Proposed Resolution For Issue #539 (with edits)

Given limitations of what can be displayed in an Excel cell, I'm sending this as the final wording including Peter's edits and our follow-on thread resolving one set of wording.

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The purpose of using a capability is to realize one or more real world effects. At its core, an interaction is “an act” as opposed to “an object” and the result of an interaction is an effect (or a set/series of effects). This effect may be the return of information or the change in the state of entities (known or unknown) that are involved in the interaction. We are careful to distinguish between public actions and private actions; private actions are inherently unknowable by other parties. On the other hand, public actions result in changes to the state, that state being shared between at least those involved in the current execution context and possibly shared by others. Real world effects are, then, couched in terms of changes to this shared state.

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Real World Effect

There is always a particular purpose associated with interacting with a service. Conversely, a service provider (and consumer) often has a priori conditions that apply to its interactions. The service consumer is trying to achieve some result by using the service, as is the service provider. At first sight, such a goal can often be expressed as “trying to get the service to do something”. This is sometimes known as the "real world effect" of using a service. For example, an airline reservation service can be used to learn about available flights and seating and eventually to book travel – the desired real world effects being needed information and eventually a seat on the right flight.

As was discussed in Section 3.1, a real world effect can be the response to a request for information or the change in the state of some defined entities shared by the service participants. In this context, the shared state does not necessarily refer to specific state variables being saved in physical storage but rather represent shared information about the affected entities. So in the example of the airline reservation, the shared state - that there is a seat reserved on a particular flight - represents a common understanding between a future passenger and the airline. The details of actual state changes – whether on the part of the passenger (e.g. fund balances required to pay for the ticket) or of the airline (e.g. that a seat is sold for that flight) - are not shared by the other.

[figure here]

Figure 1 Real World Effect and shared state

In addition, the internal actions that service providers and consumers perform as a result of participation in service interactions are, by definition, private and fundamentally unknowable. By unknowable we mean both that external parties cannot see others’ private actions and, furthermore, SHOULD NOT have explicit knowledge of them. Instead we focus on the set of facts shared by the parties. Actions by service providers and consumers lead to modifications of this shared state; and a real world effect of a service interaction is the accumulation of the changes visible through the shared state.

For example, when an airline has confirmed a seat for a passenger on a flight this represents a fact that both the airline and the passenger share – it is part of their shared state. Thus the real world effect of booking the flight is the modification of this shared state – the creation of the fact of the booking. Flowing from the shared facts, the passenger, the airline, and interested third parties may make inferences – for example, when the passenger arrives at the airport the airline confirms the booking and permits the passenger onto the airplane (subject of course to the passenger meeting the other requirements for traveling).

For the airline to know that the seat is confirmed it will likely require some private action to record the reservation. However, a passenger should not have to know the details of the airline internal procedures. Likewise, the airline does not know if the reservation was made by the passenger or someone acting on the passenger’s behalf. The passenger’s and the airline’s understanding of the reservation is independent of how the airline maintains its records or who initiated the action.

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Shared state

The combination of state information that manifests itself to service participants as a result of interacting with a service.

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