The OPeNDAP Catalog/Aggregation Server is configured by adding metadata elements of
type aggregation to catalog dataset elements. In
the example catalog fragment below (Example 3), a dataset named
"NCEP-RUC Model Output" is defined. It will have a relative URL of
"NCEP/RUC". That is, if the Aggregation Server at http://opendap.org
has a catalog with these entries in it, the aggregated data
represented by the dataset element will be at
http://opendap.org/NCEP/RUC. The data a client sees there will
be created by joining three NetCDF files along the existing
valtime dimension, specified in the variable attribute of
the aggregation element. The NetCDF files will be found at
E:/data/070516.nc and so on.
Example 3
<dataset name="NCEP RUC Model Output" urlPath="NCEP/RUC">
<service name="localGrids" serviceType="NetCDF"
base="file:///E:/data/"/>
<metadata metadataType="Aggregation">
<aggregation serviceName="localGrids"
variable="valtime" type="JoinExisting">
<fileAccess urlPath="070516.nc"/>
<fileAccess urlPath="070517.nc"/>
<fileAccess urlPath="070518.nc"/>
</aggregation>
</metadata>
</dataset>
The Aggregation Server can also aggregate files from other OPeNDAP servers. In
the following example, the aggregation dataset called "Example
JoinNew" is created from files that live on the "GSO" OPeNDAP
server. The datasets are joined by creating a new dimension called
time. The data values of that dimension are specified in the
fileAccess elements. The OPeNDAP datasets out of which this
aggregate dataset is constructed have URLs like this:
http://opendap.org/cgi/nph-dsp/htnsst/k2828.htn.
Example 4
<dataset name="Example JoinNew" urlPath="htn_sst_decloud">
<service name="GSO" serviceType="DODS"
base="http://opendap.org/cgi/nph-dsp/"/>
<metadata metadataType="Aggregation">
<aggregation serviceName="GSO" variable="time"
type="JoinNew" dateFormat="yyyy/M/d:HH:mm:ss z">
<fileAccess urlPath="htnsst/k2828.htn" coord="1985/1/1:18:28:28 GMT"/>
<fileAccess urlPath="htnsst/k1750.htn" coord="1985/1/2:18:17:50 GMT"/>
<fileAccess urlPath="htnsst/k0718.htn" coord="1985/1/3:18:07:18 GMT"/>
</aggregation>
</metadata>
</dataset>
The Aggregation Server is also an OPeNDAP server for non-aggregated NetCDF
files. The following shows a collection of OPeNDAP datasets. Since
they don't have an aggregation metadata element
(metadataType="Aggregation", they refer to
NetCDF files that are served as OPeNDAP datasets by this Aggregation Server.
There is more detail about this in Section 3.4.
Example 5
<dataset name="Non-Aggregated Netcdf Files" serviceName="this"> <property name="internalService" value="local"/> <dataset name="RUC/01070516" urlPath="01070516_ruc.nc"/> <dataset name="RUC/01070517" urlPath="01070517_ruc.nc"/> <dataset name="RUC/01070518" urlPath="01070518_ruc.nc"/> </dataset>
Note here that the this service needs no service
element to define it.