# ShEx

[ShEX](https://shex.io/shex-semantics/) is a language for validating and describing RDF data.
In `rudof` there exist several supported operations regarding ShEx, namely, obtaining information about the ShEx schema, or validating an RDF graph using ShEx.

For executing the examples in this page we assume you have a file called `user.shex` in your folder with the following contents:

```shexc
prefix : <http://example.org/> 
prefix xsd: <http://www.w3.org/2001/XMLSchema#>
prefix schema: <http://schema.org/>

start = @:User 

:User {
  schema:name   xsd:string             ;
  schema:knows  @:User               * ;
  :status       [ :Active :Waiting ] ? ;
}
```

It is located in the [examples folder](https://github.com/rudof-project/rudof/tree/master/examples) and can directly be downloaded running the following commands:

```sh
curl -o user.shex https://raw.githubusercontent.com/rudof-project/rudof/refs/heads/master/examples/user.shex
```

## Information about the ShEx schema

You can obtain information about a ShEx schema using the following command:

```sh
rudof shex -s user.shex
```

## Conversion between ShEx formats

It is possible to use `rudof` to convert between different ShEx formats as:

```sh
❯ rudof shex -s examples/user.shex -r shexj
```

the output will be:

```json
{
  "@context": "http://www.w3.org/ns/shex.jsonld",
  "type": "Schema",
  "start": ":User",
  "shapes": [
    {
      "type": "ShapeDecl",
      "id": "http://example.org/User",
      "abstract": false,
      "shapeExpr": {
        "type": "Shape",
        "expression": {
          "type": "EachOf",
          "expressions": [
            {
              "type": "TripleConstraint",
              "predicate": "http://schema.org/name",
              "valueExpr": {
                "type": "NodeConstraint",
                "datatype": "http://www.w3.org/2001/XMLSchema#string"
              }
            },
            {
              "type": "TripleConstraint",
              "predicate": "http://schema.org/knows",
              "valueExpr": "http://example.org/User",
              "min": 0,
              "max": -1
            },
            {
              "type": "TripleConstraint",
              "predicate": "http://example.org/status",
              "valueExpr": {
                "type": "NodeConstraint",
                "values": [
                  "http://example.org/Active",
                  "http://example.org/Waiting"
                ]
              },
              "min": 0,
              "max": 1
            }
          ]
        }
      }
    }
  ],
  "prefixmap": {
    "": "http://example.org/",
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "schema": "http://schema.org/"
  }
}
```

## ShEx-based validation

It is also possible to use `rudof` to validate ShEx schemas.

As an example, assuming you have the `user.shex` file as in the previous section and the following `user.ttl` file:

and a file called `user.ttl` with the contents:

```turtle
prefix : <http://example.org/>
prefix schema: <http://schema.org/>

:a schema:name  "Alice" ;
   :status      :Active ;
   schema:knows :a, :b  .

:b schema:name  "Bob"    ;
   :status      :Waiting ;
   schema:knows :c       .

:c schema:name  "Carol"  .

:d schema:name  23      .  # Should fail

:e schema:name  "Emily" ;  # Should fail
   schema:knows :d      .
```

The command runs ShEx validation:

```sh
rudof shex-validate --schema user.shex --node :a --shape-label :User user.ttl
Result:
:c-><http://example.org/User>  Shape passed for node http://example.org/c: :User
:a-><http://example.org/User>  Shape passed for node http://example.org/a: :User
:b-><http://example.org/User>  Shape passed for node http://example.org/b: :User
```

## ShEx command

The general format of the ShEx subcommand is:

```sh
❯ rudof shex --help
Show information about ShEx schemas

Usage: rudof shex [OPTIONS] --schema <Schema file name>

Options:
  -s, --schema <Schema file name>
          
  -f, --format <Schema format>
          [default: shexc] [possible values: internal, simple, shexc, shexj, turtle, ntriples, rdfxml, trig, n3, nquads]
  -r, --result-format <Result schema format>
          [default: shexj] [possible values: internal, simple, shexc, shexj, turtle, ntriples, rdfxml, trig, n3, nquads]
  -t, --show elapsed time
          
      --statistics
          
  -o, --output-file <Output file name, default = terminal>
          
      --reader-mode <RDF Reader mode>
          RDF Reader mode [default: strict] [possible values: lax, strict]
      --force-overwrite
          
  -c, --config-file <Config file name>
          Config file path, if unset it assumes default config
  -h, --help
          Print help
```

## ShEx configuration file

The parameter `--config-file`  (`-c` in short form) can be used to pass a configuration file in YAML format.

The fields that it can contain are:

- show_extends (Boolean value): If enabled it shows information about extended shapes
- show_extends (Boolean value): If enabled it shows information about imported schemas
- show_shapes (Boolean value): If enabled it shows information about the shapes in the schema
- shex_format (shexc|shexj|turtle|ntriples,rdfxml|trig|n3|nquads|...): Default ShEx format (it can be overrided with the `--schema-format` option)
- rdf_config_shex: (YAML record): Configuration in case the format is RDF, following the structure of RDF config files.

The following YAML file can be an example:

```yaml
shex:
  show_extends: true
  show_imports: true
  shex_format: shexc
```
