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SEMI E41-95 © SEM I 1995 7 the recovery action activities as q uickly as possible. The abort comman d terminates the recovery action. 8.2 Exception Condition State Mo d e l — The beha vior required for exception manag em…

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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
SEMI E41-95 © SEMI 19957
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.
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9 POSTED Reporting disabled. NOT POSTED
10 not EXSTATE Default entry into recovery
concurrent state at initial exception
condition creation.
NOTRECOVERING
11 NOTRECOVERING “EXRecover” message received
while in the SET state and accepted.
RECOVERING Initiate requested recovery action
and execute to completion.
12 RECOVERING Recovery action completed. NOTRECOVERING Send “EX Recovery Complete”
message.
13 RECOVERING “EXRecoveryAbort” message
received.
ABORTING-
RECOVERY
Perform the abort procedure to
terminate the recovery action in
progress.
14 ABORTING-RECOVERY Abort procedure is complete. NOTRECOVERING Send “EX Recovery Complete”
message.
CLEARED — The abnormal situation related to the exception condition is either not apparent or not relevant.
SET — The abnormal situation related to the exception condition is apparent and relevant.
The exception agent should generate a collection event each time an exception condition transitions from
CLEARED to SET and another from SET to CLEARED.
NOT POSTED — The latest information on the detected abnormal situation has not yet been reported by the
exception agent. This may be transient on entering the SET state or may be because reporting is disabled. NOT
POSTED is the default state when entering the SET state.
POSTED — The latest information on the detected abnormal situation has been reported by the exception agent to
the decision authority.
Recovery — Recovery is one concurrent subset of EXSTATE. It includes the substates describing the behavior in
relation to exception condition recovery actions.
NOTRECOVERING — In the NOTRECOVERING substate, there is no recovery action in progress directly related
to the exception condition. NOTRECOVERING is the default state when an exception condition is initially created.
Recovery actions may only be initiated when the exception condition is in the SET state.
RECOVERING — A recovery action related to the exception condition is in progress when in the RECOVERING
state.
ABORTINGRECOVERY — In the ABORTINGRECOVERY substate, the abort procedure is performed to
immediately terminate the recovery action. It is the responsibility of the exception agent to cease physical activity as
quickly as possible, having achieved a safe condition.
9 Object Definitions
Exception management defines one standard object, the Exception Condition.
9.1 Exception Condition Object Definition — The exception condition is a persistent object created by the
exception agent. It provides the decision authority with reporting on, access to, and the possibility to direct
resolution of an abnormal situation detected. It also tracks progress of a requested recovery action. The exception
condition is uniquely identified by the EXID attribute.
The object attribute notation used in Table 2 is described in Conventions, Section 5.2.
Table 2 Exception Condition Attributes
Attribute Name Definition Rqmt Access Form
ObjType The object type. Y RO Text:
“EXCEPTION”
ObjID Exception agent unique identifier for the
exception condition.
YROText:
Unique with respect to the exception agent.