How can we define semantic links in DPDS?

[andrea-gioia]

Let's brainstorm here on how to define semantic links in DPDS.
The ideas collected in this thread could become the foundation for a new RFC proposal.

What is a semantic link anyway?
A semantic link is an explicit connection between a data asset exposed by a data product through one of its output ports and one or more concepts defined in a central enterprise ontology.

Why it matters?
Semantic linking is a way to bring semantics to a data product and improve its capability to be discovered, reused, and composed with other data products belonging to different domains.

Some useful resources

1. What is an ontology?
2. What is a knowledge graph
3. Should factual data be added to a knowledge graph by copy or by reference?
4. Building Your Connected Data Catalog

[andrea-gioia]

Existing solutions to evaluate

DCAT

DCAT is an RDF vocabulary designed to facilitate interoperability between data catalogs published on the Web.

How semantic linking works in DCAT

TODO

see Property: conforms to

Potential Limitations

TODO

JSON-LD

JSON-LD is a lightweight Linked Data format.

How semantic linking works in JSON-LD

JSON Schema

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "Simplified Movie Object (Compact)",
  "type": "object",

  "properties": {
    "name": {
      "type": "string"
    },
    "datePublished": {
      "type": "string",
      "format": "date"
    },
    "director": {
      "type": "string"
    },
    "actor": {
      "type": "array",
      "items": {
        "type": "string"
      },
      "minItems": 1
    },
    "copyrightHolder": {  
      "type": "string"
    },
    "genre": {
      "type": "array",
      "items": {
        "type": "string"
      },
      "minItems": 1
    },
    "image": {
      "type": "string",
      "format": "uri"
    }
  }
}

JSON

{
  "name": "The Shawshank Redemption",
  "datePublished": "1994-09-23",
  "director": "Frank Darabont",
  "actor": [
    "Tim Robbins",
    "Morgan Freeman"
  ],
  "copyrightHolder": "Warner Bros. Pictures", 
  "genre": [
    "Drama",
    "Crime"
  ],
  "image": "https://example.com/shawshank-redemption.jpg"
}

JSONLD

{
  "@context": "https://schema.org",
  "@type": "Movie",
  "name": "The Shawshank Redemption",
  "description": "A seemingly dull and quiet banker is sentenced to life in prison for the murder of his wife, despite his claims of innocence. Through the years, he befriends a hardened criminal and becomes embroiled in a mysterious scheme involving contraband and redemption.",
  "datePublished": "1994-09-23",
  "director": {
    "@type": "Person",
    "name": "Frank Darabont"
  },
  "actor": [
    {
      "@type": "Person",
      "name": "Tim Robbins"
    },
    {
      "@type": "Person",
      "name": "Morgan Freeman"
    }
  ],
  "copyrightHolder": {
    "@type": "Organization",  
    "name": "Warner Bros. Pictures" 
  },
  "genre": [
    "Drama",
    "Crime"
  ],
  "image": "https://example.com/shawshank-redemption.jpg"
}

REST API Linked Data Keywords

It's a specification to apply JSON-LD mappings to JSON schema. It's well defined and easy to use to generate JSON-LD annotation on schema instances. It has the same limitation of JSNO-LD.

see REST API Linked Data Keywords

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "Simplified Movie Object (Compact)",
  
    "x-jsonld-context": "https://schema.org",
    "x-jsonld-type": "Movie",
   

  "type": "object",
  "properties": {
    "name": {
      "type": "string"
    },
    "datePublished": {
      "type": "string",
      "format": "date"
    },
    "director": {
      "type": "string"
    },
    "actor": {
      "type": "array",
      "items": {
        "type": "string"
      },
      "minItems": 1
    },
    "copyrightHolder": {  
      "type": "string"
    },
    "genre": {
      "type": "array",
      "items": {
        "type": "string"
      },
      "minItems": 1
    },
    "image": {
      "type": "string",
      "format": "uri"
    }
  }
}

Potential Limitations

It's very difficult in JSON-LD to semantically map flattened schemas like the following one:

{
    "$schema": "http://json-schema.org/draft-07/schema#",
    "title": "Simplified Movie Object (Compact)",

     "type": "object",
     "properties": {
     "movieId": {
        "type": "string"
     },
     "name": {
        "type": "string"
     },
      "directorName": {
        "type": "string"
     },
      "directorCountryName": {
        "type": "string"
      }
    }
  }

[andrea-gioia]

Proposed solution

{
    "$schema": "http://json-schema.org/draft-07/schema#",
    "title": "Simplified Movie Object (Compact)",
    "type": "object",

    "s-context": {
        "s-base": "https://schema.org",
        
        "s-type": "[Movie]",

        "movieId": null,
        "directorName": "director[Person].name",
        "directorCountryName": "director[Person].country[Country].name",
        "actors": "actor[Person].name",
        "copyright": {
            "s-type": "copyrightHolder[Organization]",
            "organizationId": null,
            "email": "contactPoint[ContactPoint].mail"
        }  
    },

  
    "properties": {
      "movieId": {
        "type": "string"
      },
      "name": {
        "type": "string"
      },
      "directorName": {
        "type": "string"
      },
      "directorCountryName": {
        "type": "string"
      },
      "actors": {
        "type": "array",
        "items": {
          "type": "string"
        },
        "minItems": 1
      },
      "copyright": {  
        "type": "object",
        "properties": {
            "organizationId": {
                "type": "string"
            },
            "legalName": {
                "type": "string"
            },
            "email": {
                "type": "string"
            }
        }
      }
    }
  }

Explanation:

• s-context: defines the semantic links. It can be defined inline or as an external reference
• s-base: the base URL used to resolve concept names
• s-type: the linked concept name or full concept URI enclosed in square brackets. The name before the brackets is the name of the parent property valorized by the linked concept. For example "copyright": {"s-type": "copyrightHolder[Organization]"} maps the property copyright of the schema to the property copyrightHolder of the parent concept (Movie) and has as value an Organization concept. If the name used in the schema is already equal to the name of the referenced concept property it can be omitted in the mapping.
• "movieId": null, the schema property movieId is not defined in the Movie concept. It exists only in the physical data
• "directorName": "director[Person].name" : the property directorName in the schema is linked to the property name of the Person who directs the Movie
• "directorCountryName": "director[Person].country[Country].name" : the property directorCountryName in the schema is linked to the property name of the Country of the Person who directs the Movie
• actors": "actor[Person].name : the property actors in the schema is linked to the property name of the Person who acts in the Movie. Because actors in the schema is an array the values are the names of the actors.

[andrea-gioia]

Ok, we have collected enough ideas to open a new RFC. Let's create an issue.