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Versions: 00 01 02 03                                                   
Network Working Group                                      J. Noerenberg
draft-ietf-calsch-mod-02.txt                               Qualcomm, Inc
Category: INTERNET DRAFT                               Expires: Apr 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
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Internet-Drafts may be updated, replaced, or made obsolete by other
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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 protocols.

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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 iRIP: Binding of iTIP to a session protocol              4
1.5 iMIP: Binding of iTIP to E-mail                          4
1.6 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                                 9
4.1 Direct Access                                           12
4.2 Calendar Service Mediation                              12
4.3 Interdomain Exchange                                    12
4.4 Node-Foreign Domain Exchange                            12
5. Security considerations                                  12
6. Copyright                                                13
7. References                                               13
8. Acknowledgments                                          14
9. Author's address                                         15
10. 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 above.

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 properties.  The
properties of a calendar object can be thought of as attributes.  The
objects that are defined in iCalendar are referred to as Calendar
components.  In this document, and others regarding Calendaring and
Scheduling, properties and attributes may be regarded as synonomous,
and components are equivalent to objects.

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

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way so as to allow multiple methods of communication between systems.

1.4 iRIP:  Binding of iTIP to a Session 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.

1.5 iMIP:  Binding of iTIP to E-mail

This document specifies an iTIP protocol over Internet e-mail.
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.

1.6 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  |    |   E-mail  |
|   iRIP   |    |    iMIP   |
 ----------      -----------

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2.  Abstract Model

A CALENDAR is a collection of logically related OBJECTs.

FREEBUSYs.  OBJECTS are also termed Calendar Components.

Each OBJECT is described using a set of OBJECT PROPERTIES such as
date&time, attendees, resources and statuses.

The complete set of OBJECT PROPERTIES 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.  When a CU creates an OBJECT,
the CU becomes the OWNER and ORGANIZER for that OBJECT.  The CU may
delegate OWNER and ORGANIZER properties to other CUs by changing the
OBJECT PROPERTIES and distributing the OBJECT to other CUs.

A CUA uses the services of a CALENDAR SERVICE (CS) via the CALENDAR
ACCESS PROTOCOL (CAP) to distribute OBJECTS from and reconcile changes
to a CALENDAR owned by a CU.  A CS delivers messages to a CUA
containing OBJECTs from other CALENDAR USERs via CAP.  A CUA uses the
iCalendar Transport-Independent Interoperability Protocol (iTIP) to
deliver OBJECTS to a CS to be distributed to other CUAs.

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.  A CUA using CAP
MUST NOT use a plaintext password to gain access to a CALENDAR stored
by a CS.  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.  OBJECTs exchanged via iTIP SHOULD be encrypted for the
recipients and signed by the sender.  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.

An 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

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CUA is also required to locate the appropriate CALENDAR DOMAIN in order
to use iTIP.  When OBJECTs are transmitted, they are encapsulated in a

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 [iTIP].
iTIP is capable of using a variety of transport mechanisms such as
Internet Mail ([RFC821], [RFC822]),and session-layer protocols, such as
those derived from iTIP ([iMIP], [iRIP]).

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 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 properties 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

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creates an event object, that user becomes the organizer and the owner.
The organizer can delegate ownership and the role of organizer to
others.  Only organizers and owners may alter any property of an event
object.  Calendar users assigned other Attendees roles may not change
event properties.

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.  Within the context of a Calendar,
these objects are called components.  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 CALSCALE property that identifies
the type of calendar year used by objects in a calendar.  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

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date-time that specifies when the To-do expires.  A To-do must have a
description.  It may also contain an alarm object. Alarms
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

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

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, CSs and CUAs contained in the domain.  It must be possible
for any Calendar User (via the facilities of a CUA and/or CS) to
determine whether they are members of a particular domain, or if other
Calendar Users are members.  CSs 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 [iCalendar].
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, the objects exchanged with iTIP are iCalendar objects.
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 to a CS.  An CS may accept or
reject delivery without interaction with a user.  But a CS may require
further confirmation of receipt of a object before it is acted upon by
the CS.

4.  Calendar Object Transport
There are several transport modes in this architecture.  The figures
below illustrate the different modes that are allowed.  Four 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 between networks, and exchanges
between an individual node in one network and the foreign network.

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

                                      |                  |
                                      | Calendar Domain  |
                                      |                  |
                                      |                  |
                                      |                  |
                                      |                  |
                                      |                  |
                                      |                  |
                                      |                  |
                                      |                  |
   ------------                       |---------         |
  | CUA  | rcvr|----------     -------|rcvr|    |        |
  |       -----|          \   /       |----     |        |
  |            |           \ /        | Gateway |        |
  |            |            X         |         |        |
  |            |           / \        |         |        |
  |       -----|          /   \       |----     |        |
  |      | sndr| ---------      ------|sndr|    |        |
   ------------           \    /      |---------         |
                           iTIP       |                  |
                                      |                  |

 Figure 5: Node-Foreign Network Exchange

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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.  To insure privacy and/or authenticity, CUAs should use
the cryptographic wrappers provided by iTIP.

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.

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.

4.4 Node-Foreign Domain Exchange
Figure 5 describes the interaction between some particular Calendar
Domain, and a node which is not part of that domain.  Like Interdomain
Exchange and Direct Access, iTIP is used to mediate the exchange of
objects between the CUA and the Calendar Domain.  Similar to those two
modes, objects exchanged in this mode should be enclosed in a crypto-
graphic wrapper to assure the privacy and authenticity of the exchange.

5.  Security considerations
There are four classes of threats with which Calendaring and Scheduling
protocols must be concerned.  These threats can be characterized as
Spoofs, Eavesdropping, Floods, and Malicious Changes.  A Spoof occurs
when a node masquerades as another node enabling it to receive objects

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to which it would not otherwise be entitled or send unauthorized
objects. Eavesdropping occurs when an intermediary node is able to
retain and interpret an object exchanged between a sender and receiver
without their knowledge or permission.  A Flood occurs when a node acts
to send more messages to a receiver than the receiver can process,
prohibiting the receiver from receiving other messages.  Malicious
Changes occur if a CU gains access to some Calendar not owned by the CU
or some CPDU in transit and makes unauthorized changes to the Calendar
or to the CPDU.  Simply gaining unauthorized access via the protocols
outlined by this model may be considered malicious,as well.

iCalendar must provides the means to classify the intended sensitivity
level of an event, to-do or journal calendar component (i.e., PUBLIC,

CAP must provide a description of the elements of the calendaring
system access 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.  This will
mitigate Malicious Changes.

iTIP must 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.  This will mitigate the threats
of Spoofs and Eavesdropping.  It must also provide a means for a
receiver to throttle the messages of a sender to prevent Flooding.

6.  Copyright
Copyright (C) The Internet Society (Oct 1997).  All Rights Reserved.

This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it or
assist in its implmentation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are
included on all such copies and derivative works.  However, this
document itself may not be modified in any way, such as by removing the
copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of developing
Internet standards in which case the procedures for copyrights defined
in the Internet Standards process must be followed, or as required to
translate it into languages other than English.

The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.

7.  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.

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[RFC-1983] Malkin, G., "Internet Users' Glossary", RFC 1983, Aug 1996

[RFC-2026] Bradner, S., "The Internet Standards Process -- Revision 3",
RFC 2026, Oct 1996

[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-2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Mar 1997

[iCalendar] Dawson, F. & Stenerson, D., "Internet Calendaring and
Scheduling Core Object Specification" ietf-calsch-ical-01.txt, March,

[iTIP] Silverberg, S., Mansour, S., Dawson, F., & Hopson, R.,
"iCalendar Transport-Independent Interoperability Protocol (iTIP)",
draft-ietf-calsch-itip-00.txt, Jul 1997

[CAP] Author U., "Calendar Access Protocol", unwritten, Oct 1997

8.  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
Steve Mansour
Steve Silverberg

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 fruition.

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9.  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 Internet
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

10.  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.

10.1 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 Component
A Calendar Object.

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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

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 allocated.

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.

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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.

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.

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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

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