GML object hierarchy

GML is a complex standard. The content in this article is based on ogc gml 3.1.0. It contains a lot of content, except the conventional two-dimensional Vector GIS information, it also includes complex targets, topology information, three-dimensional targets, temporal information, geographical coverage, annotation symbols, spatial references, metadata, and raster data. Unlike gml2, feature in gml3.1.0 is not always a geometric object, but an abstract of a practical geographical Object (entity or phenomenon. Such a feature can describe specific objects, abstract or conceptual objects, and also describe the phenomena associated with spatial locations in changes.

The following UML diagram shows the structure of the GML object. The schema documents of each object are organized around the object classification in the diagram.

 

The items starting with an underscore (such as feature) in the figure can be considered as a typical object instance of this class. For example, element GML: _ feature should be interpreted as "any GML element", which can be used to define the value of the GML feature as a variable or template of "any element.

Geographical elements include a series of spatial and non-spatial attributes. The element schema provides a framework for creating elements and element sets of GML, it defines abstract and specific element elements and types, and introduces definitions and declarations in geometric and temporal modes through <include> elements. Geometry schema describes the geometric model of geographical elements in detail. Temporal schema extends the core elements of GML to include elements that describe temporal features of geographical data. It provides a framework to describe temporal changes of dynamic elements. Coverage schema supports ing from the time-space domain to the property value. The property type is public for all geographical locations in the time-space domain, the time-space domain is directly composed of many direct locations in the coordinate space. The topology schema defines the topology object that reflects the relationship between geographical elements.