SHACL or Shapes Constraint Language is a (constraint based) specification for describing and validating RDF graphs.

‘Shapes Constraint Language (SHACL) is a World Wide Web Consortium (W3C) specification for validating graph-based data against a set of conditions. Among others, SHACL includes features to express conditions that constrain the number of values that a property may have, the type of such values, numeric ranges, string matching patterns, and logical combinations of such constraints. SHACL also includes an extension mechanism to express more complex conditions in languages such as SPARQL.’

Both SHACL and ShEx (Shape Expressions) have a similar goal: to describe and validate RDF graphs.

See Schema