Military Communications and Information Technology: A Trusted ...

216 Military Communications and Information Technology...
In Language Representation 2 (Slovak) we require:
• Commands finished with dots (.);
• Concrete syntax of the move command is Presuň do ;
• Concrete syntax of the destroy command is Znič zbraňou
cieľ .
Similarly, these concrete language requirements can be fulfilled using the following
productions:
1. → .
5. → Presuň do #process_
move
6. → Znič zbraňou cieľ
#process_destroy
The aim of semantic processing is to properly interpret language constructs
that are recognized by the parser. Of course, semantic meaning of the corresponding
language constructs in both language representations should be the same and
the aim is also to utilize language-independently as much of the semantic processing
as possible. Lexical elements (in our example, key words, identifiers of military
units and weapon systems and GPS coordinates) might be language-dependent
and that is why a separate lexical analyzer has to be constructed for each language
representation. Another aspect that must be taken into account during lexical as well
as semantic processing comes from different naming conventions, measurement
units, data formats and representations, etc.
For example, in our grammars describing concrete syntaxes we can derive
the following semantically equivalent language constructs:
• move Platoon 1 to N49˚4'1,21'' E19˚35'53,62''; destroy N49˚5'3,2''
E19˚34'33,12'' by Tank 1;
• Presuň Čata 1 do 49˚4‘1,21‘‘N 19˚35‘53,62‘‘E. Znič zbraňou Tank 1 cieľ
49˚5‘3,2‘‘N 19˚34‘33,12‘‘E.
For the majority of the semantic routines it is necessary to pass some data
(called semantic attributes) to other semantic routines. For example, the semantic
routine #process_coordinates needs to pass the GPS coordinates recognized
by the lexical analyzer to the semantic routines #process_move or
#process_destroy. This task can be accomplished using a semantic stack [13].
A semantic stack is a second stack maintained by the parser which contains semantic
records associated with the terminals and variables of productions being
parsed. Each semantic record can contain arbitrary information (semantic attributes)
that needs to be passed between individual semantic routines. The semantic
records associated with the variables of individual productions are depicted
in the pseudocode of semantic routines in the same way as the corresponding
, but using the Courier font. Next follows the description
of semantic routines: