addRelationship(i, h, d, o) {
    const l = this.entities.get(i), f = this.entities.get(d);
    if (!l || !f)
      return;
    const _ = {
      entityA: l.id,
      roleA: h,
      entityB: f.id,
      relSpec: o
    };
    this.relationships.push(_), D.debug("Added new relationship :", _);
  }
Add a relationship

@param entA - The first entity in the relationship
@param rolA - The role played by the first entity in relation to the second
@param entB - The second entity in the relationship
@param rSpec - The details of the relationship between the two entities