Glossary

Feature Schema
A set of classes and their corresponding properties and relationships. Each Feature Schema typically contains the classes for a specific domain, for example, Electrical Schema, Gas Schema, etc. The Feature Schema defines its classes in an FDO provider-independent form.
GML
OGC´s Geography Markup Language. An XML format for geographic data.
Schema
In RDBMS terms, a Schema is a collection of tables, indexes, views, etc. in a database. Feature and RDBMS schemas do not correspond 1:1. A Feature Schema may be stored in different RDBMS schemas and an RDBMS schema might be composed of multiple logical schemas.
OGC
Open GIS Consortium
Schema Mapping
A set of hints that determine how Feature Schemas are stored in an FDO data store. The contents of Schema Mappings vary depending on the FDO Provider type.
Tolerance
Used to determine when two points are close enough to be considered to be equivalent in certain spatial tests. In FDO, the tolerance value is used as a radius around a position rather than as a distance along an axis. In the majority of cases, the distance between the points is compared to the tolerance using the 'less than' predicate. If the X and Y tolerances are both 0.05, the point B (1.0, 1.0) is considered to be equivalent to point A (0.96, 0.96) and point C (1.04, 1.04), but is not considered to be equivalent to point D (0.96, 0.94) or point E (1.04, 1.06). The relationship is not transitive. That is, point A is not equivalent to point C. Repeated applications of the isEquivalentTo predicate to the same data always yields the same result.