Purpose of the profile Scope of the profile Using the AIXM GML Profile

OGC 12-028r1 54 Copyright © 2016 Open Geospatial Consortium

12. AIXM GML Profile

12.1. Introduction

AIXM is built on a foundation of ISO standards, such as ISO 19107 Spatial Schema, ISO 19108 Temporal Schema, and ISO 19136 Geography Markup Language, GML. These standards facilitate the interoperable exchange of spatial information in and between various application domains. ISO 19107 and ISO 19108 define spatial and temporal types that can be used in an application schema such as AIXM. These two standards target the conceptual level of schema modeling. A conceptual schema is implementation technology independent, meaning that it can be used as the basis for different implementations based on XML, JSON, etc.. ISO 19136 provides realizations of the types defined in ISO 19107 as well as ISO 19108, targeting an XML implementation 5 . It is important to recognize and understand the distinction between these two levels of application schema modeling conceptual and implementation. This profile starts at the conceptual level, defining which conceptual types are relevant in general. It then also establishes the link to the XML implementation based upon ISO 19136. The structure supports adding of other implementations for example based upon JSON in the future.

12.2. Purpose of the profile

In order to satisfy the needs of multiple domains regarding the representation of spatial information, the amount of concepts and functionality covered by ISO 19107, ISO 19108 and ISO 19136 is far more than that required by the Aviation domain. There is therefore a need to ‘subset’ these specifications to create a ‘profile’ that contains only the features required for Aviation. This document provides a textual description of the profile.

12.3. Scope of the profile

The GML Profile for aeronautical data is limited to 2D elements and includes only the features necessary for encoding geometries of type point, linecurve and polygonsurface outer boundaries only. The following components of GML are out of scope for the AIXM GML Profile: Topology, Linear Referencing, Coverages. This additional GML components necessary to the ISO 19139 gco basicTypes.xsd, which is imported in the GML and AIXM metadata, needs additional types. These are not included in this profile. 5 It also defines a number of conceptual types, for example ArcByCenterPoint, that are not defined in ISO 19107. The focus of ISO 19136, however, is on the realization of conceptual types in what is called an “implementation schema”. OGC 12-028r1 55 Copyright © 2016 Open Geospatial Consortium

12.4. Using the AIXM GML Profile

This section describes how to use the AIXM GML profile and how to declare that a particular application schema such as the AIXM schema adheres to that profile. According to the [ISO 19136] GML Standard, 20.4 “Instance documents of a profile shall be valid against the full GML schema”. Further more [ISO 19136, 20.5] “A GML application schema shall reference the full GML schema in the schemaLocation attribute of the import element”. Importantly whilst all GML profiles are defined in the gml namespace they must not be directly imported as a replacement for the full GML application schema. Doing so would redefine GML and break interoperability. A GML application schema document conforming to one or more GML Profiles shall provide an appInfo annotation element gml:gmlProfileSchema for every profile in the root schema document schema element where the value is a schema location of the profile schema. annotation appinfo gml:gmlProfileSchemahttp:www.aixm.aeroschemaGML_profilegml321forAIXM.xsd gml:gmlProfileSchema appinfo annotation The annotation tag is annotation of the top level xsd:schema type as shown in the full example below. Note how the full gml.xsd is still imported.

12.5. XML Namespaces