| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for implementing a content based publish-and-subscribe system in a relational database system. SOLUTION: A subscriber may request for messages by using a query language supported by a database server. The queries are then used as subscription rules for determining whether an incoming message is to be sent to the subscriber. Evaluation of incoming messages against the subscription rules involves a two-tier process. The first tier involves filtering out all the subscription rules that can not possibly apply to the incoming message by filter processing. The second tier involves further evaluation of the incoming message, if needed, to determine which subscribers are to receive the incoming message. In cases where the publisher is the relational database system itself, queries that request for messages are not stored as subscription rules because publication of the messages is implicit. COPYRIGHT: (C)2007,JPO&INPIT
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