Making Maps Navigable - Programming GPS and OpenStreetMap Applications with Java - page 120

machine power on the weekend and to find on Monday morning that the
fix was not checked back into the versioning system.
Setting up the first cycle of a compilation consumes machine and man
power and consecutive cycles or productions have to be observed carefully.
How independent are the branches of the compiler? How vital is the missing
information for the rest of the compilation? Where can the compiler be
re-started after a failure? Is there a map or a compiler problem? Is enough
disk space available?
Compiler Paradigms
As map data is constantly growing, sequential formats become more prob-
lematic to handle. The files have to be unpacked, processed, repacked, and
stored. UTF coding has to be used to represent international languages.
The OSMcompiler was use to save the reader from installing a relational
database management system (RDBMS). Nevertheless, it must be men-
tioned that the paradigm to process sequential files has given way to re-
lational data manipulation. The advantages are obviously the guaranteed
referential integrity of the delivered map data. After the data is loaded
into a relational database, the constraints can be enabled to validate the
integrity.
Once map data is in place, every compilation step can be modeled with
SQL scripts to produce intermediate tables (data states). Every conversion
step can be implicitly controlled by the database system. In addition,
most RDBMS have a built-in engine to process spatial data to calculate
distances, areas, and to simplify shapes, etc.
Therefore, it is strongly recommended to build any map compiler in
conjunction with a RDBMS. Still, post-processing is inevitable, since SQL
is not suited for route calculations, etc. Basically SQL performs best by
filtering data records, which are represented in table rows (horizontal). To
compose a route of links, the database has to vertically connect a number
of rows (of links) to a path.
PSF and the Navigational Data Standard (NDS)
Whatever compiler paradigm is used, in the end the data has to be exported
to a PSF with a well-defined file structure on the media. Historically PSFs
are static data and map compilation is always a one-way process. Every
navigation system for different cars with different features and different
coverage has its own PSF, which is created by large map compilation teams.
Since the production of a new system requires many resources the Ger-
man car industry has created a committee to define a standard PSF, the
navigational data standard NDS. The NDS is defined by a number of XML