iCalendar “Field” list (for database schema based on iCalendar standard)

Question

my application has to deal with calendar information (incl. single occurrence, recurrence, etc.). In order to easily interface with other applications I thought that it would be a good idea to create my database schema based on the iCalendar format (fields, relationships, constraints) directly so that I get iCalendar compatible objects via ORM that I can easily expose when needed.

I know that the RFC is available but it's kind of complicated because of all the additional information in it that I don't use at the moment.

Could somebody point me to an easier source to create a database schema based on the iCal standard (meaning a list of fields/fieldnames and their relationship for iCal entries)?

Thanks!

Answer 1

I've done this (for VEvents only, not supporting TODO items or Journal entires or anything like that). My implementation looks like this (after removing columns that are not specific to the question):

-- One table for each event.  An event may have multiple rRules.
Create Table [vEvent]
    (vEventID Integer Identity(1, 1) Not Null
     Constraint [vEvent.pk]
     Primary Key
     Clustered
    ,title nVarChar(200) Not Null);

-- One table for rRules.
-- My application does NOT support the "bySetPos" rule, so that is not included.
Create Table [rRule]
    (rRuleID Integer Identity(1, 1) Not Null
     Constraint [rRule.pk]
     Primary Key
     Clustered
    ,vEventID Integer Not Null
     Constraint [fk.vEvent.rRules]
     Foreign Key
     References [vEvent] (vEventID)
     On Update Cascade
     On Delete Cascade
    ,[class]            varChar(  12) Not Null Default('public')
    ,[created]         DateTime       Not Null Default(getUTCDate())
    ,[description]     nVarChar(max)      Null
    ,[dtStart]         DateTime       Not Null
    ,[dtEnd]           DateTime           Null
    ,[duration]         varChar(  20)     Null
    ,[geoLat]          Float              Null
    ,[geoLng]          Float              Null
    ,[lastModified]    DateTime       Not Null Default(getUTCDate())
    ,[location]        nVarChar(max)      Null
    ,[organizerCN]     nVarChar(  50)     Null
    ,[organizerMailTo] nVarChar( 100)     Null
    ,[seq]             Integer        Not Null Default(0)
    ,[status]           varChar(   9) Not Null Default('confirmed')
    ,[summary]         nVarChar(  75)     Null
    ,[transparent]     Bit            Not Null Default(0)
    ,[freq]             varChar(   8) Not Null Default('daily')
    ,[until]           DateTime           Null
    ,[count]           Integer            Null
    ,[interval]        Integer        Not Null Default(1)
    ,[bySecond]         varChar( 170)     Null
    ,[byMinute]         varChar( 170)     Null
    ,[byHour]           varChar(  61)     Null
    ,[byDay]            varChar(  35)     Null
    ,[byMonthDay]       varChar( 200)     Null
    ,[byYearDay]        varChar(3078)     Null
    ,[byWeekNo]         varChar( 353)     Null
    ,[byMonth]          varChar(  29)     Null
    ,[wkSt]             Char   (   2)     Null Default('mo'));

-- Class must be one of "Confidential", "Private", or "Public"
Alter Table [rRule]
Add Constraint [rRule.ck.Class]
Check ([class] In ('confidential', 'private', 'public'));

-- Start date must come before End date
Alter Table [rRule]
Add Constraint [rRule.ck.dtStart]
Check ([dtEnd] Is Null Or [dtStart] <= [dtEnd]);

-- dtEnd and duration may not both be present
Alter Table [rRule]
Add Constraint [rRule.ck.duration]
Check (Not ([dtEnd] Is Not Null And [duration] Is Not Null));

-- Check valid values for [freq]. Note that 'single' is NOT in the RFC;
-- it is an optimization for my particular iCalendar calculation engine.
-- I use it as a clue that this pattern has only a single date (dtStart),
-- and there is no need to perform extra calculations on it.
Alter Table [rRule]
Add Constraint [rRule.ck.freq]
Check ([freq] In
    ('yearly'
    ,'monthly'
    ,'weekly'
    ,'daily'
    ,'hourly'
    ,'minutely'
    ,'secondly'
    ,'single')); -- Single is NOT part of the spec!

-- If there is a latitude, there must be a longitude, and vice versa.
Alter Table [rRule]
Add Constraint [rRule.ck.geo]
Check (([geoLat] Is Null And [geoLng] Is Null)
       Or ([geoLat] Is Not Null And [geoLng] Is Not Null));

-- Interval must be positive.
Alter Table [rRule]
Add Constraint [rRule.ck.interval]
Check ([interval] > 0);

-- Status has a set of defined values.
Alter Table [rRule]
Add Constraint [rRule.ck.status]
Check ([status] In ('cancelled', 'confirmed', 'tentative'));

-- Until and Count may not coexist in the same rule.
Alter Table [rRule]
Add Constraint [rRule.ck.until and count]
Check (Not ([until] Is Not Null And [count] Is Not Null));


-- One table for exceptions to rRules.  In my application, this covers both
-- exDate and rDate.  I do NOT support extended rule logic here;  The RFC says
-- you should support the same sort of date calculations here as are supported
-- in rRules: exceptions can recur, etc.  I don't do that; mine is simply a
-- set of dates that are either "exceptions" (dates which don't appear, even
-- if the rule otherwise says they should) or "extras" (dates which do appear,
-- even if the rule otherwise wouldn't include them).  This has proved
-- sufficient for my application, and something that can be exported into a
-- valid iCalendar file--even if I can't import an iCalendar file that makes
-- use of recurring rules for exceptions to recurring rules.
Create Table [exDate]
    (exDateID Integer Identity(1, 1) Not Null
     Constraint [exDate.pk]
     Primary Key
     Clustered
    ,rRuleID Integer Not Null
     Constraint [fk.rRule.exDates]
     Foreign Key
     References [rRule] (rRuleID)
     On Update Cascade
     On Delete Cascade
    ,[date] DateTime Not Null
    ,[type] varChar(6) Not Null);  -- Type = "exDate" or "rDate" for me; YMMV.

To go along with this, I have several SQL Server 2005+ CLR functions that can be used to calculate the dates for various events. I have found the following forms to be very useful:

Select * From dbo.getDatesByVEventID(@id, @startDate, @endDate)
Select * From dbo.getEventsByDateRange(@startDate, @endDate, @maxCount)

Implementation of the above is darn fun to figure out!

Answer 2

Yes, sort of. Sunbird (the opensource mozilla calendar) is based on sqlite and I just downloaded and unzipped their source code. It has .sql files in it.

ftp://ftp.mozilla.org/pub/mozilla.org/calendar/sunbird/releases/0.9/source/

mozilla\calendar\providers\storage\schema-7.sql --this is the schema that sunbird uses to make valid iCal files, so it can't be too bad.

Answer 3

Thanks so much Chris Nielsen for his great solution above. However, I had some problems with it so I modified it. Please note that the solution above is in python sqlalchemy. I will convert it very soon.

My main difficulties with Chris's solution (and they might not apply to everyone) are

1. I didn't need many of the columns in his solution. I only needed columns which would help me with Events and Recurrences. This is the fault of the iCalendar spec, not Chris's. My solution below only considers recurrence rules in terms of their calendar restrictions and their sequence restrictions.

2. Certain columns -- most importantly dtStart and dtEnd -- belong to VEVENT, not to RRULE, but Chris placed them in RRULE. This was confusing to me. VEVENT: https://tools.ietf.org/html/rfc5545#section-3.6.1 RRULE: https://tools.ietf.org/html/rfc5545#section-3.3.10

3. I also needed to figure out how to contain a schedule which might have a variety of patterns. For example, an event might happen every week on Friday from 6PM-9PM but also all day on May Day. This requires flexibility with dtStart and dtEnd. For this reason, I created a containing Table "SCHEDULE" which maintains a many-to-many relationship with EVENTS, whereas EVENTS have a containment relationship with RRULES.

Below is my solution in sqlalchemy. I will convert this to SQL ASAP.

from app import db
from sqlalchemy import CheckConstraint
from sqlalchemy.ext.associationproxy import association_proxy


class Schedule(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    subtypes_relation = db.relationship('Event', secondary=schedule_event_association,
                                        backref=db.backref('Schedule', lazy='dynamic'))

schedule_event_association = db.Table(
    'schedule_event_association',
    db.Column('schedule_id', db.Integer, db.ForeignKey('schedule.id')),
    db.Column('event_id', db.Integer, db.ForeignKey('event.id')))

class Event(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    dt_start = db.Column(db.DateTime)  # start time
    dt_end = db.Column(db.DateTime) # end time
    tz_id = db.Column(db.String) # Time Zone

    recurrence_rule = db.Column('RecurrenceRule_id',  db.Integer, db.ForeignKey('RecurrenceRule.id'))

# Start date must come before End date
    CheckConstraint('dtEnd is NULL OR dtStart <= dtEnd', name='Valid: Time Period')

class RecurrenceRule(db.Model):
    id = db.Column(db.Integer, primary_key=True)

    # Frequency Type
    freq = db.Column(db.String(8), nullable=False, default='weekly') # type of recurrence

    # Calendar-Based Rules
    byDay = db.Column(db.String(35))   # List of Day of the Week
                                        # "mo,tu,we" for weekly
                                        # "+2MO, -1MO" = second monday, last monday for yearly or monthly
    byMonthDay = db.Column(db.String(200)) # List of Day of the Month
                                            # +1,-1"
                                            # Only for Monthly or Yearly
    byYearDay = db.Column(db.String(3078)) # List Day of the Year
                                            #"+1, -1"
                                            # Only for yearly
                                            # Take care with leap years
    byWeekNo = db.Column(db.String(353)) # Which week of Mon`enter code here`th
                                            # "+5, -3" for fifth and third-to-last
                                            # Only for yearly
    byMonth = db.Column(db.String(29))   # Month of year.

    # Sequence-Based Rules
    until = db.Column(db.DateTime)   # last day of occurence
    count = db.Column(db.Integer)    # number of occurences
    interval = db.Column(db.Integer, nullable=False, default=1) # interval between recurrences
    bysetpos = db.Column(db.String()) # Specifies specific instances of recurrence


# Valid Values
    CheckConstraint(freq in ('yearly', 'monthly', 'weekly', 'daily', 'single'),
                    name='Valid: Frequency Value')
    CheckConstraint(interval > 0, name='Valid: Positive Interval')
    CheckConstraint(byDay is not None and freq in ('daily', 'yearly', 'monthly'))
    CheckConstraint(byWeekNo is not None and freq in ('yearly', 'monthly'))
    CheckConstraint(byYearDay is not None and freq == 'yearly')

# Until and Count may not coexist in the same rule.
    CheckConstraint(not (until is not None and count is not None),
                    name='Valid: Not Both Until and Count')

Answer 4

iCal is an Apple application that follows the standard currently known as Icalendar (the successor to the previous Vcalendar). I think the wikipedia entry has all info you need for your purposes, and in a simple and easy-to-follow format, but, feel free to ask for more guidance if needed!!!

Answer 5

• you can try this docu for apple icalendar. you can replicate the fields directly into database tables. http://developer.apple.com/library/mac/#DOCUMENTATION/AppleApplications/Reference/SyncServicesSchemaRef/Articles/Calendars.html

• if you use java, ical4j provides the glue between the schema and the interface. If you do not use java, the algorithms in the source code for generation of occurrences and structure will provide good help for implementation.