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Two sample KBs that demonstrate item and object passing are:

• itempass.kb

• objpass.kb

This chapter also describes the process of cutting and pasting data between two G2 processes.

Exchanging Data Using the G2 to G2 Interface

The G2 to G2 interface is the general facility that permits one G2 to communicate with another. Each of the G2s can send and receive data. This lets you create applications that use distributed information processing on distinct G2s.

To enable communications between two or more G2s, you create a G2-TO-G2-DATA-INTERFACE object on the client G2, which is the G2 making a connection to a remote server G2. This object specifies the protocol to use, along with other useful information about the remote system. This chapter calls such an object a data interface object.

A data interface object acts as a doorway between two G2s. Through the interface object, the KB receives data from a remote G2 and sends data to that remote process. The client G2 requires only one data interface object for the connection, though multiple interface objects can be used in a single KB. The G2 server manages the connection with the client G2 internally and does not create or require a corresponding data interface object.

An active data interface object provides:

• A point-to-point connection, allowing one process to talk to a single other process. A G2 data interface is not designed to broadcast to multiple processes.

• Data service to variables, remote expression evaluation, and remote procedure (RPC) execution.

Two G2s can pass knowledge between each other in these ways:

Type of exchange	Description
Remote data service	A remote server G2 provides a value for a variable, using either another variable or a parameter, or through evaluating an expression on the remote system.
Item passing as a reference only	Passes any KB item as an integer reference, called a network handle.
Value or item passing	Passes any value or item, with some set of its attributes, and optionally also as a reference, to a remote G2 process. The reference passed is an integer network handle.

All data service and value or item passing requires the use of at least one data interface object for each remote G2.

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