LkbRpc

Background

As of late 2010, the LKB sports an XML-RPC interface to select system-internal functionality (an API of sorts). Initially, this add-on module is only available in the so-called LOGON tree (see the LogonTop page for background) and limited to quite a small number of functions, viz. those needed to enable an on-going PhD project on incremental parsing.

Server Initialization

Before going into server mode, the LKB and [incr tsdb()] code needs to be loaded, as well as the grammar to be used (e.g. the ERG). Assuming a functional and complete LOGON system, the following will start the XML-RPC server on port 4013:

  (lkb::rpc-initialize :port 4013)

A convenient short-hand to do all of the above from the command line is available in the LOGON tree, e.g.

  $LOGONROOT/lingo/lkb/server --tty --erg --rpc 4013

Note that this script will also initialize a generation server, which requires compiling a set of indices for the grammar the first time it is invoked; this process can take several minutes to complete.

The LKB XML-RPC server will bind to the custom port specified when initializing the server (4013 in the above examples) and does not use a server-specific prefix in request URLs. Hence, assuming the above example, XML-RPC requests should be directed to http://localhost:4013/ (or maybe the actual machine name, rather than using localhost).

Interface Functions

Following is a semi-formal summary of the available interface. In terms of XML-RPC data types, integer in the following corresponds to <I4> and string to <STRING>.

Many of the interface functions either create or operate on so-called chart edges, essentially a representation of a tree fragment, where the daughters (if any), in turn, are represented as edges.

• chart.create → integer This function creates a new chart object, which can subsequently serve as the (per-client) storage for chart edges. Return values greater than zero indicate success (and constitute valid chart handles for subsequent calls).

• grammar.instantiate-lexical-entry ( integer chart, string surface, string entity ) → integer

  Instantiates the lexical entry named entity, specializing its orthography to surface, and stores a new edge in chart. An edge handle (greater than zero) is returned on success; the function will fail in case entity does not name valid lexical entry in the grammar, which case a negative value is returned.

• grammar.instantiate-rule ( integer chart, string entity ) → integer

  Instantiates the grammar rule named entity and stores a new edge in chart. An edge handle (greater than zero) is returned on success; the function will fail in case entity does not name a valid grammar rule, in which case a negative value is returned.

• chart.combine ( integer chart, integer mother, integer child, integer index ) → integer

  Combines chart edges mother and child, by unifying the feature structure of child into the argument position of mother indicated by index (where argument positions are zero-based); when successful, stores a new edge in chart. A zero return value indicates unification failure.

• chart.root ( integer chart, integer edge, string entity ) → integer

  Tests the feature structure of edge against the start symbol entity, i.e. attempts to unify the two structures; a zero return value indicates failure, negative return values an invalid call, and a non-zero positive value success.

• chart.release ( integer chart ) → integer

  Release the storage associated to chart, including all edges recorded there. Upon successful completion (indicated by a zero return value), chart is no longer a valid handle, nor are any edge handles contained in chart.

In addition to the above methods, which are appropriate to (re-)build HPSG derivations, the following is a convenience method that can be used for custom setups:

• grammar.instantiate-type ( integer chart, string entity ) → integer

  Instantiates the type named entity and stores a new edge in chart. An edge handle (greater than zero) is returned on success; the function will fail in case entity does not name a valid type, in which case a negative value is returned.