This paper briefly reviews concurrent logic programming and the I/O mode system designed for the concurrent logic language Flat GHC. The mode system plays fundamental roles both in programming and implementation in almost the same way as type systems do but in different respects. It provides us with the information on how data are generated and consumed and thus the view of “data as resources”. It statically detects bugs resulting from ill-formed dataflow and advocates the “programming as wiring” paradigm. Well-modedness guarantees the safety of unification, the basic operation in concurrent logic programming. Information on the numbers of access paths to data can be obtained by slightly extending the framework, which can be used for compile-time garbage collection and the destructive update of structures.