Implement Explanations in RPC (#131)

## What is the goal of this PR?
We add Explanations, and the explain() query endpoint to the protocol. This enables all clients to retrieve all available explanations for a particular explainable concept map.

## What are the changes implemented in this PR?
* Implement `Explainable` and `Explainables` as part of `Answer` protocol
* Implement `Explanation` as part of `Logic` protocol
* Add `Explain.Req` and `Explain.Res` as part of the explain QueryManager endpoing

common/BUILD

@@ -32,7 +32,8 @@ proto_library(
 
 proto_library(
     name = "logic-proto",
-    srcs = ["logic.proto"]
+    srcs = ["logic.proto"],
+    deps = [":answer-proto"]
 )
 
 proto_library(
@@ -45,6 +46,7 @@ proto_library(
     srcs = ["query.proto"],
     deps = [
         ":answer-proto",
+        ":logic-proto",
         ":options-proto",
     ],
 )

common/answer.proto

@@ -26,7 +26,22 @@ package grakn.protocol;
 
 message ConceptMap {
     map<string, Concept> map = 1;
-    string pattern = 2;
+    Explainables explainables = 2;
+}
+
+message Explainables {
+    map<string, Explainable> relations = 1;
+    map<string, Explainable> attributes = 2;
+    map<string, Owned> ownerships = 3;
+
+    message Owned {
+        map<string, Explainable> owned = 1;
+    }
+}
+
+message Explainable {
+    string conjunction = 1;
+    int64 id = 2;
 }
 
 message ConceptMapGroup {

common/logic.proto

@@ -20,6 +20,9 @@ syntax = "proto3";
 option java_package = "grakn.protocol";
 option java_outer_classname = "LogicProto";
 
+import "common/answer.proto";
+
+
 package grakn.protocol;
 
 message LogicManager {
@@ -106,3 +109,14 @@ message Rule {
         message Res {}
     }
 }
+
+message Explanation {
+    Rule rule = 1;
+    map<string, VarList> var_mapping = 2;
+    ConceptMap condition = 3;
+    ConceptMap conclusion = 4;
+
+    message VarList {
+        repeated string vars = 1;
+    }
+}

common/query.proto

@@ -21,6 +21,7 @@ option java_package = "grakn.protocol";
 option java_outer_classname = "QueryProto";
 
 import "common/answer.proto";
+import "common/logic.proto";
 import "common/options.proto";
 
 package grakn.protocol;
@@ -39,6 +40,7 @@ message QueryManager {
             Insert.Req insert_req = 106;
             Delete.Req delete_req = 107;
             Update.Req update_req = 108;
+            Explain.Req explain_req = 109;
         }
     }
 
@@ -58,6 +60,7 @@ message QueryManager {
             MatchGroupAggregate.ResPart match_group_aggregate_res_part = 102;
             Insert.ResPart insert_res_part = 103;
             Update.ResPart update_res_part = 104;
+            Explain.ResPart explain_res_part = 105;
         }
     }
 
@@ -100,6 +103,16 @@ message QueryManager {
         }
     }
 
+    message Explain {
+        message Req {
+            int64 explainable_id = 1;
+        }
+
+        message ResPart {
+            repeated Explanation explanations = 1;
+        }
+    }
+
     message Insert {
         message Req {
             string query = 1;