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Data Management
Detailed Information About the JGOFS Distributed Database Management System (DDMS)
Manipulating Data
The system has two built-in operations -- functions which each data
object is expected to carry out:
But, although these are the most common operations, they do
not in
and of themselves satisfy all the requirements for a data system. One
significant advantage of an object-based data system is that new
operations can be added at any time. One simply builds a "method" which takes
as its input information that supplied by one (or more) objects rather than data
files, transforms the information in some
way, and passes it on to the user application.
We call the combination of the new method and the sub-objects
a "constructed object." You can also think of these as similar to UNIX
filters.
For example, we can add a column to the /test (hydrographic data)
which gives a linearized estimate of density:
rho=28.5-0.2 T +0.7 (S-35)
by using the ``math'' constructed object which takes as parameters an
input object name and formulae for changing/ adding columns. The new
object name is
math(/test,rho=28.5-0.2*temp+0.7*(sal-35))
and this can be used by the lister/plotter/... in exactly the same
way as any other object --- see figure.
As another example, there is a plot from two data objects joined
together by common station, cast, and pressure.
join(/tco2,/poc(station,cast,press,poc))
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