Publication Date: 2018-01-11

Approval Date: 2017-12-07

Posted Date: 2017-11-14

Reference number of this document: OGC 17-036

Reference URL for this document: http://www.opengis.net/doc/PER/t13-FA004

Category: Public Engineering Report

Editor: Charles Chen

Title: OGC Testbed-13: Geospatial Taxonomies ER


OGC Engineering Report

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WARNING

This document is not an OGC Standard. This document is an OGC Public Engineering Report created as a deliverable in an OGC Interoperability Initiative and is not an official position of the OGC membership. It is distributed for review and comment. It is subject to change without notice and may not be referred to as an OGC Standard. Further, any OGC Engineering Report should not be referenced as required or mandatory technology in procurements. However, the discussions in this document could very well lead to the definition of an OGC Standard.

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1. Summary

This Engineering Report (ER) documents the Geospatial Taxonomy research activities conducted by the Aviation (AVI) subthread of the Cross Community Interoperability (CCI) thread in OGC Testbed 13. One of the critical factors in the overall usability of services - and System Wide Information Management (SWIM) enabled services in particular - is the ability of a service to be discovered. The ability of a service to be discovered is assured by providing a uniformly interpretable set of service metadata that can be accessed by a service consumer through a retrieval mechanism (e.g., a service registry). Such a set of metadata (commonly referred to as a service description) has been defined by Federal Aviation Administration (FAA) and European Organization for the Safety of Air Navigation (EUROCONTROL) and formalized in a Service Description Conceptual Model (SDCM) [2].

The SDCM is currently used in standard service description documents and service registries by both FAA and EUROCONTROL. As part of the effort of enhancing service discovery, both organizations also use a number of categories that can be associated with all services and are generally referred to as taxonomies. The current set of taxonomies used by both EUROCONTROL and FAA categorizes (i.e., meta tags) services based on their availability status, interface model, data product, etc. However, despite the increasing role of OGC services in the SWIM environment, no taxonomies for categorizing services based on geographical coverage or other geospatial characteristics have been defined. This ER documents the work conducted as part of Testbed 13 CCI thread and AVI subthread to identify and classify SWIM-enabled Service Oriented Architecture (SOA) services with geographical taxonomies and the integration thereof into SDCM [2].

1.1. Requirements

The following requirements are to be addressed in this ER:

  1. Develop a concept of geospatial taxonomies that will efficiently support classification of services based on their geospatial characteristics (e.g., geographical coverage). The concept should take into account all relevant geospatial characteristics, such as nation states, flight information regions, and airspace classifications.

  2. Provide considerations for modifications of the SDCM to support the use of geospatial taxonomies.

  3. Produce one or more taxonomies in formats suitable for use by software clients (e.g., Extensible Markup Language (XML) and Resource Description Framework (RDF)).

1.2. Key Findings and Prior-After Comparison

The topic of geosemantics and taxonomies for aviation has been explored previously in OGC Testbed 12 (OGC 16-039) and in other domains in depth. In past demonstrations, analyses recommended the use of run-time registries and complex use cases for service discovery and data taxonomy/ontology, but this assumes that the information contained within those services incorporate OWS Context Specification and/or Geography Markup Language (GML) such as the Aeronautical Information Exchange Model (AIXM). However, much of the information exchanged within the FAA National Airspace System (NAS) System-Wide Information Management (SWIM) network is made up of various data models which do not conform with OGC OWS Context specifications. For example, the FAA Traffic Flow Management System (TFMS) and SWIM Terminal Data Distribution System (STDDS) data models contain an XML format which contain geography data (e.g., Lat/Lon coordinates) but do not contain OGC OWS Context data elements or GML.

Another observation is that the current FAA SWIM registry is a design-time registry and does not use the OGC Catalog Service for Web (CSW) [OGC 12-168r6]. While this could potentially change with the anticipated release of FAA Common Support Services (CSS) such as CSS-Aeronautical Information Management (AIM), CSs-Weather (Wx), and CSS-Flight Data (FD), the current direction for the FAA NAS Service Registry Repository (NSRR) is to enhance the current registry search capabilities by creating semantic taxonomies which can be used to categorize services for improved service discovery. These services must have a standard taxonomy in order to incorporate geospatial metadata to enable the discovery of geospatial services. One approach is to define and apply commonly accepted terminology through the use of international definitions at the International Civil Aviation Organization (ICAO) level and national definitions at the FAA level, and so on. Through hierarchical categorization, other nation states may also develop their own national or regional level taxonomies which can be mapped to the international taxonomy for commonality across multi-national domains.

The goal of this ER is to formulate a taxonomy that can incorporate geospatial characteristics identified within a data set into the service metadata and integrate it with SDCM to enable geospatial service discovery in the current registry. Future work areas include a proposed concept for a geospatial identification service using WPS to analyze a dataset and identify geographic characteristics according to a set of taxonomy inputs resulting in a metadata document which can be included in SDCM.

1.3. What does this ER mean for the Working Group and OGC in general

This engineering report documents the concepts of geospatial taxonomies that will efficiently support classification of services based on their geospatial characteristics such as geographical coverage for nation states, flight information regions, and airspace classifications. Thus, the considerations include the use of SDCM and required modifications to support taxonomies developed as part of this activity. The chosen working group for review of this ER is the Geosemantics Domain Working Group (DWG). This work may also be applicable to the Aviation DWG which is co-sponsored by the FAA and EUROCONTROL.

The scope of the Geosemantics DWG is any aspect of conceptual modeling and formal representation of geospatial knowledge which advances the geospatial interoperability mission of OGC. A particular focus will be the adoption or development of tools and methods in support of these activities. It is the mission of the Geosemantics DWG to establish an interoperable and actionable semantic framework for representing the geospatial knowledge domains of information communities as well as mediating between them. This ER will address the need for geospatial taxonomies using aviation-specific geographical conventions (i.e., named boundaries). The use of geospatial semantics will enable better descriptions of services, including OGC web services in the FAA’s SWIM registry as well as in OGC catalogue services.

1.4. Document contributor contact points

All questions regarding this document should be directed to the editor or the contributors:

Table 1. Contacts
Name Organization

Charles Chen

Skymantics

1.5. Future Work

The solutions described in this engineering report may provide further insights if implemented as a greater solution for service registries such as the OGC Catalogue Service. Furthermore, implementation of the recommendations for SDCM will provide a path forward for prototyping and implementation of SWIM registries and discovery of services containing geographical characteristics as described by the taxonomies contained herein.

1.6. Foreword

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. The Open Geospatial Consortium shall not be held responsible for identifying any or all such patent rights.

Recipients of this document are requested to submit, with their comments, notification of any relevant patent claims or other intellectual property rights of which they may be aware that might be infringed by any implementation of the standard set forth in this document, and to provide supporting documentation.

2. References

3. Terms and definitions

For the purposes of this report, the definitions specified in Clause 4 of the OWS Common Implementation Standard OGC 06-121r9 shall apply. In addition, the following terms and definitions apply.

3.1. Semantics

A conceptualization of the implied meaning of information that requires words and/or symbols within a usage context.

3.2. Service Description

The information needed in order to use, or consider using, a service.

3.3. Service-Oriented Architecture (SOA)

A paradigm for organizing and utilizing distributed capabilities that may be under the control of different ownership domains. A SOA provides a uniform means to offer, discover, interact with, and use capabilities to produce desired effects consistent with measurable preconditions and expectations.

3.4. Registry

An enabling infrastructure that uses a formal registration process to store, catalog, and manage metadata relevant to a service. A registry supports the search, identification, and understanding of resources, as well as query capabilities.

3.5. System Wide Information Management (SWIM)

A concept using Service Oriented Architecture to facility the exchange Air Traffic Management information amongst stakeholders in the aviation domain such as Air Navigation Service Providers, airports, and airspace users.

3.6. Taxonomy

A system or controlled list of values by which to categorize or classify objects.

3.7. Web Service

A platform-independent, loosely-coupled software component designed to support interoperable machine-to-machine interaction over a network. It has an interface described in a machine-processable format. Other systems interact with the Web service in a manner prescribed by its description by means of XML-based messages conveyed using Internet transport protocols in conjunction with other Web-related standards.

4. Abbreviated Terms

  • ATM Air Traffic Management

  • ICAO International Civil Aviation Organization

  • FAA Federal Aviation Administration (United States)

  • NAS National Airspace System (United States)

  • NSRR NAS Service Registry and Repository

  • OWL Web Ontology Language (W3C)

  • OWL-S Web Ontology Language for Services (W3C)

  • OWS OGC Web Service

  • RDF Resource Description Framework (W3C)

  • RDFS Resource Description Framework Schema (W3C)

  • SDCM Service Description Conceptual Model

  • SOA Service Oriented Architecture

  • SWIM System Wide Information Management

  • WSDOM Web Service Description Ontological Model

5. Overview

The approach in this ER activity for developing the geospatial taxonomies begins with classification of known geospatial concepts. The International Civil Aviation Organization (ICAO) manages the administration and governance of 191 member states to reach consensus on international civil aviation standards and practices. It is important to assess the status quo for ICAO taxonomies by considering the geography of nation state boundaries, flight information regions, and airspace allocations to determine how data services can be identified and discovered by its users. Once the status quo is determined, additional taxonomies may be generated to fill the gaps where certain geospatial characteristics associated to services may be defined and used for service discovery.

This report identifies existing taxonomies defined at the international, national, and regional levels. Once these taxonomies have been defined, integration of the taxonomies in the Service Description Conceptual Model with existing taxonomies can be associated for better registry discovery. Metadata within a service description is the responsibility of the service provider. However, this ER provides recommendations on geospatial service methodologies which can assist in the metadata descriptions for web service descriptions and better service discovery with the FAA SWIM registry.

5.1. Requirements

The following requirements are associated with this engineering report

  1. Develop a concept of geospatial taxonomies that will efficiently support classification of services based on their geospatial characteristics (e.g., geographical coverage). The concept should take into account all relevant geospatial characteristics, such as nation states, flight information regions, and airspace classifications.

  2. Provide considerations for modifications of the SDCM to support the use of geospatial taxonomies.

  3. Produce one or more taxonomies in formats suitable for use by software clients (e.g., XML, RDF).

5.2. Solutions

The following sections have been identified as part of the research conducted for this report:

  • Section 6.1 Taxonomy Methodology identifies the status quo which identifies three common taxonomies developed for SWIM services.

  • Section 6.2 ICAO Airspace Classifications describes the current ICAO requirements for Air Traffic Control Services based on airspace classifications.

  • Section 6.3 FAA Airspace Classifications describes the FAA airspace classification methodology. These classifications are categorized into a taxonomy in Appendix A.1 Airspace Classification Taxonomy.

  • Section 6.4 ICAO Regions describes the list of current ICAO regions. These regions are categorized into a taxonomy in Appendix A.2 ICAO Regions Taxonomy.

  • Section 6.5 ICAO Flight Information Regions describes the list of current ICAO Flight Information Regions (FIR). These FIRs are better categorized into a taxonomy based on the FIRs for a particular nation.

  • Section 6.6 Area Control Centers describes the list of FAA Air Route Traffic Control Centers (ARTCC). These ARTCCs are categorized into a taxonomy in Appendix A.3 US Flight Information Regions Taxonomy.

  • Section 6.7 Airways describes the classification methodology of U.S. Airways, which are categorized into a taxonomy in Appendix A.4 Airways Taxonomy.

The taxonomies developed for this engineering report activity are recorded in Taxonomies.

6. Taxonomy Methodology

The methodology for geospatial taxonomies begins by analyzing the various geospatial characteristics of aviation data used for identifying airspace geographies. Most airspace users identify airspaces based on naming conventions defined by ICAO such as ICAO regions, flight information regions, and air traffic control centers. By determining the naming conventions for these airspaces and their associated areas of governance, services that contain these data types can be tagged with associated metadata to assist in discovery of relevant data.

Information discovery using this method is not intended to replace advanced search and discovery of data using a run-time registry or web service based search using OGC web service interfaces such as CSW or Web Feature Services (WFS). Rather, this method complements the advanced capabilities of CSW and WFS. Much of the information accessible via SWIM does not conform to the international data model standards of AIXM, Weather Information Exchange Model (WXXM), and Flight Information Exchange Model (FIXM), and therefore is not geospatially discoverable using OGC registry methods. Overhauling all data on SWIM is not feasible considering the number of operational users. Therefore, for those data types which are not discoverable based on geospatial information, this engineering report analyzes the semantics for geospatial taxonomies such that metadata can be annotated on the service descriptions contained within the SWIM registry.

6.1. Status Quo

The FAA and SESAR have jointly developed several (SCR) semantic artifacts including common taxonomies (http://www.semantics.aero/). These taxonomies include:

As an example, these taxonomies above can be visualized in Figure 1 below.

8 taxonomies e40c1
Figure 1. SWIM Common Taxonomies

These taxonomies, written in Web Ontology Language (OWL) and RDF, provide the basis for taxonomy representation for geospatial taxonomies defined in this engineering report.

6.2. ICAO Airspace Classifications

ICAO classifies airspace in an alphabetical format (e.g., Class A, B, C, D, E, F, & G). These classes are defined based on separation, altitude, ATC services, aircraft speeds, and communication methods. Generally, airspace classifications depend on concepts of aircraft separation, air traffic control clearance, traffic information (aircraft intent and hazards), and flight rules. Figure 2 is an excerpt from the ICAO Annex 11, Appendix 4 which provides a list of defined airspace classifications. It should be noted that not all nations follow the ICAO methodology for airspace classifications.

7 airspace classifications 09dab
Figure 2. Excerpt of ICAO Annex 11, Appendix 4

6.3. FAA Airspace Classifications

Airspace classifications in the U.S. use a modified version of the ICAO Airspace classification rules. These classifications often refer to Air Traffic Management flight rules based on an aircraft’s navigational equipage and classified as Instrument Flight Rules (IFR) and Visual Flight Rules (VFR). For VFR flights, navigation must typically remain at a lower altitude and separation and landing maneuvers are made using human visual cues. In IFR operations, aircraft must be equipped with sufficient navigational equipment such as radar, altimeter, etc. such that the pilot can maneuver aircraft and maintain separation from other aircraft using minimal or sometimes no visual cues (e.g. through fog).

Figure 3 provides a visual representation of the types of airspace classifications used in the U.S. [1]:

6 solutions a81b6
Figure 3. Airspace Classes in the United States

Figure 4 provides a description for each Airspace class in the U.S.

6 solutions 92517
Figure 4. Airspace Classification

Class A Airspace is from 18,000 feet Mean Sea Level (MSL) up to and including Flight Level (FL) 600. This includes airspace up to 12 nautical miles off the coast of the contiguous United States and Alaska. Any space beyond the 12 nautical miles off the coast line is considered international airspace. Domestic radio navigational signal and ATC radar coverage is required to be considered Class A airspace. All aircraft must fly under IFR in Class A airspace.

Class B Airspace is bounded from the surface to 18,000 feet MSL surrounding major airports. The volume of airspace for Class B is designed based on the surface area of the airport and the volume of terminal airspace controlled by the airport or terminal air traffic control center. All aircraft require ATC clearance to operate within this airspace. ATC manages separation of aircraft. VFR operation may be flown if a cloud clearance is provided by ATC. Class B aeronautical charts contain geographical fixes which correlate to appropriate frequencies in which aircraft must obtain ATC clearance before entering the airspace. Currently, 12 airports have Class B airspace. A list of Class B airspaces for FAA based on airports are provided in Airports and Facilities.

Class C Airspace is bounded from the surface of the airport to 4,000 feet MSL. The first layer of the airspace is from the surface area to the ceiling boundary with 5 nautical miles radius. The second layer is from 1,200 feet MSL to the ceiling at a 10-mile radius. The outer layer extends to 20 nautical miles radius. Class C airspace surrounds airports containing regular commercial traffic of 100 passengers per flight or more. Class C airspaces contain an operational tower, radar-controlled approach system, and a minimum number of IFR approaches per year.

Class D Airspace is bounded from the surface of an airport to 2,500 feet MSL. The outer boundary radius varies but is typically 4 nautical miles. Class D airspace is classified as any airport with a functional control tower with minimal IFR approaches. The airspace reverts to Class E or G during hours when the tower is closed or under special conditions.

Class E Airspace is controlled airspace that is neither A, B, C, or D. this airspace extends from 1,200 feet Above Ground Level (AGL) up to 18,000 feet MSL. Some areas as low as 700 AGL are included and are notated in sectional charts. Most of the airspace in the United States is class E.

Class F Airspace is not used in the U.S. ICAO defines Class F airspace as a hybrid of Class E and G airspace in which ATC separation guidance is available but not required for IFR operation.

Class G Airspace includes all airspace below 14,500 feet MSL which is not otherwise classified or controlled. Class G airspace is considered uncontrolled airspace.

Special Activity Airspace (or Special Use Airspace) refers to airspace which can be designated for a given geospatial volume for reasons such as national security, public events, military exercises, etc. SAA can be contained within any given airspace classification above, and should be designated by both with a service taxonomy.

6.4. ICAO Regions

Historically, ICAO led a study to define regional air navigation (RAN) and continued to refine the air navigation regions in 1964 with the Air Navigation Commission. Further consolidation occurred in 1980, and the present regional structure is defined in the Appendix 1 of the ICAO Doc 8144-AN/874: Directives to Regional Air Navigation Meetings and Rules of Procedure for their Conduct. These regions are comprised of the following regions:

  1. ​AFRICA-INDIAN OCEAN (AFI) REGION

  2. ​ASIA (ASIA) REGION

  3. CARIBBEAN (CAR) REGION

  4. ​EUROPEAN (EUR) REGION

  5. ​MIDDLE EAST (MID) REGION

  6. ​NORTH AMERICAN (NAM) REGION

  7. ​NORTH ATLANTIC (NAT) REGION

  8. PACIFIC (PAC) REGION

  9. ​SOUTH AMERICAN (SAM) REGION

A visual depiction of an ICAO Region taxonomy is shown in the Figure 5:

5 taxonomy 2d74e
Figure 5. ICAO Regions

A taxonomy for ICAO Regions is provided in Taxonomies.

6.5. ICAO Flight Information Regions (FIR)

Each of the ICAO regions defined above also contain multiple Flight Information Regions defined based on major areas of air traffic control services such as flight information services and alerting services (ALRS). Each ICAO region contains a number of agreed upon FIRs [4]. Each FIR contains an FIR ID annotated using a four letter code. Primarily, the ICAO FIR ID will be used for identifying an ICAO designated FIR. However, when attempting to identify an Area Control Center, a different identification code may be used based on each nation.

6.6. Area Control Centers

In the U.S., Area Control Centers are called Air Route Traffic Control Centers (ARTCC), or simply Centers, which contain ARTCC codes which