Introduce Data Query

[tock-ibm]

// Query provides method to execute json query and range query on a
// given database.
interface Query {
    // ExecuteJSONQuery executes a given JSON query on a given database.
    // The JSON query is a json string which must contain predicates under the field
    // selector. The first field in the selector can be a combinational operator
    // such as "$and" or "$or" followed by a list of attributes and a list of
    // conditions per attributes. A query example is shown below
    //
    // {
    //   "selector": {
    //      "$and": {            -- top level combinational operator
    //          "attr1": {          -- a field in the json document
    //              "$gte": "a",    -- value criteria for the field
    //              "$lt": "b"      -- value criteria for the field
    //          },
    //          "attr2": {          -- a field in the json document
    //              "$eq": true     -- value criteria for the field
    //          },
    //          "attr3": {          -- a field in the json document
    //              "$lt": "a2"     -- a field in the json document
    //          }
    //      }
    //   }
    // }
    KVWithMetadata[] executeJSONQuery(String dbName, String query) throws Exception;
    // GetDataByRange executes a range query on a given database. The startKey is
    // inclusive but endKey is not. When the startKey is an empty string, it denotes
    // `fetch keys from the beginning` while an empty endKey denotes `fetch keys till the
    // the end`. The limit denotes the number of records to be fetched in total. However,
    // when the limit is set to 0, it denotes no limit. The iterator returned by
    // GetDataByRange is used to retrieve the records.
    Iterator GetDataByRange(String dbName, String startKey, String endKey, int limit) throws Exception;
}