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Compound Goals

 

One of the most powerful features of OAA is the ability of a client agent (or a user) to submit compound goals to a facilitator. A compound goal is composed using operators similar to those employed by PROLOG, that is, the comma for conjunction, the semicolon for disjunction, and the arrow for conditional execution. Three of the several significant extensions to PROLOG syntax and semantics are of particular interest here. First, a ``parallel disjunction'' operator indicates that the disjuncts are to be executed (by different agents) simultaneously. Second, it is possible to specify whether a given subgoal is to be executed breadth-first or depth-first. gif Third, each subgoal of a compound goal can have an address and/or a set of parameters attached to it. Thus, each subgoal takes the form

Address:Goal::Parameters

where both Address and Parameters are optional.

An address, if present, specifies one or more agents to handle the given goal, and may employ several different types of referring expression: unique names, symbolic names, and shorthand names. Every agent has a unique name, assigned by its facilitator, which relies upon network addressing schemes to ensure its global uniqueness. Agents also have self-selected symbolic names (for example, ``mail''), which are not guaranteed to be unique. When an address includes a symbolic name, the facilitator takes this to mean that all agents having that name should be called upon. Shorthand names include `self' and `parent' (which refers to the agent's facilitator). We emphasize that the address associated with a goal or subgoal is always optional. When an address is not present, it is the facilitator's job to supply an appropriate address, as explained in Section 5.5.

The distributed execution of compound goals becomes particularly powerful when used in conjunction with natural language or speech-enabled interfaces, as the query itself may specify how functionality from distinct agents will be combined. As a simple example, the spoken utterance ``Fax it to Bill Smith's manager.'' can be translated into the following compound ICL request:

    oaa_Solve((manager('Bill Smith', M), fax(it,M,[])), [strategy(action)])


next up previous
Next: Refining Service Requests Up: Requesting Services Previous: Requesting Services

Adam Cheyer
Mon Oct 19 17:14:26 PDT 1998