@jahed/sparql-engine
Version:
SPARQL query engine for servers and web browsers.
127 lines • 4.25 kB
JavaScript
// SPDX-License-Identifier: MIT
import { cloneDeep } from "lodash-es";
/**
* A Visitor which performs a Depth-first traversal of a SPARQL query expression tree
* and transforms each node.
* Subclasses are used to implements SPARQl query optimization rules.
*/
export default class PlanVisitor {
visit(node) {
switch (node.type) {
case "query":
const newNode = cloneDeep(node);
newNode.where = node.where?.map((n) => this.visit(n));
return newNode;
case "bgp":
return this.visitBGP(node);
case "union":
return this.visitUnion(node);
case "optional":
return this.visitOptional(node);
case "group":
return this.visitGroup(node);
case "filter":
return this.visitFilter(node);
case "service":
return this.visitService(node);
case "bind":
return this.visitBind(node);
case "values":
return this.visitValues(node);
default:
return node;
}
}
/**
* Visit and transform a Basic Graph Pattern node.
* By default, peform no transformation on the node.
* @param node - Basic Graph Pattern node
* @return The transformed Basic Graph Pattern node
*/
visitBGP(node) {
return node;
}
/**
* Visit and transform a SPARQL Group pattern node.
* By default, recursively transform all members of the group.
* @param node - SPARQL Group pattern node
* @return The transformed SPARQL Group pattern node
*/
visitGroup(node) {
const newNode = cloneDeep(node);
newNode.patterns = newNode.patterns.map((p) => this.visit(p));
return newNode;
}
/**
* Visit and transform a SPARQL OPTIONAL node.
* By default, recursively transform all members of the OPTIONAL.
* @param node - SPARQL OPTIONAL node
* @return The transformed SPARQL OPTIONAL node
*/
visitOptional(node) {
const newNode = cloneDeep(node);
newNode.patterns = newNode.patterns.map((p) => this.visit(p));
return newNode;
}
/**
* Visit and transform a SPARQL UNION node.
* By default, recursively transform all members of the UNION.
* @param node - SPARQL UNION node
* @return The transformed SPARQL UNION node
*/
visitUnion(node) {
const newNode = cloneDeep(node);
newNode.patterns = newNode.patterns.map((p) => this.visit(p));
return newNode;
}
/**
* Visit and transform a SPARQL FILTER node.
* By default, peform no transformation on the node.
* @param node - SPARQL FILTER node
* @return The transformed SPARQL FILTER node
*/
visitFilter(node) {
return node;
}
/**
* Visit and transform a SPARQL GRAPH node.
* By default, recursively transform all members of the GRAPH.
* @param node - SPARQL GRAPH node
* @return The transformed SPARQL GRAPH node
*/
visitGraph(node) {
const newNode = cloneDeep(node);
newNode.patterns = newNode.patterns.map((p) => this.visit(p));
return newNode;
}
/**
* Visit and transform a SPARQL SERVICE node.
* By default, recursively transform all members of the SERVICE.
* @param node - SPARQL SERVICE node
* @return The transformed SPARQL SERVICE node
*/
visitService(node) {
const newNode = cloneDeep(node);
newNode.patterns = newNode.patterns.map((p) => this.visit(p));
return newNode;
}
/**
* Visit and transform a SPARQL BIND node.
* By default, peform no transformation on the node.
* @param node - SPARQL BIND node
* @return The transformed SPARQL BIND node
*/
visitBind(node) {
return node;
}
/**
* Visit and transform a SPARQL VALUES node.
* By default, peform no transformation on the node.
* @param node - SPARQL VALUES node
* @return The transformed SPARQL VALUES node
*/
visitValues(node) {
return node;
}
}
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