import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.List;

interface Row {
    /*
     Single row of data.  An implementation of this interface is, roughly, a table schema.
     */

    // Get the row's partition key.  This can be any value (not necessarily unique).  We try to put
    // rows with similar partition keys in the same index.
    public int getPartitionKey();
}

interface QueryEngine {
    /*
     Lives on a query server.  Generates a query plan (query functions and target keys) for any user-submitted query.
     */

    // Generate a query plan for a user-submitted query.
    public queryPlan planQuery(String query);
}

interface Index {
    /*
     Stores a shard of data.  Probably contains an internal index structure for fast queries.
     For durability, can be saved as files to persistent storage (S3?) and reconstructed.
     */

    // Add a new row to the index.
    public int addRow(Row row);
    // Create files from which index can be reconstructed.
    public List<String> indexToData();
    // Reconstruct index from files.
    public int indexFromData(List<String> data);
}

interface queryPlan {
    /*
     Map a query on indexes, then reduce into a result.
     */

    // On which keys should the query execute?
    public List<Integer> keysForQuery();
    // Execute the query on an index (Map).
    public ObjectOutputStream queryIndex(Index index);
    // Aggregate the outputs of queries on indexes (Reduce).
    public String aggregateIndexQueries(List<ObjectInputStream> indexQueryResults);
}