Figure 13.7 The structure of presence informationThe example will now make it easier to understand some presence elements
in the PIDF standard.
■■ The PIDF object is a well formed XML document that contains the
encoding declaration <?xml version=”1.0” encoding=”UTF-8”?>.
■■ The <presence>element is associated with the XML namespace
“urn:ietf:params:xml:ns:pidf’”and has a namespace declara-
tion “xmlns” that points to the URN “‘urn:ietf:params:xml:
ns:pidf:”. The namespace is identified by a URI that must be globally
unique but does not necessarily represent an existing web resource.
■■ The <tuple>element consists of a mandatory <status>element fol-
lowed by optional extension elements, such as <contact>, <note>,
and <timestamp>.
■■ The optional <note>element is especially interesting, since it contains
comments readable by humans, such as I’ll be in Tokyo next week
in the example.Presence InformationPresence TuplePresence TupleStatusAddress of RecordOther MarkupStatusAddress of RecordOther MarkupContact AddressContact Address234 Chapter 13