Data Management
Detailed Information About the JGOFS Distributed Database Management System (DDMS)
Protocol for Communication
Methods provide three different kinds of data stream. You can view all
of these from browsers:
The rest of this document concentrates on the last case.Example
We illustrate the communication protocol with a simple example: for a
data object which looks like
list "test(station<=5&press<100,station,lat,lon,press,o2)"
# wunsch stations 3-10
# p<1000
=======================
station, lat, lon
........................
3, 38.28, -73.53
=======================
press, o2
------------------------
5.000, 5.970
25.000, 6.990
49.000, 6.060
99.000, 5.340
=======================
station, lat, lon
........................
4, 38.19, -73.52
=======================
press, o2
------------------------
5.000, 5.840
25.000, 7.090
49.000, 6.020
99.000, 5.340
=======================
station, lat, lon
........................
5, 38.16, -73.26
=======================
press, o2
------------------------
5.000, 5.770
25.000, 6.660
49.000, 5.510
99.000, 5.100
=======================
The dictionary entry is assumed to be
test=def(/usr/users/jgofs/data/t0)
The communications look like:
list -> method (def)
argv = [/usr/users/jgofs/data/t0,station<=5&press<100,station,lat,lon,press,o2
def -> list
&c***********************
wunsch stations 3-10
p<1000
&v0======================
&v1======================
station lat lon
&v2======================
press o2
&r=======================
&c***********************
wunsch stations 3-5
p<1000
&d0----------------------
&d1----------------------
3 38.28 -73.53
&d2----------------------
5.000 5.970
25.000 6.990
49.000 6.060
99.000 5.340
&d1----------------------
4 38.19 -73.52
&d2----------------------
5.000 5.840
25.000 7.090
49.000 6.020
99.000 5.340
&d1----------------------
5 38.16 -73.26
&d2----------------------
5.000 5.770
25.000 6.660
49.000 5.510
99.000 5.100
&e**** End of object ****
Thus the application begins by sending the parameters to the method
and then reading the blocks of data. The blocks are indicated by
commands with an & in the first position. There are four
types of protocol blocks: comments, variable names, data, and end.Protocol blocks
Comments
The &c introduces the plain text comments
section. Comments consist of lines of no more than 80 characters.Variables
This section gives the names, dimensions, and attributes of variables
at each hierarchical level. The outermost level, 0, is defined first
and then we work our way inward. The signal is &vn with
n=0...9 the level indicator. Each variable definition has:
- The name (avoid embedded blanks --- use _ )
- Attribute list appended to the variable name surrounded by []. The
attribute list is a comma-separated set of strings, usually (except
for units) of the form attribute=value.
The variables section is closed by a record marker, &r.
Variable fields are tab-separated.Data
The data is likewise presented in a hierarchical fashion. The
&dn intoduce the data from the n'th level. Note that the
innermost level can drop the &dn. The data from the
outermost levelis sent, followed by the next level, up to the
innermost level. The innermost level repeats until the next level up
changes or the data ends. Data fields are tab-separated.End
This indicates the end of the data object. The indicator is &e.Errors
Errors are indicated by the method returning &x
[descriptive string] and exiting.
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