connect

abstract fun connect(aggrFunName: String, maxLevel: Int, initRootContext: String): Unit (source)

Connects with the underlying database.

The connection should either recover the state left by the previous close(), or (in case no previous state is found) start a new one.

Connector should make sure that:

The connection will be opened on the existing target table, if present, otherwise a new one will be created.
The target table name should be: "tableName_aggrFunName_kpName" to achieve a unique identification.
The target table must be provided with the following columns, in order:
- level: of type Int.
- k_min: can span more columns. Its definition is specified by the KeyParser kp.
- k_max: can span more columns. Its definition is specified by the KeyParser kp.
- context: of type String. It will contain the node's serialized elements.
If a valid target table is found, Connector should ask the client whether he wants to connect or to overwrite previous data and start a new state (old table is emptied and re-populated).

aggrFunName - the aggregation function's name.

maxLevel - the level of the root for the DB-tree.

initRootContext - the identity aggregate value (for the root) wrt the aggregation function.