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Overview
Comment:Add documentation for fts5 synonym support.
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Timelines: family | ancestors | descendants | both | fts5-incompatible
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SHA1: 58aa1f435959852df74f1bca8e0bdbc4f47c256a
User & Date: dan 2015-09-03 18:05:09
Context
2015-09-03
18:57
Merge enhancements from trunk. check-in: 4b49fe99 user: dan tags: fts5-incompatible
18:05
Add documentation for fts5 synonym support. check-in: 58aa1f43 user: dan tags: fts5-incompatible
15:37
Add tests to improve coverage of fts5_varint.c. check-in: 89f24f31 user: dan tags: fts5-incompatible
Changes
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Changes to ext/fts5/extract_api_docs.tcl.

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  set res "<dl>\n"
  foreach line [split [string trim $docs] "\n"] {
    regexp {[*][*](.*)} $line -> line
    if {[regexp {^ ?x.*:} $line]} {
      append res "<dt><b>$line</b></dt><dd><p style=margin-top:0>\n"
      continue
    }



    if {[string trim $line] == ""} {
      append res "<p>\n"
    } else {
      append res "$line\n"
    }
  }
  append res "</dl>\n"

  set res
}

proc get_api_docs {data} {
  # Initialize global array M as a map from Fts5StructureApi member name
  # to member definition. i.e.
................................................................................
  switch $::extract_api_docs_mode {
    fts5_api {
      output [get_fts5_struct $data "typedef struct fts5_api" "^\};"]
    }

    fts5_tokenizer {
      output [get_fts5_struct $data "typedef struct Fts5Tokenizer" "^\};"]




    }

    fts5_extension {
      output [get_fts5_struct $data "typedef.*Fts5ExtensionApi" "^.;"]
    }

    Fts5ExtensionApi {







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  set res "<dl>\n"
  foreach line [split [string trim $docs] "\n"] {
    regexp {[*][*](.*)} $line -> line
    if {[regexp {^ ?x.*:} $line]} {
      append res "<dt><b>$line</b></dt><dd><p style=margin-top:0>\n"
      continue
    }
    if {[regexp {SYNONYM SUPPORT} $line]} {
      set line "</dl><h3>Synonym Support</h3>"
    }
    if {[string trim $line] == ""} {
      append res "<p>\n"
    } else {
      append res "$line\n"
    }
  }


  set res
}

proc get_api_docs {data} {
  # Initialize global array M as a map from Fts5StructureApi member name
  # to member definition. i.e.
................................................................................
  switch $::extract_api_docs_mode {
    fts5_api {
      output [get_fts5_struct $data "typedef struct fts5_api" "^\};"]
    }

    fts5_tokenizer {
      output [get_fts5_struct $data "typedef struct Fts5Tokenizer" "^\};"]
      output [get_fts5_struct $data \
        "Flags that may be passed as the third argument to xTokenize()" \
        "#define FTS5_TOKEN_COLOCATED"
      ]
    }

    fts5_extension {
      output [get_fts5_struct $data "typedef.*Fts5ExtensionApi" "^.;"]
    }

    Fts5ExtensionApi {

Changes to ext/fts5/fts5.h.

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** xDelete:
**   This function is invoked to delete a tokenizer handle previously
**   allocated using xCreate(). Fts5 guarantees that this function will
**   be invoked exactly once for each successful call to xCreate().
**
** xTokenize:
**   This function is expected to tokenize the nText byte string indicated 
**   by argument pText. pText may not be nul-terminated. The first argument
**   passed to this function is a pointer to an Fts5Tokenizer object returned 
**   by an earlier call to xCreate().
**
























**   For each token in the input string, the supplied callback xToken() must
**   be invoked. The first argument to it should be a copy of the pointer
**   passed as the second argument to xTokenize(). The next two arguments
**   are a pointer to a buffer containing the token text, and the size of
**   the token in bytes. The 4th and 5th arguments are the byte offsets of
**   the first byte of and first byte immediately following the text from 
**   which the token is derived within the input.
**




**   FTS5 assumes the xToken() callback is invoked for each token in the 
**   order that they occur within the input text.
**
**   If an xToken() callback returns any value other than SQLITE_OK, then
**   the tokenization should be abandoned and the xTokenize() method should
**   immediately return a copy of the xToken() return value. Or, if the
**   input buffer is exhausted, xTokenize() should return SQLITE_OK. Finally,
**   if an error occurs with the xTokenize() implementation itself, it
**   may abandon the tokenization and return any error code other than
**   SQLITE_OK or SQLITE_DONE.
**










































































































*/
typedef struct Fts5Tokenizer Fts5Tokenizer;
typedef struct fts5_tokenizer fts5_tokenizer;
struct fts5_tokenizer {
  int (*xCreate)(void*, const char **azArg, int nArg, Fts5Tokenizer **ppOut);
  void (*xDelete)(Fts5Tokenizer*);
  int (*xTokenize)(Fts5Tokenizer*, 
      void *pCtx,
      int flags,

      const char *pText, int nText, 
      int (*xToken)(
        void *pCtx,         /* Copy of 2nd argument to xTokenize() */
        int tflags,         /* Mask of FTS5_TOKEN_* flags */
        const char *pToken, /* Pointer to buffer containing token */
        int nToken,         /* Size of token in bytes */
        int iStart,         /* Byte offset of token within input text */







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** xDelete:
**   This function is invoked to delete a tokenizer handle previously
**   allocated using xCreate(). Fts5 guarantees that this function will
**   be invoked exactly once for each successful call to xCreate().
**
** xTokenize:
**   This function is expected to tokenize the nText byte string indicated 
**   by argument pText. pText may or may not be nul-terminated. The first
**   argument passed to this function is a pointer to an Fts5Tokenizer object
**   returned by an earlier call to xCreate().
**
**   The second argument indicates the reason that FTS5 is requesting
**   tokenization of the supplied text. This is always one of the following
**   four values:
**
**   <ul><li> <b>FTS5_TOKENIZE_DOCUMENT</b> - A document is being inserted into
**            or removed from the FTS table. The tokenizer is being invoked to
**            determine the set of tokens to add to (or delete from) the
**            FTS index.
**
**       <li> <b>FTS5_TOKENIZE_QUERY</b> - A MATCH query is being executed 
**            against the FTS index. The tokenizer is being called to tokenize 
**            a bareword or quoted string specified as part of the query.
**
**       <li> <b>(FTS5_TOKENIZE_QUERY | FTS5_TOKENIZE_PREFIX)</b> - Same as
**            FTS5_TOKENIZE_QUERY, except that the bareword or quoted string is
**            followed by a "*" character, indicating that the last token
**            returned by the tokenizer will be treated as a token prefix.
**
**       <li> <b>FTS5_TOKENIZE_AUX</b> - The tokenizer is being invoked to 
**            satisfy an fts5_api.xTokenize() request made by an auxiliary
**            function. Or an fts5_api.xColumnSize() request made by the same
**            on a columnsize=0 database.  
**   </ul>
**
**   For each token in the input string, the supplied callback xToken() must
**   be invoked. The first argument to it should be a copy of the pointer
**   passed as the second argument to xTokenize(). The third and fourth
**   arguments are a pointer to a buffer containing the token text, and the
**   size of the token in bytes. The 4th and 5th arguments are the byte offsets
**   of the first byte of and first byte immediately following the text from
**   which the token is derived within the input.
**
**   The second argument passed to the xToken() callback ("tflags") should
**   normally be set to 0. The exception is if the tokenizer supports 
**   synonyms. In this case see the discussion below for details.
**
**   FTS5 assumes the xToken() callback is invoked for each token in the 
**   order that they occur within the input text.
**
**   If an xToken() callback returns any value other than SQLITE_OK, then
**   the tokenization should be abandoned and the xTokenize() method should
**   immediately return a copy of the xToken() return value. Or, if the
**   input buffer is exhausted, xTokenize() should return SQLITE_OK. Finally,
**   if an error occurs with the xTokenize() implementation itself, it
**   may abandon the tokenization and return any error code other than
**   SQLITE_OK or SQLITE_DONE.
**
** SYNONYM SUPPORT
**
**   Custom tokenizers may also support synonyms. Consider a case in which a
**   user wishes to query for a phrase such as "first place". Using the 
**   built-in tokenizers, the FTS5 query 'first + place' will match instances
**   of "first place" within the document set, but not alternative forms
**   such as "1st place". In some applications, it would be better to match
**   all instances of "first place" or "1st place" regardless of which form
**   the user specified in the MATCH query text.
**
**   There are several ways to approach this in FTS5:
**
**   <ol><li> By mapping all synonyms to a single token. In this case, the 
**            In the above example, this means that the tokenizer returns the
**            same token for inputs "first" and "1st". Say that token is in
**            fact "first", so that when the user inserts the document "I won
**            1st place" entries are added to the index for tokens "i", "won",
**            "first" and "place". If the user then queries for '1st + place',
**            the tokenizer substitutes "first" for "1st" and the query works
**            as expected.
**
**       <li> By adding multiple synonyms for a single term to the FTS index.
**            In this case, when tokenizing query text, the tokenizer may 
**            provide multiple synonyms for a single term within the document.
**            FTS5 then queries the index for each synonym individually. For
**            example, faced with the query:
**
**   <codeblock>
**     ... MATCH 'first place'</codeblock>
**
**            the tokenizer offers both "1st" and "first" as synonyms for the
**            first token in the MATCH query and FTS5 effectively runs a query 
**            similar to:
**
**   <codeblock>
**     ... MATCH '(first OR 1st) place'</codeblock>
**
**            except that, for the purposes of auxiliary functions, the query
**            still appears to contain just two phrases - "(first OR 1st)" 
**            being treated as a single phrase.
**
**       <li> By adding multiple synonyms for a single term to the FTS index.
**            Using this method, when tokenizing document text, the tokenizer
**            provides multiple synonyms for each token. So that when a 
**            document such as "I won first place" is tokenized, entries are
**            added to the FTS index for "i", "won", "first", "1st" and
**            "place".
**
**            This way, even if the tokenizer does not provide synonyms
**            when tokenizing query text (it should not - to do would be
**            inefficient), it doesn't matter if the user queries for 
**            'first + place' or '1st + place', as there are entires in the
**            FTS index corresponding to both forms of the first token.
**   </ol>
**
**   Whether is is parsing document or query text, any call to xToken that
**   specifies a <i>tflags</i> argument with the FTS5_TOKEN_COLOCATED bit
**   is considered to supply a synonym for the previous token. For example,
**   when parsing the document "I won first place", a tokenizer that supports
**   synonyms would call xToken() 5 times, as follows:
**
**   <codeblock>
**       xToken(pCtx, 0, "i",                      1,  0,  1);
**       xToken(pCtx, 0, "won",                    3,  2,  5);
**       xToken(pCtx, 0, "first",                  5,  6, 11);
**       xToken(pCtx, FTS5_TOKEN_COLOCATED, "1st", 3,  6, 11);
**       xToken(pCtx, 0, "place",                  5, 12, 17);
**</codeblock>
**
**   It is an error to specify the FTS5_TOKEN_COLOCATED flag the first time
**   xToken() is called. Multiple synonyms may be specified for a single token
**   by making multiple calls to xToken(FTS5_TOKEN_COLOCATED) in sequence. 
**   There is no limit to the number of synonyms that may be provided for a
**   single token.
**
**   In many cases, method (1) above is the best approach. It does not add 
**   extra data to the FTS index or require FTS5 to query for multiple terms,
**   so it is efficient in terms of disk space and query speed. However, it
**   does not support prefix queries very well. If, as suggested above, the
**   token "first" is subsituted for "1st" by the tokenizer, then the query:
**
**   <codeblock>
**     ... MATCH '1s*'</codeblock>
**
**   will not match documents that contain the token "1st" (as the tokenizer
**   will probably not map "1s" to any prefix of "first").
**
**   For full prefix support, method (3) may be preferred. In this case, 
**   because the index contains entries for both "first" and "1st", prefix
**   queries such as 'fi*' or '1s*' will match correctly. However, because
**   extra entries are added to the FTS index, this method uses more space
**   within the database.
**
**   Method (2) offers a midpoint between (1) and (3). Using this method,
**   a query such as '1s*' will match documents that contain the literal 
**   token "1st", but not "first" (assuming the tokenizer is not able to
**   provide synonyms for prefixes). However, a non-prefix query like '1st'
**   will match against "1st" and "first". This method does not require
**   extra disk space, as no extra entries are added to the FTS index. 
**   On the other hand, it may require more CPU cycles to run MATCH queries,
**   as separate queries of the FTS index are required for each synonym.
**
**   When using methods (2) or (3), it is important that the tokenizer only
**   provide synonyms when tokenizing document text (method (2)) or query
**   text (method (3)), not both. Doing so will not cause any errors, but is
**   inefficient.
*/
typedef struct Fts5Tokenizer Fts5Tokenizer;
typedef struct fts5_tokenizer fts5_tokenizer;
struct fts5_tokenizer {
  int (*xCreate)(void*, const char **azArg, int nArg, Fts5Tokenizer **ppOut);
  void (*xDelete)(Fts5Tokenizer*);
  int (*xTokenize)(Fts5Tokenizer*, 
      void *pCtx,

      int flags,            /* Mask of FTS5_TOKENIZE_* flags */
      const char *pText, int nText, 
      int (*xToken)(
        void *pCtx,         /* Copy of 2nd argument to xTokenize() */
        int tflags,         /* Mask of FTS5_TOKEN_* flags */
        const char *pToken, /* Pointer to buffer containing token */
        int nToken,         /* Size of token in bytes */
        int iStart,         /* Byte offset of token within input text */