什么是wso2 cep中的元数据相关数据和有效载荷数据

Question

what is meta data correlation data and payload data in wso2 cep

I understood that these are 3 different types of data types in stream but which one has benefits over another that is not clear from any documentation. Or how can we use it in different situations.

All the operations that can be performed on payload data, I could also do on meta and correlation data as well.

Can someone explain difference with examples.

Answer 1

There is no difference in how each of these attributes behave internally in WSO2 CEP. This is simply a logical separation to let a user define streams with meta attributes, correlation attributes and payload separately. You can use these attribute types if you need the logical separation or simply send data as payload if there is no need for separation of meta data and correlation data.

You can store meta data related to a stream in meta data. eg attributes like event_timestamp, ip_address of a request or similar. Similarly for correlation data, you can put attributes that are used to correlate events with other events from other streams. eg something like a correlation_id. These attributes would be useful when you perform join operations on a stream.

However, please note that the Siddhi engine used within CEP does not differentiate streams based on meta, correlation, payload and processes all attributes without any distinction. The attribute types are available for streams defined at event-builder/event-formatter level which are mapped to flat Siddhi streams at runtime for processing queries.