1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
|
<HTML>
<HEAD>
<TITLE>Managing external tables for SWI-Prolog</TITLE>
</HEAD>
<BODY BGCOLOR="white">
<BLOCKQUOTE>
<BLOCKQUOTE>
<BLOCKQUOTE>
<BLOCKQUOTE>
<CENTER>
<H1>Managing external tables for SWI-Prolog</H1>
</CENTER>
<HR>
<CENTER>
<I>Jan Wielemaker <BR>
SWI, <BR>
University of Amsterdam <BR>
The Netherlands <BR>
E-mail: <A HREF="mailto:jan@swi.psy.uva.nl">jan@swi.psy.uva.nl</A></I>
</CENTER>
<HR>
</BLOCKQUOTE>
</BLOCKQUOTE>
</BLOCKQUOTE>
</BLOCKQUOTE>
<CENTER><H3>Abstract</H3></Center>
<TABLE WIDTH="90%" ALIGN=center BORDER=2 BGCOLOR="#f0f0f0"><TR><TD>
This document describes a foreign language extension to
<A HREF="http://www.swi.psy.uva.nl/projects/SWI-Prolog">SWI-Prolog</A>
for the manipulation of `external tables'. External tables are files
using a textual representation of records separated into fields. The
package allows for a flexible definition of the format of the file in
terms of records and fields, how the information in the file should be
mapped onto Prolog data types and what properties the file has to
improve the performance of lookup.
<P>The table package has been used successfully to deal with large
static databases such as dictionaries. Compared to loading the tables
into the Prolog database, this approach required much less memory and
loads much faster while providing reasonable lookup-performance on
sorted tables.
<P>This package uses read-only `mapping' of the database file into
memory and is ported to Win32 (Windows 95 and NT) as well as Unix
systems providing the mmap() system call (Solaris, SunOs, Linux and many
more modern Unices).
</TABLE>
<H1><A NAME="document-contents">Table of Contents</A></H1>
<UL>
<UL>
<LI><A HREF="#sec:1"><B>1 Introduction</B></A>
<LI><A HREF="#sec:2"><B>2 Managing external tables</B></A>
<UL>
<LI><A HREF="#sec:2.1">2.1 Creating and destroying tables</A>
<LI><A HREF="#sec:2.2">2.2 Accessing a table</A>
<UL>
<LI><A HREF="#sec:2.2.1">2.2.1 Finding record locations in a table</A>
<LI><A HREF="#sec:2.2.2">2.2.2 Reading records</A>
<LI><A HREF="#sec:2.2.3">2.2.3 Searching the table</A>
<LI><A HREF="#sec:2.2.4">2.2.4 Miscellaneous</A>
</UL>
</UL>
<LI><A HREF="#sec:3"><B>3 Flexible ordering and equivalence based on
character table</B></A>
<LI><A HREF="#sec:4"><B>4 Example: accessing the Unix passwd file</B></A>
</UL>
</UL>
<H2><A NAME="sec:1">1 Introduction</A></H2>
<P>Prolog programs sometimes need access to large sets of background
data. For example in the <font size=-1>GRASP</font> project we need
access to ontologies of art objects, a large lexicon and translation
dictionaries. Storage of such information as Prolog clauses is not
sufficiently efficient in terms of the memory requirements.
<P>The table package outlined in this document allows for easy access of
large structured files. The package uses binary search if possible and
linear search for queries that cannot use more efficient algorithms
without building additional index tables. Caching is achieved using the
file-to-memory maps supported by many modern operating systems.
<P>The following sections define the interface predicates for the
package.
<A HREF="#sec:example">Section 4</A> provides an example to access the
Unix password file.
<H2><A NAME="sec:2">2 Managing external tables</A></H2>
<H3><A NAME="sec:2.1">2.1 Creating and destroying tables</A></H3>
<P>This section describes the predicates required for creating and
destroying the access to external database tables.
<DL>
<P>
<DT><A NAME="new_table/4"><STRONG>new_table</STRONG>(<VAR>+File,
+Columns, +Options, -Handle</VAR>)</A><DD>
Create a description of a new table, stored in <VAR>File</VAR>. <VAR>Columns</VAR>
is a list of descriptions for each column. A column description is of
the form
<BLOCKQUOTE>
<VAR>ColumnName</VAR><TT>(</TT><VAR>Type [, ColumnOptions]</VAR><TT>)</TT>
</BLOCKQUOTE>
<P><VAR>Type</VAR> denotes the Prolog type to which the field should be
converted and is one of:
<P>
<CENTER>
<TABLE BORDER=2 FRAME=border RULES=group>
<TR VALIGN=top><TD><TT>integer</TT><TD>Convert to a Prolog integer. The
input is treated as a decimal number. </TR>
<TR VALIGN=top><TD><TT>float</TT><TD>Convert to a Prolog floating point
number. The input is handled by the C-library function
<TT>strtod()</TT>. </TR>
<TR VALIGN=top><TD><TT>atom</TT><TD>Convert to a Prolog atom. </TR>
<TR VALIGN=top><TD><TT>string</TT><TD>Convert to a SWI-Prolog string
object. </TR>
<TR VALIGN=top><TD><TT>code_list</TT><TD>Convert to a list of <font size=-1>ASCII</font>
codes. </TR>
</TABLE>
</CENTER>
<P><VAR>ColumnOptions</VAR> is a list of additional properties of the
column. Supported values are:
<P>
<CENTER>
<TABLE BORDER=2 FRAME=border RULES=group>
<TR VALIGN=top><TD><TT>sorted</TT><TD>The field is strictly sorted, but
may have (adjacent) duplicate entries. If the field is textual, it
should be sorted alphabetically, otherwise it should be sorted
numerically. </TR>
<TR VALIGN=top><TD><TT>sorted(+<VAR>Table</VAR>)</TT><TD>The (textual)
field is sorted using the ordering declared by the named <EM>ordering
table</EM>. This option may be used to define reverse order,
`dictionary' order or other irregular alphabetical ordering. See
<A NAME="idx:newordertable2:1"></A><A HREF="#new_order_table/2">new_order_table/2</A>. </TR>
<TR VALIGN=top><TD><TT>unique</TT><TD>This column has distinct values
for each row in the table. </TR>
<TR VALIGN=top><TD><TT>downcase</TT><TD>Map all uppercase in the field
to lowercase before converting to a Prolog atom, string or code_list. </TR>
<TR VALIGN=top><TD><TT>map_space_to_underscore</TT><TD>Map spaces to
underscores before converting to a Prolog atom, string or code_list. </TR>
<TR VALIGN=top><TD><TT>syntax</TT><TD>For numerical fields. If the field
does not contain a valid number, matching the value fails. Reading the
value returns the value as an atom. </TR>
<TR VALIGN=top><TD><TT>width(+<VAR>Chars</VAR>)</TT><TD>Field has fixed
width of the specified number of characters. The column-separator is not
considered for this column. </TR>
<TR VALIGN=top><TD><TT>arg(+<VAR>Index</VAR>)</TT><TD>For <A NAME="idx:readtablerecord4:2"></A><A HREF="#read_table_record/4">read_table_record/4</A>,
unify the field with the given argument of the record term. Further
fields will be assigned index+1, ... . </TR>
<TR VALIGN=top><TD><TT>skip</TT><TD>Don't convert this field to Prolog.
The field is simply skipped without checking for consistency. </TR>
</TABLE>
</CENTER>
<P>The <VAR>Options</VAR> argument is a list of global options for the
table. Defined options are:
<P>
<CENTER>
<TABLE BORDER=2 FRAME=border RULES=group>
<TR VALIGN=top><TD><TT>record_separator(+<VAR>Code</VAR>)</TT><TD>Character
(<font size=-1>ASCII</font>) value of the character separating two
records. Default is the newline (<font size=-1>ASCII</font> 10). </TR>
<TR VALIGN=top><TD><TT>field_separator(+<VAR>Code</VAR>)</TT><TD>Character
(<font size=-1>ASCII</font>) value of the character separating two
fields in a record. Default is the space (<font size=-1>ASCII</font>
32), which also has a special meaning. Two fields separated by a space
may be separated by any non-empty sequence of spaces and tab (<font size=-1>ASCII</font>
9) characters. For all other separators, a single character separates
the fields. </TR>
<TR VALIGN=top><TD><TT>escape(+<VAR>Code</VAR>, +<VAR>ListOfMap</VAR>)</TT><TD>Sometimes,
a table defines escape sequences to make it possible to use the
separator-characters in text-fields. This options provides a simple way
to handle some standard cases. <VAR>Code</VAR> is the <font size=-1>ASCII</font>
code of the character that leads the escape sequence. The default is
<TT>-1</TT>, and thus never matched.
<VAR>ListOfMap</VAR> is a list of
<VAR>From</VAR><TT> = </TT><VAR>To</VAR> character mappings. The default
map table is the identity map, unless <VAR>Code</VAR> refers to the
<CODE>\</CODE> character, in which case
<CODE>\b</CODE>, <CODE>\e</CODE>, <CODE>\n</CODE>, <CODE>\r</CODE> and <CODE>\t</CODE>
have their usual meaning. </TR>
<TR VALIGN=top><TD><TT>functor(<VAR>+Head</VAR>)</TT><TD>Functor used by <A NAME="idx:readtablerecord4:3"></A><A HREF="#read_table_record/4">read_table_record/4</A>.
Default is <TT>record</TT> using the maximal argument index of the
fields as arity. </TR>
</TABLE>
</CENTER>
<P>If the options are parsed successfully, <VAR>Handle</VAR> is unified
with a term that may be used as a handle to the table for future
operations on it. Note that <A NAME="idx:newtable4:4"></A><A HREF="#new_table/4">new_table/4</A>
does not access the file system, so its success only indicates the
description could be parsed, not the presence, access or format of the
file.
<P>
<DT><A NAME="open_table/1"><STRONG>open_table</STRONG>(<VAR>+Handle</VAR>)</A><DD>
Open the table. This predicate normally does not need to be called
explicitely, as all operations on the table handle will automatically
open the table if this is required. It fails if the file cannot be
accessed or some other error with the required operating-system
resources occurs. The contents of the file is not examined by this
predicate.
<P>
<DT><A NAME="close_table/1"><STRONG>close_table</STRONG>(<VAR>+Handle</VAR>)</A><DD>
Close the file and other system resources, but do not remove the
description of the table, so it can be re-opened later.
<P>
<DT><A NAME="free_table/1"><STRONG>free_table</STRONG>(<VAR>+Handle</VAR>)</A><DD>
Close and remove the handle. After this operation, <VAR>Handle</VAR>
becomes invalid and further references to it causes undefined behaviour.
<P>
</DL>
<H3><A NAME="sec:2.2">2.2 Accessing a table</A></H3>
<P>This section describes the predicates to read data from a table.
<H4><A NAME="sec:2.2.1">2.2.1 Finding record locations in a table</A></H4>
<P>Records are addressed by their offset in the table (file). As records
have generally non-fixed length, searching is often required. The
predicates below allow for finding records in the file.
<DL>
<P>
<DT><A NAME="get_table_attribute/3"><STRONG>get_table_attribute</STRONG>(<VAR>+Handle,
+Attribute, -Value</VAR>)</A><DD>
Fetch attributes of the table. Defined attributes:
<P>
<TABLE BORDER=0 FRAME=void RULES=group>
<TR VALIGN=top><TD><TT>file</TT><TD>Unify value with the name of the
file with which the table is associated. </TR>
<TR VALIGN=top><TD><TT>field(<VAR>N</VAR>)</TT><TD>Unify value with
declaration of n-th (1-based) field. </TR>
<TR VALIGN=top><TD><TT>field_separator</TT><TD>Unify value with the
field separator character. </TR>
<TR VALIGN=top><TD><TT>record_separator</TT><TD>Unify value with the
record separator character. </TR>
<TR VALIGN=top><TD><TT>key_field</TT><TD>Unify value with the 1-based
index of the field that is sorted or fails if the table contains no
sorted fields. </TR>
<TR VALIGN=top><TD><TT>field_count</TT><TD>Unify value with the total
number of columns in the table. </TR>
<TR VALIGN=top><TD><TT>size</TT><TD>Unify value with the number of
characters in the table-file, <B>not</B> the number of records. </TR>
<TR VALIGN=top><TD><TT>window</TT><TD>Unify value with a term <VAR>Start</VAR><TT>
- </TT><VAR>Size</VAR>, indicating the properties of the current window. </TR>
</TABLE>
<P>
<DT><A NAME="table_window/3"><STRONG>table_window</STRONG>(<VAR>+Handle,
+Start, +Size</VAR>)</A><DD>
If only part of the file represents the table, this call may be used to
define a window on the file. <VAR>Start</VAR> defines the start of the
window relative to the start of the file. <VAR>Size</VAR> is the size in
characters. Skipping a header is one of the possible purposes for this
call.
<P>
<DT><A NAME="table_start_of_record/4"><STRONG>table_start_of_record</STRONG>(<VAR>+Handle,
+From, +To, -Start</VAR>)</A><DD>
Enumerates (on backtracking) the start of records in the table in the
region [From, To). Together with <A NAME="idx:readtablerecord4:5"></A><A HREF="#read_table_record/4">read_table_record/4</A>,
this may be used to read the table's data.
<P>
<DT><A NAME="table_previous_record/3"><STRONG>table_previous_record</STRONG>(<VAR>+Handle,
+Here, -Previous</VAR>)</A><DD>
If <VAR>Here</VAR> is the start of a record, find the start of the
record before it. If <VAR>Here</VAR> points at an arbitrary location in
a record, the start of this record will be returned.
</DL>
<H4><A NAME="sec:2.2.2">2.2.2 Reading records</A></H4>
<P>There are two predicates for reading records. The <A NAME="idx:readtablerecord4:6"></A><A HREF="#read_table_record/4">read_table_record/4</A>
reads an entire record, while <A NAME="idx:readtablefields4:7"></A><A HREF="#read_table_fields/4">read_table_fields/4</A>
reads one or more fields from a record.
<DL>
<P>
<DT><A NAME="read_table_record/4"><STRONG>read_table_record</STRONG>(<VAR>+Handle,
+Start, -Next, -Record</VAR>)</A><DD>
Read a record from the table. <VAR>Handle</VAR> is a handle as returned
by <A NAME="idx:newtable4:8"></A><A HREF="#new_table/4">new_table/4</A>. <VAR>Start</VAR>
is the location of a record. If <VAR>Start</VAR> does not point to the
start of a record, this predicate searches backwards for the starting
position. <VAR>Record</VAR> is unified with a term constructed from the <VAR>functor</VAR>
associated with the table (default name <TT>record</TT> and arity the
number of not-skipped columns), each of the arguments containing the
converted data. An error is raised if the data could not be converted. <VAR>Next</VAR>
is unified with the start position for the next record.
<P>
<DT><A NAME="read_table_fields/4"><STRONG>read_table_fields</STRONG>(<VAR>+Handle,
+Start, -Next, -Fields</VAR>)</A><DD>
As <A NAME="idx:readtablerecord4:9"></A><A HREF="#read_table_record/4">read_table_record/4</A>,
but <VAR>Fields</VAR> is a list of terms
<VAR>+Name</VAR>(-<VAR>Value</VAR>), and the <VAR>Values</VAR> will be
unified with the values of the specified field.
<P>
<DT><A NAME="read_table_record_data/4"><STRONG>read_table_record_data</STRONG>(<VAR>+Handle,
+Start, -Next, -Record</VAR>)</A><DD>
Similar to <A NAME="idx:readtablerecord4:10"></A><A HREF="#read_table_record/4">read_table_record/4</A>,
but unifies record with a Prolog string containing the data of the
record unparsed. The returned record does <B>not</B> contain the
terminating record-separator.
<P>
</DL>
<H4><A NAME="sec:2.2.3">2.2.3 Searching the table</A></H4>
<DL>
<P>
<DT><A NAME="in_table/3"><STRONG>in_table</STRONG>(<VAR>+Handle,
?Fields, -RecordPos</VAR>)</A><DD>
Searches the table for records matching <VAR>Fields</VAR>. If a match is
found, the variable (see below) fields in <VAR>Fields</VAR> are unified
with the corresponding field value, and <VAR>RecordPos</VAR> is unified
with the position of the record. The latter handle may be used in a
subsequent call to <A NAME="idx:readtablerecord4:11"></A><A HREF="#read_table_record/4">read_table_record/4</A>
or
<A NAME="idx:readtablefields4:12"></A><A HREF="#read_table_fields/4">read_table_fields/4</A>.
<P><VAR>Fields</VAR> is a list of field specifiers. Each specifier is of
the format:
<BLOCKQUOTE>
<VAR>FieldName</VAR>(<VAR>Value</VAR> [, <VAR>Options</VAR>])
</BLOCKQUOTE>
<P><VAR>Options</VAR> is a list of options to specify the search. By
default, the package will search for an exact match, possibly using the
ordering table associated with the field (see <TT>order</TT> option in <A NAME="idx:newtable4:13"></A><A HREF="#new_table/4">new_table/4</A>).
Options are:
<P>
<CENTER>
<TABLE BORDER=2 FRAME=border RULES=group>
<TR VALIGN=top><TD><TT>prefix</TT><TD>Uses prefix search with the
default table. </TR>
<TR VALIGN=top><TD><TT>prefix(<VAR>Table</VAR>)</TT><TD>Uses prefix
search with the specified ordering table. </TR>
<TR VALIGN=top><TD><TT>substring</TT><TD>Searches for a substring in the
field. This requires linear search of the table. </TR>
<TR VALIGN=top><TD><TT>substring(<VAR>Table</VAR>)</TT><TD>Searches for
a substring, using the table information for determining the equivalence
of characters. </TR>
<TR VALIGN=top><TD><TT>=</TT><TD>Default equivalence. </TR>
<TR VALIGN=top><TD><TT>=(<VAR>Table</VAR>)</TT><TD>Equivalence using the
given table. </TR>
</TABLE>
</CENTER>
<P>If <VAR>Value</VAR> is unbound (i.e. a variable), the record is
considered not specified. The possible option list is ignored. If a
match is found on the remaining fields, the variable is unified with the
value found in the field.
<P>First, the system checks whether there is an ordered field that is
specified. In this case, binary search is employed to find the matching
record(s). Otherwise, linear search is used.
<P>If the match contains a specified field that has the property
<TT>unique</TT> set (see <A NAME="idx:newtable4:14"></A><A HREF="#new_table/4">new_table/4</A>), <A NAME="idx:intable3:15"></A><A HREF="#in_table/3">in_table/3</A>
succeeds deterministically. Otherwise it will create a backtrack-point
and backtracking will yield further solutions to the query.
<P><A NAME="idx:intable3:16"></A><A HREF="#in_table/3">in_table/3</A>
may be comfortable used to bind the table transparently to a predicate.
For example, we have a file with lines of the format.<A NAME=back-to-note-1 HREF="index.html#note-1"> (1)</A>
<P>
<TABLE WIDTH="90%" ALIGN=center BORDER=6 BGCOLOR="#e0e0e0"><TR><TD NOWRAP>
<PRE>
C1C2,Full Name
</PRE>
</TABLE>
<P><VAR>C1C2</VAR> is a two-character identifier used in the other
tables, and <VAR>FullName</VAR> is the description of the identifier. We
want to have a predicate identifier_name(?Id, ?FullName) to reflect this
table. The code below does the trick:
<P>
<TABLE WIDTH="90%" ALIGN=center BORDER=6 BGCOLOR="#e0e0e0"><TR><TD NOWRAP>
<PRE>
:- dynamic stored_idtable_handle/1.
idtable(Handle) :-
stored_idtable_handle(Handle).
idtable(Handle) :-
new_table('rootdisp.dat',
[ id(atom, [downcase, sorted, unique]),
name(atom),
],
[ field_separator(0',)
], Handle),
asserta(stored_idtable_handle(Handle)).
identifier_name(Id, Name) :-
idtable(Handle),
in_table(Handle, [id(Id), name(Name)], _).
</PRE>
</TABLE>
<P>
</DL>
<H4><A NAME="sec:2.2.4">2.2.4 Miscellaneous</A></H4>
<DL>
<P>
<DT><A NAME="table_version/2"><STRONG>table_version</STRONG>(<VAR>-Version,
-CompileDate</VAR>)</A><DD>
Unify <VAR>Version</VAR> with an atom identifying the version of this
package, and <VAR>CompileDate</VAR> with the date this package was
compiled.
</DL>
<H2><A NAME="sec:3">3 Flexible ordering and equivalence based on
character table</A></H2>
<P>This package was developed as part of the <font size=-1>GRASP</font>
project, where it is used for browsing lexical and ontology information,
which is normally stored using `dictionary' order, rather than the more
conventional alphabetical ordering based on character codes. To achieve
programmable ordering, the table package defines `order tables'. An
order table is a table with the cardinality of the size of the character
set (256 for extended <font size=-1>ASCII</font>), and maps each
character onto its `order number', and some characters onto special
codes.
<P>The default (<TT>exact</TT>) table matches all character codes onto
themselves. The default <TT>case_insensitive</TT> table matches all
uppercase characters onto their corresponding lowercase character. The
tables <TT>iso_latin_1</TT> and <TT>iso_latin_1_case_insensitive</TT>
map the ISO-latin-1 letters with diacritics into their plain
counterpart.
<P>To support dictionary ordering, the following special categories are
defined:
<P>
<CENTER>
<TABLE BORDER=2 FRAME=border RULES=group>
<TR VALIGN=top><TD>ignore<TD>Characters of the ignore set are simple
discarded from the input. </TR>
<TR VALIGN=top><TD>break<TD>Characters from the break set are treated as
word-breaks, and each non-empty sequence of them is considered equal. A
word break precedes a normal character. </TR>
<TR VALIGN=top><TD>tag<TD>Characters of type tag indicate the start of a
`tag' that should not be considered in ordering, unless both strings are
the same upto the tag. </TR>
</TABLE>
</CENTER>
<P>The following predicates are defined to manage and use these tables:
<DL>
<P>
<DT><A NAME="new_order_table/2"><STRONG>new_order_table</STRONG>(<VAR>+Name,
+Options</VAR>)</A><DD>
Create a new, or replace the order-table with the given name (an atom). <VAR>Options</VAR>
is a list of options:
<P>
<CENTER>
<TABLE BORDER=2 FRAME=border RULES=group>
<TR VALIGN=top><TD><TT>case_insensitive</TT><TD>Map all upper- to
lowercase characters. </TR>
<TR VALIGN=top><TD><TT>iso_latin_1</TT><TD>Start with an ISO-Latin-1
table </TR>
<TR VALIGN=top><TD><TT>iso_latin_1_case_insensitive</TT><TD>Start with a
case-insensitive ISO-Latin-1 table </TR>
<TR VALIGN=top><TD><TT>copy(+<VAR>Table</VAR>)</TT><TD>Copy all entries
from <VAR>Table</VAR>. </TR>
<TR VALIGN=top><TD><TT>tag(+<VAR>ListOfCodes</VAR>)</TT><TD>Add these
characters to the set of `tag' characters. </TR>
<TR VALIGN=top><TD><TT>ignore(+<VAR>ListOfCodes</VAR>)</TT><TD>Add these
characters to the set of `ignore' characters. </TR>
<TR VALIGN=top><TD><TT>break(+<VAR>ListOfCodes</VAR>)</TT><TD>Add these
characters to the set of `break' characters. </TR>
<TR VALIGN=top><TD><TT>+<VAR>Code1</VAR> = +<VAR>Code2</VAR> </TT><TD>Map <VAR>Code1</VAR>
onto <VAR>Code2</VAR>. </TR>
</TABLE>
</CENTER>
<P>
<DT><A NAME="order_table_mapping/3"><STRONG>order_table_mapping</STRONG>(<VAR>+Table,
?From, ?To</VAR>)</A><DD>
Read the current mapping. <VAR>To</VAR> is a character code or one of
the atoms <CODE>break</CODE>, <CODE>ignore</CODE> or <CODE>tag</CODE>.
<P>
<DT><A NAME="compare_strings/4"><STRONG>compare_strings</STRONG>(<VAR>+Table,
+S1, +S2, -Result</VAR>)</A><DD>
Compare two strings using the named <VAR>Table</VAR>. <VAR>S1</VAR> and
<VAR>S2</VAR> may be atoms, strings or code-lists. <VAR>Result</VAR> is
one of the atoms <CODE><</CODE>, <CODE>=</CODE> or <CODE>></CODE>.
<P>
<DT><A NAME="prefix_string/3"><STRONG>prefix_string</STRONG>(<VAR>+Table,
+Prefix, +String</VAR>)</A><DD>
Succeeds if <VAR>Prefix</VAR> is a prefix of <VAR>String</VAR> using the
named
<VAR>Table</VAR>.
<P>
<DT><A NAME="prefix_string/4"><STRONG>prefix_string</STRONG>(<VAR>+Table,
+Prefix, -Rest, +String</VAR>)</A><DD>
Succeeds if <VAR>Prefix</VAR> is a prefix of <VAR>String</VAR> using the
named
<VAR>Table</VAR>, and <VAR>Rest</VAR> is unified with the remainder of
<VAR>String</VAR> that is not matched. Please note that the existence of
an order-table implies simple contatenation using <A NAME="idx:concat3:17"></A><B>concat/3</B>
cannot be used to determine the non-matched part of the string.
<P>
<DT><A NAME="sub_string/3"><STRONG>sub_string</STRONG>(<VAR>+Table,
+Sub, +String</VAR>)</A><DD>
Succeeds if <VAR>Sub</VAR> is a substring of <VAR>String</VAR> using the
named <VAR>Table</VAR>.
</DL>
<H2><A NAME="sec:4">4 Example: accessing the Unix passwd file</A></H2>
<A NAME="sec:example"></A>
<P>The Unix passwd file is a file with records spanning a single line
each. The fields are separated by a single `:' character. Here is an
example of a line:
<P><font size=-1>
<TABLE WIDTH="90%" ALIGN=center BORDER=6 BGCOLOR="#e0e0e0"><TR><TD NOWRAP>
<PRE>
joe:hgdu3r3bce:53:100:Joe Johnson:/users/joe:/bin/bash
</PRE>
</TABLE>
<P></font>
<P>The following call defines a table for it:
<P>
<TABLE WIDTH="90%" ALIGN=center BORDER=6 BGCOLOR="#e0e0e0"><TR><TD NOWRAP>
<PRE>
?- new_table('/etc/passwd',
[ user(atom),
passwd(code_list),
uid(integer),
gid(integer),
gecos(code_list),
homedir(atom),
shell(atom)
],
[ field_separator(0':)
],
H).
</PRE>
</TABLE>
<P>To find all people of group <VAR>100</VAR>, use:
<P>
<TABLE WIDTH="90%" ALIGN=center BORDER=6 BGCOLOR="#e0e0e0"><TR><TD NOWRAP>
<PRE>
?- findall(User, in_table(H, [user(User), gid(100)], _), Users).
</PRE>
</TABLE>
<H1><A NAME="document-notes">Footnotes</A></H1>
<DL>
<DT><A NAME=note-1 HREF="index.html#back-to-note-1">note-1</A><DD>
This is the <TT>disproot.dat</TT> table from the <font size=-1>AAT</font>
database used in <font size=-1>GRASP</font>
</DL>
</BODY></HTML>
|
