I think a generic solution would mean a generic numerical index. I wrote an index recently that is very similar in principle to the timeline index Tobias mentioned below, except I allow multiple dimensions and indexing over any numerical primitive type. Then we get to the next point, combining indexes. Like in Tobias example: "give me all nodes where x=15 ordered by y". This requires an index that works on x and y at the same time. Otherwise you have to index one, and do a brute force search on the other in the result set.
I have an idea about dynamically generating a combined index based on queries received by the database. So if the user does a query like the one above, involving both x and y, and both of these are indexed, then a combined index can be added dynamically. The first query will not be fast, but subsequent ones would be. And as far as I can see, a combined index should be as simple as linking nodes between the un-combined indexes. Now who's up for a n-way combination of k-dimensional indexes? I think I'm getting a headache just thinking about it :-) On Mon, Jan 4, 2010 at 10:17 AM, Raul Raja Martinez <[email protected]>wrote: > Hi Tobias, > > Thanks for the info! > > I understand the implications of returning ordered nodes. > Do you guys plan to build such support natively to neo4j even if it is > for a basic set of node properties? > > While retrieving results ordered by property values or more extensive > queries capabilities is provably not easy when dealing with a graph, > it is currently one of > the main things a programmer encounters when comparing neo4j to > relational databases for storage and info retrieval. > > Would it make sense to have something like > node.setOrderedProperty(property, value); so that the linked list > based on the natural order of the value is kept internally by neo4j > and then have another param in the traversers to specify that the > traversal should follow the relationships established by the ordered > linked nodes? > > If you guys think ordering based on property is out of the scope > that's fine, I'm just asking in case we can avoid having to roll our > own hack or component to get it working since ordered entities is a > requirement in all of our current projects where we plan to use neo4j > > Thanks > > Raul > > > 2010/1/4 Tobias Ivarsson <[email protected]>: > > Getting ordered results from any system always requires sorting, unless > the > > ordering property is stored. And sorting always requires (at least) O(n) > > memory and O( log(n!) ) time for comparison sort, possibly O( n ) time > for > > sorting integer keys. > > > > So if you want results to be sorted on an arbitrary property you will > have > > to sort the entire result set and keep it around during your pagination > > process (possibly redoing the query + entire sorting + skipping a few > pages, > > to preserve memory). > > > > If you know which properties you will want to order your results by when > you > > are designing your database you can store the ordering information in the > > database. I would suggest a linked list of relationships in between the > > nodes, in the natural order for the sorting property. > > > > You need to be aware of two things with this approach though. > > The first one is that if the sorting property is unrelated to the > filtering > > property, if you want something like "give me all nodes where x=15 > ordered > > by y", you will either have to store separate linked lists for each value > of > > x, filter the result set while traversing through the results as they are > > ordered by y, or revert to the sorting approach. > > The second thing to be aware of is that insertion (and changing the value > of > > the ordering property in some node) will require some overhead, to > preserve > > the order. > > > > If your queries are as simple as "give me all nodes where x>LOWER_LIMIT > and > > x<UPPER_LIMIT ordered by x", and you can reduce the x property to a long > > integer value, then the timeline index will do this for you. Otherwise > there > > is no ready made component for this today. > > > > Happy hacking, > > Tobias > > > > On Mon, Jan 4, 2010 at 1:30 AM, Raul Raja Martinez <[email protected] > >wrote: > > > >> Hi, > >> > >> Anybody has any experience returning indexed nodes ordered by a given > >> property?. > >> For example return all nodes ordered by creationDate. I understand that > if > >> the node property is not indexed I'd have to iterate over all nodes > first > >> then order then limit the results which seems overkill to me. > >> I'd like to be able to do... "get me all nodes from start to limit > ordered > >> by property". > >> This is necessary when the data is iterated over using pagination and > the > >> order determines what the next start node is next. > >> _______________________________________________ > >> Neo mailing list > >> [email protected] > >> https://lists.neo4j.org/mailman/listinfo/user > >> > > > > > > > > -- > > Tobias Ivarsson <[email protected]> > > Hacker, Neo Technology > > www.neotechnology.com > > Cellphone: +46 706 534857 > > _______________________________________________ > > Neo mailing list > > [email protected] > > https://lists.neo4j.org/mailman/listinfo/user > > > > > > -- > Raul Raja > _______________________________________________ > Neo mailing list > [email protected] > https://lists.neo4j.org/mailman/listinfo/user > _______________________________________________ Neo mailing list [email protected] https://lists.neo4j.org/mailman/listinfo/user
