Data Interchange Content Models
Each feature or observation type delivered using a community data interchange format has an associated content model that defines the information contained in interchange documents for that feature or observation. The content model in its simplest form is a statement that some particular entity (feature or observation) will have some list of properties. For example a content model for a record describing a book might include: title, author, publisher, publication date, publication place, number of pages, and an ISBN number (a URI).
To document these content models, the NGDS is currently using Microsoft Excel workbooks. Each workbook includes a description of the entity type, a list of the elements (fields, attributes) in a data instance for that entity presented both as a table and a list, and lists of vocabulary terms meant as a start or example for the kinds of vocabularies that will be required in the long run for semantic interoperability. Use of the terms in these example vocabularies will facilitate migration to formal vocabularies later.
Go to Content Model Summaries for a list of currently adopted content models.
In order to actually use the content models, they must be implemented using an encoding scheme that is computer processable. NGDS is using eXtensible Markup Language (XML) to implement the content models, but other schemes may be adopted as the system matures and technology evolves. The important thing is that the information is encoded consistently in a structured, well documented format. This enables computer programs to parse the interchange documents and extract desired information, and as newer encodings are adopted, conversion between formats can be automated using software.
If data to be served are not accounted for by an existing content model, network participants are invited to propose new models. A document with guidelines for construction of a template workbook in available here. Proposed new content models are submitted for review and adoption for use in the NGDS and broader USGIN community. Models that have been reviewed by the DOE NGDS Technical Working group and elevated to the NGDS website public documents section have links to forums there for comments. Please post any discussion, review, change requests to those forums (coming soon...).
Content Models and XML schema
XML schema implementing content models in use by the AASG geothermal data project WFS services are in a repository at http://schemas.usgin.org/.
XML schemas are versioned, and the XML namespace for each document element is unique to that schema version. Thus namespace-aware client applications can determine if an instance document is using a known schema version.
