The abilities and some possible extensions of the Continuous Query Language
Antal Buza
Institute of Informatics, College of Dunaujvaros
e-mail: buza@mail.poliod.hu
Abstract
The CQL, Continuous Query Language is an expressive SQL-based declarative language for registering continuous queries against streams and updatable relations. CQL is suitable for data stream queries. There are some situations when the queries operate on relational databases and on the data streams simultaneously. The execution of CQL query takes a long time (may be several hours, days or more). It is not unambiguous which semantic is suitable for the user when the database updated during the execution of CQL query. For example, when we wish keep an eye on changing the value of the account and the official rates are updated, then the CQL system must calculate with the retroactive effect of this update. Another semantic is reasoned when the prices are changed while we use the CQL query for observing the trade of a supermarket. In this case the effect of update is valid from the moment of update. In this paper we give a short description of CQL, characterisation of update-problems and we give possible suggestions for the semantically extension of the CQL.  
Additional interesting question is the explanation of the consistent state. In classical database theory it is usually requirement that the “normal” state of a database is the consistent state. The consistency is not a permanent state, during the updates it may be damaged for a short time. Investigations were performed what the effect of the inconsistent state on currently operating CQL queries is.         
References
[1]	Arvind Arasu and Shivnath Babu and Jennifer Widom: The CQL Continuous Query Languag: SemanticFundations and Query Execution. Proceedings of the 9th International Conference on Data Base Programming Languages (DBPL 2003).
[2]	Shivnath Babu and Jennifer Widom: Continuous Queries over Data Streams. SIGMOD Record, Sept. 2001
Postal address
Antal Buza					
Institute of Informatics 		
College of Dunaujvaros		
Tancsics utca 1/a 
2400 Dunaujvaros
Hungary