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
