src/ports/postgres/modules/crf/crf_feature_gen.py_in

"""
@file crf_feature_gen.py_in

@brief Conditional Random Field: Feature Extraction for Tranining and Testing.

@namespace crf

Conditional Random Field: Feature Extraction for Training and Testing.
"""

import plpy
from utilities.validate_args import table_exists
from utilities.validate_args import columns_exist_in_table
from utilities.utilities import _assert
from utilities.utilities import add_postfix

def generate_train_features(schema_madlib, train_segment_tbl, regex_tbl, label_tbl,
                dictionary_tbl, train_feature_tbl, train_featureset_tbl, **kwargs):

    _validate_train_args(train_segment_tbl, regex_tbl, label_tbl,
            dictionary_tbl, train_feature_tbl, train_featureset_tbl)

    origClientMinMessages =  plpy.execute("SELECT setting AS setting FROM pg_settings WHERE name = \'client_min_messages\';")
    plpy.execute("SET client_min_messages TO warning;")

    plpy.execute("SELECT {schema_madlib}.create_schema_pg_temp();".format(schema_madlib=schema_madlib));
    tmp1_feature = "pg_temp._madlib_tmp1_feature"
    tmp_rtbl = "pg_temp._madlib_tmp_rtbl"
    tmp_dense_mtbl = "pg_temp._madlib_tmp_dense_mtbl"
    dense_mtbl = "pg_temp._madlib_dense_mtbl"
    sparse_rtbl = "pg_temp._madlib_sparse_rtbl"
    sparse_mtbl = "pg_temp._madlib_sparse_mtbl"
    tmp_featureset = "pg_temp._madlib_tmp_featureset"
    tmp_segmenttbl = "pg_temp._madlib_tmp_segmenttbl"
    tmp_segcount_tbl = "pg_temp._madlib_tmp_segcount_tbl"

    plpy.execute("""DROP TABLE IF EXISTS {tmp1_feature},
                                         {tmp_rtbl},
                                         {tmp_dense_mtbl},
                                         {dense_mtbl},
                                         {sparse_rtbl},
                                         {sparse_mtbl},
                                         {tmp_featureset},
                                         {tmp_segmenttbl}
                 """.format(tmp1_feature = tmp1_feature,
                            tmp_rtbl = tmp_rtbl,
                            tmp_dense_mtbl = tmp_dense_mtbl,
                            dense_mtbl = dense_mtbl,
                            sparse_rtbl = sparse_rtbl,
                            sparse_mtbl = sparse_mtbl,
                            tmp_featureset = tmp_featureset,
                            tmp_segmenttbl = tmp_segmenttbl))

    plpy.execute("""CREATE TABLE """ + tmp1_feature + """(start_pos integer,doc_id integer, f_name text, feature integer[])
                  m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (doc_id)')""")
    plpy.execute("""CREATE TABLE """ +  tmp_rtbl + """(start_pos integer,doc_id integer, feature integer[])
                  m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (doc_id)')""")
    plpy.execute("""CREATE TABLE """ + tmp_dense_mtbl + """(start_pos integer,doc_id integer, feature integer[])
                  m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (doc_id)')""")
    plpy.execute("""CREATE TABLE """ + dense_mtbl  + """(doc_id integer, dense_m integer[])
                  m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (doc_id)')""")
    plpy.execute("""CREATE TABLE """ + sparse_rtbl + """(doc_id integer,f_size integer, sparse_r integer[])
                  m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (doc_id)')""")
    plpy.execute("""CREATE TABLE """ +  sparse_mtbl + """(sparse_m integer[])
                  m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (sparse_m)')""")
    plpy.execute("""CREATE TABLE """ + tmp_featureset + """(f_name text, feature integer[])
                  m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (f_name)')""")
    plpy.execute("""CREATE TABLE """ + tmp_segmenttbl + """(start_pos int,doc_id int,seg_text text,label int)
                 m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (doc_id)')""")
    plpy.execute("""CREATE TABLE """ + tmp_segcount_tbl + """(doc_id int, doc_len int)
                 m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (doc_id)')""")


    # replace digits with "DIGIT" keyword
    plpy.execute("""INSERT INTO """ + tmp_segmenttbl + """ SELECT start_pos,doc_id,seg_text,label FROM """ + train_segment_tbl + """ WHERE
			NOT (seg_text ~ E'^[-+]?([0-9]{1,3}[,]?)*[0-9]{1,3}$' OR seg_text ~ E'^[-+]?[0-9]*[.][0-9]+$');""")
    plpy.execute("""INSERT INTO """ + tmp_segmenttbl + """ SELECT start_pos,doc_id,'DIGIT',label FROM """ + train_segment_tbl + """ WHERE
		    seg_text ~ E'^[-+]?([0-9]{1,3}[,]?)*[0-9]{1,3}$' OR seg_text ~E'^[-+]?[0-9]*[.][0-9]+$';""")

    # Create the dictionary_tbl table containing distinct tokens
    plpy.execute("""
        CREATE TABLE {dictionary_tbl} AS
            SELECT seg_text token, count(*) total FROM {tmp_segmenttbl}
            GROUP BY seg_text
            m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (token)')
        """.format(dictionary_tbl = dictionary_tbl,
                   tmp_segmenttbl = tmp_segmenttbl))

    plpy.execute("""
            DROP TABLE IF EXISTS {tmp_segcount_tbl};
            CREATE TABLE {tmp_segcount_tbl} AS
                SELECT doc_id, count(*) - 1 doc_len
                  FROM {train_segment_tbl}
                 GROUP BY doc_id
                m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (doc_id)')
                """.format(tmp_segcount_tbl = tmp_segcount_tbl,
                        train_segment_tbl = train_segment_tbl))

    # create a temporary table to store all the features

    # extract all the edge features
    plpy.execute("""INSERT INTO """ + tmp1_feature + """(start_pos, doc_id, f_name, feature)
                    SELECT doc2.start_pos, doc2.doc_id, 'E.', ARRAY[doc1.label, doc2.label]
                    FROM """ + tmp_segmenttbl + """ doc1, """ + tmp_segmenttbl + """ doc2
                    WHERE  doc1.doc_id = doc2.doc_id AND doc1.start_pos+1 = doc2.start_pos;""")

    #extract all the regex features
    plpy.execute("""INSERT INTO """ + tmp1_feature + """(start_pos, doc_id, f_name, feature)
                    SELECT start_pos, doc_id, 'R_' || name, ARRAY[-1, label]
                    FROM   """ + regex_tbl + """, """ + tmp_segmenttbl + """
                    WHERE  seg_text ~ pattern;""")

    #extract all the start feature
    plpy.execute("""INSERT INTO """ + tmp1_feature + """(start_pos, doc_id, f_name, feature)
                    SELECT start_pos, doc_id, 'S.', ARRAY[-1, label]
                    FROM  """ + tmp_segmenttbl + """
                    WHERE  start_pos = 0;""")

    #extract all the end featue
    plpy.execute("""INSERT INTO """ + tmp1_feature + """(start_pos, doc_id, f_name, feature)
                    SELECT start_pos, t.doc_id, 'End.', ARRAY[-1, label]
                    FROM  """ + tmp_segmenttbl + """ t, """ + tmp_segcount_tbl + """ q
                    WHERE  t.doc_id = q.doc_id AND t.start_pos = q.doc_len""")

    #word feature
    plpy.execute("""INSERT INTO """ + tmp1_feature + """(start_pos, doc_id, f_name, feature)
                    SELECT start_pos, doc_id, 'W_' || seg_text, ARRAY[-1, label]
                    FROM  """ + tmp_segmenttbl + """;""")

    #unknown feature
    plpy.execute("""INSERT INTO """ + tmp1_feature + """(start_pos, doc_id, f_name, feature)
                    SELECT start_pos, doc_id, 'U', ARRAY[-1, label]
                    FROM """ + tmp_segmenttbl + """ seg, """ + dictionary_tbl + """ dic
                    WHERE  seg.seg_text = dic.token AND dic.total <= 1;""")

    plpy.execute("""INSERT INTO """ + tmp_featureset + """(f_name, feature)
                    SELECT DISTINCT f_name, feature
                    FROM   """ + tmp1_feature + """;""")

    # Enforce ANALYZE to gather proper table statistics required to generate optimized query plans
    plpy.execute("""ANALYZE {tmp1_feature} """.format(tmp1_feature = tmp1_feature))

    plpy.execute("""DROP SEQUENCE IF EXISTS seq;
                    CREATE  SEQUENCE seq START 1 INCREMENT 1;""")

    #get all distcint features
    plpy.execute("""
        CREATE table {train_featureset_tbl} AS
            SELECT CAST(nextval('seq')-1 AS INTEGER) f_index, f_name, feature FROM {tmp_featureset}
            m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (f_index)')
        """.format(train_featureset_tbl = train_featureset_tbl,
                   tmp_featureset = tmp_featureset))

    # Enforce ANALYZE to gather proper table statistics required to generate optimized query plans
    plpy.execute(""" ANALYZE {train_featureset_tbl} """.format(train_featureset_tbl = train_featureset_tbl))

    rv = plpy.execute("""SELECT COUNT(*) AS total_feature FROM """ + train_featureset_tbl + """;""")

    plpy.execute("""INSERT INTO """ +  tmp_rtbl + """(start_pos,doc_id,feature)
                    SELECT start_pos, doc_id, array_cat(fset.feature,
                                                        ARRAY[f_index,start_pos,
                                                              CASE WHEN """ + tmp1_feature + """.feature = fset.feature THEN 1
                                                                   ELSE 0
                                                              END] )
                    FROM   """ + tmp1_feature + """, """ + train_featureset_tbl + """ fset
                    WHERE  """ + tmp1_feature + """.f_name = fset.f_name AND fset.f_name <> 'E.';""")

    plpy.execute("""INSERT INTO {sparse_rtbl} (doc_id, f_size, sparse_r)
                    SELECT doc_id, {f_size}, {schema_madlib}.array_union(feature::integer[] order by start_pos)
                    FROM  {tmp_rtbl}
                    GROUP BY doc_id;""".format(schema_madlib = schema_madlib,
                                               sparse_rtbl = sparse_rtbl,
                                               f_size = rv[0]['total_feature'],
                                               tmp_rtbl = tmp_rtbl))

    plpy.execute("""INSERT INTO """ + tmp_dense_mtbl + """(start_pos,doc_id,feature)
                    SELECT start_pos, doc_id,
                           array_cat(fset.feature, ARRAY[f_index,start_pos,1])
                    FROM   """ + tmp1_feature + """, """ + train_featureset_tbl + """ fset
                    WHERE  start_pos > 0 AND """ + tmp1_feature + """.f_name = fset.f_name AND """ + tmp1_feature + """.feature = fset.feature AND fset.f_name = 'E.';""")

    plpy.execute("""INSERT INTO {dense_mtbl} (doc_id, dense_m)
                    SELECT doc_id, {schema_madlib}.array_union(feature::integer[] order by start_pos)
                    FROM  {tmp_dense_mtbl}
                    GROUP BY doc_id;""".format(schema_madlib = schema_madlib,
                                               dense_mtbl = dense_mtbl,
                                               tmp_dense_mtbl = tmp_dense_mtbl))

    plpy.execute("""INSERT INTO {sparse_mtbl} (sparse_m)
                    SELECT {schema_madlib}.array_union(array_cat(ARRAY[f_index],feature))
                    FROM  {train_featureset_tbl} fset
                    WHERE  f_name = 'E.';""".format(schema_madlib = schema_madlib,
                                            sparse_mtbl = sparse_mtbl,
                                            train_featureset_tbl = train_featureset_tbl))

    plpy.execute("""
        CREATE TABLE {train_feature_tbl} AS
            SELECT {sparse_rtbl}.doc_id, f_size, sparse_r, dense_m, sparse_m
             FROM  {sparse_rtbl}, {dense_mtbl}, {sparse_mtbl}
             WHERE {sparse_rtbl}.doc_id = {dense_mtbl}.doc_id
         m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (doc_id)')
         """.format(train_feature_tbl = train_feature_tbl,
                sparse_rtbl = sparse_rtbl,
                sparse_mtbl = sparse_mtbl,
                dense_mtbl = dense_mtbl))

    # Enforce ANALYZE to gather proper table statistics required to generate optimized query plans
    plpy.execute(""" ANALYZE {train_feature_tbl} """.format(train_feature_tbl = train_feature_tbl))

    plpy.execute("""SET client_min_messages TO """ + str(origClientMinMessages[0]['setting']) + """;""")


def generate_test_features(schema_madlib, test_segment_tbl,
            dictionary_tbl, label_tbl, regex_tbl, crf_weights_tbl,
            viterbi_mtbl, viterbi_rtbl, **kwargs):

    _validate_test_args(test_segment_tbl, dictionary_tbl, label_tbl,
        regex_tbl, crf_weights_tbl, viterbi_mtbl, viterbi_rtbl)

    # Create m&r factor table
    plpy.execute("""
            CREATE TABLE {viterbi_mtbl} (score DOUBLE PRECISION[])
            m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (score)')
            """.format(viterbi_mtbl = viterbi_mtbl));

    plpy.execute("""
            CREATE TABLE {viterbi_rtbl}
            (seg_text text, label integer, score DOUBLE PRECISION)
            m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (label)')
            """.format(viterbi_rtbl = viterbi_rtbl))

    # Create index for performance
    _tablename = viterbi_rtbl.split('.')
    if len(_tablename) == 1:
        rtbl_name = _tablename[0]
    else:
        rtbl_name = _tablename[-1]

    rtbl_name_idx = add_postfix(rtbl_name, "_idx")

    plpy.execute("""
        CREATE INDEX {rtbl_name_idx} ON {viterbi_rtbl} (seg_text)
        """.format(rtbl_name_idx = rtbl_name_idx,
            viterbi_rtbl = viterbi_rtbl))

    origClientMinMessages =  plpy.execute("""SELECT setting AS setting
                                             FROM pg_settings WHERE name = \'client_min_messages\';""")
    plpy.execute("SET client_min_messages TO warning;")

    plpy.execute("SELECT {schema_madlib}.create_schema_pg_temp()".format(schema_madlib=schema_madlib))

    prev_labeltbl = "pg_temp._madlib_prev_labeltbl"
    segment_hashtbl = "pg_temp._madlib_segment_hashtbl"
    unknown_segment_hashtbl = "pg_temp._madlib_unknown_segment_hashtbl"
    rtbl = "pg_temp._madlib_rtbl"
    mtbl = "pg_temp._madlib_mtbl"
    tmp_segment_tbl = "pg_temp._madlib_tmp_segment_tbl"
    tmp_dict = "pg_temp._madlib_tmp_dict"

    plpy.execute("""DROP TABLE IF EXISTS {prev_labeltbl},
                                        {segment_hashtbl},
                                        {unknown_segment_hashtbl},
                                        {rtbl},
                                        {mtbl},
                                        {tmp_segment_tbl},
                                        {tmp_dict}
                 """.format(prev_labeltbl = prev_labeltbl,
                            segment_hashtbl = segment_hashtbl,
                            unknown_segment_hashtbl = unknown_segment_hashtbl,
                            rtbl = rtbl,
                            mtbl = mtbl,
                            tmp_segment_tbl = tmp_segment_tbl,
                            tmp_dict = tmp_dict))

    plpy.execute("""CREATE TABLE """ + prev_labeltbl + """(id int)
                 m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (id)')""")

    # Insert unique tokens into the """ +  segment_hashtbl + """
    plpy.execute("CREATE TABLE """ +  segment_hashtbl + """(seg_text text)
                 m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (seg_text)')""")

    # create a temp partial dictionary_tbl table which stores the words whose occurance
    # is below certain threshold, refer to the CRF Package
    plpy.execute("""CREATE  TABLE """ + unknown_segment_hashtbl + """(seg_text text)
                  m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (seg_text)')""")

    # Generate a sparse matrix to store the r factors
    plpy.execute("""CREATE  TABLE """ + rtbl  + """ (seg_text text NOT NULL, label integer, value double precision)
                    m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (label)')""")

    # Generate M factor table
    plpy.execute("""CREATE  TABLE """ + mtbl + """(prev_label integer, label integer, value double precision)
                    m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (label)')""")


	# temp tables to keep segments and dictionary_tbl with all digits replaced by the word 'DIGIT'
    plpy.execute("""CREATE  TABLE """ +  tmp_segment_tbl + """(start_pos int,doc_id int,seg_text text)
                    m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (doc_id)')""")
    plpy.execute("""CREATE  TABLE """+ tmp_dict + """(token text, total int)
                    m4_ifdef(`__POSTGRESQL__', `', `DISTRIBUTED BY (token)')""")

    plpy.execute("""SET client_min_messages TO """ + str(origClientMinMessages[0]['setting']) + """;""")

    # Calculate the number of labels in the label space
    rv = plpy.execute("""SELECT COUNT(*) AS total_label FROM """ + label_tbl + """;""")
    nlabel = rv[0]['total_label']

    # replace digits with "DIGIT" keyword
    plpy.execute("""INSERT INTO """ +  tmp_segment_tbl + """ SELECT start_pos,doc_id,seg_text FROM """ + test_segment_tbl + """ WHERE
		    NOT (seg_text ~ E'^[-+]?([0-9]{1,3}[,]?)*[0-9]{1,3}$' OR seg_text ~ E'^[-+]?[0-9]*[.][0-9]+$')""")
    plpy.execute("""INSERT INTO """ +  tmp_segment_tbl + """ SELECT start_pos,doc_id,'DIGIT' FROM """ + test_segment_tbl + """ WHERE
		        seg_text ~ E'^[-+]?([0-9]{1,3}[,]?)*[0-9]{1,3}$' OR seg_text ~E'^[-+]?[0-9]*[.][0-9]+$';""")

    plpy.execute("""INSERT INTO """+ tmp_dict + """ SELECT token,sum(total) FROM """ + dictionary_tbl + """ GROUP BY token
            HAVING (token NOT LIKE E'^[-+]?([0-9]{1,3}[,]?)*[0-9]{1,3}$' AND token NOT LIKE E'^[-+]?[0-9]*[.][0-9]+$')""")
    plpy.execute("""INSERT INTO """+ tmp_dict + """ SELECT 'DIGIT',sum(total) FROM """ + dictionary_tbl + """ WHERE
            (token ~ E'^[-+]?([0-9]{1,3}[,]?)*[0-9]{1,3}$' OR token ~ E'^[-+]?[0-9]*[.][0-9]+$') GROUP BY token;""")

    plpy.execute("""INSERT INTO """ +  segment_hashtbl + """(seg_text)
                    SELECT DISTINCT seg_text
                    FROM """ +  tmp_segment_tbl + """;""")

    plpy.execute("""INSERT INTO """ + unknown_segment_hashtbl + """(seg_text)
                   ((SELECT DISTINCT seg_text
                       FROM   """ +  segment_hashtbl + """)
                     EXCEPT
                        (SELECT DISTINCT token
                           FROM """+ tmp_dict + """
                           WHERE  total>1));""")

    plpy.execute("""INSERT INTO """ + prev_labeltbl + """
                        SELECT id
                        FROM   """ + label_tbl + """;
                        INSERT INTO """ + prev_labeltbl + """ VALUES(-1);
                        INSERT INTO """ + prev_labeltbl + """ VALUES( """ + str(nlabel) + """);""")

    # Generate sparse M factor table
    plpy.execute("""INSERT INTO """ + mtbl + """(prev_label, label, value)
                        SELECT prev_label.id, label.id, 0
                        FROM   """ + label_tbl + """ AS label,
                               """ + prev_labeltbl + """ as prev_label;""")

    # EdgeFeature and startFeature, startFeature can be considered as a special edgeFeature
    plpy.execute("""INSERT INTO """ + mtbl + """(prev_label, label, value)
                        SELECT prev_label_id,label_id,weight
                        FROM   """ + crf_weights_tbl + """ AS features
                        WHERE  features.prev_label_id<>-1 OR features.name = 'S.';""")

    # EndFeature, endFeature can be considered as a special edgeFeature
    plpy.execute("""INSERT INTO """ + mtbl + """(prev_label, label, value)
                        SELECT """ + str(nlabel) + """, label_id, weight
                        FROM   """ + crf_weights_tbl + """ AS features
                        WHERE  features.name = 'End.';""")

m4_ifdef(`__HAS_ORDERED_AGGREGATES__', `
    plpy.execute("""INSERT INTO """ + viterbi_mtbl + """
                        SELECT array_agg(weight ORDER BY prev_label,label)
                        FROM   (SELECT prev_label, label, (SUM(value)*1000)::FLOAT8 AS weight
                                FROM   """ + mtbl + """
                                GROUP BY prev_label,label
                                ORDER BY prev_label,label) as TEMP_MTBL;""".format(
                                    viterbi_mtbl = viterbi_mtbl
                                ))
', `
    plpy.execute("""INSERT INTO """ + viterbi_mtbl + """
                        SELECT ARRAY(
                            SELECT
                                (SUM(value) * 1000)::FLOAT8
                            FROM
                                """ + mtbl + """
                            GROUP BY
                                prev_label, label
                            ORDER BY
                                prev_label, label
                        );""".format(
                            viterbi_mtbl = viterbi_mtbl
                        ))
')

    plpy.execute("""INSERT INTO """ + rtbl  + """(seg_text, label, value)
                        SELECT segment_hashtbl.seg_text, labels.id, 0
                        FROM   """ +  segment_hashtbl + """ segment_hashtbl,
                         """ + label_tbl + """ AS labels;""")

    # RegExFeature
    plpy.execute("""INSERT INTO """ + rtbl  + """(seg_text, label, value)
                        SELECT segment_hashtbl.seg_text, features.label_id, features.weight
                        FROM   """ +  segment_hashtbl + """ AS segment_hashtbl,
                         """ + crf_weights_tbl + """ AS features,
                         """ + regex_tbl + """ AS regex
                        WHERE  segment_hashtbl.seg_text ~ regex.pattern
                               AND features.name ='R_' || regex.name;""")

    # UnknownFeature
    plpy.execute("""INSERT INTO """ + rtbl  + """(seg_text, label, value)
                        SELECT segment_hashtbl.seg_text, features.label_id, features.weight
                        FROM   """ + unknown_segment_hashtbl + """ AS segment_hashtbl,
                         """ + crf_weights_tbl + """ AS features
                        WHERE  features.name = 'U';""")

    # Wordfeature
    plpy.execute("""INSERT INTO """ + rtbl  + """(seg_text, label, value)
                        SELECT seg_text, label_id, weight
                        FROM   """ +  segment_hashtbl + """,
                        """  + crf_weights_tbl + """
                        WHERE  name = 'W_' || seg_text;""")

    # Factor table
    plpy.execute("""INSERT INTO """ + viterbi_rtbl + """(seg_text, label, score)
                        SELECT seg_text,label,(SUM(value)*1000)::FLOAT8 AS score
                        FROM   """ + rtbl  + """
                        GROUP BY seg_text,label;""")

    # Enforce ANALYZE to gather proper table statistics required to generate optimized query plans
    plpy.execute(""" ANALYZE {viterbi_mtbl} """.format(viterbi_mtbl = viterbi_mtbl))
    plpy.execute(""" ANALYZE {viterbi_rtbl} """.format(viterbi_rtbl = viterbi_rtbl))


def _validate_label_tbl(label_tbl):

    rv = plpy.execute("""SELECT count(*), max(id), min(id) FROM {label_tbl}
                      """.format(label_tbl = label_tbl))

    count = rv[0]['count']
    max_id = rv[0]['max']
    min_id = rv[0]['min']

    _assert(min_id >= 0 and max_id <= count - 1,
        "CRF error: Bound check failed for label table."
        " Expected id values between 0 to total number of elements in the table - 1")

def _validate_columns(cols, table_name, err_msg_tbl):
    """
    @brief Validate if cols exists in the table
    """

    _assert(columns_exist_in_table(table_name, cols),
        "CRF error: Missing required columns from %s table: %s" % (err_msg_tbl, ', '.join(cols)))

def _validate_train_args(train_segment_tbl, regex_tbl, label_tbl,
        dictionary_tbl, train_feature_tbl, train_featureset_tbl):

    """
    @brief Validate the arguments: Feature extraction for training.
    """

    # Validate existence of input tables.
    _assert(table_exists(train_segment_tbl),
        "CRF error: Train segment table does not exist!")
    _assert(table_exists(regex_tbl),
        "CRF error: Regex table does not exist!")
    _assert(table_exists(label_tbl),
        "CRF error: Label table does not exist!")

    # Validate required column names existence in respective tables.
    _validate_columns(['doc_id', 'start_pos', 'seg_text', 'label'],
            train_segment_tbl, "segment")
    _validate_columns(['pattern', 'name'], regex_tbl, "regex")
    _validate_columns(['id', 'label'], label_tbl, "label")

    _validate_label_tbl(label_tbl)

    # Validate output tables for valid names.
    _assert(dictionary_tbl is not None and
        dictionary_tbl.lower().strip() not in ('null', ''),
        "CRF error: Invalid dictionary table name")
    _assert(train_feature_tbl is not None and
        train_feature_tbl.lower().strip() not in ('null', ''),
        "CRF error: Invalid train feature table name")
    _assert(train_featureset_tbl is not None and
        train_featureset_tbl.lower().strip() not in ('null', ''),
        "CRF error: Invalid train fatureset table name")

    _assert(not table_exists(dictionary_tbl),
        "CRF error: Dictionary table name already exist!"
        " Please provide a different table name.")
    _assert(not table_exists(train_feature_tbl),
        "CRF error: Train feature table name already exist!"
        " Please provide a different table name.")
    _assert(not table_exists(train_featureset_tbl),
        "CRF error: Train featureset table name already exist!"
        " Please provide a different table name.")

def _validate_test_args(test_segment_tbl, dictionary_tbl, label_tbl,
        regex_tbl, crf_weights_tbl, viterbi_mtbl, viterbi_rtbl):

    """
    @brief Validate the arguments: Feature extraction for testing.
    """

    # Check existence of input tables.
    _assert(table_exists(test_segment_tbl),
        "CRF error: Test segment table does not exist!")
    _assert(table_exists(dictionary_tbl),
        "CRF error: Dictionary table does not exist!")
    _assert(table_exists(label_tbl),
        "CRF error: Label table does not exist!")
    _assert(table_exists(regex_tbl),
        "CRF error: Regex table does not exist!")
    _assert(table_exists(crf_weights_tbl),
        "CRF error: CRF weights table does not exist!")

    # Validate required column names existence in respective tables.
    _validate_columns(['doc_id', 'start_pos', 'seg_text'], test_segment_tbl, "segment")
    _validate_columns(['token', 'total'], dictionary_tbl, "dictionary")
    _validate_columns(['id', 'label'], label_tbl, "label")
    _validate_columns(['pattern', 'name'], regex_tbl, "regex")
    _validate_columns(['id', 'name', 'prev_label_id', 'label_id', 'weight'],
            crf_weights_tbl, "crf weights")

    _validate_label_tbl(label_tbl)

    # Validate output tables for valid names.
    _assert(viterbi_mtbl is not None and
        viterbi_mtbl.lower().strip() not in ('null', ''),
        "CRF error: Invalid viterbi mtable name")
    _assert(viterbi_rtbl is not None and
        viterbi_rtbl.lower().strip() not in ('null', ''),
        "CRF error: Invalid viterbi rtable name")

    _assert(not table_exists(viterbi_mtbl),
        "CRF error: Viterbi M table name already exist!"
        " Please provide a different table name.")
    _assert(not table_exists(viterbi_rtbl),
        "CRF error: Viterbi R table name already exist!"
        " Please provide a different table name.")