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SEMI E41-95 © SEM I 1995 6 EX Post is re-sent ev ery time the message or recovery action information changes as long as the exceptio n condition state remains SET . The EX Post notificatio n is not sent if repo rting on …

SEMI E41-95 © SEMI 19955

The term posting is used to describe all reporting the

transition to the SET state and while an exception

condition state is SET.

Clearing is the reporting of the occurrence of an

exception condition state transition to CLEARED. Note

that the exception agent, not the decision authority,

transitions the state to CLEARED. Any

acknowledgment at the decision authority of exception

condition posting (e.g., by the operator) is not relevant

to the exception agent.

Exception condition changes while its state is

CLEARED are not reported to the decision authority.

7.3 Enable/Disable Reporting — The decision

authority may enable and disable posting and clearing

for a particular exception condition by setting and

resetting its enabled attribute, respectively. Reporting

on an exception condition is enabled by default.

Note that the exception condition itself is not being

enabled or disabled, but the reporting of its state is

being enabled or disabled.

Posting of an exception condition shall occur upon

being enabled if the exception condition state is SET.

7.4 Recovery Actions — Recovery actions provide a

mechanism for a decision authority to assist in

resolving an abnormal situation detected in the

equipment. This is generally needed to resolve failure

or conflict where information is required beyond the

capabilities of the system. By supplying options related

to each error condition, error recovery is directed to the

problem area.

One or more recovery actions may be associated with

an error condition. A recovery action is any operation

with the aim of resolving the abnormal situation

detected. It may supply information to the exception

agent or request it to perform some activity.

A recovery action may be requested by the decision

authority only when the error condition state is SET.

Only recovery actions currently valid for the error

condition are accepted by the exception agent.

The list of valid recovery actions is supplied in the

posting of an error condition. Changes in this list are

notified by re-posting. A decision authority may request

any of the supplied recovery actions to be performed

and is notified of acceptance to perform the recovery

and, some time later, its completion. No more than one

recovery action may be in progress on a particular error

condition and it may be aborted by the decision

authority at any time.

A recovery action does not directly change the error

condition state to CLEARED. It performs activities or

provides information with the object of removing the

abnormal situation which in turn changes the state to

CLEARED. A recovery action may continue after the

state has transitioned to CLEARED, until the activity

initiated has completed. A recovery action is rejected if

received when the error condition state is CLEARED.

Since the exception agent must maintain system

integrity by ensuring that incompatible operations are

not performed concurrently, it may reject any recovery

action requested.

8 Behavior

This section provides a high-level definition of the

communications between the decision authority and the

exception agent used in exception management. It does

not define the message detail, concentrating on the

concepts. The message detail is addressed in the

Messaging Services section.

8.1 Exception Condition Communication

8.1.1 Exception Report Messaging — The message

flow for exception reporting is shown in Figure 1. The

arrows represent significant information exchange.

Figure 1

Exception Reporting Message Flow

A detailed description of each message used in

exception reporting follows:

EX Post — The exception agent has detected an

abnormal situation which is monitored by an exception

condition. It changes the exception condition state

attribute to SET. The exception agent notifies the

decision authority using the EX Post notification,

supplying the following information:

• identification of the exception condition,

• type of exception,

• time,

• a message explaining the abnormal situation,

• a list of possible recovery actions (where available

with error conditions).

SEMI E41-95 © SEMI 1995 6

EX Post is re-sent every time the message or recovery

action information changes as long as the exception

condition state remains SET.

The EX Post notification is not sent if reporting on the

exception condition is disabled, that is, if the enabled

attribute is false. The EX Post notification is sent when

an exception condition becomes enabled if the

exception condition state is SET.

Upon receipt of the EX Post, the decision authority has

the information needed to take the appropriate action.

This may include requesting the exception agent to

perform one of the supplied recovery actions.

EX Cleared — The abnormal situation detected by the

exception agent is no longer apparent or relevant. The

exception agent changes the exception condition state

attribute to CLEARED. It notifies the decision authority

using the EX Cleared notification, supplying the

following information:

• identification of the exception condition,

• type of exception,

• time,

• a message.

The EX Cleared message is not sent if reporting on the

exception condition is disabled. That is, the enabled

attribute is false.

Upon receipt of the EX Cleared, the decision authority

knows that the abnormal situation related to the

exception condition is no longer apparent or relevant.

8.1.2 Recovery Action Messaging — In this section,

the extended messaging of the recovery action is added

to the reporting messaging described above. Recovery

actions are not available for alarms. The message flow

for recovery actions is shown in Figure 2.

Figure 2

Recovery Action Message Flow

A detailed description of each message used in recovery

actions follows:

EX Recover — The decision authority requests that the

exception agent perform a recovery action. The

particular recovery action selected is identified in the

EX Recover request together with the related exception

condition identifier. It shall be one of the recovery

actions supplied for the exception condition in the EX

Post notification.

Upon receipt of the EX Recover request and before

acknowledging, the exception agent checks that the

specified recovery action is currently valid. The request

shall be accepted and initiated immediately or rejected

by the exception agent.

The exception agent rejects a recovery action request if

there is already a recovery action in progress on that

exception condition.

EX Recover Acknowledge — The exception agent

responds to the decision authority that the requested

recovery action is accepted or rejected, and if rejected,

supplies text reasons for failure.

Acceptance of a recovery action indicates that the

exception agent has initiated the operation. The

operation continues to completion without further

intervention by the decision authority. The recovery

action may or may not result in the exception condition

state changing to CLEARED and the recovery action

may continue after the state becomes CLEARED.

The exception agent may reject a requested recovery

action for a number of reasons, including:

• unknown recovery for the exception condition,

• recovery currently invalid,

• busy with recovery for this exception condition,

• currently unable to perform the recovery (e.g.,

other conflicting activity or failure).

EX Recovery Complete — The exception agent declares

the recovery action to be complete once it has

completed the associated operation. This message is

also used when a recovery action ends abnormally. The

message indicates whether the operation completed

normally and, if not, supplies text reasons for the

failure.

Note that normal completion of a recovery action does

not indicate that the abnormal situation has been

resolved. That is indicated by the EX Cleared

notification.

EX Recovery Abort — The decision authority may

command the exception agent to abort a recovery action

at any time. The goal of the abort command is to end

the recovery action activities as quickly as possible.

The abort command terminates the recovery action.

8.2 Exception Condition State Model — The behavior

required for exception management is fully specified by

the exception agent (service-provider) behavior. This is

described by the exception agent exception condition

state model. All required decision authority (service-

user) behavior is inferred by this model.

Message flow diagrams presented in the previous

section are useful to show simple situations. The

exception condition state model presented in this

section provides the information necessary to

extrapolate the message flow diagrams for all situations

within the scope of this standard.

The exception condition provides for exception agent

reporting on an abnormal situation in the equipment and

management of a recovery action requested by the

decision authority to resolve the situation. Recovery is

requested in the context of a particular exception

condition so the recovery action behavior forms a part

of the exception condition behavior.

Figure 3 shows the state diagram for an exception

condition. The Harel state model notation used is

described in Conventions, Section 5.1. The

corresponding state transition table is shown in Table 1

on the following page.

Figure 3

Exception Condition State Model

The detailed state definitions follow:

EXSTATE — When created by the exception agent, an

exception condition enters the EXSTATE. It is in this

state as long as it is in existence, irrespective of

association to the decision authority. The exception

condition has two concurrent subsets, which together

fully describe its state. These subsets are Reporting and

Recovery.

The exception condition initializes to the SET state if

the abnormal situation related to the exception

condition is apparent and relevant; otherwise, it

initializes to the CLEARED state.

Reporting — Reporting is one concurrent subset of

EXSTATE. It includes the substates describing whether

the abnormal situation related to the exception

condition is apparent and relevant, and whether the

latest information on the situation has been reported.

Table 1 Exception Condition Transition Table

# Current State Trigger New State Action(s)

1 not EXSTATE The exception agent creates the

exception condition.

EXSTATE

2 not EXSTATE Initial creation and the abnormal

situation is either not apparent or

irrelevant.

CLEARED

3 not EXSTATE Initial creation and the abnormal

situation is both apparent and

relevant.

SET

4 CLEARED The abnormal situation is detected. SET

5 not SET Default entry into SET state. NOT POSTED

6 NOT POSTED Reporting enabled. POSTED Send “EX Post” message.

7 POSTED Change in the list of possible

recovery actions.

POSTED Send “EX Post” message.

8 SET The abnormal situation is either no

longer apparent or has become

irrelevant.

CLEARED Send “EX Cleared” message.