OBSL — RDF Graph & SPARQL¶

OBSL (OrionBelt Semantic Layer vocabulary) is an RDF-based exchange format for semantic-layer models. When you load a model, OrionBelt automatically exports it as an OBSL-Core 0.1 RDF graph. You can retrieve the graph as Turtle or run read-only SPARQL queries against it — no extra setup required.

What is OBSL-Core?¶

OBSL-Core 0.1 maps every OBML concept to RDF triples using standard vocabularies:

OBML Concept	RDF Class	Key Properties
Model container	`obsl:SemanticModel`	`obsl:hasDataObject`, `obsl:hasDimension`, `obsl:hasMeasure`, `obsl:hasMetric`
Data Object	`obsl:DataObject`	`obsl:code`, `obsl:database`, `obsl:schema`, `obsl:hasColumn`, `obsl:hasJoin`
Column	`obsl:Column`	`obsl:code`, `obsl:resultType`
Join	`obsl:Join`	`obsl:joinTo`, `obsl:cardinality`, `obsl:columnFrom`, `obsl:columnTo`
Dimension	`obsl:Dimension`	`obsl:dataObject`, `obsl:column`, `obsl:resultType`, `obsl:timeGrain`
Measure	`obsl:Measure`	`obsl:aggregation`, `obsl:resultType`, `obsl:sourceColumn`, `obsl:expressionSource`
Metric	`obsl:Metric`	`obsl:metricType`, `obsl:expressionSource`, `obsl:baseMeasure`, `obsl:referencesMeasure`
Cumulative Metric	`obsl:CumulativeMetric`	`obsl:timeDimension`, `obsl:cumulativeType`, `obsl:window`, `obsl:grainToDate`
Period-over-Period Metric	`obsl:PeriodOverPeriodMetric`	`obsl:timeDimension`, `obsl:timeGrain`, `obsl:offset`, `obsl:offsetGrain`, `obsl:comparison`

Labels use rdfs:label, synonyms use obsl:synonym, and descriptions use rdfs:comment.

Namespace

@prefix obsl: <https://ralforion.com/ns/obsl#> .

Vocabulary reference: https://ralforion.com/ns/obsl/

Retrieving the Graph¶

After loading a model, retrieve its RDF graph as Turtle:

curlShortcut (single model)

curl http://localhost:8000/v1/sessions/{session_id}/models/{model_id}/graph

curl http://localhost:8000/v1/graph

The response is text/turtle:

@prefix obsl: <https://ralforion.com/ns/obsl#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .

<https://ralforion.com/ns/model/abc123> a obsl:SemanticModel ;
    obsl:hasDataObject <.../data-object/orders> ;
    obsl:hasDimension <.../dimension/country> ;
    obsl:hasMeasure <.../measure/revenue> .

<.../measure/revenue> a obsl:Measure ;
    rdfs:label "Revenue" ;
    obsl:aggregation "sum" ;
    obsl:resultType "float" ;
    obsl:expressionSource "{[Orders].[Price]} * {[Orders].[Quantity]}" .

SPARQL Queries¶

Run read-only SPARQL (SELECT and ASK) against any loaded model:

curlShortcut (single model)

curl -X POST http://localhost:8000/v1/sessions/{session_id}/models/{model_id}/sparql \
  -H "Content-Type: application/json" \
  -d '{"query": "PREFIX obsl: <https://ralforion.com/ns/obsl#> PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> SELECT ?label WHERE { ?m a obsl:Measure ; rdfs:label ?label . }"}'

curl -X POST http://localhost:8000/v1/sparql \
  -H "Content-Type: application/json" \
  -d '{"query": "PREFIX obsl: <https://ralforion.com/ns/obsl#> PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> SELECT ?label WHERE { ?m a obsl:Measure ; rdfs:label ?label . }"}'

SELECT example¶

List all measures with their aggregation:

PREFIX obsl: <https://ralforion.com/ns/obsl#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
SELECT ?label ?agg WHERE {
    ?m a obsl:Measure ;
       rdfs:label ?label ;
       obsl:aggregation ?agg .
}

Response:

{
  "type": "select",
  "variables": ["label", "agg"],
  "results": [
    {"label": "Revenue", "agg": "sum"},
    {"label": "Order Count", "agg": "count"}
  ],
  "boolean": null
}

ASK example¶

Check if any dimension exists:

PREFIX obsl: <https://ralforion.com/ns/obsl#>
ASK { ?x a obsl:Dimension }

Response:

{
  "type": "ask",
  "variables": [],
  "results": [],
  "boolean": true
}

More query ideas¶

-- Find all joins and their cardinality
PREFIX obsl: <https://ralforion.com/ns/obsl#>
SELECT ?from ?to ?card WHERE {
    ?j a obsl:Join ;
       obsl:joinTo ?to ;
       obsl:cardinality ?card .
    ?from obsl:hasJoin ?j .
}

-- Find all synonyms across the model
PREFIX obsl: <https://ralforion.com/ns/obsl#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
SELECT ?label ?synonym WHERE {
    ?x rdfs:label ?label ;
       obsl:synonym ?synonym .
}

-- Find metrics that reference a specific measure
PREFIX obsl: <https://ralforion.com/ns/obsl#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
SELECT ?metric ?measure WHERE {
    ?m a obsl:Metric ;
       rdfs:label ?metric ;
       obsl:referencesMeasure ?ref .
    ?ref rdfs:label ?measure .
}

Read-only

Only SELECT and ASK queries are allowed. Update operations (INSERT, DELETE, LOAD, DROP, etc.) return HTTP 400.

How It Works¶

The OBSL graph is generated eagerly at model load time — there is no extra step to trigger it. When you call POST /v1/sessions/{id}/models to load a model, the graph is built and cached alongside the SemanticModel. Subsequent /graph and /sparql calls read from this cache, so they are fast.

The graph is removed when the model is unloaded (DELETE /v1/sessions/{id}/models/{mid}).

Specification¶

The full OBSL-Core 0.1 specification — including all classes, properties, URI strategy, OBML mapping, and controlled value sets — is in ontology/spec.md.

The OWL ontology (obsl.ttl), SHACL shapes (obsl.shacl.ttl), and a Sales model example (example-sales.ttl) are available in the ontology/ directory and at https://ralforion.com/ns/obsl/.