Fixing Constraint Violations with spin:fix
Constraint checking is a popular feature of many Semantic Web tools to ensure that instance data meets the design objectives attached to classes and properties in an ontology. Data entry tools like TopBraid Composer and Ensemble use the SPARQL-based constraint checking language SPIN to make sure that users get warnings if the data they are entering is violating constraints. If a violation is reported, the user would read through the violation message and then change the data on the form.
The following spin:constraint (attached to the Square class) implements the suggestions above:
You can see that the constraint creates a spin:ConstraintViolation that is attached to two instances of :SetObject via spin:fix. The class :SetObject is a SPIN template with the following definition:
The SPIN templates suggested as fixes could come from a library of re-usable building blocks. I assume that most constraint violations can be repaired by replacing, adding or deleting certain triples, and these cases can be generalized easily. Furthermore, the spin:constraints themselves can be generalized into templates, so that the ontology designer in the end just needs to pick the correct template to get a really powerful and convenient constraint checking mechanism.
Also note that the constraint fixing mechanism above could be useful beyond user interfaces, for example to automatically repair incoming data streams in web service calls.
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