hi Pieter, the dev list isn't so good with embedded attachments so your images are missing. Perhaps you could make those available some other way?
On Sun, Jan 9, 2022 at 7:28 AM pieter gmail <pieter.mar...@gmail.com> wrote: > Hi, > > I have done some work on defining a meta model for Gremlin's property > graph. I am using the approach used in the modelling world, in particular > as done by the OMG <https://www.omg.org/> group when defining their > various meta models and specifications. > > However where OMG uses a subset of the UML to define their meta models I > suggest we use Gremlin. After all Gremlin is the language we use to > describe the world and the property graph meta model can also be described > in Gremlin. > > I propose that we have 3 levels of modelling. Each of which can itself be > specified in gremlin. > > 1: The property graph meta model. > 2: The model. > 3: The graph representing the actual data. > > 1) The property graph meta model describes the nature of the property > graph itself. i.e. that property graphs have vertices, edges and properties. > > 2) The model is an instance of the meta model. It describes the schema of > a particular graph. i.e. for TinkerPop's modern graph this would be > 'person', 'software', 'created' and 'knows' and the various properties > 'weight', 'age', 'name' and 'lang' properties. > > 3) The final level is an instance of the model. It is the actual graph > itself. i.e. for TinkerPop's modern graph it is 'Marko', 'Josh', 'java' ... > > > 1: Property Graph Meta Model > > public static Graph gremlinMetaModel() { > > enum GremlinDataType { > > STRING, > > INTEGER, > > DOUBLE, > > DATE, > > TIME > > //... > > } > > TinkerGraph propertyGraphMetaModel = TinkerGraph.open(); > > Vertex graph = propertyGraphMetaModel.addVertex(T.label, "Graph", > "name", "GremlinDataType::STRING"); > > Vertex vertex = propertyGraphMetaModel.addVertex(T.label, > "VertexLabel", "label", "GremlinDataType::STRING"); > > Vertex edge = propertyGraphMetaModel.addVertex(T.label, "EdgeLabel", > "label", "GremlinDataType::STRING"); > > Vertex vertexProperty = propertyGraphMetaModel.addVertex(T.label, > "VertexProperty", "name", "GremlinDataType::STRING", "type", > "GremlinDataType"); > > Vertex edgeProperty = propertyGraphMetaModel.addVertex(T.label, > "EdgeProperty", "name", "GremlinDataType::STRING", "type", "GremlinDataType"); > > > graph.addEdge("vertices", vertex); > > graph.addEdge("edges", edge); > > vertex.addEdge("properties", vertexProperty); > > vertex.addEdge("properties", edgeProperty); > > vertex.addEdge("out", edge); > > vertex.addEdge("in", edge); > > > return propertyGraphMetaModel; > > } > > > This can be visualized as, > > Notes: > 1) GremlinDataType is an enumeration of named data types that Gremlin > supports. All gremlin data types are assumed to be atomic and its life > cycle fully owned by its containing parent. How it is persisted on disc or > transported over the wire is not a concern for the meta model. > 2) Gremlin's semantics is to weak to fully specify a valid meta model. > Accompanying the meta model we need a list of constraints specified as > gremlin queries to augment the semantics of the meta model. These > constraints/queries will be able to validate any gremlin specified model > for correctness. > 3) It is trivial to extend the meta model. e.g. To specify something like > index support just add an 'Index' vertex and an edge from 'VertexLabel' to > it. > > Property graph meta model constraints, > > 1) Every 'VertexLabel' must have a 'label'. > > g.V().hasLabel("EdgeLabel").where(__.not(__.in("inEdge"))).id() > > 2) Every 'EdgeLabel' must have a 'label'. > > g.V().hasLabel("EdgeLabel").or(__.hasNot("label"), __.has("label", > P.eq(""))).id() > > 3) Every 'EdgeLabel' must have at least one 'outEdge' 'VertexLabel' > > g.V().hasLabel("EdgeLabel").where(__.not(__.in("outEdge"))).id() > > 4) Every 'EdgeLabel' must have at least on 'inEdge' 'VertexLabel' > > g.V().hasLabel("EdgeLabel").where(__.not(__.in("inEdge"))).id() > > 5) Every 'VertexProperty' must have a 'name' > > gV().hasLabel("VertexProperty").or(__.hasNot("name"), __.has("name", > P.eq(""))).id() > > 6) Every 'VertexProperty' must have a 'type' > > g.V().hasLabel("VertexProperty").or(__.hasNot("type"), __.has("type", > P.eq(""))).id() > > 7) Every 'EdgePropery' must have a 'name' > > g.V().hasLabel("EdgeProperty").or(__.hasNot("name"), __.has("name", > P.eq(""))).id() > > 8) Every 'EdgeProperty' must have a 'type' > > g.V().hasLabel("EdgeProperty").or(__.hasNot("type"), __.has("type", > P.eq(""))).id() > > 9) Every 'VertexProperty' must have a in 'properties' edge. > > g.V().hasLabel("VertexProperty").where(__.not(__.in("properties"))).id() > > 10) Every 'EdgeProperty' must have a in 'properties' edge. > > g.V().hasLabel("EdgeProperty").where(__.not(__.in("properties"))).id() > > ... > > This can be visualized as, > > > 2: The model > > What follows is an example of TinkerPop's 'modern' graph specified as an > instance of the above property graph meta model. > > public static Graph modernModel() { > > //import this from a base package > > enum GremlinDataType { > > STRING, > > INTEGER, > > DOUBLE, > > DATE, > > TIME > > //... > > } > > > TinkerGraph modernModelGraph = TinkerGraph.open(); > > > Vertex person = modernModelGraph.addVertex(T.label, "VertexLabel", > "label", "person"); > > Vertex personNameVertexProperty = modernModelGraph.addVertex(T.label, > "VertexProperty", "name", "name", "type", GremlinDataType.STRING.name()); > > Vertex personAgeVertexProperty = modernModelGraph.addVertex(T.label, > "VertexProperty", "name", "age", "type", GremlinDataType.INTEGER.name()); > > person.addEdge("properties", personNameVertexProperty); > > person.addEdge("properties", personAgeVertexProperty); > > > Vertex software = modernModelGraph.addVertex(T.label, "VertexLabel", > "label", "software"); > > Vertex softwareNameVertexProperty = > modernModelGraph.addVertex(T.label, "VertexProperty", "name", "name", "type", > GremlinDataType.STRING.name()); > > Vertex softwareLangVertexProperty = > modernModelGraph.addVertex(T.label, "VertexProperty", "name", "lang", "type", > GremlinDataType.STRING.name()); > > software.addEdge("properties", softwareNameVertexProperty); > > software.addEdge("properties", softwareLangVertexProperty); > > > Vertex knows = modernModelGraph.addVertex(T.label, "EdgeLabel", > "label", "knows"); > > Vertex knowsWeightVertexProperty = > modernModelGraph.addVertex(T.label, "EdgeProperty", "name", "weight", "type", > GremlinDataType.INTEGER.name()); > > knows.addEdge("properties", knowsWeightVertexProperty); > > > Vertex created = modernModelGraph.addVertex(T.label, "EdgeLabel", > "label", "created"); > > Vertex createdWeightVertexProperty = > modernModelGraph.addVertex(T.label, "EdgeProperty", "name", "weight", "type", > GremlinDataType.INTEGER.name()); > > created.addEdge("properties", createdWeightVertexProperty); > > > person.addEdge("outEdge", knows); > > person.addEdge("outEdge", created); > > software.addEdge("inEdge", knows); > > software.addEdge("inEdge", created); > > return modernModelGraph; > > } > > > The above gremlin constraints need to be executed against the > 'modernModelGraph' to check for the correctness of the model. If the > constraints pass we know that the model is indeed a valid Gremlin property > graph model. > > We can certainly specify more constraints but the ones defined above > passes on the 'modernModelGraph'. > > 3: The actual graph > > TinkerGraph modernGraph = TinkerFactory.createModern(); > > > And that is it. > > There are lots of details to complete, but first we need to see if there > is any appetite for a modelling approach as I realize there is some > academic abstract algebra work happening elsewhere. It seems to me to have > a lower barrier to entry for the community to partake in the discussion of > what constitutes a property graph model. > > Let me know if there are questions or criticisms. > > Thanks > Pieter >
