list of type names. Based on this signature a > >> class for the instance is dynamically created by means of the Scala > >> interpreter (unless the same class has already been created, in which case > >> it is simply looked up in the classloader), where all defined traits are > >> mixed into the instance. > >> Having a fixed singular type doesn't solve my modeling needs. First of all > >> each instance may be an instance of more than one type, but furthermore, > >> due to the subtyping relations in my type system, a node may have a > >> different type signature, because someone made some modification somewhere > >> in the type hierarchy. It would be most unpleasant if all instances of a > >> type need to be updated because somewhere a super type was added or > >> removed. > >> It is precisely the decoupling of data store and schema that makes neo4j > >> such a powerful platform. My typing needs may be very different from > >> yours, and i can imagine scenarios where one would even prefer the use of > >> an inference engine (using eg. Pellet, Drools, Jena or Prolog) to > >> determine the type of a node based on a possibly complex set of rules. > >> In such a scenario things can become even more complicated because the > >> type of a node may depend on the value of a property, the existence of a > >> relationship or even the value of a property of a related node or a > >> relationship defined on such a node (eg. someone becomes a grand parent > >> when a child begets a child). Having static types would entail updating > >> type information of possibly many nodes, simply because the value of a > >> property changes or a relationship somewhere in the graph is removed or > >> added. > >> It is not possible to accommodate all those needs within the neo4j kernel, > >> so it's better to leave it out altogether. > >> For your application it may be nice to have a type label attached to a > >> node. In my application it would be just ballast, because the only > >> reasonable label I can think of would be "node", something that doesn't > >> add any information. > >> > >>> From: rick.bullo...@thingworx.com > >>> To: user@lists.neo4j.org > >>> Date: Thu, 5 May 2011 10:25:58 -0700 > >>> Subject: Re: [Neo4j] First-class "type" property on relationships but not > >>> nodes; why? > >>> > >>> Respectfully disagree. In many domains, it is valuable to know the > >>> "type" of the domain object a node represents "in situ" with no knowledge > >>> whatsoever of its place in the graph relative to other nodes. > >>> > >>> -----Original Message----- > >>> From: user-boun...@lists.neo4j.org [mailto:user-boun...@lists.neo4j.org] > >>> On Behalf Of Niels Hoogeveen > >>> Sent: Thursday, May 05, 2011 1:22 PM > >>> To: user@lists.neo4j.org > >>> Subject: Re: [Neo4j] First-class "type" property on relationships but not > >>> nodes; why? > >>> > >>> > >>> I think the basic confusion surrounding this issue stems from the term > >>> RelationshipType. It is not a type, but just a key to the relationships > >>> value store (resulting in nodes). > >>> When you consider a node as a consisting of two maps, one from property > >>> keys to property values and one from the tuple (RelationshipType, > >>> Direction) to a node, you see there is actually no type there, only keys. > >>> From a navigational point of view there is no need for a name for a node, > >>> because each node already has a name relative to the node pointing to it > >>> (the name of the relationship, unfortunately labeled RelationshipType). > >>> When you work in Java or any other language supporting maps, you can add > >>> entries to map keys to maps (this is essentially what a relationship > >>> does, it maps a key (name + direction) to a list of maps). In those > >>> scenarios you don't care about a name for that map either. It is > >>> accessible through the keys which can be assigned specifically for each > >>> entry, making it much more flexible than using a fixed singular name. > >>> The addition of type labels for nodes doesn't make the implementation > >>> more consistent, since there is no way to directly navigate from a node > >>> to another node (you always need a relationship for that). A property key > >>> is there to find a property relative to a node. A relationship label > >>> (unfortunately named RelationshipType) is there to find a node relative > >>> to another node. For consistency reasons there is no need for additional > >>> labels, keys or names. > >>>> From: rick.bullo...@thingworx.com > >>>> To: user@lists.neo4j.org > >>>> Date: Thu, 5 May 2011 08:51:59 -0700 > >>>> Subject: Re: [Neo4j] First-class "type" property on relationships but > >>>> not nodes; why? > >>>> > >>>> I would say that the same is true of a "type" on a node - it could be a > >>>> significant performance optimization, depending on how properties are > >>>> loaded vs the "node itself". If it saves a major step by not having to > >>>> search around in property "stuff", there's an immediate advantage. > >>>> Also, I suspect that many (most) people would store "type" properties as > >>>> string(s) (we don't, but that's only because we've basically implemented > >>>> node type as a special kind of enum, similar to relationship type), the > >>>> various performance issues related to string storage/retrieval exist. > >>>> > >>>> Also, the very essence of a "type" on a node creates a basic sort of > >>>> atomicity in terms of knowing what a node "represents", given only its > >>>> node id, with no dependencies on relationships for facilitating type > >>>> identity (though we use relationships in our model as a form of > >>>> "implementation inheritance" similar to Tobias' comments on the subject). > >>>> > >>>> I really think that there are enough potential benefits to at least > >>>> consider a native "type" concept it for the future, if for no other > >>>> reason that uniformity of implementation, though I suspect there will be > >>>> inherent performance optimizations and new types of traversals made > >>>> possible and faster. > >>>> > >>>> The good (great) news is that the flexibility and capability of Neo4J as > >>>> it already exists allows us to model all of these scenarios today! > >>>> > >>>> > >>>> -----Original Message----- > >>>> From: user-boun...@lists.neo4j.org [mailto:user-boun...@lists.neo4j.org] > >>>> On Behalf Of Craig Taverner > >>>> Sent: Thursday, May 05, 2011 10:08 AM > >>>> To: Neo4j user discussions > >>>> Subject: Re: [Neo4j] First-class "type" property on relationships but > >>>> not nodes; why? > >>>> > >>>> Another view of things would be to say that ideally there should be no > >>>> first > >>>> class type on either relationships or nodes, since that is a domain > >>>> specific > >>>> concept (as Neils says he wants two types, but Rick wants one, and some > >>>> object models type nodes by relating them to a separate node > >>>> representing a > >>>> class). > >>>> > >>>> Then the addition of a type to a relationship is, in my opinion, a > >>>> performance optimization for many graph algorithms since the traverser > >>>> will > >>>> perform well if it has 'first class' access to this information, instead > >>>> of > >>>> hitting the property store. I guess this is my take on Tobias point that > >>>> the > >>>> type is a navigational feature. > >>>> > >>>> Now I wonder if the traverser, and many known graph algorithms, would be > >>>> possible to make faster or easier to code if the nodes also had first > >>>> class > >>>> types? I don't know the answer to this, but assume that if it did really > >>>> help, it would have been done already ;-) > >>>> > >>>> On Thu, May 5, 2011 at 3:52 PM, Niels Hoogeveen > >>>> <pd_aficion...@hotmail.com>wrote: > >>>> > >>>>> > >>>>> The meta model component (though in need of some attention), already > >>>>> allows > >>>>> the typing of a node. An important difference between the typing in the > >>>>> meta > >>>>> model component and the suggestion made in this thread is the fact that > >>>>> a > >>>>> node according to the meta model can have more than one type, while the > >>>>> RelationshipType in kernel only allows one type per relationship. > >>>>> For my modeling need, the ability to assign more than one type per node > >>>>> is > >>>>> essential. Adding a singular type at kernel level would only make things > >>>>> more confusing. > >>>>> I would go further than what Tobias says and would say RelationshipType > >>>>> is > >>>>> nothing but a name, just like various properties have names. Types would > >>>>> require much more information, like cardinality, source/target > >>>>> constraints > >>>>> etc. Those are all part of the meta model where they belong. > >>>>> > >>>>>> From: tobias.ivars...@neotechnology.com > >>>>>> Date: Thu, 5 May 2011 15:33:04 +0200 > >>>>>> To: user@lists.neo4j.org > >>>>>> Subject: Re: [Neo4j] First-class "type" property on relationships but > >>>>>> not > >>>>> nodes; why? > >>>>>> > >>>>>> The RelationshipType isn't a type. It is a navigational feature. > >>>>>> > >>>>>> I've slapped this link around for a few years now, every time this > >>>>> question > >>>>>> has been brought up: > >>>>>> http://lists.neo4j.org/pipermail/user/2008-October/000848.html > >>>>>> > >>>>>> The fact that RelationshipType is a navigational feature and not a type > >>>>>> means that there is in fact already a corresponding thing for nodes: > >>>>>> the > >>>>>> Indexes. > >>>>>> > >>>>>> But I agree that there would be things we could gain by adding a Type > >>>>>> concept to Nodes. Such as for example better automatic indexing. But I > >>>>> don't > >>>>>> know what it would look like. And I want it to be clear that such a > >>>>> feature > >>>>>> is very different from what RelationshipType is today. > >>>>>> > >>>>>> Cheers, > >>>>>> Tobias > >>>>>> > >>>>>> On Thu, May 5, 2011 at 10:29 AM, Aseem Kishore <aseem.kish...@gmail.com > >>>>>> wrote: > >>>>>> > >>>>>>> I've found it interesting that Neo4j has a mandatory "type" property > >>>>>>> on > >>>>>>> relationships, but not nodes. Just curious, what's the reasoning > >>>>>>> behind > >>>>> the > >>>>>>> design having this distinction? > >>>>>>> > >>>>>>> If you say "you need to know what type of relationship these two nodes > >>>>>>> have", I would reply, "don't you also need to know what type of nodes > >>>>> they > >>>>>>> are, as well?" > >>>>>>> > >>>>>>> Similarly, if you say "because there can be many different types of > >>>>>>> relationships", I would reply, "there can also be many different types > >>>>> of > >>>>>>> nodes, and in both cases, there doesn't need to be". > >>>>>>> > >>>>>>> A perfect example is in the documentation/tutorial: movies and actors. > >>>>> Just > >>>>>>> the fact that we talk about the nodes in the database as "movies" and > >>>>>>> "actors" -- wouldn't it be helpful for the database to support that > >>>>>>> categorization first-class? > >>>>>>> > >>>>>>> To be precise, it's easy for us to add a "type" property to nodes > >>>>> ourselves > >>>>>>> (we do in our usage), but it's not a first-class property like > >>>>>>> relationships, where queries and traversals can easily and naturally > >>>>>>> specify > >>>>>>> the type or types they expect. > >>>>>>> > >>>>>>> Thanks! > >>>>>>> > >>>>>>> Aseem > >>>>>>> _______________________________________________ > >>>>>>> Neo4j mailing list > >>>>>>> User@lists.neo4j.org > >>>>>>> https://lists.neo4j.org/mailman/listinfo/user > >>>>>>> > >>>>>> > >>>>>> > >>>>>> > >>>>>> -- > >>>>>> Tobias Ivarsson <tobias.ivars...@neotechnology.com> > >>>>>> Hacker, Neo Technology > >>>>>> www.neotechnology.com > >>>>>> Cellphone: +46 706 534857 > >>>>>> _______________________________________________ > >>>>>> Neo4j mailing list > >>>>>> User@lists.neo4j.org > >>>>>> https://lists.neo4j.org/mailman/listinfo/user > >>>>> > >>>>> _______________________________________________ > >>>>> Neo4j mailing list > >>>>> User@lists.neo4j.org > >>>>> https://lists.neo4j.org/mailman/listinfo/user > >>>>> > >>>> _______________________________________________ > >>>> Neo4j mailing list > >>>> User@lists.neo4j.org > >>>> https://lists.neo4j.org/mailman/listinfo/user > >>>> _______________________________________________ > >>>> Neo4j mailing list > >>>> User@lists.neo4j.org > >>>> https://lists.neo4j.org/mailman/listinfo/user > >>> > >>> _______________________________________________ > >>> Neo4j mailing list > >>> User@lists.neo4j.org > >>> https://lists.neo4j.org/mailman/listinfo/user > >>> _______________________________________________ > >>> Neo4j mailing list > >>> User@lists.neo4j.org > >>> https://lists.neo4j.org/mailman/listinfo/user > >> > >> _______________________________________________ > >> Neo4j mailing list > >> User@lists.neo4j.org > >> https://lists.neo4j.org/mailman/listinfo/user > _______________________________________________ > Neo4j mailing list > User@lists.neo4j.org > https://lists.neo4j.org/mailman/listinfo/user _______________________________________________ Neo4j mailing list User@lists.neo4j.org https://lists.neo4j.org/mailman/listinfo/user
