This page provides an in-depth discussion of the so-called PET Input Chart (PIC) input mode for the cheap parser. PIC is an XML-based generalization of the older YY input mode (see the PetInput page for background). However, PIC too has its limitations and issues, including its (apparent) incompatibility with the [incr tsdb()] profiler, see below. Where YY input mode is sufficient, it may still be the most versatile and widely supported option.

XML input mode is very similar to YY input mode. It allows you to specify only simple tokens that get analysed internally by \cheap or to put all kinds of preprocessing information \cheap can handle into the input directly, namely POS, morphology, lexicon lookup and multi-component entries.

It extends the YY mode in that it allows to have structured input tokens to provide a means to encode, say, named entities resulting from base tokens. It also allows to specify modifications to feature structures (coming from lexicon entries).

It is called with -tok=pic_counts and can be used in combination with -default-les (see the PetInput page for details) to trigger unknown words with POS tags, much like in YY mode.


A typical way of calling it, with xml input and the best ranked xml rmrs output) would be:

  cat input.xml | cheap -tok=pic_counts -default-les -packing -mrs=rmrx -results=1 grammar.grm

A simple example input is given below:

<?xml version="1.0" encoding="utf-8" standalone="no" ?>
<!DOCTYPE pet-input-chart
 SYSTEM "/use/local/lib/xml/pic.dtd">
<!-- This FAQ is short -->
  <w id="W1" cstart="1" cend="5">
    <pos tag="DD1" prio = "1.0" />
  <w id="W2" cstart="7" cend="9">
    <pos tag="NP1" prio = "1.0" />
   <w id="W2" cstart="7" cend="9" constant="yes">
    <typeinfo id="n_-_pn_le" baseform="no" prio="1.0">
      <fsmod path="SYNSEM.LKEYS.KEYREL.CARG" value="F.A.Q."/>
  <w id="W3" cstart="11" cend="12">
    <pos tag="BE" prio = "1.0" />
  <w id="W4" cstart="14" cend="18">
    <pos tag="JJ" prio = "1.0" />

Note: the two empty lines at the end of the input file appear necessary when piping data into PET using the above command. This is possibly the reason why folks have not succeeded in recording PIC inputs in [incr tsdb()] profiles and sending them to PET via the [incr tsdb()] API: trailing newlines are truncated in this mode of operation. Someone should look into this more ...

The input is broken up into tokens <w>...</w>, which must have unique ids. Each token gives its start (cstart) and end (cend) (inclusive) character position. It can also include a pos element, with the tag and confidence (priority).

It also allows more detailed specifications (named entities, modified feature structures, ...).

You can only enter a single pet-input-chart in a stream, and it must start with the XML declaration and finish with at least two empty lines. Alternatively, you can give the name of a file consisting of a single pet-input-chart, or a list of such filenames, one on each line.

The example given below illustrates most of the available features. Tokens W0 and W1 are not analysed at all by cheap because the (boolean) constant attribute is yes.

the token W3 will be analysed by all of the activated preprocessing modules in cheap.

<?xml version="1.0" encoding="ISO-8859-1" standalone="no" ?>
<!DOCTYPE pet-input-chart
  SYSTEM "/path/to/src/pet/doc/pic.dtd">
  <w id="W0" cstart="1" cend="3" constant="yes">
  <w id="W1" cstart="5" cend="9" constant="yes">
  <ne id="NE0" prio="1.0">
    <ref dtr="W0">
    <ref dtr="W1">
    <pos tag="PN" prio="1.0">
    <typeinfo id="TNE0" baseform="no">
      <fsmod path="SYNSEM.LOCAL.HEAD.FORM" value="Kim Novak"/>
  <w id="W2" cstart="11" cend="16" constant="yes">
    <pos tag="VVFIN" prio="7.80000e-1"/>
    <pos tag="NN" prio="2.30000e-2"/>
    <typeinfo id="W1A1">
      <infl name="$third_sg_fin_verb_infl_rule"/>
    <typeinfo id="W1A2">
      <infl name="$plur_noun_infl_rule"/>
  <w id="W3" cstart="18" cend="22">
    <pos tag="ADV" prio="1.00000e+1"/>

Token NE0 is an example of a complex token referencing a sequence of two base tokens. Its typeinfo directly gives the HPSG type name whose feature structure should be used as lexical item in cheap. While in YY mode this was triggered by a leading special character, in XML the attribute baseform decides if the string enclosed by the <stem> tag is to be interpreted as lexical base form or as type name. The default value of baseform is yes. In this token, the surface string is unified into the feature structure under path SYNSEM.LOCAL.HEAD.FORM, which is specified with the <fsmod> tag. The value of an <fsmod> may be an arbitrary string. cheap will add a dynamic symbol if the string is not a known type or symbol name.

Every <typeinfo> tag potentially generates a lexical item (if it leads to a valid lexical feature structure). Thus, there will be two readings for the token W2 (sleeps), whereas internal analysis of the surface form has been inhibited. This need not be necessarily so. It is possible to provide external analyses and have a <w> token also being analysed internally if the constant flag is omitted or set to no.

The XML tag <surface> encloses the surface string, <pos> and <path> tags are analogous to YY mode; multiple <infl> rules in a <typeinfo> will have to be considered from first to last.

XML input mode can be used in two different ways, either by specifying a file name containing the XML data (preferably with correct XML header and DTD or DTD URL specification) or by giving the XML data directly.

If the XML data is put directly into the standard input, it must start with a valid XML header <?xml version="1.0" ... ?> with no leading whitespace, because recognition of the header triggers the reading of XML from standard input. The end of the data is marked by an empty line (two consecutive newline characters), therefore, the data itself, including an eventually given DTD, may not contain empty lines.

PIC (pet-input-chart) DTD

This is the pic.dtd from the Heart of Gold.

<!ELEMENT pet-input-chart ( w | ne )* >
  <!-- base input token -->
  <!ELEMENT w ( surface, path*, pos*, typeinfo* ) >
  <!ATTLIST w         id ID      #REQUIRED
                  cstart NMTOKEN #REQUIRED
                    cend NMTOKEN #REQUIRED
                    prio CDATA   #IMPLIED
                constant (yes | no) "no" >
  <!-- constant "yes" means: do not analyse, i.e., if the tag contains
       no typeinfo, no lexical item will be build by the token -->
  <!-- The surface string -->
  <!ELEMENT surface ( #PCDATA ) >

  <!-- numbers that encode valid paths through the input graph (optional) -->
  <!ELEMENT path EMPTY >
  <!ATTLIST path     num NMTOKEN #REQUIRED >
  <!-- every typeinfo generates a lexical token -->
  <!ELEMENT typeinfo ( stem, infl*, fsmod* ) >
  <!ATTLIST typeinfo   id ID     #REQUIRED
                     prio CDATA  #IMPLIED
                 baseform (yes | no) "yes" >
  <!-- Baseform yes: lexical base form; no: type name -->

  <!-- lexical base form or type name -->
  <!ELEMENT stem ( #PCDATA ) >

  <!-- type name of an inflection rule-->
  <!ELEMENT infl  EMPTY >
  <!ATTLIST infl    name CDATA   #REQUIRED >

  <!-- put type value under path into the lexical feature structure -->
  <!ELEMENT fsmod  EMPTY >
  <!ATTLIST fsmod   path CDATA   #REQUIRED
                   value CDATA   #REQUIRED >

  <!-- part-of-speech tags with priorities -->
  <!ELEMENT pos  EMPTY >
  <!ATTLIST pos      tag CDATA   #REQUIRED
                    prio CDATA   #IMPLIED >

  <!-- structured input items, mostly to encode named entities -->
  <!ELEMENT ne  ( ref+, pos*, typeinfo+ )  >
  <!ATTLIST ne        id ID      #REQUIRED
                    prio CDATA   #IMPLIED >
  <!-- reference to a base token -->
  <!ELEMENT ref  EMPTY >
  <!ATTLIST ref      dtr IDREF   #REQUIRED >

Encoding issues

By default the XML parser used with cheap (libxerces) can handle iso-8859-1 and utf-8. To get other encodings, such as euc-jp, you need to link the xml parser against the icu libraries.

For debian and derivatives this means:

apt-get install sudo apt-get install libxercesicu25 icu

rather than:

apt-get install sudo apt-get install libxerces25 

PetInputChart (last edited 2011-10-08 21:12:08 by localhost)

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