The conceptual design of the model was patterned after the PODS Pipeline Data Model such that feature tables from PODS might be incorporated into GDM or vice versa. GDM uses basically the same schema for linear referencing as the PODS Pipeline Data Model, with the exception that GDM supports both stationed and unstationed pipe.
Modeling Geometry in the Distribution Model
The GDM incorporates the approach of providing a single field that can be used to store geometry. Both SQL Server Spatial and Oracle Spatial state their data types are compliant with the OGC standard. Some issues involving transferring data between different systems remain to be resolved but the single field approach is supported by most systems.
Modeling Distribution Pipe in GDM
Gas distribution system facilities have a hierarchical nature that requires the operator to provide spatial data in a manner compatible with facility parent/child relationships. Due to the nature of these relationships orphaned data is not permitted or able to be inserted. Therefore, although distribution facilities can be broken down to their least part, they are also a part of the whole system.
The tables in the GDM directly related to facilities can be viewed as belonging to separate categories for the purpose of isolating information levels and maintaining reporting relationships. This hierarchy defines the elements that make up the model.