The RDF Calendar Task Force
by Leigh Dodds
July 25, 2001
This week the XML Deviant reports on a community effort that's
producing interesting building blocks for the Semantic Web.
Overview
RDF has been experiencing something of a renaissance lately with
progress occurring on many fronts. Tools, APIs, and datastore
implementations are leading RDF out of academia and into mainstream
projects. The RDF Core
Working Group is currently chartered to move the activity forward
under the umbrella of the W3C Semantic Web efforts. The charter notes
that the group will:
- update and maintain the RDF Issue Tracking document
- publish a set of machine-processable test cases corresponding to
technical issues addressed by the WG
- provide an update of the errata and status pages for the RDF
specifications
- update the RDF Model and Syntax Specification (as one, two or more
documents) clarifying the model and fixing issues with syntax
- complete work on RDF Schema 1.0 Specification
- provide an account of the relationship between RDF and the XML
family of technologies (particularly Schemas and Infoset/Query)
These targets address many of the issues and concerns raised in
previous RDF debates. The reference to "two or more documents"
suggests that the previously mooted separation
of the description of the Model from the Syntax may still be on
the cards.
In the meantime the Working Group continues to receive feedback
from the wider community through the RDF Interest Group, a group
of RDF developers and researchers that collaborate through the rdf-interest
mailing list and an associated IRC channel. Interestingly the IRC channel is
monitored by bots that generate logs and harvest links from the
ongoing discussion for publication on the Web. Naturally an RDF
representation of this data is also available.
One area in which community collaboration has been progressing is
through the RDF Calendar task force, which is lead by Libby
Miller. The group is exploring ways of describing and manipulating
calendar and event schedules using RDF, leveraging some existing work
carried out within the IETF. iCalendar has a large
installed base; it's used in Outlook Express, Netscape, and Palm
hand-held devices, among others. To learn more about IETF's caledaring
efforts, read this
useful overview.
Developer Chat
The XML Deviant spent some time on the #rdfig IRC channel
this week chatting to RDF developers about the task force's
efforts. In the following IRC extracts "DanCon" is Dan Connolly,
"danbri" is Dan Brickley, and "libby" is, of course, Libby
Miller. (Note also that some comments have been collated to gather
comments from individuals that were separated in the flow of
conversation on the channel.)
Interested in the background to the group, the Deviant asked
the developers how they would describe the calendaring efforts.
[20:18]
<DanCon> ...as I've said, the bane of my existence is doing things
I know the computer could do for me. I'm having a great time getting
the computer to figure out things about my schedule
[20:18]
<DanCon> e.g. I wrote a tool to convert semi-structured plain-text
itineraries in the format that our travel agent spits them out into
RDF...
[20:19]
<DanCon> then I took two such itineraries, as RDF, and wrote some
rules expressing constraints that my wife and I had agreed to, and I
was able to get the machine to decide that one of the itineraries
didn't meet our constraints.
[20:29]
<danbri> ...here's why the calendaring work appeals to me: its a
very practically grounded (palm pilots; meetings etc) area that shows
some of the potential strengths and challenges of the Semantic
Web. Specifically, the need for calendar/schedule data to be
intermingled with other related information, e.g. RSS for syndication,
DC for document metadata, white pages info etc.
[20:30]
<danbri> The sorts of things I want to do with calendaring data
usually require me to draw on other sources of info at same time;
e.g. who else is attending a meeting, what the required reading
was.
[20:31]
<danbri> iCalendar, vCard, etc. sort of live in little islands;
RDF's grand claims tend to be that it builds up some commonality
between these islands. www-rdf-calendar is a group trying to find out
if we can live up to the rhetoric...
[20:19]
<libby> ... I'd charaterise the effort as trying to get an RDF
model for event data - specifically things like meetings and
conferences - as quickly as we can
[20:19]
<libby> at Danc's suggestion we've been trying to make data
av[a]ilable in the schema and write demos to test it on real data
Have you started using RDF to integrate
disparate data sources? Share your experiences in the forum.
Post your comments
It's reasonable to ask whether simply recreating iCalendar using an
alternative syntax is worth the work. Libby Miller explored this
question in a recent posting to the RDF
calendar mailing list. At first glance iCalendar offers the same
level of extensibility as RDF and a more mature toolset. However, as
Miller noted,
the answer is in the additional relationships that RDF can
exploit.
One example might be: I'm learning about SMIL; I find the W3C
recommendation for SMIL; from this document and other RDF documents on
the W3C site and elsewhere I can find meetings at which the document
was produced and altered. I can then find out who attended the
meetings and more about their connections and affiliations from other
RDF databases such as RDFWeb. I can also find other documents that
were inputs to the meetings and also other outputs from the meetings
such as minutes and photos.
Much of this data is already available on the web. Putting all these
types of information, including meetings and other events in an RDF
calendar format connects up this information to make my life easier
when I start doing research on SMIL. Putting calendar information in
RDF is only a part of the project of putting all these different kinds
of information in RDF.
The RDF calendar effort is therefore about more than just
exploiting a handy test bed for RDF applications. The developers are
looking to achieve immediate practical benefits, as Dan Connolly
explained:
[20:20]
<DanCon> ...I'm aiming at automating my day-to-day decisions and
queries. e.g. "I've got yet another invitation for tuesday at 2pm. Do
I have any pre-existing obligations?"
[20:21]
<DanCon> the reality is: my schedule info is never collected in one
place. it's a multi-party (peer to peer) setup.
However Dan Brickley also observed that having a real dataset to
exploreprovides useful experience.
[20:32]
<danbri> It's also a good testbed area for the specs: people have
long asked how we should deal with XML Schema datatypes in RDF; some
of the discussion on xmlschema-dev and the rdf cal list gets (at last)
stuck into the detail.
Current Progress
Also in XML-Deviant
The More Things Change
Agile XML
Composition
Apple Watch
Life After Ajax?
The early work of the group has been concentrated in two
areas. First, Libby Miller and Michael Arick have been collaborating
to producde
an RDF Schema for calendar information. It's currently heavily
influenced by the iCalendar specification. Second, others have been
producing tools that will extract information from existing data
sources and make it available as RDF.
Dan Connolly has written palmagent which
takes datebook information from a Palm device and makes it available
as RDF and HTML. Supplementing this data with other sources such as
conference proceedings allows for some very interesting
possibilities. In fact Libby Miller has already produced RDF calendar
data for the Semantic Web
Working Symposium in RDF format and an online
demonstration of querying this data.
The group is, then, following an iterative process: define a
suggested schema, generate data, write tools, and then feed this
experience back into refining the schema. Indications are that a
fuller draft may be available over the next few weeks, although Miller
noted during the discussion that there is still a large amount of
testing to be done.
Indeed the group is also beginning to plan its next round of
effort. Miller is seeking input from the group on
a draft TODO list, which includes write-ups of the current
implementations, modularizing the schema using namespaces, tutorials,
and potentially an RSS 1.0
Event module for syndicating event related information. Additional
data sources -- conference agendas and flight schedules -- are on the
list too.
One of the intriguing aspects to the calendaring work is that
there is a steady learning curve involved. Designing a simple calendar
and address exchange system is initially a fairly simple task. But as
the system grows its becomes clear that not everyone has the same
concept of what constitutes an "event". Additional difficulties like
determining the location of an event are not as simple as they might
seem. How does one associate a plane flight with a location? And in
which timezone?
In practice this means that the calendar group is beginning to deal
with issues that will need resolving on a larger scale in all Semantic
Web efforts. Developers looking to gain some experience with a
distinctly practical RDF project could do worse than join the task
force. The iterative development approach is a refreshing change to
the protracted specification work occurring elsewhere. Coupled with
the friendly community atmosphere, this is definitely one of the more
interesting areas on the XML landscape.
The Deviant wishes to thank Libby Miller, Dan Brickley, Dan
Connolly and other developers on the #rdfig channel for their input to
this article.