gql-path-patterns

name	gql-path-patterns
description	Use when building or debugging variable-length paths, reachability, shortest/cheapest path, or fan-out control in GQL/Cypher-like graph queries. Triggers: variable-length path, reachability, DEPENDS_ON walk, path explode, bounded hops.
metadata	{"pattern":"tool-wrapper","specialization":"graph-paths","domain":"data","version":"1.1"}
token_guardrails	- Always bound hop depth (e.g. {1,4}); never bare unbounded walks by default. - Anchor at least one endpoint with label + selective property. - Prefer DISTINCT + LIMIT when projecting nodes from fan-out paths.

GQL Path Patterns

Thin skill for paths and reachability. Pair with graph-query-language for basics.

Rules of thumb

• Bound every variable-length hop ({1,3} not bare *).
• Anchor at least one end with label + selective property.
• Prefer typed relationships (:REL) over untyped walks.
• Decide directed vs undirected before writing the pattern.

Bounded walk

MATCH (start:System { id: $id })-[:DEPENDS_ON]->{1,4}(dep:System)
RETURN DISTINCT dep.id AS dependency
LIMIT 200

Exists / reachability

MATCH (a:Node { id: $a })
FILTER EXISTS {
  MATCH (a)-[:LINK]->{1,6}(b:Node { id: $b })
}
RETURN a.id AS reachable_from

(If EXISTS subquery is unsupported, use a bounded MATCH + count(*) > 0.)

Fan-out control

1. Filter early (FILTER / WHERE on start node).
2. Constrain rel types.
3. Cap depth.
4. DISTINCT + LIMIT on projection.
5. For analytics, aggregate (count, collect) instead of returning every path.

Path objects

MATCH p = (a:Person)-[:KNOWS]->{1,3}(b:Person)
FILTER a.id = $a AND b.id = $b
RETURN p
LIMIT 20

Return nodes/rels extracted from p if the client cannot render path values.

Common failure modes

Symptom	Likely cause
Timeout / OOM	Unbounded depth or missing labels
Empty result	Wrong direction or tighter type than data
Duplicate rows	Missing DISTINCT on node projection
Wrong end node	Undirected pattern absorbing reverse edges

Deliverable style

Give the bounded query first. State max depth and relationship types assumed. Add a stricter variant if the first is for exploration.

Related

• Core GQL: graph-query-language
• MemNet agent wire: memnet-format, mcp-memnet
• SysML modeling + MemNet: sysml-gql