Geospatial fragmentation

Geospatial fragmentation will create fragments based on geospatial tiles selected of the fragmentationPath. This allows you to fragment the data on geolocations.

Properties

  @prefix tree: <https://w3id.org/tree#> .
  
  tree:fragmentationStrategy [
        a tree:GeospatialFragmentation ;
        tree:maxZoom { Mandatory: Required zoom level } ;
        tree:fragmentationPath { Mandatory: defines which property will be used for bucketizing } ;
        tree:fragmenterSubjectFilter { Optional: regex to filter the subjects matching the fragmentationPath } ;
    ] .

Algorithm

1. The fragmentationObjects of the member are determined
   • We filter the RDF statements where the predicate matches the fragmentationPath.
   • If an optional regex is provided through the fragmenterSubjectFilter property, we filter on subjects that match this regex.
   • We select all the object that pass the above filters.
2. A bucket of tiles is created using the coordinates and provided zoomLevel. This is done using the Slippy Map algorithm.
3. The tiles are iterated. The member is added to every tile, or sub-fragmentations of these tiles. Taking into account:
   • A new fragment is created if no fragment exists for the given tile.
   • There is no memberLimit or max size for a fragment. They do not become immutable.
   • The member is added to every related fragment.
4. When the member could not be added to any tile (ex. the fragmentation property is missing or not valid), then the member will be added to a default bucket tile=unknown.

flowchart TD
    A[First statement is selected where the 
    predicate matches fragmenterProperty 
    AND subject matches fragmenterSubjectFilter] --> B
    B[Coordinates of this statement are selected] --> C
    C[Bucket of tiles is
    created using the coordinates 
    and zoomLevel] --> D{Next tile?}
    
    D --> |true| E{Fragment for 
    tile exists?}
    E --->|false| F[Create Fragment]
    E -->|true| G[Add member to fragment]
    F ----> G
    D -------> |false| END(END)
    G --> D
  

Example

Example properties:

  @prefix tree: <https://w3id.org/tree#> .
  
  tree:fragmentationStrategy [
        a tree:GeospatialFragmentation ;
        tree:maxZoom 15 ;
        tree:fragmentationPath <http://www.opengis.net/ont/geosparql#asWKT> ;
    ] .

With following example input:

@prefix dc: <http://purl.org/dc/terms/> .
@prefix ns0: <http://semweb.mmlab.be/ns/linkedconnections#> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
@prefix ns1: <http://vocab.gtfs.org/terms#> .
@prefix prov: <http://www.w3.org/ns/prov#> .
@prefix ns2: <http://www.opengis.net/ont/geosparql#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix geo: <http://www.w3.org/2003/01/geo/wgs84_pos#> .

<http://njh.me/original-id#2022-09-28T17:11:28.520Z>
  dc:isVersionOf <http://njh.me/original-id> ;
  ns0:arrivalStop <http://example.org/stops/402161> ;
  ns0:arrivalTime "2022-09-28T07:14:00.000Z"^^xsd:dateTime ;
  ns0:departureStop <http://example.org/stops/402303> ;
  ns0:departureTime "2022-09-28T07:09:00.000Z"^^xsd:dateTime ;
  ns1:dropOffType ns1:Regular ;
  ns1:pickupType ns1:Regular ;
  ns1:route <http://example.org/routes/Hasselt_-_Genk> ;
  ns1:trip <http://example.org/trips/Hasselt_-_Genk/Genk_-_Hasselt/20220928T0909> ;
  a ns0:Connection ;
  prov:generatedAtTime "2022-09-28T17:11:28.520Z"^^xsd:dateTime .

<http://example.org/stops/402161>
  ns2:asWKT "POINT (5.47236 50.9642)"^^ns2:wktLiteral ;
  a ns1:Stop ;
  rdfs:label "Genk Brug" ;
  geo:lat 5.096420e+1 ;
  geo:long 5.472360e+0 .

<http://example.org/stops/402303>
  ns2:asWKT "POINT (5.49661 50.9667)"^^ns2:wktLiteral ;
  a ns1:Stop ;
  rdfs:label "Genk Station perron 11" ;
  geo:lat 5.096670e+1 ;
  geo:long 5.496610e+0 .

The selected objects would be "POINT (5.47236 50.9642)"^^ns2:wktLiteral and "POINT (5.49661 50.9667)"^^ns2:wktLiteral

When we convert these coordinates to tiles, the bucket of tiles would be:

• “15/16884/10974”
• “15/16882/10975”

When geospatial fragmentation is the lowest level

After ingestion the member will be part of the following two fragments

• http://localhost:8080/addresses/by-zone?tile=15/16884/10974&pageNumber=1
• http://localhost:8080/addresses/by-zone?tile=15/16882/10975&pageNumber=1