Continuity policy with tweaks per telecon discussion

[David Hull <dmh@tibco.com>]

Description

The properties of a subscription may be mutable via the SubscriptionManager interface.  In this case, the Base Notification specification does not specify the exact nature of the transition in the face of such changes.  In all cases, there will be a time, t₀, during which the initial properties apply, and a time, t₁, after which the new properties apply, but the exact behavior between t₀ and t₁ is left unspecified.

The SubscriptionContinuity policy described here specifies two particular behaviors, and may be extended to describe further variations.  The behaviors specified are:

• Unconstrained: Changing a subscription property is equivalent similar to canceling the existing subscription and creating a new one (except that the SubscriptionManager endpoint remains the same).  Between t₀ and t₁, notifications for the subscription may be produced according to either set of properties, or both, or neither. This may have several effects, for example:
• If a given notification would have been produced according to both sets pf properties, it may be produced twice.
• Between t₀ and t₁, messages produced according to the old properties may be arbitrarily interleaved with those produced according to the new properties.
• Atomic:  Effectively, t₀ = t₁.    Each notification produced will be produced according to either the old properties or the new properties, but not both.  Before t₀, all notifications for the subscription will be produced according to the old properties.  After t₀ (or equivalently, after t₁), all such notifications will be produced according to the new properties.

These rules apply to production.  Absent any constraints placed on delivery, notifications may be dropped, duplicated or reordered in transit, obscuring the effect of this policy.  The constraints of this policy apply per property.  For example, for a given NotificationProducer, changing the ConsumerReference of a subscription might not affect production, while changing the filters of a subscription might well.

Syntax

The SubscriptionContinuity policy has the following pseudo-schema

<SubscriptionContinuityPolicy ...>
	<Continuity property=string>[Unconstrained|Atomic]</Continuity>*
</SubscriptionContinuityPolicy ...>

The value of the property attribute may be one of

"ConsumerReference"
"Filter"
"SubscriptionPolicy"
"AllDefault"

The default value for properties not mentioned is "Unconstrained", unless specified otherwise by a child with property = "default".  A given SubscriptionContinuityPolicy element MUST NOT contain multiple Continuity children with the same property attribute.