SHACL: add String-based constraints

[abrokenjester]

From @barthanssens on March 5, 2018 10:40

SHACL 4.4, most of the string-based constraints are probably fairly easy to add: minLength / maxLength / pattern / languageIn

(uniqueLang is more difficult / resource intensive)

See also https://www.w3.org/TR/shacl/#core-components-string

Copied from original issue: eclipse/rdf4j-storage#49

[abrokenjester]

From @hmottestad on March 13, 2018 7:14

Datatype based restrictions are also useful and as simple as string based ones.

[abrokenjester]

From @hmottestad on March 13, 2018 7:30

The plan for validating such data should kick in (requiresEvalutation()) if:

• a node of type targetClass is added
• a statement that matches the path is added

The plan should handle the following cases:

1. data added, type statement and path in added
2. data added, path in added, type statement in underlying store
3. data added, type statement added, path in underlying store

Note that it is possible with combinations of these cases.

Case 1 can easily degrade into case 3 by adding in the statements matching path for added nodes of type targetClass. This can then degrade into case 2 by filtering on the type statement from the underlying store.

[abrokenjester]

From @barthanssens on March 13, 2018 7:30

Indeed. I think I've managed the string constraints working, but probably suboptimal (seem to run more than they should)

[abrokenjester]

From @hmottestad on March 13, 2018 7:31

That's great. Do you have a branch?

[abrokenjester]

From @barthanssens on March 13, 2018 7:45

https://github.com/fedict/rdf4j-storage/tree/issues/%2349-shacl-stringconstraints

Still pretty much work in progress, I'll check this evening if the code on github is actually the latest version of the I'm working on.
I did some renaming and code rework (factories in separate classes e.g).

Currently I'm checking minLength,maxLength and pattern in 1 single check, although I'm not sure that is the best option - or at least it may require additional return values - if there is a need to also implement the sh:ValidationReport reports.

[abrokenjester]

From @hmottestad on March 14, 2018 8:34

I had a quick look now. Lots of nice cleanup :)

A couple of things I would like to keep though. Factory classes in the classes they belong to, makes it easier to understand and find, having them outside doubles the number of files and makes it harder to figure out which factory is for which class. Also a pain when renaming things later. Also, the queries with the binds, point here was to be able to track which statements in the database were used in evaluating a shacl rule, so that we can give an “explanation”. Currently this is being logged.

Try to make some tests for your added rules. Remember that shacl rules with target class trigger for two cases, when an rdf:type statement is added or when a statement matching the path is added (for min count also when removed, but that’s not applicable here).

[abrokenjester]

From @barthanssens on March 19, 2018 19:39

Thanks for the review :-)
I'll move the factories back into the original file, and I'll try to keep working on it (if time permits...)