The Elvin Publish/Subscribe Model
Elvin is most distinguished from other such systems by its support of a sophisticated content-based subscription system. Elvin clients subscribe to events using a language that resembles C boolean expressions. For example:
Department == "IT" && Percent-Disk-Free <= 10This expression selects messages that have a field named Department with a string value matching "IT" and a Percent-Disk-Free field with an integer value less than or equal to 10. The Elvin subscription language supports a range of operations for matching numeric and string values, including the use of regular expression matching.
Elvin is oriented around providing a fast, flexible event service that can be federated to form wide-area event notification networks. In order to achieve these goals it does not provide persistence, durability or guaranteed delivery. Elvin can thought of as providing a middle ground between low-level network multicast and higher-level, more complex, event brokers such as JMS.
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