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| United States Patent |
5,749,074
|
|
Kasso
, et al.
|
May 5, 1998
|
Method and apparatus for representing recurring events
Abstract
A method and apparatus for representing and storing the schedules of
recurring events is provided. The schedules are represented by recurrence
rules generated according to a specific grammar. According to the grammar,
each recurrence rule is composed of one or more recurrence commands. Each
recurrence command corresponds to a cycle and includes a time interval
indicator that specifies the duration of the cycle and a repeat quantity
that determines the number of times the cycle is repeated in the schedule.
Each recurrence command may also include an occurrence list that specifies
at what times during a particular cycle the event occurs. The occurrence
list may specify times in absolute or relative terms. Thus, the grammar
supports recurrence rules for representing the schedule "first and tenth
of every month" as well as the schedule "second Thursday and last Friday
of every month". To represent schedules that terminate before the last
event in the last cycle is completed, a symbol may be inserted into the
occurrence list to distinguish the events that are performed on the last
cycle from the events that are not performed on the last cycle. Complex
schedules that involve cycles repeated within cycles are represented by
multiple-command recurrence rules. The stored recurrence rules may be
parsed to determine when events will occur. The grammar may be applied to
a variety of applications, including calendar programs, video cassette
recorders and home automation devices.
| Inventors:
|
Kasso; Chris S. (Sunnyvale, CA);
Knutson; Martin Arthur (Cupertino, CA);
Tso; Yvonne Yuen-Yee (Milpitas, CA);
Dawson; Frank R. (Keller, TX)
|
| Assignee:
|
Sun Microsystems, Inc. (Mountainview, CA);
International Business Machines Corporation (Armonk, NY)
|
| Appl. No.:
|
395458 |
| Filed:
|
February 27, 1995 |
| Intern'l Class: |
G06F 017/60; G06G 007/52 |
| Field of Search: |
395/201,207,208
364/705.07,705.08
368/1,9,10,243,244,250,251,327
705/1,7,8,9,11
|
References Cited
U.S. Patent Documents
| 5260868 | Nov., 1993 | Gupta et al.
| |
| 5416473 | May., 1995 | Dulaney, III et al. | 340/824.
|
| 5491626 | Feb., 1996 | Williams et al.
| |
Other References
Fresko-Weiss; "Microsoft Adds Scheduling to its E-mail System"; PC
Magazine; v11 n19; p56(1); Nov. 10, 1992; Dialog: File 148, Acc# 06140060.
"Introduction to Schedule+"; The Professional Development Group, Inc.; pp.
14-41; Copyright May, 1993.
Taylor; "Now Up-to-Date, Now Contact Need to Improve Integration";
InfoWorld; v15 n52-1; p81(1); Dec. 27, 1993; Dialog: File 148, Acc#
06783739.
Printout from Schedule+ Help File from Microsoft Windows for Workgroups
Version 3.11; Copyright 1985-1993; Microsoft Corporation.
Gilliland; "Keeping Track of Your Time"; Computer Shopper; v14 n1; p486(2);
Jan., 1994; Dialog: File 275, Acc# 01664633.
Warner; "Controlling Appointments"; CPA Journal; v64 n11; p40(4); Nov.,
1994; Dialog. File 148, Acc# 07584594.
|
Primary Examiner: Weinhardt; Robert A.
Assistant Examiner: Tkacs; Stephen R.
Attorney, Agent or Firm: Blakely Sokoloff Taylor & Zafman
Claims
What is claimed is:
1. A method for representing a schedule of a recurring event in an
electronic device, wherein the schedule includes one or more cycles,
wherein each of said one or more cycles has a length, the method
comprising causing the electronic device to perform the steps of:
a) for each cycle in said schedule, performing the steps of
a1) receiving a first input that specifies a unit of time used to measure
the length of said cycle;
a2) receiving a second input that specifies a number of time units;
a3) generating a time-interval indicator representing the length of said
cycle;
wherein said step of generating said time-interval indicator includes the
steps of
generating a unit-type indicator corresponding to said unit of time;
generating a unit-frequency indicator corresponding to said number of time
units;
a4) generating a repeat-quantity indicator representing how many times said
cycle is repeated in said schedule;
a5) generating a recurrence command to represent said cycle, said
recurrence command including said time-interval indicator and said
repeat-quantity indicator; and
b) constructing a recurrence rule to represent said schedule, wherein said
recurrence rule includes the recurrence command generated for each cycle
of said one or more cycles.
2. The method of claim 1 further comprising the steps of:
invoking an operation at an initial occurrence time;
parsing said recurrence rule to determine subsequent occurrence times; and
invoking said operation at said subsequent occurrence times.
3. The method of claim 1 wherein:
said electronic device is a computer system;
said computer system includes a display device and a storage device;
the method includes the steps of
storing data representing said recurrence rule on said storage device; and
generating on said display device user interface controls for receiving
said first input and said second input from a user.
4. The method of claim 3 wherein:
the method further comprises the steps of
executing a client application in said computer system;
executing a server application in said computer system;
said client application performs said step of generating on said display
device user interface controls;
said client application performs said step of receiving said first input;
said client application performs said step of receiving said second input;
said client application performs said step of constructing said recurrence
rule to represent said schedule;
said client application transmits said recurrence rule to said server
application; and
said server application performs said step of storing data representing
said recurrence rule on said storage device.
5. The method of claim 1 wherein a given cycle of said one or more cycles
includes a plurality of occurrences of said recurring event, wherein said
plurality of occurrences do not occur according to a uniform interval, the
method further comprising the step of:
receiving a third input indicating when said plurality of occurrences occur
during said given cycle; and
wherein said step of generating said recurrence command to represent said
given cycle includes generating an occurrence list representing when said
plurality of occurrences occur.
6. The method of claim 5 wherein said occurrence list represents when at
least one of said plurality of occurrences occurs with an absolute
occurrence specifier.
7. The method of claim 6 wherein said occurrence list includes data
representing a weekday and data representing a relative occurrence of said
weekday within a month.
8. The method of claim 5 wherein said occurrence list represents when at
least one of said plurality of occurrences occurs with a relative
occurrence specifier.
9. The method of claim 1 wherein said step of constructing said recurrence
rule includes placing said recurrence command in an order based on the
length of the cycle represented by said recurrence command for each cycle
of said one or more cycles.
10. The method of claim 1 wherein the cycle is repeated N times during said
schedule, wherein N represents a non-negative integer, wherein said
recurring event takes place on a relative occurrence of a certain weekday
in a month, the method further comprising the steps of:
generating a repeat-quantity indicator representing the value of N; and
generating a relative occurrence specifier that indicates said relative
occurrence of said certain weekday in said month.
11. A method for representing in an electronic device a schedule of a
recurring event, wherein the schedule includes a cycle of a certain
duration, wherein the cycle is repeated N times during the schedule,
wherein N is at least two, wherein during the first N-1 iterations of the
cycle said recurring event occurs at a first set of times and a second set
of times, wherein during the Nth iteration of said cycle said recurring
event occurs at said first set of times but not at said second set of
times, the method comprising the steps of:
generating a time-interval indicator representing said certain duration;
generating a repeat-quantity indicator representing the value of N;
generating an occurrence list including data representing said first set of
times and said second set of times;
inserting at least one symbol into said occurrence list to distinguish
between said first set of times and said second set of times.
12. The method of claim 11 wherein said step of generating said occurrence
list includes generating an occurrence list in which data indicating said
first set of times precedes data indicating said second set of times,
wherein said step of inserting one or more symbols includes inserting one
or more symbols between the data indicating said first set of times and
the data representing said second set of times.
13. An apparatus for storing a representation of a schedule of a recurring
event, the apparatus comprising:
an input device for receiving input representing said schedule;
a processor coupled to said input device, said processor receiving said
input from said input device and generating a recurrence rule based on a
grammar, wherein said recurrence rule represents said schedule of said
recurring event; and
a storage device coupled to said processor, said processor storing data
representing said recurrence rule on said storage device;
wherein said recurrence rule includes one or more recurrence commands,
wherein each recurrence command of said recurrence rule represents a
repeating cycle in said schedule;
wherein said grammar includes rules for constructing time-interval
indicators for representing cycles that repeat every N.sub.1 minutes,
every N.sub.2 days, every N.sub.3 weeks, every N.sub.4 months on a
relative day and week, every N.sub.5 months on an absolute day, every
N.sub.6 years on one or more specific months, and every N.sub.7 years on
one or more specific days of the year, where N.sub.1 -N.sub.7 are each any
natural number.
14. The apparatus of claim 13 wherein said grammar includes rules for
constructing repeat-quantity indicators for representing how many times a
cycle repeats in said schedule.
15. The apparatus of claim 14 wherein said repeat-quantity indicators
comprise a repeat-quantity symbol and a number.
16. The apparatus of claim 13 wherein said grammar includes rules for
constructing occurrence lists, wherein said occurrence lists indicate
times that said recurring event occurs during said repeating cycle.
17. The apparatus of claim 16 wherein said grammar includes rules for
constructing occurrence lists that represent specific hours in a day,
specific weekdays in a week, specific days in a month, specific months in
a year and specific days in a year.
18. The apparatus of claim 16 wherein said grammar includes rules for
constructing occurrence lists that represent relative occurrences of
weekdays in a month.
19. The apparatus of claim 13 wherein said grammar includes rules for
specifying any number of occurrences of said recurring event within a
repeating cycle in said schedule.
20. The apparatus of claim 13 wherein said grammar includes a first rule
for specifying an absolute end time and a second rule for determining an
end time by specifying a number of repetitions of each repeating cycle in
said schedule.
21. A method for representing a schedule of a recurring event in an
electronic device, wherein the schedule includes a plurality of cycles,
wherein each of said plurality of cycles has a length, the method
comprising causing the electronic device to perform the steps of:
a) for each cycle in said schedule, performing the steps of
a1) generating a time-interval indicator representing the length of said
cycle;
a2) generating a recurrence command to represent said cycle, said
recurrence command including said time-interval indicator; and
b) constructing a recurrence rule to represent said schedule, wherein said
recurrence rule includes the recurrence command generated for each cycle
of said plurality of cycles.
22. The method of claim 21 wherein:
said schedule includes a first cycle and a second cycle;
said schedule includes repeating one of said first cycle and said second
cycle within the other of said first cycle and said second cycle;
said first cycle has a duration that does not vary;
said second cycle has a duration that varies based on a selected relative
occurrence;
said step of a1) generating a time-interval indicator includes the steps of
generating a first time-interval representing the length of said first
cycle; and
generating a second time-interval indicator representing the length of said
second cycle;
wherein said step of a2) generating a recurrence command includes
generating a first recurrence command to represent said first cycle; and
generating a second recurrence command to represent said second cycle;
wherein said step of b) constructing a recurrence rule includes
constructing a recurrence rule that includes said first recurrence command
and said second recurrence command.
23. The method of claim 22 wherein said selected relative occurrence is a
relative occurrence of a weekday in a month.
Description
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for generating and
storing data representing recurring calendar events, and more
specifically, to a method and apparatus for representing in a concise,
parsable grammar the timing of events that recur according to complex
timing patterns.
BACKGROUND OF THE INVENTION
Numerous software programs have been developed that allow users to store
schedules of events into a computer. Typically, such programs also
generate visual displays that illustrate the events that will occur during
a specified time period (e.g. calendars). Using such programs, users may,
for example, enter information about events that are scheduled to occur
during a particular month. The software stores the information on a
storage device. At any time thereafter, users may instruct the software to
generate a calendar of the month. When generating the calendar, the
software generates indications of the scheduled events on the appropriate
days of the calendar.
Calendar applications that use a client/server model have been developed.
With such applications, a user interacts with a client application to
enter information about events, including when the events will occur. The
client application transmits data representing the events to a server
application. The server application stores data representing the events.
Subsequently, the client application may transmit data representing a time
period, such as a particular month or year, to the server application. The
server application reads the stored event data, determines which events
are scheduled to occur during the specified time period, and transmits
data representing the appointments that are scheduled to occur during the
specified time period back to the client application. The client
application then generates a calendar of the specified time period along
with visual indications of the events that will occur during the specified
time period.
Some events occur on a regular basis. Rather than require a user to enter
information for each occurrence of a recurring event, most calendar
applications allow the user to specify a first occurrence of the event and
a recurrence interval for the event. For example, a user may have to
attend a certain meeting every Friday at 10:00 am. Rather than enter
information for each occurrence of the meeting, the user can enter
information about the first occurrence of the meeting and an indication
that the meeting takes place on a weekly basis (the "recurrence
interval").
When generating a calendar for a particular time period, calendar
applications that support recurring events must calculate if and when the
event will occur during the particular time period. The calendar
application makes this determination based on the initial occurrence time
and the recurrence interval. Typically, a calendar application makes this
determination when a user requests a calendar display of a particular
period.
Current calendar applications support many typical recurrence intervals.
For example, some current calendar applications allow a user to specify
that an event recurs daily, weekly, monthly, or Monday through Friday.
However, events that recur at less typical intervals may require multiple
entries. For example, to specify an event that occurs every Monday and
Wednesday, a user may have to schedule the event as if it were two weekly
events. That is, the user may have to input a first event entry to
indicate that the event occurs weekly every Monday, and then a second
event entry to indicate that the event occurs weekly every Wednesday.
Events that recur at less regular patterns may be even more difficult to
specify. Consider, for example, an event that occurs on the second Tuesday
and the fourth Friday of every month.
Events that recur at smaller intervals within larger intervals may be
impossible to specify using current calendar applications. For example,
consider an event that occurs every Monday (weekly) of every third month
(monthly). Similarly, consider an event that occurs every hour (hourly) of
every Wednesday (weekly).
It is clearly desirable to provide a mechanism to represent complex
schedules with single event entries. It is further desirable that the
schedules be represented and stored in a concise format to minimize the
storage space required for event schedule information.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a method and apparatus for
representing and storing the schedules of recurring events is provided.
The schedules are represented by recurrence rules generated according to a
grammar. According to the grammar, each recurrence rule is composed of one
or more recurrence commands. Each recurrence command corresponds to a
cycle in a schedule and includes a time interval indicator that specifies
the duration of the cycle and a repeat quantity that specifies the number
of times the cycle is repeated in the schedule.
Each recurrence command may also include an occurrence list that specifies
at what times during a particular cycle the event occurs. The occurrence
list may specify times in absolute or relative terms. For example, the
grammar supports recurrence rules for representing the schedule "first and
tenth of every month" as well as the schedule "second Thursday and last
Friday of every month".
For schedules that terminate before the last event in the last cycle is
completed, a symbol is inserted into the occurrence list to distinguish
the events that are performed on the last cycle from the events that are
not performed on the last cycle. Complex schedules that involve cycles
repeated within cycles are represented by multiple-command recurrence
rules.
The stored recurrence rules may be parsed to determine when events will
occur. The grammar may be applied to a variety of applications, including
calendar programs, video cassette recorders and home automation devices.
By storing complex schedules as concise rules, electronic devices may save
storage space and reduce schedule-related communication traffic.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is illustrated by way of example, and not by way of
limitation, in the figures of the accompanying drawings and in which like
reference numerals refer to similar elements and in which:
FIG. 1 is a block diagram illustrating a computer system upon which an
embodiment of the invention may be implemented;
FIG. 2 is a block diagram illustrating a client/server calendar application
according to one embodiment of the invention;
FIG. 3 illustrates an exemplary user interface for receiving information
about a complex event schedule from a user; and
FIG. 4 illustrates a calendar generated by a calendar application based on
recurrence rules according to an embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A method and apparatus for representing recurring events are described. In
the following description, for the purposes of explanation, numerous
specific details are set forth in order to provide a thorough
understanding of the present invention. It will be apparent, however, to
one skilled in the art that the present invention may be practiced without
these specific details. In other instances, well-known structures and
devices are shown in block diagram form in order to avoid unnecessarily
obscuring the present invention.
Referring to FIG. 1, a computer system 100 upon which an embodiment of the
present invention can be implemented is shown. Computer system 100
comprises a bus or other communication means 101 for communicating
information, and a processing means 102 coupled with bus 101 for
processing information computer system 100 further comprises a random
access memory (RAM) or other dynamic storage device 104 (referred to as
main memory), coupled to bus 101 for storing information and instructions
to be executed by processor 102. Main memory 104 also may be used for
storing temporary variables or other intermediate information during
execution of instructions by processor 102. Computer system 100 also
comprises a read only memory (ROM) and/or other static storage device 106
coupled to bus 101 for storing static information and instructions for
processor 102. Data storage device 107 is coupled to bus 101 for storing
information and instructions.
Furthermore, a data storage device 107 such as a magnetic disk or optical
disk and its corresponding disk drive can be coupled to computer system
100. Computer system 100 can also be coupled via bus 101 to a display
device 121, such as a cathode ray tube (CRT), for displaying information
to a computer user. An alphanumeric input device 122, including
alphanumeric and other keys, is typically coupled to bus 101 for
communicating information and command selections to processor 102. Another
type of user input device is cursor control 123, such as a mouse, a
trackball, or cursor direction keys for communicating direction
information and command selections to processor 102 and for controlling
cursor movement on display 121. This input device typically has two
degrees of freedom in two axes, a first axis (e.g., x) and a second axis
(e.g., y), which allows the device to specify positions in a plane.
In the currently preferred embodiment, computer system 100 is used for
executing a calendar application. Processor 102 executes instructions
stored in memory 104 which implement the calendar application. Execution
of the instructions causes the calendar application to generate user
interface controls on display 121 through which a user can enter
information about recurring events, including the schedules of the
recurring events.
When a user enters the schedule of a recurring event, the calendar
application generates a recurrence rule that represents the schedule. In
the preferred embodiment, recurrence rules are generated according to a
concise, parsable grammar that will be described hereafter. The calendar
application stores data representing the recurrence rules on storage
device 107.
Using the grammar that will be described hereafter, even the schedules of
events that recur according to complicated interval patterns can be
represented with relatively concise recurrence rules. Consequently, by
storing the schedules of events as recurrence rules according to the
grammar, a significant amount of storage space may be saved. Further, in
systems that implement client/server models of calendaring applications,
the event scheduling information is often sent from the client application
to the server application over a network. Therefore, by representing
complex event schedules with concise rules, network traffic associated
with the calendaring applications may be significantly reduced.
GRAMMAR FOR CONSTRUCTING RECURRENCE RULES
In the preferred embodiment of the invention, applications represent the
schedules of recurring events in the form of recurrence rules. A
recurrence rule is made up of one or more recurrence commands. Each
recurrence command corresponds to a cycle within the represented schedule.
Within a recurrence command, the duration of the corresponding cycle is
represented by a time-interval indicator. Time-interval indicators as well
as other components of recurrence commands are described in detail
hereafter.
TIME-INTERVAL INDICATORS
A time-interval includes two components: a unit-type and a unit-frequency.
The unit-type component expresses the granularity of the time-interval.
Table 1 illustrates various unit-types supported in the preferred
embodiment of the invention.
TABLE 1
______________________________________
Unit-type
Symbol Meaning
______________________________________
minuteop M Defines a cycle that repeats on a particular
minute interval.
daily D Defines a cycle that repeats on a daily basis.
weekly W Defines a cycle that repeats on a weekly basis.
monthlybypos
MP Defines a cycle that repeats on a monthly basis
on a relative day and week.
monthlybyday
MD Defines a cycle that repeats on a monthly basis
on an absolute day.
yearlybymonth
YM Defines a cycle that repeats on specific months
of the year.
yearlybyday
YD Defines a cycle that repeats on specific days
of the year.
______________________________________
To indicate a time-interval, each unit-type is combined with a
unit-frequency. In the preferred embodiment, the unit-frequency is
indicated by a number immediately following the unit-type symbol to which
it applies. For example, an interval of two days is represented by the
unit-type "D" followed by the integer "2". The meaning of the
unit-frequency depends on the unit-type. Thus, the 5 in M5 is in minutes
while the 3 in D3 is in days. Other examples of time-interval indicators
are shown in Table 2.
TABLE 2
______________________________________
Time-interval Indicators
Meaning
______________________________________
M5 Repeat every five minutes
D1 Repeat daily
D2 Repeat every other day
D3 Repeat every third day
W1 Repeat weekly
W2 Repeat every other week
W3 Repeat every third week
______________________________________
REPEAT-QUANTITY INDICATORS
In the preferred grammar, every recurrence command within a recurrence rule
begins with a time-interval indicator and ends with a repeat-quantity
indicator. The repeat-quantity indicator specifies the number of times a
recurring cycle occurs (including the first time). In the preferred
embodiment, the repeat-quantity is indicated by a repeat-quantity symbol
(e.g. "#") followed by a number. For example, in the recurrence command
"D2 #5", the "#5" serves as the repeat-quantity indicator. In this
example, the interval indicator "D2" indicates that an event occurs on a
two day cycle and the repeat-quantity indicator "#5" indicates that the
cycle occurs 5 times. In the preferred embodiment of the invention, the
repeat-quantity indicator #0 is used to indicate that a cycle is to be
repeated indefinitely.
CYCLES WITHIN CYCLES
Each recurrence command includes one time-interval indicator. Thus, the
schedules of events that repeat in a single cycle with a uniform interval
are represented by recurrence rules that consist of a single recurrence
command. To represent more complex event schedules, recurrence commands
may be combined to form multiple-command recurrence rules.
Consider, for example, an event that occurs according to the schedule:
A) three occurrences at five minute intervals
B) Repeat (A) five times at two day intervals
C) Repeat (B) five times at six month intervals
This schedule may be represented by the multiple-command recurrence rule:
MP6 #5 D2 #5 M5 #3
This recurrence rule is made up of three recurrence commands: "MP6 #5", "D2
#5" and "M5 #3". As shall be explained below, recurrence commands of
smaller granularity execute first, and then are repeated at cycles
determined by the recurrence commands of larger granularity.
To begin, recurrence rules generate an initial event. The initial event
counts against the repeat-quantity of the recurrence command with the
smallest granularity. In the illustrated grammar, this will always be the
rightmost recurrence command. Thus, after the initial event, the
recurrence command "M5 #3" repeats for only two five-minute cycles. That
is, five minutes after the initial event a second event will be generated.
Five minutes after the second event a third event will be generated. After
the generation of the third event, the recurrence comand "M5 #3" has been
fully executed.
The full execution of a recurrence command counts as one execution of the
next recurrence command in the rule. The next recurrence command in the
rule is the recurrence command that is next with respect to the
granularity of the interval that it specifies. In the present example, the
recurrence command "D2 #5" is the next recurrence command, in terms of
granularity, after "M5 #3". Thus, the full execution of "M5 #3" counts as
one execution of the recurrence rule "D2 #5".
After the full execution of "M5 #3", the cycle specified by the recurrence
command "D2 #5" will be executed. Because "M5 #3" has completely executed,
the two-day cycle defined by "D2 #5" will be repeated four more times. At
the end of each of the four two-day cycles, the "M5 #3" cycle is executed
again.
After the full execution of "D2 #5", the recurrence command "M5 #3" will
have completely executed five times, with two-day intervals between each
of the five complete executions. The full execution of "D2 #5" will count
as one execution of the next recurrence command, "MP6 #5". Therefore, the
six month cycle specified by the recurrence command "MP6 #5" will be
repeated four more times. At the end of each six month cycle, the "D2 #5"
cycle is executed again.
After the full execution of "MP6 #5", the recurrence command "D2 #5" will
have completely executed five times, with six month intervals between each
of the five complete executions. During each of the five executions of the
recurrence command "D2 #5", the recurrence command "M5 #3" will have
completely executed five times, for a total of twenty-five executions.
During each execution of "M5 #3", three events will be generated. Thus,
the total events generated during the execution of the rule "MP6 #5 D2 #5
M5 #3" will be seventy-five (5*5*3) events.
NON-UNIFORM INTERVALS WITHIN CYCLES
As illustrated above, multiple-command rules can be used to represent the
schedules of events that occur at uniform cycles, even where the cycles
themselves are repeated at uniform cycles. However, some events are
repeated at non-uniform intervals within uniform cycles. Consider, for
example, an event that occurs every Monday, Wednesday and Thursday of
every week. Such an event schedule is uniform in that it occurs according
to a weekly cycle. However, within a given week, the event occurs at
intervals that are not uniform.
In the present embodiment of the invention, occurrences that cannot be
expressed by an interval are expressly recited by an occurrence list
inserted between the interval-indicator and the repeat-quantity indicator
of the appropriate recurrence command. For example, the recurrence command
"W1 #0" indicates that an event repeats every week. To indicate that
during every week the event takes place on Monday, Wednesday and Friday,
the occurrence list "MO WE FR" is inserted into the recurrence command to
produce the recurrence command "W1 MO WE FR #0".
The example given above illustrates how an occurrence list can indicate
specific days within a weekly cycle. Occurrence lists may be also used to
indicate specific hours or minutes within a daily cycle, specific weeks,
days or hours within a monthly cycle, and specific months or days within a
yearly cycle.
For example, in the schedule represented by the rule "D2 1200 1600 #5", an
event occurs every other day at 1200 (noon) and 1600 (4:00 p.m.) for a
total of 10 events. The repeat-quantity indicator "#5" controls the number
of times the cycle is repeated. The occurrence list indicates when and how
many times an event occurs during each repeated interval. In the present
example, two events occur during each cycle (one at 1200 and the other at
1600) so a total of ten (2.times.5) events are generated.
OCCURRENCE SPECIFIERS
Occurrence lists indicate specific event occurrences through the use of
absolute occurrence specifiers and/or relative occurrence specifiers.
Absolute occurrence specifiers represent time in absolute terms. For
example, in the rule "D2 1200 1600 #5", "1200" and "1600" respectively
represent noon and 4:00 p.m. in absolute terms. Similarly, in the rule "W1
TU WE FR #5", the occurrence specifiers "TU", "WE" and "FR" represent
Tuesday, Wednesday and Friday in absolute terms, respectively.
In contrast to absolute occurrence specifiers, relative occurrence
specifiers indicate a particular day with reference to the relative
occurrence of the day within a longer time period. For example, relative
occurrence specifiers may be used to indicate the third Friday in a month,
the last Monday in a month, the last day of the month, etc. A relative
occurrence specifier consists of one or more offset indicators followed by
a day identifier. In the preferred embodiment, offset indicators are a
number followed by either a plus symbol or a minus symbol. Offset
indicators followed by a plus symbol represent offsets taken from the
start of the month. Offset indicators followed by a minus symbol represent
offsets taken from the end of the month.
For example, the rule "MP2 1+ 2- FR #3" includes two offset indicators,
"1+" and "2-", followed by "FR", which represents "Friday". The offset
indicator "1+" followed by "FR" represents the first Friday of the month.
The offset indicator "2-" followed by "FR" indicates the second to last
Friday of the month. Therefore, the rule "MP2 1+ 2- FR #3" defines an
event which happens every other month on the first Friday and second to
the last Friday of the month. It generates a total of six events.
EARLY TERMINATION
Often, events that otherwise take place according to a regular schedule
terminate before the final cycle of the schedule is complete. For example,
an event may occur every Monday, Wednesday and Friday for five weeks, but
only occur on the Monday and Wednesday of the sixth week. The rule "W1 MO
WE FR #6" cannot be used to represent the schedule of such an event, since
the rule would erroneously cause an event to be generated on the Friday of
the sixth week.
The grammar used in the present invention employs an end marker symbol
(e.g. "$") to indicate the early termination of a cycle. In the preferred
embodiment, the end marker symbol is inserted after the last occurrence
specifier to be executed during the last iteration of a cycle. In the
present example, the end marker symbol "$" would be placed after the
occurrence specifier "WE" to indicate that the cycle terminates after the
Wednesday of the last weekly cycle. The resulting rule would therefore be
"W1 MO WE$ FR #6". Similarly, the rule "W1 0100$ 0200 0300 #4" generates
events weekly for three weeks at 0100, 0200 and 0300. On the last (fourth
week) an event is generated at 0100 only.
In addition to the end marker symbol, an enddate specifer can also be used
to specify early termination of a rule. An enddate specifier simply
designates a date after which no events will be generated for a rule,
regardless of whether the cycles defined in the rule have been completely
executed by the specified date.
Various aspects of the grammar used by the present invention to represent
the schedule of recurring events have been described above. Specifically,
recurrence commands are used to represent the cycles associated with
recurring events. Each recurrence command includes time-interval indicator
composed of a unit-type and unity-quantity to indicate the interval of a
cyclical schedule. Repeat-quantities indicate how many times a cycle is
repeated.
To represent a schedule that includes one repeat interval within another
repeat interval, a rule may include more than one recurrence command.
Occurrence lists may be used to specify multiple occurrences of an event
within a cycle. Within a recurrence list, specific occurrences may be
represented by absolute occurrence specifiers and/or relative occurrence
specifiers. In addition, a terminating symbol may be used to indicate an
early termination to a repeat pattern.
Table 4 includes the definition of an exemplary grammar that supports the
above-described features. Table 4 uses standard BNF syntax. In the grammar
definition contained in Table 4, terms and symbols have the meanings set
forth in Table 3.
TABLE 3
______________________________________
TERM/SYMBOL MEANING
______________________________________
{} zero or more of the enclosed elements
! zero or one of the enclosed elements
enddate Controls when a repeating event terminates.
The enddate is the last time an event can occur.
unit-frequency
Controls the number of time units in an interval
repeat-quantity
Controls the number of events a rule generates
lastday Can be used as a replacement to daynumber to
indicate the last day of the month. May be used
as an occurrence specifier in MD (monthly-by-
day) cycles.
daynumber A number representing a day of the month.
month A number representing a month of the year.
day A number representing a day of the year
occurrence Controls which week of the month a particular
weekday event occurs.
weekday A symbol representing a day of the week
time The time in hours and minutes using a 24 hour
clock.
daytime Controls which days (and hours) of the week a
weekly event occurs.
weekdaytime Used in monthly events to specify which
weeks, days and times an event occurs.
______________________________________
TABLE 4
______________________________________
start ::= <minuteop> <enddate>! .vertline. <daily>
<enddate>! .vertline. <weekly> <enddate>! .vertline.
<monthlybypos> <enddate>! .vertline. <monthlybyday>
<enddate>! .vertline.
<yearlybymonth> <enddate>! .vertline. <yearlybyday>
<enddate>!
endmarker ::=
$
enddate ::=
ISO 8601 (clause 5.4.1) string(e.g.
19940712T101530Z) in UTC
digits ::= natural numbers
unit-frequency ::=
<digits>
repeat-quantity ::=
#<digits>
lastday ::=
LD
plus ::= +
minus ::= -
daynumber ::=
<1-31><endmarker>! .vertline. <lastday>
daynumberlist ::=
daynumber {<daynumber>}
month ::= <1-12><endmarker>!
monthlist ::=
<month> {<monthlist>}
day ::= <1-366><endmarker>!
daylist ::=
<day> {<daylist>}
occurrence ::=
<1-5><plus><endmarker>! .vertline.
<1-5><minus><endmarker>!
occurrencelist ::=
<occurrence> {<occurrencelist>}
weekday ::=
<SU.vertline.MO.vertline.TU.vertline.WE.vertline.TH.vertline.FR
.vertline.SA><endmarker>!
weekdaylist ::=
<weekday> {<weekdaylist>}
hhmm ::= hours and minutes, where hh specifies two digits
representing hours (00 to 23) and mm specifies two
digits representing minutes (00 to 59).
time ::= <hhmm><endmarker>!
timelist ::=
<time> {<timelist>}
daytime ::=
<weekday> {<timelist>} {<daytime>}
weekdaytime ::=
<occurrencelist> <weekdaylist> {<timelist>}
{<weekdaytime>}
minuteop ::=
M<unit-frequency> repeat-quantity>!
daily ::= D<unit-frequency> <timelist>! <repeat-quantity>!
<minuteop>!
weekly ::= W<unit-frequency> <daytime> repeat-quantity>!
<minuteop>!
monthlybypos ::=
MP<unit-frequency> <weekdaytime>! <repeat-
quantity>!<weekly> .vertline.
<daily> .vertline. <minuteop>!
monthlybyday ::=
MD<unit-frequency> <daynumberlist>! <repeat-
quantity>!<weekly> .vertline.
<daily> .vertline. <minuteop>!
yearlybymonth ::=
YM<unit-frequency> <monthlist>! <repeat-
quantity>!<monthlybyday> .vertline. <monthlybypos> .vertline.
4
<weekly> .vertline.<daily> .vertline.
<minuteop>!
yearlybyday ::=
YD<unit-frequency> <daylist>! <repeat-
quantity>!<monthlybyday> .vertline.
<monthlybypos> .vertline. <weekly> .vertline.<daily>
.vertline. <minuteop>!
______________________________________
To minimize the possibility of inconsistent implementations of the
illustrated grammar, the preferred embodiment of the invention implements
the grammar according to certain policies. The policies followed in the
preferred embodiment are set forth below. However, it should be noted that
these policies as well as the grammar defined in Table 4 are merely
exemplary. The present invention is not limited to any specific grammar
implementation.
POLICIES
In the preferred embodiment of the invention, the grammar defined in Table
4 is implemented according to the following policies:
The repeat-quantity portion of a rule defines the total number of events
the rule generates, including the first event. For example, the rule "MP1
#3 W1 #3" starting on 1/1/94 would generate events on 1/1/94, 1/8, 1/15,
2/5/94, 2/12, 2/19, 3/5/94, 3/12, 3/19.
The repeat-quantity granularity is defined by the interval indicator
immediately preceding the repeat-quantity portion of the rule. For
example, "D1 #5 M15 #4" establishes a repeating event which happens for
five days, four times per day.
Information, not contained in the rule, necessary to determine the next
event time and date is derived from the start time of the initial
occurrence of the event.
If no specific time is indicated in the recurrence rule, the time is
assumed to be the time specified for the first occurrence of the
appointment.
If an end date and a repeat-quantity for the first recurrence command in
the rule are specified in the rule, then the recurring event ceases when
the end date is reached or the number of events indicated in the
repeat-quantity occur, whichever comes first.
If neither a repeat-quantity nor an end date are established for a
recurrence command (e.g. "D3"), then it is assumed that the event occurs
twice. That is "D3" is equivalent to "D3 #2".
If an endmark is used in a second or later recurrence command of a rule,
then the endmark is applied each time that recurrence command is executed
by the previous recurrence command. For example, the rule "YM1 1 6 #1 MD1
7$ 14" generates events on 1/7 1/14 2/7 6/7 6/14 7/7.
Each cycle in a rule may have an associated endmark. Therefore, rules that
define multiple cycles may have more than one endmark. However, any given
cycle may be associated with no more than one endmark. For example, "YM1
1$ 5 7 #3 MD1 7 9$ 11 #5" is a valid rule, but "YM1 1$ 5$ 7 #3" is not.
If an endmark is used on a day of the week which is followed by several
times (TU$ 1200 1300) or an endmark is used on a week occurrence that is
followed by several weekdays (1+$ TU WE), then the repeating event stops
after the last time or week day in the list is executed.
If a rule has an ambiguity with respect to whether it will repeat on a
specific day (12th of the month) vs on a relative day (2nd Friday of the
month), the specific day takes precedence. The only exception to this
policy is the following policy.
If the optional <weekdaytime> information is missing from a <monthlybypos>
unit-type the information is derived from the initial appointment. The
<occurrence> used in the recurring event is a count from the beginning of
the month to the start time and the <weekday> used is the day of the week
the initial appointment is scheduled to occur on. If the <monthlybypos>
unit-type does not list a week day (e.g. SU) in the rule, the week day is
established from the start time. For example, the rule MP1 #3 used in an
appointment with a start date of 7/20/94 (which is the third Wed of the
month) will repeat on 8/17/94 which is the third Wed of the month.
A repeat-quantity of #0 means repeat the cycle forever.
Only the first recurrence command of a multiple-command rule can have a
repeat-quantity of 0. Consequently, the following rules are not allowed:
"YM1 6 #10 MP1 1+ SA #0", "D5 0600 0800 #5 M5 #0".
Using the relative occurrence specifier 5+ (e.g. 5th Friday) or 5- (e.g.
5th from last Friday) in a month that does not contain 5 weeks does not
generate an event and thus does not count against the repeat-quantity. The
same applies to providing a day of the month that does not occur in the
month. For example, the 30th in the month of February.
The next cycle of a higher order rule does not execute until all the events
of a subrule are generated. If the next event of a higher order rule comes
earlier in time than the last event of a subrule, then the missed events
are not generated. In other words, subrules can not interleave events with
other subrules. The rule "D1 0630 0700 #4 M45 #5" results in indeterminate
results because the minute subrule which begins to execute at 0630
generates events beyond 0700 which is when the daily subrule begins
executing again. The rule "MP1 1+1- #3 W2 TU TH #5" is also incorrect.
EXEMPLARY RECURRENCE RULES
The following examples illustrate how particular schedules are represented
according to the exemplary grammar based on the policies described above:
The schedule of an event which occurs hourly for 12 hours (12:00, 1:00, . .
. 10:00, 11:00) may be represented by the recurrence rule "M60 #12".
The schedule of an event which occurs every 5 minutes for 1 hour (1:00,
1:05, 1:10, . . . 1:50, 1:55) may be represented by the recurrence rule
"M5 #12".
The schedule of an event which occurs daily for 5 days may be represented
by the recurrence rule "D1 #5".
The schedule of an event which occurs daily, for 5 days repeating at 10
minute intervals for 1 hour.(e.g. 6/1 at 12:00, 12:10, 12:20, . . . 12:50;
6/2 at 12:00, 12:10, etc.) may be represented by the recurrence rule "D1
#5 M10 #6".
The schedule of an event which occurs every other day, two times may be
represented by the recurrence rule "D2".
The schedule of an event which occurs every other day at 6 a.m., 12 noon
and 3 p.m. for a span of three days (e.g. 6/1/94 at 6, 12 and 3 p.m. and
6/3/94 at 6, 12 and 3 p.m.) may be represented by the recurrence rule "D2
0600 1200 1500 #2".
The schedule of an event which occurs every other day at 6 a.m., 12 noon
and 3 p.m. for a span of 5 days, stopping at noon on the fifth day (e.g.
6/1/94 at 6, 12, and 3, 6/3/94 at 6, 12 and 3 and 6/5/94 at 6 and 12) may
be represented by the recurrence rule "D2 0600 1200$ 1500 #3".
The schedule of an event which occurs weekly at 6 am, repeated every 15
minutes for an hour, for five weeks (e.g. 6:00, 6:15, 6:30, 6:45 on 6/1,
6/8, 6/15, 6/22 and 6/29) may be represented by the recurrence rule "D7
0600 #5 M15 #4".
The schedule of an event which occurs weekly at 6 am, repeats every 15
minutes for an hour, for four weeks stopping at 6 a.m. on the last event
day (e.g. 6:00, 6:15, 6:30, 6:45 on 6/1, 6/8, 6/15 and 6:00 on 6/22) may
be represented by the recurrence rule "D7 0600$ #4 M15 #4".
The schedule of an event which occurs once at 6 am, repeats every 15
minutes for an hour, for 1 week stopping at 6:45 a.m. (e.g. 6:00, 6:15,
6:30, 6:45 on 6/1), may be represented by any one of the recurrence rules
"D7 0600 #1 M15 #4", "D7 #1 M15 #4", and "M15 #4". Note that the latter
two rules require that the start time be defined in initial occurrence
information.
The schedule of an event which occurs weekly for four weeks may be
represented by the recurrence rule "W1 #4".
The schedule of an event which occurs biweekly on Monday and Tuesday for 2
occurrences ending on a Monday may be represented by the recurrence rule
"W2 MO$ TU #2".
The schedule of an event which occurs weekly on Tuesday and Thursday at the
time specified in the first occurrence information and repeated again with
a five minute interval between repetitions may be represented by the
recurrence rule "W1 TU TH #3 M5 #2".
The schedule of an event which occurs weekly on Tuesday at 1200 and 1230
and Thursday at 1130 and 1200 for 10 weeks may be represented by the
recurrence rule "W1 TU 1200 TH 1130 #10 M30". The recurrence rule "W1 TU
1200 1230 TH 1130 1200 #10" may represent the schedule as well.
The schedule of an event which occurs weekly on Tuesday at 1200 and 1230
and Thursday at 1130 and 1200 for 10 weeks stopping on the last Tuesday at
1230 may be represented by the recurrence rule "W1 TU$ 1200 TH 1130 #10
M30". The recurrence rule "W1 TU$ 1200 1230 TH 1130 1200 #10" represents
the schedule as well.
The schedule of an event which occurs weekly on Tuesday at 1200 and 1230
and Thursday at 1130 and 1200 for 10 weeks stopping on the last Tuesday at
1200 may be represented by the recurrence rule "W1 TU 1200$ 1230 TH 1130
1200 #10".
The schedule of an event which occurs monthly for 1 year may be represented
by the recurrence rule "MP1 #12".
The schedule of an event which occurs every other month on the first and
last Friday of the month for 5 months may be represented by the recurrence
rule "MP2 1+1- FR #3".
The schedule of an event which occurs every other month on the first and
last Friday of the month for 5 months stopping on the first Friday in the
fifth month may be represented by the recurrence rule "MP2 1+$ 1- FR #3".
The schedule of an event which occurs every six months on the first Monday
of the month (repeat for 5 days) for 24 months may be represented by the
recurrence rule "MP6 1+ MO #5 D1 #5".
The schedule of an event which occurs every six months on the first Monday
of the month (repeat every other day at 0600, 1200 and 1500 for 20 days)
for 24 months may be represented by the recurrence rule "MP6 1+ MO #5 D2
0600 1200 1500 #10".
The schedule of an event which occurs every six months on the first Monday
of the month (repeat every other day at 0600, 1200 and 1500 for 20 days
(repeat every 5 minutes for 3 times)) for 24 months may be represented by
the recurrence rule "MP6 1+ MO #5 D2 0600 1200 1500 #10 M5 #3".
The schedule of an event which occurs every six months on the first Monday
of the month and the second to last Thursday of the month (repeated five
minutes later) for 24 months may be represented by the recurrence rule
"MP6 1+ MO 2- TH #5 M5 #2".
The schedule of an event which occurs every six months on the first Sunday
and Monday at Noon, the second Tuesday and Wednesday at 1:00 p.m. and the
third Thursday and Friday at 2:00 p.m. may be represented by the
recurrence rule "MP6 1+ SU MO 1200 2+ TU WE 1300 3+ TH FR 1400 #4".
The schedule of an event which occurs every month on the 7th for 12 months
may be represented by the recurrence rule "MD1 7 #12".
The schedule of an event which occurs every month on the 7th, 14th, 21st,
28th for 12 months may be represented by the recurrence rule "MD1 7 14 21
28 #12".
The schedule of an event which occurs every month on the 10th and 20th for
24 months--daily for 5 days at 0600,1200 and 1600--every 15 minutes for an
hour may be represented by the recurrence rule "MD1 10 20 #24 D1 0600 1200
1600 #5 M15 #4".
The schedule of an event which occurs yearly on the 1st, 6th and 12 month
on the first Monday and last Friday of the month may be represented by the
recurrence rule "YM1 1 6 12 #5 MP1 1+ MO 1- FR".
The schedule of an event which occurs every other year on the 6th month (on
the 12th day) for 5 years may be represented by the recurrence rule "YM2 6
#3 MD1 12".
The schedule of an event which occurs yearly on the 7th 14th 21st and 28th
of the 1st 3rd and 8th month and on the 7th and 14th of the 2nd, 4th and
9th months ending on the 4th month, 14th day of the 5th year may be
represented by the recurrence rule "YM1 1 3$ 8 #5 MD1 7 14$ 21 28".
The schedule of an event which occurs yearly on the 6th, 9th and 10th month
on all weekends of the month may be represented by the recurrence rule
"YM1 6 9 10 #10 MP1 1+ 2+ 3+ 4+ 1- SA SU #1".
The schedule of an event which occurs yearly on the 6th month for 10 years,
weekly on Tuesday and Thursday at 1100 and 1300 for 4 weeks may be
represented by the recurrence rule "YM1 6 #10 W1 TU TH 1100 1300 #4".
The schedule of an event which occurs yearly on the 1st, 100th, 200th and
300th day for 4 years may be represented by the recurrence rule "YD1 1 100
200 300 #4".
The schedule of an event which occurs yearly on the 1st-5th days and
100th-104th days may be represented by the recurrence rule "YD1 1 100 #5
D1 #5".
The schedule of an event which occurs yearly on the 1st-5th days and
100th-104th days stopping on 1/2/99 may be represented by the recurrence
rule "YD1 1 100 D1 #5 19990102T000000Z".
Having described the features of the exemplary grammar used to represent
the schedule of recurring events, a calendar application which implements
the grammar shall now be described with reference to FIGS. 2 through 4.
CLIENT/SERVER CALENDARING APPLICATION
Referring to FIG. 2, it illustrates a computer system 200 executing a
calendar application according to a server/client embodiment of the
invention. Computer system 200 includes two computers 214 and 216
connected to communicate over a bus or line 208. Computers 214 and 216 may
be, for example, two stations that belong to the same computer network.
The calendar application executing on computer system 200 includes a server
program 210 and a client program 202. The server program 210 executes on
computer 214, while the client program 202 executes on computer 216. The
server program 210 and the client program 202 communicate with each other
over line 208.
Computer 216 also includes a display screen 204 and a user input device
206. User input device 206 represents any device through which a user may
communicate with a computer.
Client program 202 generates user interface controls on display screen 204
that allow a user to specify information about an event. The user enters
the event information through operation of user input device 206. For
recurring events, the information entered by the user includes an initial
occurrence date and information describing at least one cycle. An
exemplary user interface for receiving event information from a user is
illustrated in FIG. 3.
Referring to FIG. 3, it illustrates user interface controls generated on
display screen 204 according to one embodiment of the invention. The user
interface controls include a pop-up window or dialog box 302 that includes
a plurality of text boxes 304, 306 and 308. Through text boxes 304, 306
and 308, the user enters the name, time and date of an event. For
recurring events, the time and date entered in text boxes 306 and 308 will
be the time and date of the first occurrence of the event. For the
purposes of explanation, it shall be assumed the event at issue is a board
meeting that takes place at 9:00 a.m. on Mondays, Wednesdays and Fridays
every other week.
In addition to text boxes 304, 306 and 308, dialog box 302 includes a
plurality of recurrence command definition mechanisms 310 and 312. Each
recurrence command definition mechanism contains controls for specifying a
recurring cycle. In the illustrated example, recurrence command definition
mechanism 310 includes a check box 330, a repeat-quantity text box 314, a
unit-frequency text box 316, a unit-type selection tool 318, and an
additional parameters text box 334. Similarly, recurrence command
definition mechanism 312 includes a check box 332, a repeat-quantity text
box 320, a unit-frequency text box 322, a unit-type selection tool 324,
and an additional parameters text box 336.
To specify the schedule of a recurring event, a user selects check box 330
to indicate that recurrence command definition mechanism 310 is being used
to specify a cycle for the event named in text box 304 (the "current
event"). If the schedule of the current event involves a cycle within a
cycle, then the user also selects check box 332 to indicate that
recurrence command definition mechanism 312 is being used to specify
second cycle for the current event. In the present example, the current
event occurs at daily intervals (every other day) which themselves occur
at weekly intervals (every other week). Therefore, both check box 330 and
check box 332 are checked.
The user specifies a first recurrence command to represent the daily cycle
by interacting with the controls of recurrence command definition
mechanism 310. Specifically, the user operates unit-type selection tool
318 to select a type of time unit (e.g. minute, hour, day, week, etc.) and
the user enters a number into unit-frequency text box 316 to specify a
unit-frequency value. The combination of the specified unit-frequency
value and the specified unit-type indicates a time-interval for the first
recurrence command. The user enters a number into repeat-quantity text box
314 to specify the repeat-quantity for the first recurrence command. A
user may enter text into the additional parameters text box 334 to specify
further details about the schedule of the event. For example, if the event
will occur at 9:00 and 11:00, then the user may enter the text "900 1100"
into the additional parameters text box 334.
In the present example, the board meeting occurs three times at two day
intervals (Monday, Wednesday and Friday). The two day time interval is
specified by setting unit-type selection tool 318 to "day", and entering
the number "2" into unit-frequency text box 316. The number "3" is entered
into repeat-quantity text box 314 to specify that the meeting takes place
three times a week.
Responsive to the information entered in recurrence command definition
mechanism 310, the client program 202 of the calendar application
generates a first recurrence command. For the purposes of explanation, it
shall be assumed that the calendar application implements the exemplary
grammar illustrated in Table 4. Based on that grammar, the client program
202 generates the recurrence command "D2 #3".
In the present example, the Monday, Wednesday, Friday schedule of the
current event is repeated every other week. Therefore, the rule that
represents the schedule of the current event must indicate that the
Monday, Wednesday, Friday cycle occurs within a larger cycle of two weeks.
The user enters information about this larger cycle by interacting with
the controls of recurrence command definition mechanism 312.
In the present example, the Monday, Wednesday, Friday cycle repeats every
other week. The two week time interval is specified by setting unit-type
selection tool 324 to "week", and entering the number "2" into
unit-frequency text box 322. The number "0" is entered into
repeat-quantity text box 320 to specify that the every-other-week cycle
will repeat indefinitely.
Responsive to the information entered in recurrence command definition
mechanism 312, the client program 202 of the calendar application
generates a second recurrence command. Based on the exemplary grammar, the
client program 202 generates the recurrence command "W2 #0".
According to the exemplary grammar, when a schedule involves a cycle within
a cycle, the recurrence command that corresponds to the longer cycle
precedes the recurrence command that corresponds to the shorter cycle.
Therefore, the rule constructed by client program 202 in the present
example would be "W2 #0 D2 #3".
Referring again to FIG. 2, once client program 202 has generated the rule
data for a particular event, the client program 202 transmits the rule
data along with other data about the event to server program 210 over line
208. The data transmitted along with the rule data includes data
specifying the date and time of the initial occurrence of the event. The
event data may also include other information, such as information about
who may access the event data, if, how and when notification messages are
to be sent to notify a user of the occurrence of an event, etc. Server
program stores the event information, including the rule data, on a
storage device 212.
Once a user has entered information about events, the user may wish to view
a calendar that illustrates when the scheduled events will occur. To
generate such a calendar, the user transmits to client program 202 the
time range for which a calendar is desired. The client program 202
generates a calendar display on display screen 204 that covers the
specified time period. In addition, the client program 202 transmits data
that indicates the specified range to server program 210 over line 208.
When server program 210 receives the time range information, server program
210 reads the event information stored on storage device 212. For each
event that includes a recurrence rule, the server program parses the rule
to determine if and when the event associated with the recurrence rule
will occur during the specified time period. Server program 210 then
transmits to client program 202 data that indicates the events that will
occur during the specified time period. The client program 202 receives
the event data from the server program 210 and generates a visual
indication of the events on the calendar.
If, for example, a user instructs client program 202 to generate a calendar
of October, 1994, the client program 202 would transmit information
indicating the month of October, 1994 to server program 210. Server
program 210 reads the event information stored on storage device 212 to
determine whether any events occur during October, 1994.
In the present example, the initial occurrence of the board meeting event
takes place at 9:00 a.m. on Oct. 10th, 1994. Stored along with this
initial occurrence information is the recurrence rule "W2 #0 D2 #3". By
parsing this rule, the server program 210 determines that, in addition to
the first occurrence, the event will also occur on October 12th, 14th,
24th, 26th and 28th. The server program 210 transmits back to client
program 202 data indicating that the board meeting event will take place
at 9:00 a.m. on the appropriate dates in October, 1994.
Client program 202 receives the event occurrence information from server
program 210 and generates a calendar that includes indications of the
events that will occur during the period covered by the calendar.
Referring to FIG. 4, it illustrates an exemplary calendar 400 generated on
display screen 204 by client program 202. Calendar 400 includes
indications of the board meeting event on the appropriate days.
EVENT NOTIFICATION
In addition to passively responding to requests for event occurrence
information, server program 210 may actively initiate operations based on
the schedules stored on storage device 212. For example, server program
210 may periodically scan the stored recurrence rules to determine when
events are scheduled to occur. When the server program 210 determines that
an event is going to occur, the server program transmits a notification
signal over line 208 to client program 202. In response to the
notification signal, client program 202 generates a visual notification
message on display screen 204 to notify a user that an event is going to
occur. Server program 210 may be configured to generate the signal at the
moment the event is scheduled to occur, or at some point in time relative
to the moment the event is scheduled to occur. For example, server program
210 may generate notification notices one hour or one day before the event
is scheduled to occur.
OTHER APPLICATIONS
The foregoing paragraphs describe a client/server calendaring application
that generates recurrence rules, based on the grammar described herein, to
represent the schedules of recurring events. The described client/server
calendaring application is merely one example of an apparatus that
implements the grammar of the present invention. The grammar may be
implemented in numerous other types of devices. The concise nature of the
recurrence rules constructed using the grammar, coupled with the power of
the grammar to specify complex schedules, makes the grammar ideal for a
variety of applications.
For example, the grammar may be implemented in devices that perform or
invoke operations according to schedules, such as video cassette
recorders. According to one embodiment of the invention, a video cassette
recorder implements the grammar to store rules representing the schedules
of television programs to be recorded. The video cassette recorder
receives input from a user specifying a particular schedule. The video
cassette recorder generates a recurrence rule to represent the schedule
according to the grammar described above. The video cassette recorder
parses the stored rules to determine when to initiate recording
operations. When a rule indicates that a particular program is going to
occur, the video cassette recorder initiates a recording operation.
In many applications, complex schedules are preferable to simple schedules.
For example, burglars may notice if lights are turned on and off at the
same time every day. Human occupancy is better emulated if lights are
turned on and off according to more complex patterns. Therefore, according
to yet another embodiment, home automation devices generate and store
recurrence rules based on the grammar described herein to represent
complex schedules for activating and deactivating appliances, such as
lights.
Other applications of the present invention include the metering of power
or water consumption. In many cases, the rates that apply to power or
water consumption vary based on the time of the day and/or the day of the
week in which the power or water is consumed. Higher rates apply to power
or water consumed during "peak" periods. The device which calculates the
applicable rates may store the relevant rate cycles according to the
grammar described herein.
While specific embodiments of the present invention have been described,
various modifications and substitutions will become apparent to one
skilled in the art by this disclosure. Such modifications and
substitutions are within the scope of the present invention, and are
intended to be covered by the following claims.
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