On 09/12/2021 13:50, Andy Seaborne wrote: > > > On 09/12/2021 11:32, Pierre-Antoine Champin wrote: >> >> On 09/12/2021 12:23, Andy Seaborne wrote: >>> >>> >>> On 08/12/2021 08:07, Pierre-Antoine Champin wrote: >>>> >>>> On 07/12/2021 22:25, Peter Patel-Schneider wrote: >>>>> On Tue, 2021-12-07 at 14:52 +0100, Pierre-Antoine Champin wrote: >>>>>> In LPGs as well, there is a point were modelling marriages or pipes >>>>>> as edges will hit a wall. More specifically, if you want to relate >>>>>> them to other *nodes* of the graph (link a marriage to its location, >>>>>> link a pipe to its manufacturer), you also need to reifiy them as >>>>>> nodes. >>>>> I see some formulations of property graphs where edges can only be >>>>> related to values, but is that really the case for all property >>>>> graphs? >>>> >>>> I have never seen an explicit definition of "Property Graphs" where >>>> this was not the case (but I have not seen them all, of course). >>>> >>>> I also have the feeling that allowing nodes as property values >>>> would pervert the idea of PGs, where the distinction between the >>>> internal structure of nodes (properties) and relation with other >>>> nodes (edges) is considered an important feature. >>> >>> >>> Looking at some of the JSON serializations at property graphs - they >>> don't allow for edges to be nodes. >>> >>> There are two styles: >>> >>> * Nodes have integer ids, and edges are represented by start-end id >>> pairs and a label. >>> >>> * Edges have ids but the numbering of nodes and edges starts >>> separately at 0 so there are different numbering spaces. >>> >>> Both cases mean only attributes on edges. >> >> The way I read Peter's question was : are there PG implementation in >> which properties (I assume that's what you mean by "attributes") have >> nodes as their value? > > >>>> where edges can only be related to values > > I haven't found any serializations that put nodes or edge ids in the > data model. > > The serializations have values that are strings and numbers > (JSON-centric). Nothing else. > > Which formalizations have a type system for values? Ian Hidders and Juan Sequeda presented the model used by the PG Schemas working group, during the SCG workshop [1] (slides and video are available). IIRC, they envision structured types for property values. But I don't think Nodes and Edges can be the value of properties. [1] https://mosaicrown.github.io/scg2021/#mu-schedule > > Andy > >> >>> >>> Andy >>> >>>> >>>>> (Well, if you think of Wikibase as a property graph formulation then >>>>> there is at least one counterexample.) >>>> >>>> It never occurred to me to put Wikibase in the "Property Graph" >>>> family. I see some similarities, but also many differences. In >>>> particular, the distinction I mentioned above (between "properties" >>>> and "edges" of a node, in PG parlance) does not exist in Wikibase, >>>> where there all represented as "statements" (except for labels and >>>> descriptions... but I hope you see my point). >>>> >>>> pa >>>> >>>>> >>>>> peter >>>>> >>>>> >>> >
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