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ErfGeo Verrijkingen

API description

The API to the Digitale Collectie ErfGeo Enrich service consists of an OAI-PMH endpoint as well as a /search endpoint.

(In addition to these an SRU endpoint exists at /sru, but that is currently not specified other than by example by including the specific request as part of the JSON response to a /search request.)

Search

The /search interface takes at least a query parameter that follows the Contextual Query Language (CQL). It returns a JSON response containing search result items that are described in JSON-LD.

A simple query takes the form http://erfgeo.data.digitalecollectie.nl/search?query=nachtwacht+AND+rembrandt

Fields

Queries can refer to specific fields, e.g.: dc:title=nachtwacht AND dc:creator=rembrandt

A bounding box can be specified as part of the query by specifying ranges for the fields dcterms:spatial.geo:lat and dcterms:spatial.geo:long. E.g.: dcterms:spatial.geo:lat>50.2 AND dcterms:spatial.geo:long>3.6 AND dcterms:spatial.geo:lat<53.1 AND dcterms:spatial.geo:long<7.1.

However, for convenience (and url readability) the bounding box can also be specified by using the (virtual) fields minGeoLat, minGeoLong, maxGeoLat and maxGeoLong. E.g.: minGeoLat=50.2 AND minGeoLong=3.6 AND maxGeoLat=53.1 AND maxGeoLong=7.1.

A year range can be specified by way of the dc:date.year field in which normalized year values from dc:date and dcterms:created fields are indexed. E.g. dc:date.year>1720 AND dc:date.year<1722.

Records can be queried by the size of the referred images by way of the schema:width and schema:height fields. E.g. schema:width>200.

Having obtained a record id in response to an earlier search request, that specific record can be requested by referring to the id field. E.g. /search?query=id exact "NIOD_BBWO2:niod:3379966"/

 

Currently the following fields are distinguished in the search index:

Facets

Facets can be requested with the facets parameter, with separate facet fields separated by a , character (%2C url encoded). More than the default number of 10 facets can be requested by adding a colon and a number (250 max.) to specified facet fields. E.g. http://erfgeo.data.digitalecollectie.nl/search?query=nachtwacht+AND+rembrandt&facets=dc:subject%2Cedm:dataProvider:40

Currently, the following fields are available as facets:

Paging

By default a maximum of 10 records is returned. More records can be requested, up to a maximum of 30 per request, by providing a maximumRecords parameter. More search results can be requested by specifying an offset by means of the startRecord parameter. E.g. http://erfgeo.data.digitalecollectie.nl/search?query=nachtwacht+AND+rembrandt&startRecord=10&maximumRecords=3

Random

The random parameter was added for the purpose of content discovery. So, by passing random=true the results in the query reponse are taken randomly (thus ignoring relevance scores) from a larger set of matching results. E.g. http://erfgeo.data.digitalecollectie.nl/search?query=rembrandt&random=true

Note: for performance reasons a limit applies to the number of matching results that are considered (i.e. instead of the most relevant 10 results, the most relevant 1000 results will make up the population of which a sample of 10 is taken).

OAI-PMH

The OAI-PMH interface(s) implements the Open Archives Initiative Protocol for Metadata Harvesting.

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