# Data Validation

LinkML is designed to allow for a variety of strategies for data validation. The overall philosophy is to provide maximum expressivity in the language to allow model designers to state all consraints in a declarative fashion, and then to leverage existing frameworks and to allow the user to balance concerns such as expressivity vs efficiency.

Currently there are 4 supported strategies:

• validation via Python object instantiation

• validation through JSON-Schema

• validation of triples in a triplestore or RDF file via generation of SPARQL constraints

• validation of RDF via generation of ShEx

However, others will be supported in future

## Validation of JSON documents

The linkml-convert command will automatically perform data validation.

Currently it performs two level validation:

• it will convert data to in-memory Python objects, using dataclass validation

• it will then convert the LinkML schema to JSON-Schema and employ JSON-Schema validation

Note that you can easily generate JSON-Schema and use your validator of choice, see JSON Schema Generation

## Validation of RDF triplestores using generated SPARQL

The LinkML framework can also be used to validate RDF, either in a file, or a triplestore. There are two steps:

• generation of SPARQL constraint-style queries (see sparqlgen )

• execution of those queries on an in-memory graph or external triplestore

The user can choose to run only the first step, to obtain a bank of SPARQL queries that can be applied selectively

linkml-sparql-validate --help

Validates sparql

Example:

tests/test_validation/input/omo.yaml

Options:
-G, --named-graph TEXT          Constrain query to a named graph
-i, --input TEXT                Input file to validate
-U, --endpoint-url TEXT         URL of sparql endpoint
-L, --limit TEXT                Max results per query
-o, --output TEXT               Path to report file
-f, --input-format [yaml|json|rdf|csv|tsv]
Input format. Inferred from input suffix if
not specified

-t, --output-format [yaml|json|rdf|csv|tsv]
Output format. Inferred from output suffix
if not specified

-s, --schema TEXT               Path to schema specified as LinkML yaml
--help                          Show this message and exit.


## Future plans

Future versions of LinkML will employ a powerful constraint and inference language.

One of the use cases here is being able to specify that the length field is equal to end - start. This declarative knowledge can then be used to either (1) infer the value of length if unspecified (2) infer either start or end if only one of these is specified alongside length (3) check consistency if all three are specified.

These constraints can then be executed over large databases via a variety of strategies including:

• generation of datalog programs for efficient engines such as souffle

• generation of SQL queries to be used with relational databases

We also plan to support generation of SHACL from LinkML