Querying EDC

[galanisd]

We use EDC for our project and we create assets like the following

{
  "@context": {
    "edc": "https://w3id.org/edc/v0.0.1/ns/",
    "dcat": "http://www.w3.org/ns/dcat/",
    "dct": "https://purl.org/dc/terms/",
    "adms": "https://www.w3.org/TR/vocab-adms/",
    "ms": "http://w3id.org/meta-share/meta-share/",
    "loc": "http://id.loc.gov/vocabulary/iso639-1/",
    "iana": "http://www.iana.org/assignments/media-types/application/",
    "rdf": "http://www.w3.org/1999/02/22-rdf-syntax-ns#",
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "foaf": "http://xmlns.com/foaf/0.1/",
    "@base": "https://lds.eu/",
    "omtd": "http://w3id.org/meta-share/omtd-share/"
  },
  "@id": "asset-id2",
  "edc:properties": {
    "@type": "edc:Asset",
    "dcat:version": "1.0.0",
    "dct:title": [
      {
        "@value": "title",
        "@language": "en"
      }
    ],
    "ms:domain": {
      "@id": "http://publications.europa.eu/resource/authority/data-theme/AGRI"
    },
    "dct:alternative": {
      "@value": "alternative",
      "@language": "en"
    },
    "dct:description": [
      {
        "@value": "a nice description for a very nice corpus",
        "@language": "en"
      },
      {
        "@value": "ένα πολύ ωραίο σύνολο δεδομένων",
        "@language": "el"
      }
    ],
    "dct:identifier": "testId1",
    "adms:identifier": "testId3",
    "dct:publisher": {
      "@id": "ILSP",
      "@type": "foaf:Agent",
      "foaf:name": [
        {
          "@value": "ILSP",
          "@language": "en"
        },
        {
          "@value": "ILSPs",
          "@language": "el"
        }
      ],
      "dct:identifier": "testId1"
    },
    "ms:iprHolder": {
      "@id": "ILSPh",
      "@type": "foaf:Agent",
      "foaf:name": [
        {
          "@value": "ILSP",
          "@language": "en"
        },
        {
          "@value": "ILSPS",
          "@language": "el"
        }
      ],
      "dct:identifier": "testId1"
    },
    "ms:isDocumentedBy": {
      "@id": "mydoc",
      "@type": "foaf:Document",
      "dct:title": [
        {
          "@value": "my doc",
          "@language": "en"
        }
      ],
      "dct:description": [
        {
          "@value": "my doc description",
          "@language": "en"
        }
      ]
    },
    "dct:license": {
      "@type": "dct:LicenseDocument",
      "@id": "ms:CC-BY4"
    },
    "ms:lrType": {
      "@id": "ms:Corpus"
    },
    "dcat:keyword": [
      {
        "@value": "corpus",
        "@language": "en"
      }
    ],
    "ms:cost": {
      "ms:amount": 998.01,
      "ms:currency": {
        "@id": "ms:euro"
      }
    },
    "ms:mediaType": {
      "@id": "ms:text"
    },
    "ms:anonymized": {
      "@id": "ms:noA"
    },
    "ms:anonymizationDetails": {
      "@value": "anonymization Details",
      "@language": "en"
    },
    "ms:sensitiveDataIncluded": {
      "@id": "ms:noS"
    },
    "ms:sensitiveDataDetails": {
      "@value": "sensitive Data Details",
      "@language": "en"
    },
    "ms:personalDataIncluded": {
      "@id": "ms:noP"
    },
    "ms:personalDataDetails": {
      "@value": "personal Data Details",
      "@language": "en"
    },
    "ms:lingualityType": {
      "@id": "ms:bilingual"
    },
    "ms:multilingualityType": {
      "@id": "ms:parallel"
    },
    "ms:language": [
      {
        "@id": "loc:de"
      },
      {
        "@id": "loc:el"
      }
    ],
    "dct:language": [
      {
        "@id": "http://publications.europa.eu/resource/authority/language/DEU"
      }
    ],
    "dcat:distribution": [
      {
        "@type": "dcat:Distribution",
        "ms:size": [
          {
            "ms:amount": 100,
            "ms:sizeUnit": {
              "@id": "ms:sentence1"
            }
          },
          {
            "ms:amount": 200,
            "ms:sizeUnit": {
              "@id": "ms:translationUnit"
            }
          }
        ],
        "dcat:packageFormat": {
          "@id": "szip",
          "@type": "dct:MediaType"
        },
        "dcat:byteSize": 300254687,
        "dcat:downloadURL": {
          "@id": "http//www.example.com"
        },
        "dcat:accessURL": {
          "@id": "http//www.example.com"
        },
        "dcat:mediaType": {
          "@id": "http://www.iana.org/assignments/media-types/application/zip"
        }
      }
    ],
    "ms:corpusSubclass": {
      "@id": "ms:rawCorpus"
    },
    "ms:annotationType": {
      "@id": "omtd:Stem"
    },
    "dct:temporal": {
      "@type": "dct:PeriodOfTime",
      "dcat:startDate": {
        "@value": "1998-01-01",
        "@type": "xsd:date"
      },
      "dcat:endDate": {
        "@value": "1998-01-02",
        "@type": "xsd:date"
      }
    }
  },
  "edc:dataAddress": {
    "@type": "edc:DataAddress",
    "edc:name": "Asset Name",
    "edc:baseUrl": {
      "@value": "https://jsonplaceholder.typicode.com/users",
      "@type": "xsd:anyURI"
    },
    "edc:type": "HttpData"
  }
}

The asset is saved in the respective postgres tables. For example ms:cost is saved in edc_asset_property using two columns
property_name and property_value.

property_name = "http://w3id.org/meta-share/meta-share/cost"
and property_value = "{"http://w3id.org/meta-share/meta-share/amount":[{"@value":998.01}],"http://w3id.org/meta-share/meta-share/currency":[{"@id":"http://w3id.org/meta-share/meta-share/euro"}]}"

My question is how (based on the current queryAssets endpoint) someone can create queries for the such cases where
property_value is a JSON with some uknown structure. For example how I can ask for the assets that
property_name = "http://w3id.org/meta-share/meta-share/cost"
and in the respective property_value http://w3id.org/meta-share/meta-share/currency points to
http://w3id.org/meta-share/meta-share/euro via @id.

I read the source code and seems that this is not possible to create a query that somehow expresses the fact that we are searching
in this path http://w3id.org/meta-share/meta-share/currency -> @id
Is this true or do I miss something?

For this reason we are creating our own version of QuerySpec which would allow to write such queries.
Also we are creating the respective code that gets the new QuerySpec and creates the appropriate queries using PG JSON operators.
https://www.postgresql.org/docs/9.5/functions-json.html

[ndr-brt]

IT should be possible separating the nested levels with a dot, e.g.:
http://w3id.org/meta-share/meta-share/currency.@id
if that's not working, then it's a bug

[galanisd]

Interesting...

How exactly the filter criterion should be written?
Where I should put
http://w3id.org/meta-share/meta-share/currency.@id
in the following message? I assume that
edc:operandLeft have to set to "http://w3id.org/meta-share/meta-share/cost" and
edc:operandRight to "http://w3id.org/meta-share/meta-share/euro"

{
	"@context": {
		"edc": "https://w3id.org/edc/v0.0.1/ns/"
	},
	"edc:filterExpression": [
		{
			"edc:operandLeft": "?",
			"edc:operator": "=",
			"edc:operandRight": ?"
		}
	]
}

Any pointers to online documentation for the query service will also be much appreciated.

[ndr-brt]

operand left is the name of the field, so, e.g:

{
  "edc:operandLeft": "http://w3id.org/meta-share/meta-share/cost.http://w3id.org/meta-share/meta-share/currency.@id",
  "edc:operator": "=",
  "edc:operandRight": "http://w3id.org/meta-share/meta-share/euro"
}

[galanisd]

I sent this one

{
	"@context": {
		"edc": "https://w3id.org/edc/v0.0.1/ns/"
	},
	"edc:filterExpression": [
		{
			"edc:operandLeft": "http://w3id.org/meta-share/meta-share/cost.http://w3id.org/meta-share/meta-share/currency.@id",
			"edc:operator": "=",
			"edc:operandRight": "http://w3id.org/meta-share/meta-share/euro"
		}
	]
}

and got empty result
[]
Maybe it is a bug. Not sure. You know better.

When I am using my own implementation the service returns what is expected.
The format is similar but has some differences

{
	"@context": {
		"edc": "https://w3id.org/edc/v0.0.1/ns/"
	},
        "https://w3id.org/edc/v0.0.1/ns/filterExpression": [
		{
			"edc:propertyName": "http://w3id.org/meta-share/meta-share/cost",
			"edc:operator": "=",
			"edc:fields": "http://w3id.org/meta-share/meta-share/currency[0]|@id",
			"edc:values": "http://w3id.org/meta-share/meta-share/euro"
		}
	]
}

E.g. I explicitly define that @id should be found at index = 0 (using [0]) of the json array and use this info to construct the SQL query.

{"http://w3id.org/meta-share/meta-share/amount":[{"@value":998.01}],"http://w3id.org/meta-share/meta-share/currency":[{"@id":"http://w3id.org/meta-share/meta-share/euro"}]}

[ndr-brt]

surely the dot . used as a separator does not work well because it's widely used for urls. This is the first time someone is reporting it after we switched to json-ld, so it seems like a bug to me. Could you report it as an issue please?

[galanisd]

surely the dot . used as a separator does not work well because it's widely used for urls.

Yes indeed

Opened an issue
#3423