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Extend essglobal vocab to include geolocation #15

Open matt-wallis opened 7 years ago

matt-wallis commented 7 years ago

Use case

The specific use-case that drives this requirement is as follows:

We are generating LOD from the co-ops-uk open data CSV files. That data will use the essglobal vocab. The co-ops-uk data includes UK postcodes. In order to put the UK co-ops onto a geographic map we need to convert UK postcodes into lat/long. UK Ordnance Survey provides LOD to describe UK postcodes, including the lat/long (of the "centre"?) of the postcode. For example, http://data.ordnancesurvey.co.uk/id/postcodeunit/SO160AS describes the postcode "SO16 0AS". So we want our LOD for co-ops-uk to include links to these postcodeunit URIs.

Requirements

We do not want essglobal to contain anything that is specific to UK postcodes. However, linking into GeoSPARQL is acceptable.

Investigation

The ontology used for the UK postcode data is http://data.ordnancesurvey.co.uk/ontology/postcode/. The postcode ontology has links to http://data.ordnancesurvey.co.uk/ontology/spatialrelations/, which imports GeoSPARQL.

So, we hope (subject to further investigation) that we can use GeoSPARQL within essglobal, and http://data.ordnancesurvey.co.uk/ontology/postcode/ within the co-ops-uk LOD, and that the SubClass and/or SubProperty relationships defined in the above ordnance survey ontologies will be sufficient to make this work! See the section below for details.

See https://www.w3.org/2011/02/GeoSPARQL.pdf and try following 1.5 "Illustrative Examples" for a possible way forward.

Details of existing ontologies

Looking at the definition of http://data.ordnancesurvey.co.uk/ontology/postcode/PostcodeUnit:

<owl:Class rdf:about="http://data.ordnancesurvey.co.uk/ontology/postcode/PostcodeUnit">
    <rdfs:label rdf:datatype="&xsd;string">Postcode Unit</rdfs:label>
    <rdfs:subClassOf>
        <owl:Restriction>
            <owl:onProperty rdf:resource="&spatialrelations;within"/>
            <owl:someValuesFrom rdf:resource="http://data.ordnancesurvey.co.uk/ontology/postcode/PostcodeSector"/>
        </owl:Restriction>
    </rdfs:subClassOf>
    <rdfs:comment>An area covered by a particular postcode. Postcodes are an alphanumeric abbreviated form of address. Postcode units are unique references and identify an average of 15 addresses. In some cases, where an address receives a substantial amount of mail, a postcode will apply to only one address (a large-user postcode). The maximum number of addresses in a postcode is 100.

A sub-area of a postcode sector, indicated by the two letters of the inward postcode, which identifies one or more small-user postcode delivery points or an individual large-user postcode. There are approximately 1.7 million postcode units in the UK.</rdfs:comment>
    <rdfs:isDefinedBy rdf:resource="http://www.ordnancesurvey.co.uk/ontology/postcode.owl"/>
</owl:Class>

we see that PostcodeUnits are a SubClassOf the set of things that are &spatialrelations;within a PostcodeSector.

Looking at the definition of &spatialrelations;within:

<owl:ObjectProperty rdf:about="&spatialrelations;within">
    <rdf:type rdf:resource="&owl;TransitiveProperty"/>
    <rdfs:label xml:lang="en">within</rdfs:label>
    <rdfs:comment rdf:datatype="&xsd;string">The interior of one object is completely within the interior of the other object. Their boundaries may or may not intersect.</rdfs:comment>
    <owl:inverseOf rdf:resource="&spatialrelations;contains"/>
    <rdfs:range rdf:resource="http://www.opengis.net/ont/geosparql#SpatialObject"/>
    <rdfs:domain rdf:resource="http://www.opengis.net/ont/geosparql#SpatialObject"/>
    <owl:equivalentProperty rdf:resource="http://www.opengis.net/ont/geosparql#sfWithin"/>
    <rdfs:subPropertyOf rdf:resource="&owl;topObjectProperty"/>
    <owl:propertyChainAxiom rdf:parseType="Collection">
        <rdf:Description rdf:about="&spatialrelations;within"/>
        <rdf:Description rdf:about="&spatialrelations;equals"/>
    </owl:propertyChainAxiom>
    <owl:propertyChainAxiom rdf:parseType="Collection">
        <rdf:Description rdf:about="&spatialrelations;equals"/>
        <rdf:Description rdf:about="&spatialrelations;within"/>
    </owl:propertyChainAxiom>
</owl:ObjectProperty>

we see that the domain of &spatialrelations;within is http://www.opengis.net/ont/geosparql#SpatialObject. We can therefore infer that a PostcodeUnit isa http://www.opengis.net/ont/geosparql#SpatialObject.

BUT ... http://www.opengis.net/ont/geosparql#SpatialObject makes no mention of latitude and longitude, but this is what we want to know in order to put something on a map.

Looking at the RDF for http://data.ordnancesurvey.co.uk/id/postcodeunit/SO160AS, as returned by:

curl -H "Accept: application/rdf+xml" -L http://data.ordnancesurvey.co.uk/id/postcodeunit/SO160AS

we see that it uses the following properties:

http://www.w3.org/2003/01/geo/wgs84_pos#lat
http://www.w3.org/2003/01/geo/wgs84_pos#lon

TODO - how to relate lat/long from wgs84_pos to geosparql? There is no mention of geosparql in wgs84_pos

Other sources of postcode data

Initially http://opendatacommunities.org/data/postcodes showed promise, but it turns out to be a 'portal' into the OS postcodeunit dataset that we already plan to use.

Proposals

Propose that an essglobal:Address has a geosparql:SpatialObject

hasa, or isa? This allows us to make assertions about that SpatialObject: for example that it is within some other SpatialObject (like a postcodeunit).

The isa relationship has been implemented in https://github.com/p6data-coop/ise-linked-open-data/commit/b54a49d62c932b139d9814ea0f3dd73e594fa052 .

Implementation

Note that postcode.owl seems to have disappeared from http://data.ordnancesurvey.co.uk/ontology/postcode/. However, there is a version of it here. Perhaps we will need to load this into our OntoWiki?

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