2023-02-27

selector expressions to filter relations of a directed graph by set relations between nodes

- matching of paths of arbitrary length
- expressions can be nested
- divergent searches and skipping of intermediate path parts
- minimum and maximum number of intermediate nodes to skip

integers stand for nodes/node-identifiers

(1) (1 *) (1 * 2) ((only 14 15) *) (11 21 31) (* (1 2) (3 4)) ((and 11 12) (not 24) (or 32 31)) ((and 11 12) (not 24) (not (or (and 41) (or 32 31) 32 31))) (11 (* 3 2) 12) ;a path between 11 and 12 with a maximum and minimum number of nodes inbetween

path: (skip/node ..1) path: (source target/source ...) node: (combinator id/node ..1) combinator: and/or/only/not skip: */(* integer:max [integer:min]) id: integer null: () direction: "left"/"right" result: ((relation-left relation-right) ...)

the relations in path between the last two node-expressions

- source and target are the left and right (or start and end) nodes of a relation
- interpretation: ((targets in relation with these sources) (sources in relation with these targets) _ ...)
- reversing the order of the path is not the same as reversing the search direction

matches relations whose targets are each...

- or: in relation to any of the given sources. union
- and: in relation to all of the given sources. intersection
- not: not in relation to any of the given sources. complement
- only: only in relation with all of the given sources

(not _ ...) = (not (or _ ...)) (and (and)) = (and) (or (or)) = (or) (not (not)) != (not)

all non-negating combinators match subsets of "or". "not" is semantically unary

if any node-expression or non-negated sub-expression matches no nodes then result is an empty set. the rationale for this is that this allows simpler composition of path-find paths. only sets have to be considered as input arguments and if there is an empty set in one part of a node-expression that is not a negation then the result will also be empty

search direction for directed graphs. for example "left" or "right"

an implementation is part of the discontinued but still available sph-lib-dg