Hi Nathan,
Nathan Potter wrote:
>
> Ethan,
>
> Is it allowed for a dataset to have the serviceName and/or the urlPath
> specified as child elements? (I think the answer is yes to serviceName
> and no to urlPath)
That is correct. There is a "serviceName" element; there is no "urlPath"
element.
> Examples:
>
> <dataset name="level2_b" ID="nc/level2_b.nc" >
> <serviceName>s2</serviceName>
> <urlPath>nc/level2b_.nc</urlPath>
> </dataset>
>
>
> <dataset name="level2_b" urlPath="nc/level2_b.nc" ID="nc/level2_b.nc" >
> <serviceName>s2</serviceName>
> </dataset>
>
>
> <dataset name="level2_b" serviceName="s2" ID="nc/level2_b.nc" >
> <urlPath>nc/level2b_.nc</urlPath>
> </dataset>
>
>
>
> Is it allowed for a dataset to have both a serviceName/urlPath pair as
> attributes AND as child elements?
> If so, which has priority? (My guess is that none of these are allowed)
The XML Schema does not expressly forbid a dataset having both a
"serviceName" child element and a "serviceName" attribute. However, the
"serviceName" attribute is documented as deprecated in both the schema
and the specification document:
http://www.unidata.ucar.edu/projects/THREDDS/tech/catalog/v1.0.2/InvCatalogSpec.html#dataset
So, we don't write datasets that use the "serviceName" attribute but we
don't choke when reading a dataset with the attribute or both the
attribute and element (our code uses the element if it is avialable).
> Examples:
>
> <dataset name="level2_b" serviceName="s2" urlPath="nc/level2_b.nc"
> ID="nc/level2_b.nc" >
> <serviceName>s3</serviceName>
> </dataset>
>
>
> <dataset name="level2_b" serviceName="s2" urlPath="nc/level2_b.nc"
> ID="nc/level2_b.nc" >
> <serviceName>s3</serviceName>
> <urlPath>data/level2b_.nc</urlPath>
> </dataset>
>
> <dataset name="level2_b" serviceName="s2" urlPath="nc/level2_b.nc"
> ID="nc/level2_b.nc" >
> <urlPath>data/examples/level2b_.nc</urlPath>
> </dataset>
>
>
> Is a dataset allowed to have a serviceName/urlPathr via inheritance,
> attribute, or children and also have access element children?
Yes.
> If so are there rules about precedence? Is it cumulative?
It is cumulative. A dataset can have multiple access methods. That is, a
dataset can define multiple service/urlPath combinations that each
define a service type and an access URL. Each access method provides
access to the same dataset.
There are two ways for a dataset to define its access methods:
1) The dataset's "urlPath" attribute value is combined with the
dataset's "default" service [*]. If that service is a "Compound"
service, this results in multiple access methods/URLs.
2) Each child "access" element results in a single access method/URL. A
dataset can have any number of "access" elements; the service referenced
by an "access" element can be a "Compound" service. [If the "access"
element does not include a "serviceName" attribute, the dataset's
"default" service [*] is used.]
[*] By "default" service, I mean the service named by the highest
precedence local or inherited "serviceName" value. Precedence:
1) Local
a) child "serviceName" element (XPath: "./serviceName")
b) child "serviceName" element of a child "metadata" element
(XPath: "./metadata/serviceName")
c) "serviceName" attribute (XPath: "@serviceName")
2) Inherited:
- the closest ancestor "dataset" with an inherited metadata
that contains a serviceName element (XPath-ish: the first
item in the set given by
"ancestor::dataset/metadata[@inherited=true]/serviceName")
Some examples and more details (though, without the precedence
discussion, yet) are given in the "Dataset Access Methods" section of
the catalog spec document:
http://www.unidata.ucar.edu/projects/THREDDS/tech/catalog/v1.0.2/InvCatalogSpec.html#Dataset_Access_Methods
> Examples:
>
> <dataset name="level1" ID="degenerate examples">
>
> <metadata inherited='true'>
> <serviceName>s1</serviceName>
> </metadata>
>
> <dataset name="level2_a" urlPath="nc/level2_a.nc" ID="nc/level2_a.nc">
> <access serviceName="s2" urlPath="nc/level2_a" dataFormat="NetCDF" />
> </dataset>
>
> <dataset name="level2_b" serviceName="s2" urlPath="nc/level2_b.nc"
> ID="nc/level2_b.nc" >
> <access serviceName="s3" urlPath="nc/level2_a" dataFormat="NetCDF" />
> </dataset>
>
> <dataset name="level2_b" urlPath="nc/level2_b.nc" ID="nc/level2_b.nc" >
> <serviceName>s2</serviceName>
> <access serviceName="s3" urlPath="nc/level2_a" dataFormat="NetCDF" />
> </dataset>
>
> </dataset>
>
>
>
>
> Thanks for all of your help with this!
No problem. Hope I didn't muddy the waters even more.
Ethan
>
>
> N
>
>
> = = =
> Nathan Potter ndp at opendap.org
> OPeNDAP, Inc. +1.541.231.3317
