also the traffic flow on this geometric object. The geographic data 
file (GDF) models by attributes like ’’direction of traffic flow” 
(one way streets) or relations like ’’prohibited turn” the topology 
of the traffic network. 
Picture 3: GDF Structure in a NIAM Diagram 
Airports 
Large Airports started to use CAD software to create information 
systems known today as facility management systems. In these 
information systems the taxiway network is included with a high 
geometric accuracy. The data model uses many of area objects to 
describe the apron. A topological network for the taxiway 
network is not implemented. 
Due to the fact that non standardized airport data models are 
available the CAD Systems or GIS Systems are set up by 
companies designing individually the data models for airports. 
The effort to homogenize these different datasources to get an 
applicable database for a taxi guidance system is excessive. Field 
survey leads in this application to tremendous cost, but 
sometimes it is not avoidable for safety relevant systems. 
4 ADAPTION OF A DATA STRUCTURE TO THE 
TAXIWAY NETWORK 
For the creation of the data specification of a taxiway network on 
airports the data specification of Geographic Data File (GDF; 
Specification of digital road maps for car navigation / GDF /) was 
used as a base to model the traffic of the aircrafts in an airport. 
Due to the strong analogies to the street network the description 
of the geometric objects seemed quite easy. In reality about 90 % 
of the important object and relation definitions had to be 
modified just slightly. 
On this base the adaptation of objects, attributes and relations to 
the new requirements was quickly possible. 
5 SOME SPECIFIED FEATURES 
5.1 Objects 
Taxiway network objects could be defined analogously to the 
road elements and junctions. Only the short distance before the 
parking position the geometry of the trajectory of the aircraft is 
varying in dependency of the type of the aircraft. 
5.2 Attributes 
The attribute definition was the part of the data model in which 
the major changes took place. The main item was to introduce 
specific quality items. This quality is modeled in the GDF more 
on the level of sections or the data sets. In this case the quality 
was connected directly to the objects or objects groups. 
5.3 Relationships 
The relations building the topology of the traffic flow were 
transferable almost completely to the application of the taxiway 
network. Some new relations concerning the regulation of the 
traffic had to be introduced. 
6 DATA QUALITY 
The quality of the data for systems in an aircraft is very 
important. Some system designs in the use of an airport database 
give benefits to the optimization of the capacity or the comfort for 
the pilot , driving on the way to the parking position to the 
runway or vice versa. These systems will get more weight if they 
become relevant for the safety of the traffic flow. In fact also a 
simple assistance system for the pilot will influence the traffic 
flow and will lead to an advantage if the driving on the taxiway is 
done with good orientation information. 
In the following passages of the paper some key definitions of the 
quality will be considered. 
The error rate of objects has to be tested and the data set has to 
be checked carefully close to the production circle. It is naturally 
clear that the result of the production has to be checked by 
software packages and the data capturing environment check the 
plausibility of each input. GDF follows in case of data production 
the philosophy used in industrial production processes. 
The up-to-dateness is the next topic closely related to the error 
rate. The result of a changed information is the same as it is false 
from the beginning. The deviations of these two quality 
parameters are reasonable because the information channels are 
attributed separately. Out of this information the reliability can be 
estimated and used in that way to exploit this information. 
The completeness of the data set is by far not risk relevant if the 
information is still correct. The function used on the date 
indicates if this quality criteria will show a lack for the reliability 
of the system. 
The accuracy of the date base is the last criteria discussed here 
sketchily. The geometric accuracy is depending on the 
application. While for an automatic driving system the 
coordinates of the taxiway must have at least lm accuracy the 
requirement for a moving map for the orientation of the pilot is 
next to 20 m accuracy.