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Saving the Date: Exploring Calendar and Scheduling Formats

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Each January, my family picks out a new wall calendar to hang in our kitchen. Its main appeal these days is nostalgic decoration since we no longer use it to write down our appointments or important dates. Like many people, we now rely on electronic calendar and scheduling tools built into personal information manager software applications to manage our appointments.

Rhombic Dodecareuleaux Calendar 2013
Photo by Philip Chapman-Bell courtesy of Flickr

PIM applications, such as Microsoft Outlook or Novell Groupwise or web-based integrated toolsets available through Google and Yahoo, offer suites of related applications that help us stay connected and organized. They often include functionality for email, instant messaging, tasks, contact lists as well as calendars and scheduling among others.

It is their relationship to email formats that first sparked my interest in calendar and scheduling formats. After talking with colleagues both at the Library of Congress, where for example both calendar and email files appear in the recently acquired personal papers of Senator Joseph Lieberman in the Library’s Manuscript Division, and other institutions including the National Archives and Records Administration, I came to discover that the commingling of email, scheduling and other organizational tools through PIM applications are a shared concern for archiving and preservation.

Typically, calendar and scheduling files contain information such as meeting date, location, time and attendees (as well as those that declined the invitation). They may also contain attachments including documents relevant to the meeting topic. Because calendar records are treasure troves of data on how the calendar owner spends his or her time, they have high research value and may fall under records management guidelines.

Perhaps one of the best known calendar formats is iCal, the most recent addition to the Sustainability of Digital Formats website.  iCal, not to be confused with the now-obsolete Apple iCal calendaring application, is short for iCalendar and uses the .ics file extension. It has its early roots in the mid-1990s vCalendar effort lead by the Internet Mail Consortium and was standardized as a format through RFC 2445 by the Internet Engineering Task Force in 1998. The current standard is RFC 5545, published in 2009. iCal files can reflect an appointment, to-do or journal entry.

Calendaring the old school way. Photo by Kelly Lannert courtesy of Flickr

It is this firm footing in international standards that makes iCal successful as a format to exchange calendar and scheduling information between applications or systems. It can be exchanged between several transport protocols including SMTP and HTTP, as well as interactive practices such as through a memory-based clipboard or even drag-and-drop interactions. Some of the applications that use the iCal format include Google Calendar, Yahoo! Calendar, IBM Lotus Notes, Mozilla Thunderbird, Microsoft Outlook and Novell GroupWise.

Because it is designed to be an exchange format, iCalendar files have a well-defined structure where the first line is always “BEGIN:VCALENDAR” and the last line is always “END:VCALENDAR.” In between these bracketing lines is the iCalendar body which specifies the details of the appointment, to-do or journal entry. Typical properties are the time and date, time zone, attendees and organizer just to name a few. Aiding the data exchange is the UTF-8 default character encoding. In addition, applications that support iCal must also read, but are not required to write, US-ASCII.

Accessibility and functionality are the two main reasons why many of us have moved on from the paper calendar to an electronic calendar.  Electronic calendars are accessible online from wherever I am so I don’t have to be standing in front of my kitchen wall calendar to know what’s on the docket for the day. Moreover, the functionality of electronic calendar and scheduling tools with PIM applications makes “penciling in” appointments a thing of the past.  

iCalendar files, for example, can support interactive operations such as requesting, replying to, modifying and canceling meetings or appointments. Through the iCalendar Transport-independent Interoperability Protocol (iTIP) defined in RFC 2446, iCalendar files also can be used to define other calendaring and scheduling operations such as requesting for and replying with free/busy time data across compliant systems.

Additional PIM formats such as hCalendar and cc:Mail are already in the works and will be added to the Sustainability of Digital Formats website in the coming months.


  1. Ah…the paper calendars.
    I am a convert and find the digital calendar (apple) very useful. However, I am not a digital native which may have its downfalls. I am still the type of learner that needs to read it and write it to remember it (or to fully comprehend it). Due to my learning style, I feel as if I have to look at the calendar many times just to remember what I had planned, but what if I were to write it? I just may remember it the first time…but that would defeat the purpose of convenience 😉

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