The only temporal information which was available in EMME/2 before Release 6.0 was the current date (i.e. year, month, day) which was displayed on each plot and on each report page. No time-of-day information was available and the date was read only at the beginning of each session, assuming that a single session would never span more than one calendar day.
With Release 6.0, the EMME/2 system has now access to much more precise time information, including year, month, day, hours, minutes and seconds. This information is obtained from the system clock whenever actually needed and it is displayed in the standard format YY-MM-DD hh:mm:ss (e.g. at the very moment I write this sentence it would read 92-10-01 20:42:19). In many cases the seconds are not displayed, since the hours and minutes yield adequate precision.
The most evident use of this new precise time information is to replace the old date information which was used on plots, in reports and in the log book. In addition to this, the standard error messages which are written to the ERRORS file now also include the precise time, which makes analyzing and tracing errors much easier.
But having a more precise notion of time can also be used by the system in a more systematic way, allowing it to perform verifications that would not be possible otherwise. This is achieved by introducing time stamp attributes which are associated with certain data bank elements. These time stamps are used to store the time of certain events associated with the element, such as the time of the last modification. In Release 6.0, time stamps are implemented at the following levels:
By themselves, these time stamps are already very useful to trace the history of the various data bank elements. But their real power derives from the fact that the system can now automatically compare these time stamps to test for inconsistencies and flag them to the user. Such tests are now implemented in the assignments: by comparing the assignment preparation time stamp with the time stamps of the matrices used in the assignment, the system will now detect if the contents of a matrix has been altered between the preparation of an assignment and the actual assignment. Similarly, the system can now assess if more iterations can be performed safely on an existing assignment, or if some of the involved matrices have been used otherwise in the mean time.