State Transition Diagrams

State transition diagrams (STDs) are another technique to document domain knowledge. In many cases,  information flows from one place to the other and at each place certain action is taken on that piece of  information before it moves to the next place. A file in an office is a typical office is example of such system.  In this case, different people make comments and add information to that file and it moves from one table to the other this movement is controlled by a pre-defined set of rules which define under what condition the file moves from place A to place B and so on. We can easily document these set of rules with the help of state transition diagrams.

Following is an example of a use of STD to document the life cycle of a trouble ticket (this example has been taken from ITU-X.790 document).

A Trouble report and its life cycle – and introduction
From time to time all systems, including communications networks, develop problems or malfunctions  referred to in this Recommendation as “troubles”. A “trouble” in a communications network is a problem that  has an adverse effect on the quality of service perceived by network users. When a trouble is detected,  possibly as a result of an alarm report, a trouble report may be entered by a user or the system may raise a report automatically. Management of that trouble report is necessary to ensure that it receives attention and  that the trouble is cleared to restore the service to its previous level of capability.

At the time of a trouble, a network may have been inter-working with another network to provide a service,  and the problem or malfunction may be due to the other network. Therefore it may be necessary to exchange  trouble management information between management systems across interfaces which may be  client to service provider or service provider to service provider interfaces and may represent inter- jurisdictional as well as intra-jurisdictional boundaries. In addition to exchanging information on trouble that  has already been detected, advance information on service inaccessibility may also need to be exchanged.  Thus, a service provider may need to inform a customer of future service inaccessibility (because of planned   maintenance, for example).

Trouble report states and status
Referring to the State transition diagram in Figure 2, a trouble report may go through any of six states during its life cycle. In addition, a T
rouble Status attribute is defined which qualifies the state (finer granularity) e.g. cleared
awaiting customer verification. The time at which the status attribute change is also
captured in the trouble report
.
Following is a description of states of a trouble report.

Queued
A trouble report is in a queued state when it has been instantiated but the trouble resolution process has not  yet been initiated. A trouble report which is in the queued state may be cancelled by the manager. The agent  on receiving such a request will attempt to close the trouble report.

Open/active
The trouble report becomes “open/active” when appropriate actions to resolve the trouble are initiated. An  “open/active” trouble report may be “referred” to another Hand-off Person, or “transferred” to another  Responsible Person for further processing. The state however remains unchanged as “open/active”. A  trouble report in the open/active state may be cancelled by the manager. The agent on receiving such a  request will attempt to close the trouble report.

Deferred
This state indicates that corrective action to resolve the trouble has been postponed. This can occur when the  faulty resource is inaccessible for a period and repair activity cannot proceed. A deferred  Telecommunications Trouble Report may become “open/active” again, or move directly to the “closed” state  if it is cancelled for some reason. A trouble report in the deferred state may be cancelled by the manager.  The agent on receiving such a request will attempt to close the trouble report.

Cleared
A trouble report is moved by the agent to the “cleared” state when it determines that the trouble has been  resolved. If the manager needs to verify that the trouble has been resolved, verification may optionally be  awaited by the agent prior to closure of the trouble report.

Closed
This state indicates that the trouble resolution process is complete. Upon closure, the trouble report attributes  are captured in a historical event generated at trouble report closure which may then be stored in a  log of trouble history records, for future reference. The trouble report may then be eliminated at the  agent’s convenience. However, the agent may be required to maintain such records for a period of time as  per business agreements.

Disabled
A “disabled” value is exhibited when a trouble report’s information cannot be updated due to local  conditions. In the “disabled” condition only read operations can be performed. The following figure shows  the STD for a trouble ticket. This diagram depicts the movement of a trouble ticket from one state to the  other, thus making it easy to understand.

State Transition Diagram - Click to Enlarge

The next topic will be Arranging Information in Tabular Form.