DESCRIPTION OF RELATED ART A database of a limited size which continually is having new records added to it will ultimately become full, if steps are not taken to remove obsolete records. It is not always possible to state precisely at which point a record will become obsolete.

One example of this problem would be in a mobile communications system, which supports neither periodic updating from a stationary mobile unit nor detaching when the mobile unit is switched off. There may be inactive records in the database, but these inactive records may or may not be obsolete, as follows: The record for a subscriber located in the database whose mobile unit has been switched off will be inactive and obsolete.

The record for a subscriber located in the database whose mobile unit is switched on but stationary and who does not make or receive any calls will be inactive but not obsolete.

The problem is to find a method of identifying the inactive records that are most likely to be obsolete so that they can be removed from the database.

One known solution is to set a timer on each record and when a timer expires the corresponding record is removed from the database. The timer will be reset each time the record is accessed or updated. A problem with this solution is high processor load due to the maintaining and supervision of many timers. The database is scanned and records are removed even though the database is not at a critical load level.

Other methods are based on FIFO (First In First Out) order, where the oldest record, or the record which has been inactive for the longest period, is removed or overwritten when the database load becomes critical. This solution could lead to load problems-once the database load becomes critical it will always be critical. Data must be ordered, and re-ordered when a record is accessed or updated.

SUMMARY OF THE INVENTION The object of the invention is to find a scheme and arrangement for removing obsolete records in a database of a communications system, particularly in a database handling subscriber data, such as a VDB (visitor database) of a DECT network.

A further object is to avoid the problems as described above.

This is accomplished by a supervision scheme and arrangement, which comprises assigning an upper load limit (ULL) and a lower load limit (LLL) to the database, assigning a minimum active period (MIP) to the records for at least which period they should not be removed, assigning a duration of inactivity indicator (DII) to each record, repeatedly updating the duration of inactivity indicators (DII) for the records so as to indicate the time they have been inactive, and in dependence of reaching the upper load limit (ULL) removing inactive records in order so that records that have been inactive longest are removed first until reaching the lower load limit (LLL) or until only records which have been inactive for a shorter time than the minimum active period (MIP) remain.

Preferably, the duration of inactivity indicator of a record is set to zero initially when it is created and further always when it is accessed in a predetermined way, e. g. by a subscriber. The duration of inactivity indicator is further increased by one when a pre-decided time has passed and if it has not reached its maximum value.

The removing of records is commenced when the upper load limit is reached. A variable DIIn is set to the maximum value of the duration of inactivity indicator. The database is scanned and all records with a duration of inactivity indicator that equals DIIn are removed, whereafter the variable DIIn is decreased by one and the database is scanned again, whereby all records with duration of inactivity indicator that equals the new DIIn are removed. This step continues with successive decrement of DIIn until that the lower load limit is reached or until only records

with a duration of inactivity indicator equal to or lower than the minimum active period remain.

The supervision scheme and arrangement according to the invention remove effectively inactive records that are most likely to be found obsolete when an upper load limit is reached.

The number of records to be removed depends on a lower load limit as well as a minimum inactive period for which at least a record shall remain in the database.

An advantage of the invention is that it is dynamic and hence only removes records when necessary.

A further advantage of the invention is that a certain amount of records are always free for use unless the database is badly dimensioned or the upper load limit is set too close to the maximum database capacity.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention.

Fig. 1 shows database activity and status according to an embodiment of the present invention, Fig. 2 shows schematically the interoperability between the supervision arrangement, the database, a CPU, I/O-ports and other system blocks, respectively, according to the present invention,

Fig. 3 and 4 show a flow chart for initiating the supervision scheme and arrangement according to the present invention, Fig. 5 shows a flow chart for updating the DII of the records in the database, Fig. 6 and 7 show a flow chart for removing inactive records according to the invention.

TERMS AND ABBREVIATIONS DII Duration of inactivity indicator. Preferably, a number in the range (0,15), the value corresponding to a given time period indicating how long time a record in the database has been inactive.

I-time The minimum period for which a record must be inactive before it can be removed from the database.

This value is entered by the operator as a time period (yy mm dd/hh).

Level Supervision level. Defines the length of time between updates in multiples of 3 and 24 hours. It is set per application and defined during startup of the supervision scheme.

LLL Lower load limit. The lower limit for acceptable memory load. When LLL is reached during reset of the database, the reset is stopped.

Lsup Load supervision mechanism. This is used to notify when critical memory load is reached, according to the ULL and LLL values entered by the operator.

MIP Minimum active period. The DII value corresponding to (and calculated from) the I-time.

Scheme 1 Update scheme indicating that the time between subsequent increments of DII will be three hours times the supervision level when DII < 8 and twenty- four-hours times the supervision level when DII > 7.

Scheme 2 Update scheme indicating that the time between subsequent increments of DII will be twenty-four- hours times the supervision level.

T1 Time period. T1 = level * 3 hours T2 Time period. T2 = level * 24 hours Tsup Time supervision mechanism. Tsup (T1) indicates that time supervision will initiate updating of the DII at intervals of T1 and Tsup (T2) indicates that time supervision will initiate updating of the DII at intervals of T2 (preferably at midnight).

ULL Upper load limit. The upper limit for acceptable memory load. When ULL is reached, the reset of the oldest data in the database is initiated.

DETAILED DESCRIPTION OF EMBODIMENTS The present invention proposes a supervision scheme and arrangement for removing inactive records when the database reaches a critical memory load level defined as the upper load limit ULL.

The invention will make it possible to first remove the records which have been inactive for the longest period of time. This will reduce the risk of removing records which are not yet obsolete.

The inventive database supervision scheme and arrangement will be controlled by means of an indicative time field, e. g., of four bits, which will be added to each record in the database.

This will be referred to as the duration of inactivity indicator DII. The DII will preferably be numbered in the range (0,15). A new record will always be assigned a DII = 0. The DII is repeatedly updated, i. e. increased if it does not have reached its maximum value, i. e., 15. When a record is accessed the DII is reset to zero.

Table 1. Record ages for update schemes 1 and 2 at supervision level 1 as defined by the DII. Scheme 1 Scheme 2 DII Record Record Record Record age, age, min. age, max. age, min. max. 0 0 3 hours 0 1 day 1 3 hours 6 hours 1 day 2 days 2 6 hours 9 hours 2 days 3 days 3 9 hours 12 hours 3 days 4 days 4 12 hours 15 hours 4 days 5 days 5 15 hours 18 hours 5 days 6 days 6 18 hours 21 hours 6 days 7 days 7 21 hours 24 hours 7 days 8 days 8 1 day 2 days 8 days 9 days 9 2 days 3 days 9 days 10 days 10 3 days 4 days 10 days 11 days 11 4 days 5 days 11 days 12 days 12 5 days 6 days 12 days 13 days 13 6 days 7 days 13 days 14 days 14 7 days 8 days 14 days 15 days 15 8 days 15 days

The invention may be adapted to suit a wide variety of applications by using different supervision levels. At each level two different update schemes are possible to use; scheme 1 and scheme 2. In table 1 is shown the different DII values and their corresponding record ages for the two schemes at supervision level 1.

Using scheme 2 the DII is updated once a day, preferably during low traffic load, e. g., at night time. Using scheme 1 the DII is updated every third hour until DII = 8, and after that every 24th hour. The maximum data storage periods are 15 days for scheme 2 and 8 days for scheme 1 (records inactive for longer than these periods will keep their maximum DII value and they will always be removed when the database reaches critical memory load level). As the supervision level is increased these updating periods are increased in multiples of these values, e. g. at level 3 the DII's are updated every third day and every ninth hour, respectively, as shown in table 2.

Table 2. Record ages for update schemes 1 and 2 at supervision level 3 as defined by the DII.

Scheme 1 Scheme 2 DII Record Record Record Record age, age, min. age, max. age, min. max. 0 0 9 hours 0 3 days 1 9 hours 18 hours 3 days 6 days 18 hours 27 hours 6 days 9 days 3 27 hours 36 hours 9 days 12 days 4 36 hours 45 hours 12 days 15 days 5 45 hours 54 hours 15 days 18 days 6 54 hours 63 hours 18 days 21 days 7 63 hours 3 days 21 days 24 days 8 3 days 6 days 24 days 27 days 9 6 days 9 days 27 days 30 days 10 9 days 12 days 30 days 33 days 11 12 days 15 days 33 days 36 days 12 15 days 18 days 36 days 39 days 13 18 days 21 days 39 days 42 days 14 21 days 24 days 42 days 45 days 15 24 days 45 days By increasing the DII more frequently when having a low value (< 8) and more seldom when having higher values (> 7) as is the case using scheme 1 it is possible to set a very short MIP (minimum period for which a record has to be inactive before it can be deleted) and still obtaining rather long maximum data storage periods.

The description will in the continuing refer to the values applicable for level 1. The level of the supervision scheme is as already stated defined for the application.

The operator must enter values for the following parameters before activating the supervision scheme and arrangement according to the present invention.

* Upper load limit ULL and lower load limit LLL values, * respectively, which may be stated as percentages of the database capacity or as absolute figures.

MIP value, the DII value corresponding to the minimum period for which a record must be inactive before it can be removed from the database. Preferably, the MIP value is calculated from an entered I-time.

According to the present invention records are removed from the database when the ULL is reached. The records are removed in order with the ones with highest DII values first. The removing continues until the LLL is reached or until only records with DII zu MIP remain.

An example of database activity and status according to the invention is presented in Fig. 1. The upper half of the Figure shows database activity and the lower half the status of the database. Activity is indicated by solid-line arrows and status by dotted-line arrows. The DII values are updated according to scheme 1. For illustrative reasons the ULL is set to five

records and the LLL is set to three records. The I-time is chosen to fifteen hours, giving a MIP value of five.

At the beginning the database 11 contains four records REC 1-4, which have been inactive for different periods of time, i. e., they have different DII values as indicated. A three-hours time period ends, which is detected by the time supervision mechanism Tsup (3). The DII values are updated. After a while a new record is added to the database with a DII value of zero (in accordance with the inventive scheme), which is indicated in the resulting database 12. Another three-hours time period ends. This is detected by Tsup (3) and the DII values are updated. The resulting database 13 with actual DII values are shown.

Particularly, it is noticed that the DII values for REC 1 and 2 have not been increased this far as they exceed 7 and hence, are only increased when a twenty-four-hour time period ends. Still another three-hour time periods ends, after which REC 3 is accessed in a manner that resets the DII value to zero. Later, both a three-hour period and a twenty-four-hour period end at the same time, which independently are detected by the time supervision mechanisms Tsup (3) and Tsup (24). Thus, the DII values of all records REC 1-5 are increased by one as indicated in the resulting database 14. REC 4 is thereupon activated and its DII value is reset. Yet another three hour DII update takes place, after which a database 15 as indicated is obtained. Still another three-hour DII update occurs and a new record is added.

At this point the load supervision mechanism Lsup detects that the current load, six records, exceeds the ULL value, five records, and a reset mechanism is activated. First all records with DII = 15 are removed. In our example, this corresponds to

remove REC 2. At this point the load is compared with LLL and if the load exceeds LLL the records with DII = 14 are removed as long as the current value of DII is higher than the MIP specified, which is the case in our example. However, no records exist with DII = 14, whereby the value is decreased further. At DII = 9 REC 1 is removed, but still the load exceeds the LLL. No more records are to be removed until DII = 5 is reached. This is the same value as the MIP and the reset mechanism is deactivated despite the fact that LLL was not reached. The load of the database is, however, decreased. Records that are removed are shown as crossed out in the database 16.

In Fig. 2 is shown schematically a complete system with the interoperability between the supervision arrangement SA, the database DB, a CPU, I/O-ports and other system blocks, respectively, according to the present invention. The main purposes of the supervision arrangement SA is as already described: * Time supervision * Updating of DII values (increasing and resetting) * Load supervision Removing of records The operator may change parameters, such as, e. g., I-time, supervision level, ULL and LLL, of the supervision scheme through the I/O ports. Alarms may be given to the operator.

In Fig. 3-7 are shown flow charts for implementing the supervision scheme and arrangement according to the present

invention. Fig. 3 and 4 show a flow chart for initiating the supervision scheme, Fig. 5 shows a flow chart for updating the DII values of the records in the database and Fig. 6 and 7 show a flow chart for removing obsolete records, respectively.

In Fig. 3-7 there are several boxes A, B, C and D with reference numerals 118,304,319 and 326, respectively, which are indicating the flow of flow charts covering more than one Figure and page, and hence, not indicating any action. Note also that for clarifying reasons a reference numeral directly preceded by a Figure is written in italic style in the text.

The supervision scheme SS is initiated 101. The administration Adm, i. e., the operator, is asked for values of I-time, level, ULL and LLL, respectively 103. The operator gives the values, which are received by the inventive supervision scheme 105. The scheme checks thereafter the format of the received values and that I-time > 0, level > 0 and ULL > LLL 107. If this is not the case an error is reported to the operator 108, which also is requested to enter new parameter values.

Tl and T2 are calculated as follows 109: * Tl = level * 3 T2 = level * 24 Furthermore, the following parameters are set 109: * No reset = 0 * Status = IDLE * Update = FALSE * Reset = FALSE

The No reset is indicating the number of times the database have been reset by a reset macro 129 of the invention. The status may be set to IDLE or BUSY. It is BUSY when, e. g., the administration is accessing the database and hence other procedures are prevented from being prosecuted. The parameters Update and Reset are set to FALSE when the corresponding macros 121,125,201,133,301 are not running and set to TRUE while they are running.

When the operator enters an I-time, which is less than T2 111 then update scheme 1 will automatically be selected. This is manifested by setting a variable 2timers to TRUE 113. Otherwise the variable 2timers is set to FALSE 112 and scheme 2 will be selected.

The MIP value is calculated from chosen I-time and employed update scheme as follows.

* MIP = INTEGER (I-time/T1) if I-time < T2 113 * MIP = INTEGER (I-time/T2) if I-time > T2 112 The MIP should always be less than 15. If the I-time entered by the operator results in a calculated MIP value greater than 14, the error is reported to the operator, not shown in the Figs.

If a new updating scheme is to be employed all records of the database have to be scanned and their DII value changed according to the new scheme.

The time supervision Tsup, which will initiate the increments of the DII is started and the system Sys is informed. If scheme 1 has been selected both Tsup (T1) and Tsup (T2) are started 115 and if scheme 2 has been selected only Tsup (T2) is started 114.

The load supervision Lsup (ULL) is started 117. This checks continuously the database load and activates the database reset macro 133 when ULL is reached. Furthermore, it handles the checking of the load of the database versus both ULL and LLL during the database reset.

If an indication of Tsup (T1) or Tsup (T2) is received 119,123 a macro Update is started 121,125,201. A variable U is given as input in the update macro 201, whose value is set to zero if Tsup (T1) is indicating and to one if Tsup (T2) is indicating.

The Update macro is shown in Fig. 5. The variable update is set to TRUE 203 and the status is checked 205. If status = BUSY the macro waits 207 until it receives status = IDLE. Then the first record is selected 210. It is checked whether the variable 2timers is set to TRUE 211. If the answer is negative variables (X, Y) are set to (0,14) 212. If the answer is positive the variable U is checked whether it is set to zero 213. If the answer is positive (X, Y) are set to (0,7) 215 and otherwise they are set to (8,14) 214. (X, Y) corresponds to the interval of DII values, which are to be increased. The first record's DII is compared with the interval (X, Y) 217 and if it falls within the interval the DII is increased by one. Then next record is fetched 222 and its DII is increased by one if it falls within the interval. This continues until the last record is reached

221. The variable Update is set to FALSE 223 and the macro is ended 225.

If updating scheme 1 is employed the DII for each record in the database will be increased at three-hour intervals until the record has been inactive for one day. Thereafter it will be increased at twenty-four hour intervals, e. g., at 00: 00, until DII reaches 15.

If updating scheme 2 is employed the DII for each inactive record in the database will be increased at twenty-four-hour intervals, e. g., at 00: 00, for level 1. Once a DII reaches 15 it will not be increased further.

When a new record is to be created or an old one accessed or activated 127 a macro Insert Rec is started. This macro, not shown in the Figs., may be implemented in a known way with one addition that the DII value of added or accessed record is reset or set to zero.

If there is a request to store a new record in the database, which is full, a priority 3 alarm will be raised, which indicates urgency or high priority.

The definition of an active record may differ between database applications. It may not be the case that every access to a record means that it is activated. For instance, in a visitor database of a mobile telecommunications system, a subscriber record may be considered activated only when an action by the subscriber causes the database to be accessed. In this case, the subscriber record would be activated if accessed as a result of

the subscriber making an outgoing call, but would not be activated in this context if accessed as a result of the operator providing the subscriber with a supplementary service.

When the load increases above the ULL the supervision mechanism Lsup (ULL) indicates that the load limit is reached 131. This initiates a macro Reset 133,301, which resets the database according to the flow diagram in Fig. 6 and 7. If status = BUSY 303 the macro is ended 333. This happens when the database is accessed by, e. g., the administration. The database load is always checked after such an access. If the status is IDLE the variable Reset is set to TRUE 305. No reset is increased with one and a variable DIIn, indicating the current value of DII for which records are to be removed, is set to 15 307. The first record is fetched 309 and it is removed 313 if its DII equals current DIIn, i. e., 15 311. Next record is fetched 314 and removed 313 if its DII equals current DIIn 311. This continues until the last record is fetched 315. The database load is checked 317 and if it is lower than LLL 321 the resetting is ended 331,333. Otherwise the DIIn is decreased by one 323 and the DIIn is compared with the MIP value 325. If they do not agree the records are fetched again and all records with DII = DIIn, which now is 14, are removed 309-315. This procedure continues until load < LLL 321, i. e. the reset is successful, or DIIn = MIP 325, i. e., the reset is unsuccessful-the load is not reduced enough.

In the unsuccessful case, if DIIn = MIP 325 and load < ULL 327 then a priority 1 alarm 329 is raised indicating low priority.

If DIIn = MIP 325 and the load is greater than or equal to the ULL 327 then a priority 2 alarm 328 is raised indicating medium

priority. In these cases the operator should take action to adjust either the ULL and/or LLL values or the I-time. The variable Reset is then set to FALSE 331 and the macro is ended 333.

The number of resets No_reset that have taken place is kept and may be reported to the operator on demand 135, along with a report of the current ULL, LLL and I-time values 139. The No reset will then be reset 141.

If the operator sees that there are too many resets taking place then it may be necessary to adjust the ULL, LLL or I-time values or to redimension the database. This may be performed through a macro Keys, not shown in the Figs. The macro may let the administration change parameters such as level, I-time, ULL and LLL. The status is set to BUSY during these changing, thus, preventing other procedures from being run.

The supervision scheme SS may from the operator Adm get a request to end the supervision 155. Consequently the load and time supervision mechanisms are stopped 157,159. The operator is notified success 161 and the inventive supervision scheme is ended 163.

The inventive supervision scheme and arrangement may be employed in a variety of fields such as, e. g., databases handling mobile subscribers, network topology and routing databases.

The invention may in particular be implemented in a database such as an electronic mail box handling electronic mail messages. The invention will prevent the mail box from becoming

full. If mail messages are to be removed, they shall preferably be stored on a storing medium, e. g., a hard disk.

Advantages of the present invention include a dynamic mechanism only removing records when necessary, i. e. when reaching the upper load level, and guarantees of always finding space for a new record provided that the database is accurately dimensioned and that the upper load level is not set too high, i. e. too close to the maximum capacity of the database.

The invention being thus described, it will be obvious that the same may be varied in a plurality of ways. Such variations are not to be regarded as a departure from the scope of the invention. All such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.