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https://issues.apache.org/jira/browse/S4-21?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13148666#comment-13148666
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Leo Neumeyer commented on S4-21:
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Makes sense to have a generic stream, I think.
We could have a factory method for the generic stream that only takes these
arguments:
- stream name
- key finder class -or- key finder string
- target PE
(finder string is in the todo list, we already have it in 0.4. the string is
parsed to generate the finder class. It's an option for developers who dont'
want to write key finder classes.)
Another thought is, should the Event base class be the generic event class? If
the map is not created the overhead would be limited to one reference field.
The benefit is that all events will be augmentable without having to subclass.
Why would we do this? because it provides an easy way to add meta-data or
annotations to events. For example, for 2-way communication we need to send the
origin address in the event over several hops. In NLP, we may want to add
annotations to the event as it traverses several PEs. The annotator chain may
change often, making it impractical to use dedicated event classes. The Map in
base Event will make it possible to append these type of info using a simple
pattern. (Of course this is more costly than using event classes but requires
less boilerplate and fewer classes.) This design provide flexibility to use
classes for static typing and speed or maps for flexibility or a combination of
both.
> Create standard PEs, and Event classes
> --------------------------------------
>
> Key: S4-21
> URL: https://issues.apache.org/jira/browse/S4-21
> Project: Apache S4
> Issue Type: Improvement
> Affects Versions: 0.5
> Reporter: Leo Neumeyer
> Priority: Minor
> Fix For: 0.5
>
>
> We should provide some reusable classes such as JoinPE and a MapEvent. The
> MapEvent is a schema-less reusable event class.
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