RDF-Lens

Look into a dataset with RDF-Lens.
Here the term Lens, is the same concept of Haskell lenses available in this well known library.

A lens looks at a point in a dataset, for RDF-Lens this usually is looking at a Term inside a store.
Lenses can be combined to from a point, look furthur inside the dataset, as long as the types allow for it.

Currently two lenses exist in RDF-Lens BasicLens and BasicLensM (M stands for Multiple: BasicLensM is a subclass of BasicLens).
C stands for Container, a combination of the store and the current target. T stands for resulting type.

BasicLens can be combined with BasicLens and will result in BasicLens.

Examples

$3

A very common Lens is created with pred and takes in a predicate term and returns BasicLensM.
So it starts pointing inside the dataset and results in pointing to multiple things inside the dataset.
Using the function .thenFlat another predicate can be chained to explore the dataset deper.

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RDF-Lens tries to make it developer friendly and typed to extract data from a RDF store.
This example shows how to extract a point with two coordinates from the data.
``typescript
import { pred } from "rdf-lens";
import { DataFactory, Parser } from "n3";

const { namedNode } = DataFactory;

const extractX = pred(namedNode("x")) // Follow predicate
.one() // We expect only to find one term
.map(({id}) => ({x: id.value})); // Map that term to a Json Object

const extractY = pred(namedNode("y")) // Follow predicate
.one() // We expect only to find one term
.map(({id}) => ({y: id.value})); // Map that term to a Json Object

const pointLens = extractX.and(extractY) // Combine both lenses
.map(([{x}, {y}]) => ({x, y})); // Map them together to a point object

const turtle = " 42; 43.";
const quads = new Parser().parse(turtle); // Parser quads
const point = pointLens.execute({id: namedNode("a"), quads}); // Execute the lens over the dataset
`

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Extracting point data is not very exciting, this example shows how to extract all items from a RDF List.

`typescript
const RDFListElement = pred(RDF.first).one().and(pred(RDF.rest).one());

// RdfList is a Lens that takes in a Container pointing to a Term and returns a list of Terms
const RdfList: BasicLens = new BasicLens((c) => {
if (c.id.equals(RDF.nil)) {
return [];
}

const [first, rest] = RDFListElement.execute(c);
const els = RdfList.execute(rest);
els.unshift(first.id);
return els;
});
`

$3

Shacl shapes are used widely to constrain rdf data to some shape.
With rdf-lens you can extract data starting from a shape to a plain old javascript object.
The field names are defined by the sh:name, that is part of the sh:property object.

This examples shows how to define and extract a point.
`turtle


The shacl shape for a point