Continuous Query Language
CQL is a query language for stream data processing, proposed by the STREAM (Stanford Stream Data Manager) Project of Stanford University in the U.S. The language has a grammar that has added "window operations" and "stream operations," which are peculiar to stream data processing, to the data retrieval syntax of the SQL, and can define the data processing details.
With the CQL, the analysis objects are narrowed down under such specific conditions as "latest 10 cases" or "latest 10 minutes" (window operations), and a relational table is created as an interim result. The relational table undergoes such processing operations as selection and projection based on the data retrieval syntax of the SQL, and the processing results are re-converted to stream data (stream operations). Complicated processing operations can also be performed by repeating data conversion and data retrieval between the stream data and the relational table.
The relational table and the data retrieval results always change in accordance with the flow of the input data. Characteristically, the CQL can handle these changes by conducting such dynamic operations as reactive programming (in which data automatically changes in accordance with the relations between pieces of data) easily under the same syntax as the SQL.
