afs commented on code in PR #2536:
URL: https://github.com/apache/jena/pull/2536#discussion_r1670222980
##########
jena-arq/src/main/java/org/apache/jena/sparql/engine/main/JoinClassifier.java:
##########
@@ -235,4 +243,85 @@ private static boolean safeModifier(Op op) {
return false ;
return op instanceof OpDistinct || op instanceof OpReduced || op
instanceof OpProject || op instanceof OpList ;
}
+
+ /** Enumeration of the primitive op types in the SPARQL algebra. */
+ private enum Basis {
+ PATTERN,
+ TABLE,
+ PFUNCTION
+ }
+
+ /**
+ * This method checks whether the given op is based on {@link OpTable} or
{@link OpPropFunc}.
+ * If neither is the case then the result is {@link Basis#PATTERN}.
+ * <p>
+ * This method is called for each side of a join from {@link #isLinear(Op,
Op)}.
+ * If that side of the join is a property function then {@link
Basis#PFUNCTION} is returned.
+ *
+ * <p>
+ * The special handling of property functions is due to that
+ * OpJoin(TABLE, PFUNCTION) needs to be linearized to OpSequence(TABLE,
PFUNCTION).
+ *
+ * <p>
+ * This method resolves OpExt to its effective op.
+ */
+ private static Basis getBasis(Op op) {
Review Comment:
This will look better when switch/case/instanceof is available! (Java21, not
Java17)
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