<!ENTITY % DataType "Grid | Image | Station">
<!ELEMENT dataset (service*, (documentation | metadata | property)*, access*, (dataset | catalogRef)*)>
<!ATTLIST dataset
name CDATA #REQUIRED
dataType (%DataType;) #IMPLIED
authority CDATA #IMPLIED
ID ID #IMPLIED
alias IDREF #IMPLIED
serviceName CDATA #IMPLIED
urlPath CDATA #IMPLIED
>
A dataset element represents a logical set of data at a level of granularity appropriate for presentation to a user. A dataset is selectable if it contains at least one access path, otherwise it is just a container for nested datasets. If selectable, upon selection, an event is sent to the client software.
A dataset element contains 0 or more service elements followed by 0 or more documentation, metadata, or property elements in any order, followed by 0 or more access elements, followed by 0 or more nested dataset or catalogRef elements. The data represented by a nested dataset element should be a subset, a specialization or in some other sense "contained" within the data represented by its parent dataset element.
A dataset must have one or more access paths, specified implicitly through a urlPath attribute, or explicitly in contained access elements. An access path should be thought of as a URL, but its actually information from which a protocol-aware layer can construct URLs. When there is only one URL, this is typically specified in the dataset element itself. When there are multiple URLs, these may be specified in the dataset element and/or in contained access elements. Multiple URLs specify different services for accessing the dataset. Choices among these different services should be filterered by client software or presented to the user for selection. A URL specified in the dataset element itself is the default URL, which should be the preferred URL when no filtering or user choice is possible. Also see forming URLs.
A dataset may have a dataType, specified within itself or in a containing aggregation, whose value comes from a controlled vocabulary.
If a dataset has an alias attribute, the value of the attribute must be an ID of another dataset within the same catalog. Note it may not refer to a dataset in another catalog referred to by a catalogRef element. In this case, any other properties of the dataset are ignored, and the dataset to which the alias refers is used in its place.
A dataset may have a authority specified within itself or in a containing aggregation. If a dataset has an ID and a authority attribute, then the combination of the two should be globally unique for all time. If the same dataset is specified in multiple catalogs, then its authority - ID should be identical if possible.
Many of the properties of a dataset become the default for contained dataset elements. This includes property elements, and dataType, authority and serviceName attributes. Any documentation elements are displayed at the dataset itself when presenting the catalog to the user. Any metadata elements apply to all contained datasets.