<!ELEMENT catalogRef EMPTY>
<!ATTLIST catalogRef
xlink:type (simple) #FIXED "simple"
xlink:href CDATA #REQUIRED
xlink:title CDATA #REQUIRED
>
A catalogRef element refers to another catalog that becomes a dataset inside this catalog. This is used to seperately maintain catalogs and to break up large catalogs. The referenced catalog should not be read until the user explicitly requests it, so that very large dataset collections can be represented with catalogRef elements without large delays in presenting them to the user. The referenced catalog is not textually substituted into the containing catalog, but remains a self-contained object. The referenced catalog must be a valid THREDDS catalog, but it does not have to match versions with the containing catalog.
The value of xlink:href is the URL of the referenced catalog. The value of xlink:title is displayed as the name of the dataset that the user can click on to follow the XLink. Note that the XLink has a fixed type of "simple" that is part of the DTD, so does not have to be specified in the catalog XML.
The dataset chooser software should seamlessly present a catalogRef to the user, for example by eliminating the referenced catalog's top-level dataset in its presentation of the catalog when its name matches the title of the catalogRef title attribute.