EMS Manual

EMS Manual—426909-005
14-1
14 EMS Definitions
This section describes EMS tokens and values associated with event-message
processing, and discusses conventions for their use, focusing on the reference needs
of programmers who must retrieve information from event messages:
For information about writing a program to retrieve event information through a
consumer distributor, see Section 4, Retrieving Event Messages Programmatically.
For a detailed discussion of the EMSGET and EMSGETTKN procedures and the
special-operation tokens that they support, see EMSGET and EMSGETTKN
Procedures on page 15-12.
Event-Message Overview
This overview of terminology and token types builds a base for the definitions of
specific event-message tokens in this section.
Terminology
A process is said to report an event if the process generates:

An event message through the EMS procedures and sends the message to $0
through the WRITEREAD procedure. This is the standard way to report an event.

A text message and sends the message to the collector ($0) through the WRITE
procedure. Before the release of EMS, this was the only way to report events. $0
uses the text message to generate an event message for the reporting process.
A subject of an event message is a token that represents an object that is central to the
event. An event message can have more than one subject but must have at least one.
For example, if a device goes down, the event message that reports the event includes
as an event subject a token that represents the device. The same token might occur in
another event message but not be a subject token.
For information on retrieving subject tokens from event messages, see the description
of the ZEMS-TKN-SUBJECT token in Definitions of EMS Special Token Codes
on
page 14-8.
Like command messages, event messages are based on tokens, and many general
statements apply to both message types. For a discussion of general messages based
on tokens, see the SPI Programming Manual.
Each event message consists of a header and a data portion. In many cases, you can
ignore whether a token is a header token or a data-portion token. You get the value of
Topic Page
Event-Message Overview
14-1
Definitions of Event-Message Tokens 14-3