Get data as of a specific time

You can use the as_of_time attribute in the mql envelope to get data that was present at a specific time.

this query: 

{
   "q1" : {
     "as_of_time" : "2007-01-09T22:00:56.0000Z",
     "query" : [
       {
         "domain" : "/architecture",
         "id" : null,
         "return" : "count",
         "timestamp" : null,
         "type" : "/type/type"
       }
     ]
   }
 }

returns 12 (there were 12 types in the /architecture domain last january).

{
   "q1": {
     "code": "/api/status/ok",
     "result": [
       12
     ]
   },
   "status": "200 OK",
   "code": "/api/status/ok"
 }

this query (no as_of_time attribute):

 {
   "q1" : {
     "query" : [
       {
         "domain" : "/architecture",
         "id" : null,
         "return" : "count",
         "timestamp" : null,
         "type" : "/type/type"
       }
     ]
   }
 }

returns the current number of types in the architecture domain:

 {
   "q1": {
     "code": "/api/status/ok",
     "result": [
       25
     ]
   },
   "status": "200 OK",
   "code": "/api/status/ok"
 }

This example was extracted from a response on the developers@freebase mailing list.

One interesting use of this feature is to create a kind of trust authority application. Establish your own trusted view of topics by store the timestamp of a known good version. Then query to get the trusted version.

More information on as_of_time and other envelope parameters can be found in section 4.2.4 of the Complete MQL Reference Guide.

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