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Versions: 00 01 02 03                                                   
Network Working Group                                 J.  Noerenberg

ietf-draft-calsch-mod-01.txt                           Qualcomm, Inc

Category: INTERNET DRAFT                            Expires: Jan 1998

             Internet Calendar Model Specification

Status of this Memo

This document is an Internet-Draft. Internet-Drafts are working

documents of the Internet Engineering Task Force (IETF), its areas,

and its working groups. Note that other groups may also distribute

working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months.

Internet-Drafts may be updated, replaced, or made obsolete by other

documents at any time. It is not appropriate to use Internet-Drafts as

reference material or to cite them other than as a "working draft" or

"work in progress".

To learn the current status of any Internet-Draft, please check the

1id-abstracts.txt listing contained in the Internet-Drafts Shadow

Directories on ds.internic.net (US East Coast), nic.nordu.net

(Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim).

Distribution of this document is unlimited.


Internet Calendaring and Scheduling protocols require the definition

of objects to encapsulate an event to be scheduled, a calendar on

which the event will be stored, and means for exchanging these objects

across the Internet between calendars on behalf of people for whom the

calendars are meaningful. This document gives an abstract model of the

objects and the protocols necessary to accomplish this kind of

information exchange.  It will establish the context in which other

Calendaring and Scheduling RFCs can be interpreted.  Included are

brief introductions to the other components of Internet calendar

protocols and definitions of nomenclature common to all documents

defining these protocols. Reading this document will enable

implementors and users of Internet Calendaring and Scheduling

protocols to understand the goals and constraints chosen for related


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Table of Contents

1. Document framework                                        3

1.1 Model Specification                                      3

1.2 iCalendar: Core Object Specification                     3

1.3 iTIP: Transport Independent Interoperability Protocol    3

1.4 CAP: Calendar Access Protocol Specification              4

2. Abstract Model                                            5

3. Principal Model Components                                6

3.1 Calendar User                                            6

3.2 Calendar                                                 7

3.3 Calendar User Agent (CUA)                                8

3.4 Calendar Service                                         8

3.5 Calendar Domain                                          9

3.6 Calendar Access Protocol (CAP)                           9

3.7 Transport Independent Interoperability Protocol (iTIP)       9

4. Calendar Object Transport                                10

4.1 Direct Access                                           11

4.2 Calendar Service Mediation                              11

4.3 Interdomain Exchange                                    12

5. Security considerations                                  12

6. References                                               13

7. Acknowledgments                                          14

8. Author's address                                         14

9. Appendix -- Calendar protocol nomenclature               15

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The Internet Calendar Model specification provides a framework for the

set of protocols that define Calendaring and scheduling for the

Internet.  The protocols specify the contents of calendars, and how

the objects stored on calendars are represented during transmission

across the Internet.  These protocols also define the interaction

between a calendar user agent and a calendar store, as well as the

actions performed by calendar transfer agents that facilitate

communication between calendar stores.  These terms will be defined

more precisely in the section on nomenclature below.  The protocols

are the:

"Core Object Specification" [iCalendar]

"iCalendar Interoperability Protocol" [iTIP]

"Calendar Access Protocol" [CAP]

1. Document framework Calendar and Scheduling Protocols are contained

in a series of related documents. This section describes the

relationship between the documents.  Section 2 presents the abstract

model for Internet Calendaring and Scheduling.

Following sections amplify the principal concepts defined in the

abstract model, provide a schematic representation of information flow

in Internet Calendaring and Scheduling, and supply other, useful

background information.

1.1 Model Specification This document - see abstract and introduction


1.2 iCalendar: Core Object Specification The Core Object Specification

is the authoritative definition of all properties that may be used in

the Internet Calendar and Scheduling Protocols as well as the rules

for encoding and representing the objects that are constructed from

those properties. iCalendar also specifies the method to be used to

define new attributes.

1.3 iTIP: Transport Independent Interoperability Protocol This

document specifies how calendaring systems use iCalendar objects to

interoperate with other calendar systems.  It does so in a general way

so as to allow multiple methods of communication between systems.

Binding of iTIP to a real-time protocol This document specifies a

session-layer iTIP protocol.  Multiple bindings are possible. This WG

will specify and foster implementation of at least one binding.

Binding of iTIP to E-mail This document specifies an iTIP protocol

over Internet e-mail using MIME. Internet e-mail protocols are given

by RFCs 821, 822, 2045-2049 [RFC-821] [RFC-822] [RFC- 2045] [RFC-2046]

[RFC-2047]. [RFC-2048] [RFC-2049].  See the references for details for

constructing Internet e-mail messages.

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1.4 CAP: Calendar Access Protocol Specification This document

specifies how a Calendar User Agent (CUA) will interact with a

Calendar Service using iCalendar objects.

A graphical representation of the relationship between the documents

is shown below:


                       | Model Document   |






                       |    iCalendar     |






              |                                   |

      ------------------                 ------------------

     |      iTIP        |               |        CAP       |

      ------------------                 ------------------



      |               |

 ----------      -----------

| session  |    |   email   |

|   iTIP   |    |    iTIP   |

 ----------      -----------

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2. Abstract Model

A CALENDAR is a collection of logically related OBJECTs.



Each OBJECT is described using a set of OBJECT ATTRIBUTES such as

date&time, attendees, resources and statuses.

The complete set of OBJECT ATTRIBUTES and their representation is

defined in [iCalendar].

A specific CALENDAR has a unique CALENDAR IDENTIFIER (CI).

A CALENDAR USER (CU) views and modifies a CALENDAR using a CALENDAR

USER AGENT (CUA).  Via a CUA a CU can modify a CALENDAR by adding or

modifying OBJECTs stored in the CALENDAR.  A CUA uses the services of


publish changes to a CALENDAR.  A CS also delivers messages containing

OBJECTs from other CALENDAR USERs via CAP, or via the iCalendar

Transport-Independent Interoperability Protocol, iTIP.

A CS stores a set of CALENDARs which are accessible according to

ACCESS RULES maintained by the CS.  CAP enables the CUA and CS to

request access to CALENDARs according to the ACCESS RULES.  CAP also

enables a CUA and CS to modify the current ACCESS RULES for particular

CALENDAR USERs and particular CALENDARs.

iTIP supports the exchange of OBJECTs without the use of ACCESS RULES.

It enables the exchange of objects between CSs, as well as between

CUAs and CSs.  A set of CSs may cooperate in a CALENDAR DOMAIN.  A

CALENDAR DOMAIN appears to be a single CS through iTIP, from the point

of view of another CS.

A minimal INTERNET CALENDAR SYSTEM comprises a CUA, a CS and the

services of CAP and iTIP, all of which which may, or may not, be

integrated together in a given implementation.

NOTE: It is not required that interacting CUA, CS, CAP and iTIP

entities be matched implementations, though it is required that all

implementations must comply with the specified CAP and iTIP.

A CS is responsible for locating the appropriate CALENDAR DOMAIN for

CIs specified in OBJECTs to be transmitted between CALENDAR DOMAINS. A

CUA is also required to locate the appropriate CALENDAR DOMAIN in

order to use iTIP.  When OBJECTs are transmitted, they are


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CPDUs are MIME encoded objects that specify a requested action and/or

response and carry associated data.  Thus, the format of all

information exchanged among CALENDAR SYSTEM ENTITIES is defined in


BODY PART CONTENT.  CONTENT is defined in terms of iCalendar.

The complete set of CPDUs and the corresponding finite state machine

for unauthenticated exchange make up iTIP.  iTIP is defined in

[iTIP1], [iTIP2], and [iTIP3].  iTIP is capable of using a variety of

transport mechanisms including INTERNET MAIL ([RFC821], [RFC822]),

HTTP, [RFC2091], as well as session-layer protocols derived directly

from iTIP.

ACCESS RULES and the cooresponding finite state machine for

authenticated exchange make up CAP.  CAP is defined in [CAP].

3. Principal Model Components

There are several principal components in a Calendaring and Scheduling

system. Their relationship can be seen in Figure 2 below.  This

section identifies some of the salient features of the components. The

syntax and semantics for creating and transmitting these objects are

completely specified in [iCalendar], [CAP], and [iTIP].

3.1 Calendar User

A calendar user interprets objects on a calendar, creates them, and

exchanges them with other calendar users.  A calendar user may be a

person (Ken Caminiti), a group of people (the the San Diego Padres

baseball club), or a resource (Qualcomm Stadium). From the point of

view of other calendar users, groups and resources appear as a single

Calendar user, regardless of their composition in the physical world.

Calendar users that are resources generally contain properties that

identify them as inanimate objects -- anything from a fruit bowl to

rubber bats to settle disputes during a meeting.

A calendar user owns his own calendar, and can manipulate objects

stored there via a CUA.  Access control attributes condition access to

calendars and their components and properties.

A calendar user can also manipulate the contents of other calendar

users' calendars by sending messages containing calendar objects to

them.  For example, The San Diego Padres sends calendar events for the

1997 season to Ken Caminiti, so he knows when to show up at the

ballpark.  The Padres sends calendar events for games to be played at

home to the Qualcomm Stadium calendar so the concessionaires can order

hot dogs.

A calendar user can also organize and own events.  When a calendar

user creates an event object, that user becomes the organizer and the

owner.  The organizer can delegate ownership and the role of organizer

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to others.  Only organizers and owners may alter any attribute of an

event object.  Calendar users assigned other Attendees roles may not

change event attributes.

3.2 Calendar

3.2.1 Collection of objects

Calendar users own calendars.  This is a one to many relationship.  A

single calendar user may have multiple calendars.  However, each

calendar must have a unique identifier.  A calendar is an information

store containing information about events,to-dos, alarms, journals and

free time, the objects stored in it.  Also stored in a calendar are

properties that are global to all of the objects in the calendar.  An

example of a global property is the GEO property that identifies the

physical location where the calendar user can be found. Global

properties such as this establish the context used to interpret the

objects stored in the calendar.  The principal structural features of

a calendar are described below in section 3.2.3.  When objects or

properties of a calendar are exchanged between actors in a calendaring

and scheduling network (Calendar User Agents and Calendar Services),

they are expressed in the form defined in [iCalendar].  Figure 1 below

is a schematic representation of a calendar.

3.2.2 Properties

Properties are attributes of an object or a calendar.  They consist of

a name and a value.  Properties are strongly typed.  Some properties

are multivalued.  A property may have parameters that distinguish

between related properties.  Some properties may occur multiple times

in the same object instance, and may be gathered into a logical group.

Some properties may be unique to a particular calendar or object.

3.2.3 Objects

Objects are collections of property values.  A particular set of

values for the properties of a object define a particular object.

Some objects may contain certain other objects.  The set of objects in

a calendar are identified below. Events

Event objects are defined for specific starting date-time, have a

duration on a calendar, and a description.  Other properties of an

event may specify a location or other attributes that define the

event, such as resources that are part of the event.  Events may also

contain an Alarm object. To-do

While like an event, a To-do doesn't reserve a specific block of time

on a calendar.  A To- do component must have a starting date-time that

identifies its first appearance on the calendar.  It must also have a

date-time that specifies when the To-do expires.  A To-do must have a

description.  It may also contain an alarm object.

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An alarm object may occur in an Event or To-do.  It contains a

date-time. When present, and the date-time is passed, it will cause a

CUA or CS to notify the user the date-time has passed. Journal

A journal object is a textual item that is associated with a

particular date. As its name suggests, its purpose is to record

information meaningful about the date, but not necessarily tied to

other calendar objects on a calendar. Timezone

Timezone objects encapsulate rules for calculating local time from

UTC. Including this object in an event object enables a receiver to

calculate the universal time value for time values expressed in the

sender's local time. This object is especially useful for expressing

recurring events whose instances span a change in the time reference

such as the transition between Standard time and Daylight Savings

time.  Time values expressed in local time are always interpreted in

the receiver's local time.  The sender must provide another context

using UTC values and Timezone objects if this is not the

interpretation intended by the sender.




  |         |            |           |            |           |

to-do     event       journal    freebusy     timezone    property...



    |              |

property...      alarm



Figure 1: Calendar Object Model

3.3 Calendar User Agent (CUA)

A CUA mediates the interactions between a calendar user and his

calendar.  It represents the information stored in the calendar to the

user, and enables the user to manipulate it. This is a particular

instance of the interactive process used by a calendar user.

3.4 Calendar Service

A Calendar Service (CS) stores a collection of calendars and interacts

with the Calendar User Agent (CUA) via the Calendar Access Protocol


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3.5 Calendar Domain

A collection of calendars that can be grouped together constitutes a

Calendar Domain. The relation used to bound the group is arbitrary.

Frequently membership in an organization will be used to define the

domain, but it could be a shared Internet address domain, as well.  A

Calendar Domain provides a contiguous address space for all the

calendars, CTAs and CUAs contained in the domain.  It must be possible

for any Calendar User (via the facilities of a CUA and/or CTA) to

determine whether they are members of a particular domain, or if other

Calendar Users are members.  CTAs and CUAs can take advantage of

domain information when routing event messages.

3.6 Calendar Access Protocol (CAP)

When calendar users need to manipulate calendars that are not stored

on the same computer where the CUA executes, the CUA will use the

Calendar Access Protocol to exchange objects with the Calendar Service

(CS). CAP specifies the beginning and ending of the session between

the CUA and the CS.  Using CAP, the CUA will mediate authentication of

the user to the service.  CAP requires calendar objects and calendar

properties to be expressed in the on-the-wire data format defined in

[CalObjSpec]. A CUA must not be required to maintain a connection to a

CS via CAP in order to display a Calendar for a Calendar User or

accept commands from a user to change a Calendar's content.  By using

CAP a CUA need not have specific information on how a particular CS

stores a Calendar and vice versa. This enables specification and

exchange of objects and properties independently of Calendar storage

models adopted by particular CUAs or CSs.

3.7 Transport Independent Interoperability Protocol (iTIP)

CSs in a domain or across domains exchange objects and properties

using iTIP. Like CAP, iTIP uses iCalendar formats to represent objects

and properties. iTIP defines the beginning and ending of the exchange

session, as well the users for whom the messages are intended.  iTIP

permits unauthenticated delivery of objects and properties to a CS.  A

CS may accept or reject delivery without interaction with a user.  But

a CS may require further confirmation of receipt of a object or

property before it is acted upon by the CS.

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4. Calendar Object Transport

There are several transport modes in this architecture.  The figures

below illustrate the different modes that are allowed.  Three modes

are required to handled the different kinds of calendar exchanges

across the Internet, person to person, group interactions local to a

particular network, and exchanges across networks.

 ------------                  ------------

| CUA  | rcvr| -----      ----|rcvr|  CUA  |

|       -----|      \   /     |----        |

|            |       \ /      |            |

|            |        X       |            |

|            |       / \      |            |

|       -----|      /   \     |----        |

|      | sndr| -----      ----|sndr|       |

 ------------       \    /     ------------


Figure 2: Direct Access

 ------------                  ------------

| CUA        |                |       CUA  |

|            |                |            |

|            |                |            |

 ------------                  ------------

        \                          /

         \   ------- CAP -------  /

          \                      /

           \   --------------   /

            \ |      CS      | /

              |              |

              |              |


Figure 3: Calendar Service Mediation

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 -----------------                     ------------------

|                 |                   |                  |

| Calendar Domain |                   | Calendar Domain  |

|                 |                   |                  |

|                 |                   |                  |

|  -------        |                   |                  |

| |  CUA  |       |                   |                  |

|  -------        |                   |                  |

|     |           |                   |                  |

|     | -- CAP    |                   |                  |

|     |           |                   |                  |

|  ------------   |                   |---------         |

| | CS   | rcvr|----------     -------|rcvr|    |        |

| |       -----|  |       \   /       |----     |        |

| |            |  |        \ /        | Gateway |        |

| |            |  |         X         |         |        |

| |            |  |        / \        |         |        |

| |       -----|  |       /   \       |----     |        |

| |      | sndr| ---------      ------|sndr|    |        |

|  ------------   |       \    /      |---------         |

|                 |        iTIP       |                  |

|                 |                   |                  |

 -----------------                     ------------------

 Figure 4: Interdomain Exchange

4.1 Direct Access

For direct access, two calendar user agents (CUA) exchange calendar

components by using iTIP.  Each CUA provides an iTIP sender and

receiver.  As is generally the case, the methods used by the CUA to

store calendar data locally are not relevant to the transport model.

For this mode, calendar users must be uniquely identifiable across the

Internet, and access to CUAs must conform with privacy and security

considerations.  Because the transport itself is not authenticated, it

is crucial the objects themselves be capable of carrying

authentication information.

4.2 Calendar Service Mediation

Using Calendar Service Mediation a CUA interoperates with a Calendar

Service (CS) using CAP to exchange calendar components.  The CS takes

responsibility for mediating receipt and delivery of components with

other collaborating CUAs.  The principal difference between this mode

and Interdomain Exchange is that CSs do not need to use iTIP to

facilitate exchange of components.  A consequence of this mode is that

CUAs and CSs need not use addresses that are unique across the

Internet.  However, consistency with other modes makes a consistent

address model an obvious simplification for implementors.  Moreover,

because CAP access provides authentication, objects exchanged through

a CAP channel need not carry authenication information.

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4.3 Interdomain Exchange

With Interdomain Exchange a Calendar Service (CS) supporting a group

of users in one domain can exchange calendar components with a

different calendar domain. Domains may or may not be within the same

Internet network domain.  Like Direct Access, iTIP is the vehicle

which permits component exchange.  In the figure, one domain is

illustrated with a Calendar Service providing iTIP service.  The 2nd

domain in this figure has a distinct iTIP sender and receiver.  In

order to provide end-to-end privacy components must be wrapped in a

cryptographically secure wrapper to insure only the intended

corespondents can interpret the components.  This wrapper is not

required unless privacy must be assured.  In order to provide backward

compatibility with existing calendar and scheduling systems, a privacy

wrapper cannot be a required aspect of the component exchange.

5. Security considerations

The Core Object Specification must provides the means to classify the

intended sensitivity level of an event, to-do or journal calendar

component (i.e., PUBLIC, PRIVATE, or CONFIDENTIAL).  It must also

provide a means to wrap all components in an exchange in a

cryptographically secure envelope so that only the intended

correspondents can decode the message.

The Calendar Access Protocol must provide a description of the

elements of the calendaring system security model and the protocol

elements for creating and manipulating the access control to a

calendar.  This protocol must also describe the authentication

procedure between a CUA and CS.

So that iCalendar objects may be securely transmitted across the

Internet and may be verified by recipients, iCalendar must describe

how objects will be covered and authenticated.

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6. References

[RFC-821] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC

821, USC/Information Sciences Institute, August 1982.

[RFC-822] Crocker, D., "Standard for the Format of ARPA Internet Text

Messages", STD 11, RFC 822, UDEL, August 1982.

[RFC-2045] Borenstein, N. & Freed, N., "Multipurpose Internet Mail

Extensions (MIME) Part One: Format of Internet Message Bodies", RFC

2045, Nov 1996

[RFC-2046] Borenstein, N. & Freed, N., "Multipurpose Internet Mail

Extensions MIME) Part Two: Media Types", RFC 2046, Nov 1996

[RFC-2047] Borenstein, N. & Freed, N., "MIME (Multipurpose Internet

Mail Extensions) Part Three: Message Header Extensions for Non-ASCII

Text", RFC 2047, Nov 1996

[RFC-2048] Borenstein, N. & Freed, N., "Multipurpose Internet Mail

Extensions (MIME) Part Four: Registration Procedures", RFC 2048, Nov


[RFC-2049] Borenstein, N. & Freed, N., "Multipurpose Internet Mail

Extensions (MIME) Part Five: Conformance Criteria and Examples", RFC

2049, Nov 1996

[RFC-2068] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,

Berners-Lee, T., "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2068,

Jan 1997

[iCalendar] Dawson, F. & Stenerson, D., "Internet Calendaring and

Scheduling Core Object Specification" ietf-calsch-ical-01.txt, March,


[iTIP1] Silverberg, S., Mansour, S., Dawson, F., & Hopson, R.,

"iCalendar Transport-Independent Interoperability Protocol (iTIP) Part

One: Scheduling Events and BusyTime",

draft-ietf-calsch-itip-part1-00.txt, Jul 1997

[iTIP2] Silverberg, S., Mansour, S., Dawson, F., & Hopson, R.,

"iCalendar Transport-Independent Interoperability Protocol (iTIP) Part

Two: Scheduling To-Dos", draft-ietf-calsch-itip-part2-00.txt, Jul 1997

[iTIP3] Silverberg, S., Mansour, S., Dawson, F., & Hopson, R.,

"iCalendar Transport-Independent Interoperability Protocol (iTIP) Part

Three: Scheduling Journal Entries",

draft-ietf-calsch-itip-part3-00.txt, Jul 1997

[CAP] "Calendar Access Protocol"

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7. Acknowledgments

The author is extremely grateful for the assistance, patience and

tolerance of the members of the CalSch working group.  Their ideas and

suggestions are crucial to making this a useful document.  In

particular, the author would like to thank

Anik Ganguly

Derik Stenerson

Frank Dawson

Gilles Fortin

Einar Stefferud

Their comments and ideas were particularly important in the

formulation of this draft.  I would also like to thank Qualcomm,

Incorporated for allowing the time necessary to bring this effort to


8. Author's address

For more information, please contact the author via Internet Mail.

John W. Noerenberg, II

Qualcomm, Incorporated

6455 Lusk Blvd

San Diego, CA 92131


email: jwn2@qualcomm.com

ph: +1 619 658 3510

The "Internet Calendar Model Specification" is the work of the

Engineering Task Force Working Group on Calendaring and Scheduling.

The chairman of that group, Anik Ganguly, may be reached at:

Anik Ganguly

Campbell Services, Inc.

21700 Northwestern Highway

10th Floor

Southfield, MI 48075

email: anik@ontime.com

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9. Appendix -- Calendar protocol nomenclature

Calendaring and Scheduling uses a rich lexicon of terms that are

specific to the problems of scheduling events and reconciling

conflicting requests for time and resources.  This document will

identify the major components of these systems, and show component

relationships.  However, for the sake of completeness and to serve as

an introduction to the protocols in general, a more extensive list of

terms, and brief definitions are included here. Essential parts of the

system model have expanded definitions in this document where the

components of the model are introduced.

9.1 Calendaring lexicon

Alarm, Reminder

An asynchronous mechanism providing feedback for a pending or past

event or to-do.

Busy Time

A period of time that is not available for scheduling.


A particular collection of calendar objects.

Calendar Object

The objects that can be found in a calendar.  The objects are

events, to-dos, journals, free/busies, time zones and alarms.

Objects also include properties and may include other objects.

A calendar object is identified by unique delimiters.

Calendar Date

A day identified by its position within the calendar year.

Calendar Scale

A particular type of calendar year, for example, Gregorian, Buddhist

Era, Japanese Emperor Era, Chinese Lunar, Islamic, and Jewish


Calendar Service

A Calendar Service (CS) stores a collection of calendars and interacts

with the Calendar User Agent (CUA) via the Calendar Access Protocol


Calendar User Agent (CUA)

A CUA mediates the interactions between a calendar user and his

calendar.  It represents the information stored in the calendar to the

user, and enables the user to manipulate it. This is a particular

instance of the interactive process used by a calendar user.

Coordinate Universal Time (UTC)

The time scale maintained by the Bureau International de l'Heure

(International Time Bureau). UTC is often incorrectly referred to as


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Daylight Saving Time (DST)

An adjustment to local time to accommodate annual changes in the

number of daylight hours. DST is also known as Advanced Time, Summer

Time, or Legal Time. Daylight Saving Time adjustments in the Southern

Hemisphere are opposite to those in the Northern Hemisphere.


A calendar object that defines a scheduled activity, minimally

specified by a start and end calendar date and time of day and a


Free Time

A period of time available for scheduling on a calendar.


FreeBusy objects describe blocks of allocated and unallocated time

on a calendar. They do not contain a description why the time is


Gregorian Calendar

A calendar scale in general use beginning in 1582.  The Gregorian

Calendar scale is based on a solar calendar consisting of common years

made up of 365 days and leap years made up of 366 days; both divided

into 12 sequential months.


A calendar object that defines a collection of information intended

for human presentation and is minimally specified by a calendar date

and one or more descriptions.

Local Time

The clock time in public use in a locale. Local time is often

referenced by the customary name for the time zone in which it is

located. The relationship between local time and UTC is based on the

offset(s) that are in use for a particular time zone. In general, the

formula is as follows:

local time = UTC + (offset)


A duration of time, specified as either a defined length of time or by

its beginning and end points.


Attributes that apply to calendar objects or calendars. A calendar

object is a named set of properties.  Properties can also be used

to produce variants to suit a particular purpose.

Recurrence Rule

A notation used to represent repeating occurrences, or the exceptions

to such a repetition of an event or a to-do. The recurrence rule can

also be used in the specification of a time zone description.

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ietf-draft-calsch-mod-01.txt   Internet Calendar Model   J. Noerenberg

Repeating Event or To-do

An event or to-do that repeats for one or more additional occurrences.

The recurrence may be defined with discrete dates and times and/or

with a recurrence rule.

Standard Time

Introduced by Sir Sanford Fleming and others around 1870, standard

time is a scheme for dividing the world into zones where the same time

would be kept. The original proposal was to divide the world into 24

zones, each zone having a width of 15 degrees of longitude. The center

zone was originally the meridian passing through Greenwich, England,

called Greenwich Mean Time (GMT). The time in the zones was

decremented by one hour per zone going westwards and was incremented

by one hour per zone going eastwards from GMT. Changes have been made

to the original proposal to accommodate political boundaries. In

addition, some countries and regions specify 30 or 45 minute offsets,

rather than the full 60 minute offset. Standard time is also known as

Winter Time in some regions.

GMT and UTC are generally equivalent. However, by international

agreement, the GMT term is discouraged in favor of the term UTC for

all general time keeping.

Time Zone

A geographic region to which a specified offset from UTC applies.

While offsets can frequently be calculated by knowing the longitudinal

distance from Greenwich, England, local conventions frequently alter

the calculation, complicating the determination of local time.  Local

convention may also assign a label to identify the time zone.  There

is no world-wide standard for labels.


A calendar object that defines an action item and is minimally

specified by an effective calendar date and time of day, a due

calendar date and time of day, a priority and a description.

Noerenberg                   Expires Jan 1998                [Page 17]

john noerenberg


pager: jwn2@pager.qualcomm.com