7.4.1 Mapping from source data
The following outline describes the basic ETL workflow:
- Determine which fields in the source data contain the information that is to be delivered in the interchange format fields. Multiple source fields may be combined into single interchange fields, and a single source field may impact values in multiple interchange fields.
- Determine what steps are necessary to get the content into the interchange format. This may involve some calculation, such as concatenating text from multiple fields to populate the text fields in interchange format. Use of the standard vocabularies for interoperability will likely require mapping vocabulary terms in the source data to identifiers for concepts in the controlled vocabularies for the fields that require URI’s (see next section).
- Set up a query to generate a table with field names exactly matching the field names in the interchange schema. In some cases it may be convenient to generate the interchange schema table in several steps, populating subsets of the fields each time. It may be useful to generate a table with unique combinations of contact, fault, or geologic unit properties from the source data, and map each combination to corresponding properties in the interchange format. Depending on individual situations, the unique descriptions can be identified using the specification_uri, name, or generic-Symbolizer field; identifiers in this field can then be used to join the interchange format properties with individual features.
- The table of unique descriptions can then be joined with the geometry elements to generate the final feature classes for the portrayal view service. ESRI Shapefiles and PostGIS tables are useful representations for the final feature class that the WMS server will use. Shapefiles will truncate field names longer that 10 characters, so in order to use them, the map server must support defining XML element names distinct from data table field names that are longer than 10 characters. Note that this requires installing an extension for GeoServer.
Section last modified: 21 October 2015