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Subject: Re: [sca-assembly] [Issue 251] Some early thoughts
> For example, an order processing component may have a dependency on a > credit-card service. Unless that dependency is satisfied, the order > processing component just won't work. Again, back to different interpretations of eventing. Just because I'm using eventing doesn't always mean that I'm throwing *any* notion of coupling to the wind. Your statement above can have the same validity in eventing use cases. Therefore, I think it's necessary to make a distinction between a lower bound of 0 and a lower bound of 1. I do agree, though, that upper bounds have less meaning in the pub/sub world. On 12/14/2010 12:41 AM, Anish Karmarkar wrote: > I took an AI to come up with a proposal for issue 251 [1]. > Here are my initial thoughts: > > Issue 251 points out that currently the cardinality (number of channel > connections) of producers and consumers is 0..n. It also suggests that > we allow 0..1 and 1..1. > > It seems obvious that this is coming from the fact that in the > service-reference model these possibilities exists. I believe that > such a comparison isn't appropriate. In the service-reference model, a > component-reference specifies an interface-based dependency. Sometimes > such dependencies must to be satisfied to get the component/composite > to work correctly. For example, an order processing component may have > a dependency on a credit-card service. Unless that dependency is > satisfied, the order processing component just won't work. Similarly, > the same order processing component may want to allow the dependency > to be satisfied by multiple credit-card services (requirement being, > there be at least one). These dependencies get injected into the > component and the component, based on its internal logic, may decide > which services to call. > > The pub-sub model is different than this. A consumer may express > interest in certain events, but there is absolutely no guarantee that > an event may ever be delivered to it. Similarly, a producer may > produce events, but there is not guarantee that any consumer is either > listening for those events or even if a consumer is listening, it may > decide to just drop it on the floor and not take any action based on > that event. Furthermore, these kind of connections are meant to be > many-to-many. As far as cardinality goes, the cardinality has to be > wrt how many channels the producer/consumer is connected to regardless > of how many consumer/producers are on those channels. This makes > cardinality in pub-sub tricky. As far as cardinality upper bound goes, > what is the difference between a consumer connected to 2 channels each > with 5 producers and the same consumer connected to a single channel > with 10 producers? > > Therefore, for the cardinality upper bound, I don't think it makes > sense to have a "1" restriction. IOW, it should always be "n". > > WRT cardinality lower bound, there are two possibilities "0" or "1". > I'm leaning towards saying it is always "0", since there is no > guarantee that even if you connect the producer/consumer to a channel > that anyone else is participating. But I have a feeling that there > *might* be good reasons to allow a "1" restriction on the lower bound > > Thoughts? > > -Anish > -- > > [1] http://osoa.org/jira/browse/ASSEMBLY-251 > > --------------------------------------------------------------------- > To unsubscribe from this mail list, you must leave the OASIS TC that > generates this mail. Follow this link to all your TCs in OASIS at: > https://www.oasis-open.org/apps/org/workgroup/portal/my_workgroups.php
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