RDG

Regular Dependency Grammars

Alto supports grammars in the Regular Dependency Grammar formalism. RDG is a dependency grammar formalism which is strongly equivalent to (slightly restricted) LCFRS; in particular, it can describe non-projective dependency structures.

Grammar format

Alto can read RDG grammars (with filename extension .rdg) in a file format that looks pretty much like one would write RDGs on paper:

S -> <wird:101>(VP)
VP -> <gegeben:1,20>(NP, NP)
NP -> <hans:0>
NP -> <kaesebrot:10>(Det)
Det -> <ein:0>

Each rule expands a nonterminal symbol (such as S or VP) into a right-hand side, which may specify a number of nonterminals as children and connects them with a terminal symbol of the form <word:oa>. Here word is a word that may appear in the string, and oa is an order annotation, which specifies how the string tuples derived by the nonterminals on the right-hand side are combined into a string tuple for the parent nonterminal. Each order annotation may contain an arbitrary number of blocks, which are separated by commas.

Unlike in the standard RDG literature, a comma may occur as the first or last character of an order annotation, indicating a string tuple where the first or last block is an empty string. Thus for instance, the order annotation ,0 describes a pair of strings; the first element of the pair is an empty string, and the second element of the pair is the word itself.

RDGs in Alto always use the start symbol S.

Parsing RDGs from the GUI

You can load an RDG grammar (with filename extension .rdg) from the Alto GUI, using File -> Load IRTG. This will open a grammar window, from which you can parse input strings (on the string interpretation) as usual.

Specialized RDG Parser

You can start Alto in a special mode in which you can simply type sentences and they will be parsed with a given RDG grammar. To this end, start Alto as follows:

java -cp <alto.jar> de.up.ling.irtg.script.RdgParser <grammar.rdg>

where <alto.jar> is the name of your Alto Jarfile, and <grammar.rdg> is the filename of your RDG grammar. This will open an interactive parser shell which looks as follows:

You can then type a sentence, and Alto will try to parse it. If parsing succeeded, Alto will show a window in which you can scroll through the different parses:

You can type quit to exit the parser shell, and help to get help on the commands you can use within the parser shell.