288 lines
12 KiB
C
288 lines
12 KiB
C
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// fstext/grammar-context-fst.h
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// Copyright 2018 Johns Hopkins University (author: Daniel Povey)
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// See ../../COPYING for clarification regarding multiple authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// THIS CODE IS PROVIDED *AS IS* BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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// KIND, EITHER EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION ANY IMPLIED
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// WARRANTIES OR CONDITIONS OF TITLE, FITNESS FOR A PARTICULAR PURPOSE,
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// MERCHANTABLITY OR NON-INFRINGEMENT.
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// See the Apache 2 License for the specific language governing permissions and
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// limitations under the License.
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//
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#ifndef KALDI_FSTEXT_GRAMMAR_CONTEXT_FST_H_
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#define KALDI_FSTEXT_GRAMMAR_CONTEXT_FST_H_
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/* This header defines a special form of the context FST "C" (the "C" in "HCLG")
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that integrates with our framework for building dynamic graphs for grammars
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that are too big to statically create, or graphs with on-the-fly pieces that
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you want to create at recognition time without building the whole graph.
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This framework is limited to only work with models with left-biphone context.
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(Fortunately this doesn't impact results, as our best models are all 'chain'
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models with left biphone context).
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The main code exported from here is the class InverseLeftBiphoneContextFst,
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which is similar to the InverseContextFst defined in context-fst.h, but
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is limited to left-biphone context and also supports certain special
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extensions we need to compile grammars.
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See \ref grammar (../doc/grammar.dox) for high-level
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documentation on how this framework works.
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*/
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#include <algorithm>
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#include <string>
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#include <vector>
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#include <fst/fstlib.h>
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#include <fst/fst-decl.h>
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#include "util/const-integer-set.h"
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#include "fstext/deterministic-fst.h"
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#include "fstext/context-fst.h"
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namespace fst {
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/**
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An anonymous enum to define some values for symbols used in our grammar-fst
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framework. Please understand this with reference to the documentation in
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\ref grammar (../doc/grammar.dox). This enum defines
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the values of nonterminal-related symbols in phones.txt. They are not
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the actual values-- they will be shifted by adding the value
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nonterm_phones_offset which is passed in by the command-line flag
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--nonterm-phones-offset.
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*/
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enum NonterminalValues {
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kNontermBos = 0, // #nonterm_bos
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kNontermBegin = 1, // #nonterm_begin
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kNontermEnd = 2, // #nonterm_end
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kNontermReenter = 3, // #nonterm_reenter
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kNontermUserDefined = 4, // the lowest-numbered user-defined nonterminal, e.g. #nonterm:foo
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// kNontermMediumNumber and kNontermBigNumber come into the encoding of
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// nonterminal-related symbols in HCLG.fst. The only hard constraint on them
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// is that kNontermBigNumber must be bigger than the biggest transition-id in
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// your system, and kNontermMediumNumber must be >0. These values were chosen
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// for ease of human inspection of numbers encoded with them.
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kNontermMediumNumber = 1000,
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kNontermBigNumber = 10000000
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};
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// Returns the smallest multiple of 1000 that is strictly greater than
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// nonterm_phones_offset. Used in the encoding of special symbol in HCLG;
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// they are encoded as
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// special_symbol =
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// kNontermBigNumber + (nonterminal * encoding_multiple) + phone_index
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inline int32 GetEncodingMultiple(int32 nonterm_phones_offset) {
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int32 medium_number = static_cast<int32>(kNontermMediumNumber);
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return medium_number *
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((nonterm_phones_offset + medium_number) / medium_number);
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}
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/**
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This is a variant of the function ComposeContext() which is to be used
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with our "grammar FST" framework (see \ref graph_context, i.e.
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../doc/grammar.dox, for more details). This does not take
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the 'context_width' and 'central_position' arguments because they are
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assumed to be 2 and 1 respectively (meaning, left-biphone phonetic context).
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This function creates a context FST and composes it on the left with "ifst"
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to make "ofst".
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@param [in] nonterm_phones_offset The integer id of the symbol
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#nonterm_bos in the phones.txt file. You can just set this
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to a large value (like 1 million) if you are not actually using
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nonterminals (e.g. for testing purposes).
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@param [in] disambig_syms List of disambiguation symbols, e.g. the integer
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ids of #0, #1, #2 ... in the phones.txt.
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@param [in,out] ifst The FST we are composing with C (e.g. LG.fst).
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@param [out] ofst Composed output FST (would be CLG.fst).
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@param [out] ilabels Vector, indexed by ilabel of CLG.fst, providing information
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about the meaning of that ilabel; see \ref tree_ilabel
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(http://kaldi-asr.org/doc/tree_externals.html#tree_ilabel)
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and also \ref grammar_special_clg
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(http://kaldi-asr.org/doc/grammar#grammar_special_clg).
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*/
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void ComposeContextLeftBiphone(
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int32 nonterm_phones_offset,
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const std::vector<int32> &disambig_syms,
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const VectorFst<StdArc> &ifst,
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VectorFst<StdArc> *ofst,
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std::vector<std::vector<int32> > *ilabels);
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/*
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InverseLeftBiphoneContextFst represents the inverse of the context FST "C" (the "C" in
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"HCLG") which transduces from symbols representing phone context windows
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(e.g. "a, b, c") to individual phones, e.g. "a". So InverseContextFst
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transduces from phones to symbols representing phone context windows. The
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point is that the inverse is deterministic, so the DeterministicOnDemandFst
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interface is applicable, which turns out to be a convenient way to implement
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this.
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This doesn't implement the full Fst interface, it implements the
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DeterministicOnDemandFst interface which is much simpler and which is
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sufficient for what we need to do with this.
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Search for "hbka.pdf" ("Speech Recognition with Weighted Finite State
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Transducers") by M. Mohri, for more context.
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*/
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class InverseLeftBiphoneContextFst: public DeterministicOnDemandFst<StdArc> {
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public:
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typedef StdArc Arc;
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typedef typename StdArc::StateId StateId;
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typedef typename StdArc::Weight Weight;
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typedef typename StdArc::Label Label;
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/**
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Constructor. This does not take the arguments 'context_width' or
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'central_position' because they are assumed to be (2, 1) meaning a
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system with left-biphone context; and there is no subsequential
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symbol because it is not needed in systems without right context.
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@param [in] nonterm_phones_offset The integer id of the symbol
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#nonterm_bos in the phones.txt file. You can just set this to
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a large value (like 1 million) if you are not actually using
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nonterminals (e.g. for testing purposes).
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@param [in] phones List of integer ids of phones, as you would see in phones.txt
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@param [in] disambig_syms List of integer ids of disambiguation symbols,
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e.g. the ids of #0, #1, #2 in phones.txt
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See \ref graph_context for more details.
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*/
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InverseLeftBiphoneContextFst(Label nonterm_phones_offset,
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const std::vector<int32>& phones,
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const std::vector<int32>& disambig_syms);
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/**
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Here is a note on the state space of InverseLeftBiphoneContextFst;
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see \ref grammar_special_c which has some documentation on this.
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The state space uses the same numbering as phones.txt.
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State 0 means the beginning-of-sequence state, where there is no left
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context.
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For each phone p in the list 'phones' passed to the constructor (i.e. in
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the set passed to the constructor), the state 'p' corresponds to a
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left-context of that phone.
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If p is equal to nonterm_phones_offset_ + kNontermBegin (i.e. the
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integer form of `\#nonterm_begin`), then this is the state we transition
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to when we see that symbol starting from left-context==0 (no context). The
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transition to this special state will have epsilon on the output. (talking
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here about inv(C), not C, so input/output are reversed).
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The state is nonfinal and when we see a regular phone p1 or #nonterm_bos, instead of
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outputting that phone in context, we output the pair (#nonterm_begin,p1) or
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(#nonterm_begin,#nonterm_bos). This state is not final.
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If p is equal to nonterm_phones_offset_ + kNontermUserDefined, then this
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is the state we transition to when we see any user-defined nonterminal.
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Transitions to this special state have olabels of the form (#nonterm:foo,p1)
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where p1 is the preceding context (with #nonterm_begin if that context was
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0); transitions out of it have olabels of the form (#nonterm_reenter,p2), where
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p2 is the phone on the ilabel of that transition. Again: talking about inv(C).
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This state is not final.
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If p is equal to nonterm_phones_offset_ + kNontermEnd, then this is
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the state we transition to when we see the ilabel #nonterm_end. The olabels
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on the transitions to it (talking here about inv(C), so ilabels and olabels
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are reversed) are of the form (#nonterm_end, p1) where p1 corresponds to the
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context we were in. This state is final.
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*/
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virtual StateId Start() { return 0; }
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virtual Weight Final(StateId s);
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/// Note: ilabel must not be epsilon.
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virtual bool GetArc(StateId s, Label ilabel, Arc *arc);
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~InverseLeftBiphoneContextFst() { }
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// Returns a reference to a vector<vector<int32> > with information about all
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// the input symbols of C (i.e. all the output symbols of this
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// InverseContextFst). See
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// "http://kaldi-asr.org/doc/tree_externals.html#tree_ilabel".
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const std::vector<std::vector<int32> > &IlabelInfo() const {
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return ilabel_info_;
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}
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// A way to destructively obtain the ilabel-info. Only do this if you
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// are just about to destroy this object.
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void SwapIlabelInfo(std::vector<std::vector<int32> > *vec) { ilabel_info_.swap(*vec); }
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private:
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inline int32 GetPhoneSymbolFor(enum NonterminalValues n) {
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return nonterm_phones_offset_ + static_cast<int32>(n);
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}
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/// Finds the label index corresponding to this context-window of phones
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/// (likely of width context_width_). Inserts it into the
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/// ilabel_info_/ilabel_map_ tables if necessary.
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Label FindLabel(const std::vector<int32> &label_info);
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// Map type to map from vectors of int32 (representing ilabel-info,
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// see http://kaldi-asr.org/doc/tree_externals.html#tree_ilabel) to
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// Label (the output label in this FST).
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typedef unordered_map<std::vector<int32>, Label,
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kaldi::VectorHasher<int32> > VectorToLabelMap;
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// The following three variables were also passed in by the caller:
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int32 nonterm_phones_offset_;
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// 'phone_syms_' are a set of phone-ids, typically 1, 2, .. num_phones.
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kaldi::ConstIntegerSet<Label> phone_syms_;
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// disambig_syms_ is the set of integer ids of the disambiguation symbols,
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// usually represented in text form as #0, #1, #2, etc. These are inserted
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// into the grammar (for #0) and the lexicon (for #1, #2, ...) in order to
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// make the composed FSTs determinizable. They are treated "specially" by the
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// context FST in that they are not part of the context, they are just "passed
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// through" via self-loops. See the Mohri chapter mrentioned above for more
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// information.
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kaldi::ConstIntegerSet<Label> disambig_syms_;
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// maps from vector<int32>, representing phonetic contexts of length
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// context_width_ - 1, to Label. These are actually the output labels of this
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// InverseContextFst (because of the "Inverse" part), but for historical
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// reasons and because we've used the term ilabels" in the documentation, we
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// still call these "ilabels").
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VectorToLabelMap ilabel_map_;
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// ilabel_info_ is the reverse map of ilabel_map_.
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// Indexed by olabel (although we call this ilabel_info_ for historical
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// reasons and because is for the ilabels of C), ilabel_info_[i] gives
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// information about the meaning of each symbol on the input of C
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// aka the output of inv(C).
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// See "http://kaldi-asr.org/doc/tree_externals.html#tree_ilabel".
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std::vector<std::vector<int32> > ilabel_info_;
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};
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} // namespace fst
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#endif // KALDI_FSTEXT_GRAMMAR_CONTEXT_FST_H_
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