\subsection{Activity Element}
\label{sec:activity}

The \xmlelement{activity} indication describes what the presentity is
currently doing.  This can be quite helpful to the watcher in judging
how appropriate a communication attempt is and which means of
communications is most likely to succeed and not annoy the presentity. 
The activity indications correspond roughly to the category field in
calendar entries, such as Section 4.8.1.2 of RFC 2445 [9]. 

\motivation{Use of an enumerated, but extensible, set of activity
categories simplifies automated generation and processing of presence
information.  The categories can be readily selected from a drop-down
list by the user or translated from the corresponding activity field in
calendars.  Recipients of this information can render at least a subset
as icons, automatically translate them into different languages or
convert them to sound "jingles" and speech, or use them to generate call
processing rules.}

An activity indication consists of one or more values drawn from the list
below, any other token string or IANA-registered values
(Section~\ref{sec:iana}).  Communities of interest such as a profession
or an organization may define additional activity labels for their
internal use.

Depending on the presentity intent, all but the ``available'' indication
can be used with either status OPEN or CLOSED.

\begin{description}

\item[Available:] The presentity is available for communication.

\item[On-the-phone:] The presentity is talking on the telephone.  This
activity is included since it can often be derived automatically.

\item[Away:] The presentity is physically away from the device location. 
This activity was included since it can often be derived automatically
from security systems, energy management systems or entry badge systems.

\item[Appointment:] The presentity has a calendar appointment.

\item[Holiday:] This is a scheduled national or local holiday. This
information can typically be derived automatically from calendars.

\item[Meal:] The presentity is scheduled for a meal.  This activity
category can often be generated automatically from a calendar.

\item[Meeting:] This activity category can often be generated
automatically from a calendar.

\item[Steering:] The presentity is controlling a vehicle, ship or plane.

\item[In-transit:] The presentity is riding in a vehicle, such as a car,
but not steering. Alternatively, the presentity {\MAY} offer more
specific information.

\item[Travel:] The presentity is on a business or personal trip, but not
necessarily in-transit.  This category can often be generated
automatically from a calendar.

\item[Vacation:] This activity category can often be generated
automatically from a calendar.

\item[Sleeping:] This activity category can often be generated
automatically from a calendar, local time information or biometric data.

\item[Busy:] User is busy, without further details.  This activity
category would typically be indicated manually.

\item[Permanent-absence:] Presentity will not return for the foreseeable
future, e.g., because it is no longer working for the company.

\end{description}

The \element{activity} element {\MAY} be qualified with the 'from' and
'until' attributes to describe the time when the element assumed this
value and the time until which is element is expected to be valid.
