gistfile1.clj

(def g
  [[:a1 :rdf/type :sdx/FederationService]
   [:a1 :sdx/exposesServices :a2]
   [:a2 :rdf/type :sdx/ServiceCollection]
   [:a2 :sdx/service :b1]
   [:a2 :sdx/service :c1]
   [:a2 :sdx/service :d1]

   [:b1 :rdf/type :sdx/FederatedService]
   [:b1 :sdx/exposesServices :b2]
   [:b2 :sdx/service :b3]
   [:b3 :rdf/type :sd/Service]
   [:b3 :sd/endpoint "http://my/url-b"]

   [:c1 :rdf/type :sdx/FederatedService]
   [:c1 :sdx/exposesServices :c2]
   [:c2 :sdx/service :c3]
   [:c3 :rdf/type :sd/Service]
   [:c3 :sd/endpoint "http://my/url-c"]

   [:d1 :rdf/type :sdx/FederatedService]
   [:d1 :sdx/exposesServices :d2]
   [:d2 :sdx/service :d3]
   [:d3 :rdf/type :sd/Service]
   [:d3 :sd/endpoint "http://my/url-d"]])

(run* [q]
      (fresh [a b c d e f]
             (membero [a :rdf/type :sdx/FederationService] g)
             (membero [a :sdx/exposesServices b] g)
             (membero [b :sdx/service c] g)
             (membero [c :rdf/type :sdx/FederatedService] g)
             (membero [c :sdx/exposesServices d] g)
             (membero [d :sdx/service e] g)
             (membero [e :rdf/type :sd/Service] g)
             (membero [e :sd/endpoint q] g)))

; => ("http://my/url-b" "http://my/url-c" "http://my/url-d")