# TrustGraph Triples Query API

This is a service which queries the knowledge graph for triples ("facts").

## Request/response

### Request

The request contains the following fields:
- `s`: Optional, if included specifies a match for the subject part of a
  triple.
- `p`: Optional, if included specifies a match for the subject part of a
  triple.
- `o`: Optional, if included specifies a match for the subject part of a
  triple.
- `limit`: Optional, if included specifies the maximum number of triples to
  return.  If not specified, an arbitrary value is used.

Returned triples will match all of `s`, `p` and `o` where provided.

### Response

The response contains the following fields:
- `response`: A list of triples.

Each triple contains `s`, `p` and `o` fields describing the
subject, predicate and object part of each triple.

Each triple element uses the same schema:
- `value`: the entity URI or literal value depending on whether this is
  graph entity or literal value.
- `is_uri`: A boolean value which is true if this is a graph entity i.e.
  `value` is a URI, not a literal value.

## Data Format Details

### Triple Element Format

To reduce the size of JSON messages, triple elements (subject, predicate, object) are encoded using a compact format:

- `v`: The value as a string (maps to `value` in the full schema)
- `e`: Boolean indicating if this is an entity/URI (maps to `is_uri` in the full schema)

Each triple element (`s`, `p`, `o`) contains:
- `v`: The actual value as a string
- `e`: Boolean indicating the value type
  - `true`: The value is a URI/entity (e.g., `"http://example.com/Person1"`)
  - `false`: The value is a literal (e.g., `"John Doe"`, `"42"`, `"2023-01-01"`)

### Examples

**URI/Entity Element:**
```json
{
    "v": "http://trustgraph.ai/e/space-station-modules",
    "e": true
}
```

**Literal Element:**
```json
{
    "v": "space station modules", 
    "e": false
}
```

**Numeric Literal:**
```json
{
    "v": "42",
    "e": false
}
```

## REST service

The REST service accepts a request object containing the `s`, `p`, `o`
and `limit` fields.
The response is a JSON object containing the `response` field.

e.g.

This example query matches triples with a subject of
`http://trustgraph.ai/e/space-station-modules` and a predicate of
`http://www.w3.org/2000/01/rdf-schema#label`.  This predicate
represents the RDF schema 'label' relationship.

The response is a single triple - the `o` element contains the
literal "space station modules" which is the label for
`http://trustgraph.ai/e/space-station-modules`.

Request:
```
{
    "id": "qgzw1287vfjc8wsk-4",
    "service": "triples-query",
    "flow": "default",
    "request": {
        "s": {
            "v": "http://trustgraph.ai/e/space-station-modules",
            "e": true
        },
        "p": {
            "v": "http://www.w3.org/2000/01/rdf-schema#label",
            "e": true
        },
        "limit": 5
    }
}
```

Response:

```
{
    "response": [
        {
            "s": {
                "v": "http://trustgraph.ai/e/space-station-modules",
                "e": true
            },
            "p": {
                "v": "http://www.w3.org/2000/01/rdf-schema#label",
                "e": true
            },
            "o": {
                "v": "space station modules",
                "e": false
            }
        }
    ]
}
```

## Websocket

Requests have a `request` object containing the query fields (`s`, `p`, `o`, `limit`).
Responses have a `response` object containing `response` field.

e.g.

Request:

```
{
    "id": "qgzw1287vfjc8wsk-4",
    "service": "triples-query",
    "request": {
        "s": {
            "v": "http://trustgraph.ai/e/space-station-modules",
            "e": true
        },
        "p": {
            "v": "http://www.w3.org/2000/01/rdf-schema#label",
            "e": true
        },
        "limit": 5
    }
}
```

Responses:

```
{
    "id": "qgzw1287vfjc8wsk-4",
    "response": {
        "response": [
            {
                "s": {
                    "v": "http://trustgraph.ai/e/space-station-modules",
                    "e": true
                },
                "p": {
                    "v": "http://www.w3.org/2000/01/rdf-schema#label",
                    "e": true
                },
                "o": {
                    "v": "space station modules",
                    "e": false
                }
            }
        ]
    },
    "complete": true
}
```

## Pulsar

The Pulsar schema for the Triples Query API is defined in Python code here:

https://github.com/trustgraph-ai/trustgraph/blob/master/trustgraph-base/trustgraph/schema/graph.py

Default request queue:
`non-persistent://tg/request/triples-query`

Default response queue:
`non-persistent://tg/response/triples-query`

Request schema:
`trustgraph.schema.TriplesQueryRequest`

Response schema:
`trustgraph.schema.TriplesQueryResponse`

## Pulsar Python client

The client class is
`trustgraph.clients.TriplesQueryClient`

https://github.com/trustgraph-ai/trustgraph/blob/master/trustgraph-base/trustgraph/clients/triples_query_client.py