are there referentially equivalent selectors for the first/last position inside a subtree?

[lueck]

In general, for a given selector, which selects the first/last position inside a subtree, there exists a referentially equivalent and the XPath components of this referentially equivalent selector selects a subtree outside of the substree selected by the given selector! Exceptions are the first and last position in a document.

Example:

<r>Sol<t1>ar</t1><t2>pan</t2>el!</r>

Should the two selectors /r[1]/t1[1]; char=2 and /r[1]/t2[1]; char=0
be treated as referentially equivalent and be normalized to the same selector?
Both select the position between Solar and panel!

If referential equivalence is transitive, we must conclude, that the selectors are equivalent:

/r[1]; char=5 = /r[1]/t1[1]; char=2 and

/r[1]; char=5 = /r[1]/t2[1]; char=0

ergo: /r[1]/t1[1]; char=2 = /r[1]/t2[1]; char=0.

Cf. Wiki!

Assignees: @memowe, @inormann, @lueck

Migrated from GitLab: https://zivgitlab.uni-muenster.de/SCDH/selectors/selection-engine/-/issues/12

[lueck]

added to epic SCDH&16

[lueck]

mentioned in commit ee9a5c6

[lueck]

ee9a5c6 added a test for referentially equivalent selectors in ambiguity class 2.

All implemented normalization algorithms fail the test.

[lueck]

mentioned in commit 9a42760

[lueck]

9a42760 added an algorithm that passes the test with equivalent selectors in ambiguity class 2.

[lueck]

added 7h of time spent

[lueck]

Use --mode=FIRST or --mode=SECOND on the command line interface to test the new algorithms.

[lueck]

added 20m of time spent