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Subject: Earthquake Report (A.3) Example: Questions -- typo, etc.
At PubSub.com, we've been trying to take live USGS earthquake data and
faithfully produce CAP messages based on our reading of the CAP
specification, including the example of earthquake data which is given
within it. Some questions have arisen in this project...
For instance, the sample earthquake report given in A.3 of CAP
includes the following line:
<parameter>Magnitude=3.4 Ml</parameter>
We are a bit mystified about the "Ml" in the "value" portion
of the name/value pair here. Clearly, the intention is to communicate
that the magnitude of the reported earth quake was "3.4", but what is
the "Ml"? In actual USGS data, we sometimes see "M" used in this
context, but never "Ml"... Is this a typo? (Note: We're now pumping
out large numbers of messages with the " Ml" in them and people keep
asking me what the "l" is for. Please help me explain this. It is
getting embarrassing to not have an answer...)
Additionally, I would like to mention that "values" such as
"3.4 Ml" are unnecessarily hard to match against or prepare for
insertion into a database since they are strings whereas most
applications will want to treat them as numbers. In this case, it is
necessary to strip the " Ml" from the value to prepare the value for
processing in most applications. Unfortunately, the " Ml" doesn't seem
to provide any information that is not redundant, since the "name"
part of the parameter clearly marks the value as a "Magnitude". This
increase in the complexity of processing, as well as the requirement
to do micro-parsing on the fields, will inevitably increase the costs
of implementing CAP as well as increasing the opportunity for interop
problems.
Yes, this is another call for the use of attributes... The way
that the USGS encodes these values in their own XML feeds[1] is the
rather sensible:
<param name="magnitude" value="3.4" />
If one wanted to be sure that the unit of measure (i.e. the
"Ml") was communicated, then you could do something like:
<param name="magnitude" value="3.4" unit="Ml"/>
Such an attribute based approach can, of course, be shown to
handle anything that could have been done with the current "="
delimited name/value pairs.
bob wyman
[1] ftp://ghtftp.cr.usgs.gov/pub/cnss/merge_14.xml
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