CadmusRefsDbpediaLookup

📦 npm i @myrmidon/cadmus-refs-dbpedia-lookup

This library was generated with Angular CLI version 17.3.0.

DBPedia lookup is currently limited to the DBPedia API keyword lookup. You can configure this service via DbediaOptions, which provides the following properties:

• searchUri: the search function URI. Default is https://lookup.dbpedia.org/api/search.
• prefixUri: the prefix lookup function URI. Default is https://lookup.dbpedia.org/api/prefix.
• limit (default=10): the maximum number of documents in result. AFAIK the DBPedia service does not provide paging via an offset, so this is the only available option here.
• prefix (default=true): true for a prefix lookup (=match the beginning of the input string, rather than the whole input string).
• types: the types filters. These are one or more DBpedia classes from the DBpedia ontology that the results should have. Using this parameter will only retrieve resources of the passed type(s). For instance, you might want to use http://dbpedia.org/ontology/Person for persons, http://dbpedia.org/ontology/Place for places, etc.

Essential types from DBPedia ontology:

• person: http://dbpedia.org/ontology/Person
• place: http://dbpedia.org/ontology/Place
• organisation: http://dbpedia.org/ontology/Organisation

Main properties:

• docs (array):
  • resource: array with (usually a single?) DBPedia URI.
  • label: array with (usually a single?) string.
  • type: array with DBPedia ontology types (you can use typeName to get their user friendly names, which are just the last token in the corresponding type URI).
  • category: array with DBPedia category URIs.
  • comment: array with comment.

Note that all the values may include <B></B> for bold, and presumably also <I> and <U>.

Usage

Should your DBPedia endpoint not support CORS nor JSONP, you can use a proxy as follows:

(1) in your backend API, add a proxy API controller like this (ProxyController.cs):

[ApiController]
[Route("api/proxy")]
public sealed class ProxyController : ControllerBase
{
    private readonly HttpClient _httpClient;

    public ProxyController(HttpClient httpClient)
    {
        _httpClient = httpClient;
    }

    /// <summary>
    /// Gets the response from the specified URI.
    /// </summary>
    /// <param name="uri">The URI, e.g.
    /// <c>https://lookup.dbpedia.org/api/search?query=plato&format=json&maxResults=10</c>
    /// .</param>
    /// <returns>Response.</returns>
    [HttpGet]
    [ResponseCache(Duration = 60 * 10, VaryByQueryKeys = ["uri"], NoStore = false)]
    public async Task<IActionResult> Get([FromQuery] string uri)
    {
        try
        {
            HttpResponseMessage response = await _httpClient.GetAsync(uri);

            if (response.IsSuccessStatusCode)
            {
                string content = await response.Content
                    .ReadAsStringAsync();
                return Content(content, "application/json");
            }

            return StatusCode((int)response.StatusCode);
        }
        catch (Exception ex)
        {
            Debug.WriteLine(ex.ToString());
            return StatusCode(500, ex.Message);
        }
    }
}

This requires CORS, which should already be setup for the API, and the following services:

builder.Services.AddHttpClient();
// for caching
builder.Services.AddResponseCaching();

If you are not using response caching (i.e. you remove the ResponseCacheAttribute from the sample code above) you can remove AddResponseCaching.

Also, if you use response caching (which is the default) add this middleware to your app's pipeline (immediately after CORS):

app.UseResponseCaching();

(2) Once you provide this proxy endpoint, configure the Angular app like this:

{ provide: HTTP_INTERCEPTORS, useClass: ProxyInterceptor, multi: true },
{ provide: PROXY_INTERCEPTOR_OPTIONS, useValue: {
    proxyUrl: 'http://localhost:5161/api/proxy',
    urls: [
      'http://lookup.dbpedia.org/api/search',
      'http://lookup.dbpedia.org/api/prefix'
    ]
  }
},

This configures the proxy interceptor, whose task is intercepting requests to services not supporting CORS, like DBPedia, and rewrite them so that they are redirected to the proxy service endpoint shown above under (1). Using a proxy bypasses the issues of browsers in consuming services not providing support for CORS or JSONP.