History
The Physical
Markup Language not only describes the current state
of the physical world, but previous states of the
physical world. In other words, PML records history
- both changes to physical objects and their environments.
Rather
than assuming only some elements within PML change
with time, we assume all elements may change, although
with greater or lesser frequency.
Therefore
we introduce a timestamp element that is an optional
component of every other component within the language.
We
include in this version of the Physical Markup Language
a simple data structure to reference these protocol
and to provide high level interpretation of the incoming
data streams.
Timestamp
We
introduce a ts
(timestamp) element to record events. The ts
element includes a mandatory type
attribute that indicates the nature of the timestamp.
The type attribute may assume the following values:
"begin" for the
beginning of an on-going state,
"end" for the end of a particular
state and "span"
for a time interval. If the type
attribue is not set, the time is assumed to be for
a discrete event - a point in time.
Depending
on the type
, timestamp may contain one or two date
elements. If the type
attribute is not set, the timestamp is assume to
record a discrete event and, therefore a single
date
element is required. Similarly, if type
is set to "begin"
and "end" types
one date
element is needed. However, if
type is set to "span"
requires two data elements
are required.
Usage
Because
we assume every element
in the Physical Markup Language may change, the
timestamp element is allowed
very broad application.
Specifically,
the ts
(timestamp) element may be
included in any element of the Physical Markup
Language and the ts element
may contain any element
in PML.
In
this way the timestamp element may associate an
element or a group of elements with a specific point
in time or a duration of time.
The
timestamp element allows users to specify not only
where an object is ,
but where an object was
. The timestamp specification may trace the path
of a product, case or shipment as it moves through
the supply chain.
