45
11.2.1.1 Compaction analysis 11.2.1.1.1 First family – small files
Figure 9 - Compaction results on D-Notams
The EXI compression with post compression and schema knowledge reduces the size of D-Notams by almost 90 and makes it the most efficient algorithm for small files.
11.2.1.1.2 Second family – medium size files
In the following sequences of tests family 2 3, the differentiation has been made between the types of features contained in the samples. The different features are
runways, routes, airspaces, geo borders, vertical structures, navaids and taxiways.
46
Figure 10 - Compaction results on second family
For medium size files, EXI performs better even without schema than Fast Infoset. Without post compression, runways, routes, vertical structures and taxiways are
compressed below 30 with both FI and EXI.
The schema knowledge of EXI offers significant improvement for runway elements, geo borders taxiways and airspaces, but not for runways, route, vertical structures and
navaids.
47 Finally, when considering post compression, no algorithm performs significantly better
than simple gzip compression XML document. Some of them even perform worse, due to incompatibility between the output of the EXIFI compression and the post
compression algorithm. As a matter of fact the maximum upgrade we can obtain is about 5 more compression compared to gzip. Additionally, section 11.2.1.2.2 demonstrates
that this small gain can come with great costs.
11.2.1.1.3 Third family – bigger files
The results for compression algorithms without post compression are very similar to family 2 here, so we directly consider comparing them with post compression:
Figure 11 - Compaction results with post compression for bigger files
Those charts confirm what has been seen previously: EXI offers a good level of compaction for taxiways, runways and airspaces compared to Gzip, showing the
efficiency of EXI on files composed of few elements with limited string data coordinates and dates
48
11.2.1.1.4 Conclusion
EXI with post compression offers very interesting performance in terms of compaction, always better than post compression only and Fast Infoset, though the latter offers quite
good performances overall. Adding the schema to EXI with post compression will improve the performance even more for the following types of data:
Taxiways Airspaces
Runway elements Geo borders
11.2.1.2 CPU consumption
