a new object-oriented model of the gregorian calender

A New Object-Oriented Model of the Gregorian Calendar

Hernán Wilkinson* Mercap Development Manager

Tacuarí 202, 7mo Piso C1071AAF, Buenos Aires, Argentina

54-11-4878-1118 (ext. 120) [email protected]

Máximo Prieto** Lifia œ Facultad de Informática

Universidad Nacional de La Plata cc11, 1900, La Plata, Argentina

+54 221 422-8252 (ext. 215) [email protected]

Luciano Romeo Mercap Software Architect

Tacuarí 202, 7mo Piso C1071AAF, Buenos Aires, Argentina

54-11-4878-1118 [email protected]

* Also Universidad de Buenos Aires, UBA, Argentina ** Also Universidad Nacional de la Patagonia Austral, Unidad Académica Caleta Olivia (UNPA-UACO)

Problem Presentation

n  Time Domain is pervasive n  Cross Cutting n  Related with Financial Domain n  Related with almost every Domain…

n  We concentrated our work on the Gregorian Calendar

Gregorian Calendar n  Main Design Challenges

n  Irregularity n  Months have 28,29, 30 or 31 days n  Leap years n  Associated with natural events (i.e. day/nigth, seasons, earth

movement, etc.) n  Comparing

n  January < July n  January first < February twentyninth n  3 months < 1 year or 5 days < 1 week

n  Distance n  (January distanceTo: July) = (January, 2005 distanceTo: July, 2005)

n  Time line filtering n  workingDays includes: (January first, 2005) n  workingDays from: (April first, 2005) to: (April thirty, 2005) n  14 days from: (April first, 2005) counting: workingDays

Current Models’ Limitations n  Lack of abstractions

n  Smalltalk-80: #Monday < #Friday (It returns false) n  Abstractions not matching reality

n  Squeak: Date dates (There are no days in a date time…) n  Some models have one, or a few, general purpose abstractions

n  aCalendar.set ( Calendar.MONTH, 1) (Does this mean January?) n  Calendar.getInstance () (Are calendar a singleton?)

n  These problems show lack of understanding, they provide a poor domain language, therefore: n  It is difficult to express common situations with them n  They are difficult to learn n  They offer different possible interpretations

n  These problems imply: n  Ad-hoc implementations n  Code duplication n  Error prone situations

Matching Reality R M

April first

01/01/2005

April 2005

01/01/2005

?

? Smalltalk-80

R M

April first

01/01/2005

April 2005

Java / .Net

aCalendar

R M

01/01/2005

April 2005

01/01/2005

Squeak

April 2005

R M

April first

01/01/2005

April 2005

01/01/2005

The Best Solution

April first

April 2005

Our Metaphor

Year 2005

Year 2007

Year 2003 Year Granularity

Jan. 2005 Dec.

2005

Zoom in

July 2005 Month of Year

Granularity

15/07/05 00:00:00

15/07/05 23:59:59

Zoom in

15/07/05 12:00:00 Date Time

Granularity

01/07/05 31/07/05

Zoom in

Date Granularity 15/07/05

Main Abstraction

+< aMagnitude(A)Magnitude

+to:aMagnitude+to:aMagnitude by: aMeasurement+...

IntervalAwareMagnitude

+previous: aMeasurement+next: aMeasurement (A)+distanceTo: aPointInTime (A)+distanceFrom: aPointInTime

PointInTimeprevious: aMeasurement ^self next: aMeasurement negated

distanceFrom: aPointInTime ^aPointInTime distanceTo: self

Year Granularity

+numberOfDays+numberOfDaysInFebruary(A)+isLeap (A)+number+...

GregorianYear

+numberOfDays+numberOfDaysInFebruary+isLeap+...

GregorianLeapYear+numberOfDays+numberOfDaysInFebruary+isLeap+...

GregorianNonLeapYearnumberOfDaysInFebruary ^28 days

isLeap ^false


PointInTime

The programmer should not careabout this implementation desicion

numberOfDays ^366 days

GregorianYear number: 2005.

Y2005

GregorianYear number: 2004.

Y2004

Month of Year Granularity


PointInTime

+month+year+next:aMeasurement+distanceTo:aGregorianMonthOfYear+< aGregorianMonthOfYear+...

GregorianMonthOfYear

y2005 april April, 2005 April of: 2005

April2005

April Y2005

Date Granularity

+year+monthOfYear+day+distanceTo: aGregorianDate+< aGregorianDate+...

GregorianDateBehavior

+next:aMeasurement+...

GregorianDate+calendar-timespan+absoluteDate+next:aMeasurement+...

RelativeGregorianDate

absoluteDate ^calendar next: timespan


PointInTime

April first, 2005

01/04/2005

1 April2005

Date Granularity

+year+monthOfYear+day+distanceTo: aGregorianDate+< aGregorianDate+...

GregorianDateBehavior

+next:aMeasurement+...

GregorianDate+calendar-timespan+absoluteDate+next:aMeasurement+...

RelativeGregorianDate

absoluteDate ^calendar next: timespan


PointInTime 14 days from: (April first, 2005) counting: workingDays

aRelDate

workingDays

01/04/2005

aTimespan

14 days

Date Time Granularity


PointInTime

+date+time+...

GregorianDateTime

(April first, 2005) atNoon

01/04/2005 12:00:00

aDateTime

Recurrent Time Entities

n  Month

+name(A)+numberOfDaysIn: aGregorianYear (A)+...

GregorianMonth

+numberOfDaysIn: aGregorianYear+numberOfDaysFromJanuaryFirst+...

JanuaryGregorianMonth+numberOfDaysIn:aGregorianYear+numberOfDaysFromJanuaryFirst+...

FebruaryGregorianMonth+numberOfDaysIn:aGregorianYear+numberOfDayFromJanuaryFirst+...

NonSpecificGregorianMonth

numberOfDayFromJanuaryFirst ^self zeroDays

numberOfDayIn: aGregorianYear ^aGregorianYear numberOfDaysInFebruary


PointInTime

Programmer should not care aboutthis implementation decision

February January April

Recurrent Time Entities

n  Day of Month n  January first n  December twentyFifth

n  Day of Week n  Monday n  Tuesday

n  Time of Day n  TimeOfDay noon n  TimeOfDay hours: 10 minutes: 11

Time measurements and Their Relevance

+nameBaseUnit

+name+baseUnit

DerivedUnit

-sameDomainAs:aUnitUnitBehavior

January distanceTo: February January, 2005 distanceTo: February, 2005

(GregorianYear number: 2000) distanceTo: (GregorianYear number: 2005)

1 month

5 years year

month

1

5

+amount+unit++ aMeasurement+- aMeasurement+* aMeasurment+/ aMeasurement

Measurement

Measurements

n  Generic Model n  Will be presented at OOPSLA 2005 n  Examples:

n  1 year + 6 months à 18 months n  3 months + 5 days à 3 months + 5 days (A “Bag”) n  5 days + 3 weeks à 26 days n  1 day + 1 hour à 25 hours n  0.10 / 1 year à Yearly Interest Rate of 10 % n  40 km / 1 hour à Speed n  40 km / 1 hour * 2 hours à 80 km

Time Units

year

month

century decade week

day

minute hour

second millisec.

Base Units

Derived Units

n  Gregorian calendar irregularity

Intervals

anInterval

Jan2005

January, 2005 to: November, 2006 by: 2 months

Nov2006

2 month

Collection

SequenceableCollection

+from+to+size+...

MeasurementIntervalInterval

Segments

01/01/2005

15 days

theEndOfTime theBeginningOfTime

-15 days

aTimespan

n  Absolute and Relative

Time Line Filtering Object

+from+duration+to+...

Timespan+setDefinedByRules+includes: aTimepoint (A)+between:and:+negated (A)

TimelineViewBehavior

+includes:anObject+negated

TimelineView+includes:anObject+negated

NegatedTinelineView

14 days from: (April first, 2005) counting: workingDays

aRelDate

workingDays

01/04/2005

aTimespan

14 days

nonWorkDys

Conclusions n  Object model of the Gregorian calendar n  Metaphor: Different resolution points of the time line

n  Total order between time points n  Distance n  Move from one point to another n  Move between points of different resolution

n  Representation of time line segments and intervals n  Generic Measurement Model to reify Time Measurements n  Time line filtering allows Relative points in time n  Abstractions for time entities such as a day, a day of a

month and months.

Future Work

n  Time zone support n  Expand Timespan protocol n  New abstractions like Hour, Minute, etc.

(not units) n  Reify time lines n  Allow relative points of any granularity

Questions

a new object-oriented model of the gregorian calender

Technology