1 <!-- $Id: tools.xml,v 1.16 2003-01-23 20:26:37 adam Exp $ -->
2 <chapter id="tools"><title>Supporting Tools</title>
5 In support of the service API - primarily the ASN module, which
6 provides the pro-grammatic interface to the Z39.50 APDUs, &yaz; contains
7 a collection of tools that support the development of applications.
10 <sect1 id="tools.query"><title>Query Syntax Parsers</title>
13 Since the type-1 (RPN) query structure has no direct, useful string
14 representation, every origin application needs to provide some form of
15 mapping from a local query notation or representation to a
16 <token>Z_RPNQuery</token> structure. Some programmers will prefer to
17 construct the query manually, perhaps using
18 <function>odr_malloc()</function> to simplify memory management.
19 The &yaz; distribution includes two separate, query-generating tools
20 that may be of use to you.
23 <sect2 id="PQF"><title>Prefix Query Format</title>
26 Since RPN or reverse polish notation is really just a fancy way of
27 describing a suffix notation format (operator follows operands), it
28 would seem that the confusion is total when we now introduce a prefix
29 notation for RPN. The reason is one of simple laziness - it's somewhat
30 simpler to interpret a prefix format, and this utility was designed
31 for maximum simplicity, to provide a baseline representation for use
32 in simple test applications and scripting environments (like Tcl). The
33 demonstration client included with YAZ uses the PQF.
38 The PQF have been adopted by other parties developing Z39.50
39 software. It is often referred to as Prefix Query Notation
44 The PQF is defined by the pquery module in the YAZ library.
45 There are two sets of function that have similar behavior. First
46 set operates on a PQF parser handle, second set doesn't. First set
47 set of functions are more flexible than the second set. Second set
48 is obsolete and is only provided to ensure backwards compatibility.
51 First set of functions all operate on a PQF parser handle:
54 #include <yaz/pquery.h>
56 YAZ_PQF_Parser yaz_pqf_create (void);
58 void yaz_pqf_destroy (YAZ_PQF_Parser p);
60 Z_RPNQuery *yaz_pqf_parse (YAZ_PQF_Parser p, ODR o, const char *qbuf);
62 Z_AttributesPlusTerm *yaz_pqf_scan (YAZ_PQF_Parser p, ODR o,
63 Odr_oid **attributeSetId, const char *qbuf);
66 int yaz_pqf_error (YAZ_PQF_Parser p, const char **msg, size_t *off);
69 A PQF parser is created and destructed by functions
70 <function>yaz_pqf_create</function> and
71 <function>yaz_pqf_destroy</function> respectively.
72 Function <function>yaz_pqf_parse</function> parses query given
73 by string <literal>qbuf</literal>. If parsing was successful,
74 a Z39.50 RPN Query is returned which is created using ODR stream
75 <literal>o</literal>. If parsing failed, a NULL pointer is
77 Function <function>yaz_pqf_scan</function> takes a scan query in
78 <literal>qbuf</literal>. If parsing was successful, the function
79 returns attributes plus term pointer and modifies
80 <literal>attributeSetId</literal> to hold attribute set for the
81 scan request - both allocated using ODR stream <literal>o</literal>.
82 If parsing failed, yaz_pqf_scan returns a NULL pointer.
83 Error information for bad queries can be obtained by a call to
84 <function>yaz_pqf_error</function> which returns an error code and
85 modifies <literal>*msg</literal> to point to an error description,
86 and modifies <literal>*off</literal> to the offset within last
87 query were parsing failed.
90 The second set of functions are declared as follows:
93 #include <yaz/pquery.h>
95 Z_RPNQuery *p_query_rpn (ODR o, oid_proto proto, const char *qbuf);
97 Z_AttributesPlusTerm *p_query_scan (ODR o, oid_proto proto,
98 Odr_oid **attributeSetP, const char *qbuf);
100 int p_query_attset (const char *arg);
103 The function <function>p_query_rpn()</function> takes as arguments an
104 &odr; stream (see section <link linkend="odr">The ODR Module</link>)
105 to provide a memory source (the structure created is released on
106 the next call to <function>odr_reset()</function> on the stream), a
107 protocol identifier (one of the constants <token>PROTO_Z3950</token> and
108 <token>PROTO_SR</token>), an attribute set reference, and
109 finally a null-terminated string holding the query string.
112 If the parse went well, <function>p_query_rpn()</function> returns a
113 pointer to a <literal>Z_RPNQuery</literal> structure which can be
114 placed directly into a <literal>Z_SearchRequest</literal>.
115 If parsing failed, due to syntax error, a NULL pointer is returned.
118 The <literal>p_query_attset</literal> specifies which attribute set
119 to use if the query doesn't specify one by the
120 <literal>@attrset</literal> operator.
121 The <literal>p_query_attset</literal> returns 0 if the argument is a
122 valid attribute set specifier; otherwise the function returns -1.
126 The grammar of the PQF is as follows:
130 query ::= top-set query-struct.
132 top-set ::= [ '@attrset' string ]
134 query-struct ::= attr-spec | simple | complex | '@term' term-type
136 attr-spec ::= '@attr' [ string ] string query-struct
138 complex ::= operator query-struct query-struct.
140 operator ::= '@and' | '@or' | '@not' | '@prox' proximity.
142 simple ::= result-set | term.
144 result-set ::= '@set' string.
148 proximity ::= exclusion distance ordered relation which-code unit-code.
150 exclusion ::= '1' | '0' | 'void'.
152 distance ::= integer.
154 ordered ::= '1' | '0'.
156 relation ::= integer.
158 which-code ::= 'known' | 'private' | integer.
160 unit-code ::= integer.
162 term-type ::= 'general' | 'numeric' | 'string' | 'oid' | 'datetime' | 'null'.
166 You will note that the syntax above is a fairly faithful
167 representation of RPN, except for the Attribute, which has been
168 moved a step away from the term, allowing you to associate one or more
169 attributes with an entire query structure. The parser will
170 automatically apply the given attributes to each term as required.
174 The @attr operator is followed by an attribute specification
175 (<literal>attr-spec</literal> above). The specification consists
176 of optional an attribute set, an attribute type-value pair and
177 a sub query. The attribute type-value pair is packed in one string:
178 an attribute type, a dash, followed by an attribute value.
179 The type is always an integer but the value may be either an
180 integer or a string (if it doesn't start with a digit character).
184 Z39.50 version 3 defines various encoding of terms.
185 Use the @term operator to indicate the encoding type:
186 <literal>general</literal>, <literal>numeric</literal>,
187 <literal>string</literal> (for InternationalString), ..
188 If no term type has been given, the <literal>general</literal> form
189 is used which is the only encoding allowed in both version 2 - and 3
190 of the Z39.50 standard.
194 The following are all examples of valid queries in the PQF.
202 @or "dylan" "zimmerman"
206 @or @and bob dylan @set Result-1
210 @attr 4=1 @and @attr 1=1 "bob dylan" @attr 1=4 "slow train coming"
212 @attr 4=1 @attr 1=4 "self portrait"
214 @prox 0 3 1 2 k 2 dylan zimmerman
216 @and @attr 2=4 @attr gils 1=2038 -114 @attr 2=2 @attr gils 1=2039 -109
218 @term string "a UTF-8 string, maybe?"
220 @attr 1=/book/title computer
224 <sect2 id="CCL"><title>Common Command Language</title>
227 Not all users enjoy typing in prefix query structures and numerical
228 attribute values, even in a minimalistic test client. In the library
229 world, the more intuitive Common Command Language (or ISO 8777) has
230 enjoyed some popularity - especially before the widespread
231 availability of graphical interfaces. It is still useful in
232 applications where you for some reason or other need to provide a
233 symbolic language for expressing boolean query structures.
237 The <ulink url="http://europagate.dtv.dk/">EUROPAGATE</ulink>
238 research project working under the Libraries programme
239 of the European Commission's DG XIII has, amongst other useful tools,
240 implemented a general-purpose CCL parser which produces an output
241 structure that can be trivially converted to the internal RPN
242 representation of &yaz; (The <literal>Z_RPNQuery</literal> structure).
243 Since the CCL utility - along with the rest of the software
244 produced by EUROPAGATE - is made freely available on a liberal
245 license, it is included as a supplement to &yaz;.
248 <sect3><title>CCL Syntax</title>
251 The CCL parser obeys the following grammar for the FIND argument.
252 The syntax is annotated by in the lines prefixed by
253 <literal>‐‐</literal>.
257 CCL-Find ::= CCL-Find Op Elements
260 Op ::= "and" | "or" | "not"
261 -- The above means that Elements are separated by boolean operators.
263 Elements ::= '(' CCL-Find ')'
266 | Qualifiers Relation Terms
267 | Qualifiers Relation '(' CCL-Find ')'
268 | Qualifiers '=' string '-' string
269 -- Elements is either a recursive definition, a result set reference, a
270 -- list of terms, qualifiers followed by terms, qualifiers followed
271 -- by a recursive definition or qualifiers in a range (lower - upper).
273 Set ::= 'set' = string
274 -- Reference to a result set
276 Terms ::= Terms Prox Term
278 -- Proximity of terms.
282 -- This basically means that a term may include a blank
284 Qualifiers ::= Qualifiers ',' string
286 -- Qualifiers is a list of strings separated by comma
288 Relation ::= '=' | '>=' | '<=' | '<>' | '>' | '<'
289 -- Relational operators. This really doesn't follow the ISO8777
293 -- Proximity operator
298 The following queries are all valid:
310 (dylan and bob) or set=1
314 Assuming that the qualifiers <literal>ti</literal>, <literal>au</literal>
315 and <literal>date</literal> are defined we may use:
321 au=(bob dylan and slow train coming)
323 date>1980 and (ti=((self portrait)))
328 <sect3><title>CCL Qualifiers</title>
331 Qualifiers are used to direct the search to a particular searchable
332 index, such as title (ti) and author indexes (au). The CCL standard
333 itself doesn't specify a particular set of qualifiers, but it does
334 suggest a few short-hand notations. You can customize the CCL parser
335 to support a particular set of qualifiers to reflect the current target
336 profile. Traditionally, a qualifier would map to a particular
337 use-attribute within the BIB-1 attribute set. However, you could also
338 define qualifiers that would set, for example, the
343 Consider a scenario where the target support ranked searches in the
344 title-index. In this case, the user could specify
348 ti,ranked=knuth computer
351 and the <literal>ranked</literal> would map to relation=relevance
352 (2=102) and the <literal>ti</literal> would map to title (1=4).
356 A "profile" with a set predefined CCL qualifiers can be read from a
357 file. The YAZ client reads its CCL qualifiers from a file named
358 <filename>default.bib</filename>. Each line in the file has the form:
362 <replaceable>qualifier-name</replaceable>
363 <replaceable>type</replaceable>=<replaceable>val</replaceable>
364 <replaceable>type</replaceable>=<replaceable>val</replaceable> ...
368 where <replaceable>qualifier-name</replaceable> is the name of the
369 qualifier to be used (eg. <literal>ti</literal>),
370 <replaceable>type</replaceable> is a BIB-1 category type and
371 <replaceable>val</replaceable> is the corresponding BIB-1 attribute
373 The <replaceable>type</replaceable> can be either numeric or it may be
374 either <literal>u</literal> (use), <literal>r</literal> (relation),
375 <literal>p</literal> (position), <literal>s</literal> (structure),
376 <literal>t</literal> (truncation) or <literal>c</literal> (completeness).
377 The <replaceable>qualifier-name</replaceable> <literal>term</literal>
378 has a special meaning.
379 The types and values for this definition is used when
380 <emphasis>no</emphasis> qualifiers are present.
384 Consider the following definition:
393 Two qualifiers are defined, <literal>ti</literal> and
394 <literal>au</literal>.
395 They both set the structure-attribute to phrase (1).
396 <literal>ti</literal>
397 sets the use-attribute to 4. <literal>au</literal> sets the
399 When no qualifiers are used in the query the structure-attribute is
400 set to free-form-text (105).
404 <sect3><title>CCL API</title>
406 All public definitions can be found in the header file
407 <filename>ccl.h</filename>. A profile identifier is of type
408 <literal>CCL_bibset</literal>. A profile must be created with the call
409 to the function <function>ccl_qual_mk</function> which returns a profile
410 handle of type <literal>CCL_bibset</literal>.
414 To read a file containing qualifier definitions the function
415 <function>ccl_qual_file</function> may be convenient. This function
416 takes an already opened <literal>FILE</literal> handle pointer as
417 argument along with a <literal>CCL_bibset</literal> handle.
421 To parse a simple string with a FIND query use the function
424 struct ccl_rpn_node *ccl_find_str (CCL_bibset bibset, const char *str,
425 int *error, int *pos);
428 which takes the CCL profile (<literal>bibset</literal>) and query
429 (<literal>str</literal>) as input. Upon successful completion the RPN
430 tree is returned. If an error occur, such as a syntax error, the integer
431 pointed to by <literal>error</literal> holds the error code and
432 <literal>pos</literal> holds the offset inside query string in which
437 An English representation of the error may be obtained by calling
438 the <literal>ccl_err_msg</literal> function. The error codes are
439 listed in <filename>ccl.h</filename>.
443 To convert the CCL RPN tree (type
444 <literal>struct ccl_rpn_node *</literal>)
445 to the Z_RPNQuery of YAZ the function <function>ccl_rpn_query</function>
446 must be used. This function which is part of YAZ is implemented in
447 <filename>yaz-ccl.c</filename>.
448 After calling this function the CCL RPN tree is probably no longer
449 needed. The <literal>ccl_rpn_delete</literal> destroys the CCL RPN tree.
453 A CCL profile may be destroyed by calling the
454 <function>ccl_qual_rm</function> function.
458 The token names for the CCL operators may be changed by setting the
459 globals (all type <literal>char *</literal>)
460 <literal>ccl_token_and</literal>, <literal>ccl_token_or</literal>,
461 <literal>ccl_token_not</literal> and <literal>ccl_token_set</literal>.
462 An operator may have aliases, i.e. there may be more than one name for
463 the operator. To do this, separate each alias with a space character.
467 <sect2 id="tools.cql"><title>CQL</title>
469 <ulink url="http://www.loc.gov/z3950/agency/zing/cql/">CQL</ulink>
470 - Common Query Language - was defined for the
471 <ulink url="http://www.loc.gov/z3950/agency/zing/srw/">SRW</ulink>
473 In many ways CQL has a similar syntax to CCL.
474 The objective of CQL is different. Where CCL aims to be
475 an end-user language, CQL is <emphasis>the</emphasis> protocol
476 query language for SRW.
480 If you are new to CQL, read the
481 <ulink url="http://zing.z3950.org/cql/intro.html">Gentle
482 Introduction</ulink>.
486 The CQL parser in &yaz; provides the following:
490 It parses and validates a CQL query.
495 It generates a C structure that allows you to convert
496 a CQL query to some other query language, such as SQL.
501 The parser converts a valid CQL query to PQF, thus providing a
502 way to use CQL for both SRW/SRU servers and Z39.50 targets at the
508 The parser converts CQL to
509 <ulink url="http://www.loc.gov/z3950/agency/zing/cql/xcql.html">
511 XCQL is an XML representation of CQL.
512 XCQL is part of the SRW specification. However, since SRU
513 supports CQL only, we don't expect XCQL to be widely used.
514 Furthermore, CQL has the advantage over XCQL that it is
520 <sect3 id="tools.cql.parsing"><title>CQL parsing</title>
522 A CQL parser is represented by the <literal>CQL_parser</literal>
523 handle. Its contents should be considered &yaz; internal (private).
525 #include <yaz/cql.h>
527 typedef struct cql_parser *CQL_parser;
529 CQL_parser cql_parser_create(void);
530 void cql_parser_destroy(CQL_parser cp);
532 A parser is created by <function>cql_parser_create</function> and
533 is destroyed by <function>cql_parser_destroy</function>.
536 To parse a CQL query string, the following function
539 int cql_parser_string(CQL_parser cp, const char *str);
541 A CQL query is parsed by the <function>cql_parser_string</function>
542 which takes a query <parameter>str</parameter>.
543 If the query was valid (no syntax errors), then zero is returned;
544 otherwise a non-zero error code is returned.
548 int cql_parser_stream(CQL_parser cp,
549 int (*getbyte)(void *client_data),
550 void (*ungetbyte)(int b, void *client_data),
553 int cql_parser_stdio(CQL_parser cp, FILE *f);
555 The functions <function>cql_parser_stream</function> and
556 <function>cql_parser_stdio</function> parses a CQL query
557 - just like <function>cql_parser_string</function>.
558 The only difference is that the CQL query can be
559 fed to the parser in different ways.
560 The <function>cql_parser_stream</function> uses a generic
561 byte stream as input. The <function>cql_parser_stdio</function>
562 uses a <literal>FILE</literal> handle which is opened for reading.
566 <sect3 id="tools.cql.tree"><title>CQL tree</title>
568 The the query string is validl, the CQL parser
569 generates a tree representing the structure of the
574 struct cql_node *cql_parser_result(CQL_parser cp);
576 <function>cql_parser_result</function> returns the
577 a pointer to the root node of the resulting tree.
580 Each node in a CQL tree is represented by a
581 <literal>struct cql_node</literal>.
582 It is defined as follows:
584 #define CQL_NODE_ST 1
585 #define CQL_NODE_BOOL 2
586 #define CQL_NODE_MOD 3
594 struct cql_node *modifiers;
595 struct cql_node *prefixes;
599 struct cql_node *left;
600 struct cql_node *right;
601 struct cql_node *modifiers;
602 struct cql_node *prefixes;
607 struct cql_node *next;
612 There are three kinds of nodes, search term (ST), boolean (BOOL),
616 The search term node has five members:
620 <literal>index</literal>: index for search term.
621 If an index is unspecified for a search term,
622 <literal>index</literal> will be NULL.
627 <literal>term</literal>: the search term itself.
632 <literal>relation</literal>: relation for search term.
637 <literal>modifiers</literal>: relation modifiers for search
638 term. The <literal>modifiers</literal> is a simple linked
639 list (NULL for last entry). Each relation modifier node
640 is of type <literal>MOD</literal>.
645 <literal>prefixes</literal>: index prefixes for search
646 term. The <literal>prefixes</literal> is a simple linked
647 list (NULL for last entry). Each prefix node
648 is of type <literal>MOD</literal>.
655 The boolean node represents both <literal>and</literal>,
656 <literal>or</literal>, not as well as
661 <literal>left</literal> and <literal>right</literal>: left
662 - and right operand respectively.
667 <literal>modifiers</literal>: proximity arguments.
672 <literal>prefixes</literal>: index prefixes.
673 The <literal>prefixes</literal> is a simple linked
674 list (NULL for last entry). Each prefix node
675 is of type <literal>MOD</literal>.
682 The modifier node is a "utility" node used for name-value pairs,
683 such as prefixes, proximity arguements, etc.
687 <literal>name</literal> name of mod node.
692 <literal>value</literal> value of mod node.
697 <literal>next</literal>: pointer to next node which is
698 always a mod node (NULL for last entry).
705 <sect3 id="tools.cql.pqf"><title>CQL to PQF conversion</title>
707 Conversion to PQF (and Z39.50 RPN) is tricky by the fact
708 that the resulting RPN depends on the Z39.50 target
709 capabilities (combinations of supported attributes).
710 Furthermore, the CQL and SRW operates on index prefixes
711 (URI or strings), whereas the RPN uses Object Identifiers
715 The CQL library of &yaz; defines a <literal>cql_transform_t</literal>
716 type. It represents a particular mapping between CQL and RPN.
717 This handle is created and destroyed by the functions:
719 cql_transform_t cql_transform_open_FILE (FILE *f);
720 cql_transform_t cql_transform_open_fname(const char *fname);
721 void cql_transform_close(cql_transform_t ct);
723 The first two functions create a tranformation handle from
724 either an already open FILE or from a filename.
727 The handle is destroyed by <function>cql_transform_close</function>
728 in which case no further reference of the handle is allowed.
731 When a <literal>cql_transform_t</literal> handle has been created
732 you can convert to RPN.
734 int cql_transform_buf(cql_transform_t ct,
735 struct cql_node *cn, char *out, int max);
737 This function converts the CQL tree <literal>cn</literal>
738 using handle <literal>ct</literal>.
739 For the resulting PQF, you supply a buffer <literal>out</literal>
740 which must be able to hold at at least <literal>max</literal>
744 If conversion failed, <function>cql_transform_buf</function>
745 returns a non-zero error code; otherwise zero is returned
746 (conversion successful).
749 If you wish to be able to produce a PQF result in a different
750 way, there are two alternatives.
752 void cql_transform_pr(cql_transform_t ct,
754 void (*pr)(const char *buf, void *client_data),
757 int cql_transform_FILE(cql_transform_t ct,
758 struct cql_node *cn, FILE *f);
760 The former function produces output to a user-defined
761 output stream. The latter writes the result to an already
762 open <literal>FILE</literal>.
765 <sect3 id="toolq.cql.xcql"><title>CQL to XCQL conversion</title>
767 Conversion from CQL to XCQL is trivial and does not
768 require a mapping to be defined.
769 There three functions to choose from depending on the
770 way you wish to store the resulting output (XML buffer
773 int cql_to_xml_buf(struct cql_node *cn, char *out, int max);
774 void cql_to_xml(struct cql_node *cn,
775 void (*pr)(const char *buf, void *client_data),
777 void cql_to_xml_stdio(struct cql_node *cn, FILE *f);
779 Function <function>cql_to_xml_buf</function> converts
780 to XCQL and stores result in a user supplied buffer of a given
784 <function>cql_to_xml</function> writes the result in
785 a user defined output stream.
786 <function>cql_to_xml_stdio</function> writes to a
792 <sect1 id="tools.oid"><title>Object Identifiers</title>
795 The basic YAZ representation of an OID is an array of integers,
796 terminated with the value -1. The &odr; module provides two
797 utility-functions to create and copy this type of data elements:
801 Odr_oid *odr_getoidbystr(ODR o, char *str);
805 Creates an OID based on a string-based representation using dots (.)
806 to separate elements in the OID.
810 Odr_oid *odr_oiddup(ODR odr, Odr_oid *o);
814 Creates a copy of the OID referenced by the <emphasis>o</emphasis>
816 Both functions take an &odr; stream as parameter. This stream is used to
817 allocate memory for the data elements, which is released on a
818 subsequent call to <function>odr_reset()</function> on that stream.
822 The OID module provides a higher-level representation of the
823 family of object identifiers which describe the Z39.50 protocol and its
824 related objects. The definition of the module interface is given in
825 the <filename>oid.h</filename> file.
829 The interface is mainly based on the <literal>oident</literal> structure.
830 The definition of this structure looks like this:
834 typedef struct oident
839 int oidsuffix[OID_SIZE];
845 The proto field takes one of the values
854 If you don't care about talking to SR-based implementations (few
855 exist, and they may become fewer still if and when the ISO SR and ANSI
856 Z39.50 documents are merged into a single standard), you can ignore
857 this field on incoming packages, and always set it to PROTO_Z3950
858 for outgoing packages.
862 The oclass field takes one of the values
884 corresponding to the OID classes defined by the Z39.50 standard.
886 Finally, the value field takes one of the values
944 again, corresponding to the specific OIDs defined by the standard.
948 The desc field contains a brief, mnemonic name for the OID in question.
956 struct oident *oid_getentbyoid(int *o);
960 takes as argument an OID, and returns a pointer to a static area
961 containing an <literal>oident</literal> structure. You typically use
962 this function when you receive a PDU containing an OID, and you wish
963 to branch out depending on the specific OID value.
971 int *oid_ent_to_oid(struct oident *ent, int *dst);
975 Takes as argument an <literal>oident</literal> structure - in which
976 the <literal>proto</literal>, <literal>oclass</literal>/, and
977 <literal>value</literal> fields are assumed to be set correctly -
978 and returns a pointer to a the buffer as given by <literal>dst</literal>
980 representation of the corresponding OID. The function returns
981 NULL and the array dst is unchanged if a mapping couldn't place.
982 The array <literal>dst</literal> should be at least of size
983 <literal>OID_SIZE</literal>.
987 The <function>oid_ent_to_oid()</function> function can be used whenever
988 you need to prepare a PDU containing one or more OIDs. The separation of
989 the <literal>protocol</literal> element from the remainder of the
990 OID-description makes it simple to write applications that can
991 communicate with either Z39.50 or OSI SR-based applications.
999 oid_value oid_getvalbyname(const char *name);
1003 takes as argument a mnemonic OID name, and returns the
1004 <literal>/value</literal> field of the first entry in the database that
1005 contains the given name in its <literal>desc</literal> field.
1009 Finally, the module provides the following utility functions, whose
1010 meaning should be obvious:
1014 void oid_oidcpy(int *t, int *s);
1015 void oid_oidcat(int *t, int *s);
1016 int oid_oidcmp(int *o1, int *o2);
1017 int oid_oidlen(int *o);
1022 The OID module has been criticized - and perhaps rightly so
1023 - for needlessly abstracting the
1024 representation of OIDs. Other toolkits use a simple
1025 string-representation of OIDs with good results. In practice, we have
1026 found the interface comfortable and quick to work with, and it is a
1027 simple matter (for what it's worth) to create applications compatible
1028 with both ISO SR and Z39.50. Finally, the use of the
1029 <literal>/oident</literal> database is by no means mandatory.
1030 You can easily create your own system for representing OIDs, as long
1031 as it is compatible with the low-level integer-array representation
1038 <sect1 id="tools.nmem"><title>Nibble Memory</title>
1041 Sometimes when you need to allocate and construct a large,
1042 interconnected complex of structures, it can be a bit of a pain to
1043 release the associated memory again. For the structures describing the
1044 Z39.50 PDUs and related structures, it is convenient to use the
1045 memory-management system of the &odr; subsystem (see
1046 <link linkend="odr-use">Using ODR</link>). However, in some circumstances
1047 where you might otherwise benefit from using a simple nibble memory
1048 management system, it may be impractical to use
1049 <function>odr_malloc()</function> and <function>odr_reset()</function>.
1050 For this purpose, the memory manager which also supports the &odr;
1051 streams is made available in the NMEM module. The external interface
1052 to this module is given in the <filename>nmem.h</filename> file.
1056 The following prototypes are given:
1060 NMEM nmem_create(void);
1061 void nmem_destroy(NMEM n);
1062 void *nmem_malloc(NMEM n, int size);
1063 void nmem_reset(NMEM n);
1064 int nmem_total(NMEM n);
1065 void nmem_init(void);
1066 void nmem_exit(void);
1070 The <function>nmem_create()</function> function returns a pointer to a
1071 memory control handle, which can be released again by
1072 <function>nmem_destroy()</function> when no longer needed.
1073 The function <function>nmem_malloc()</function> allocates a block of
1074 memory of the requested size. A call to <function>nmem_reset()</function>
1075 or <function>nmem_destroy()</function> will release all memory allocated
1076 on the handle since it was created (or since the last call to
1077 <function>nmem_reset()</function>. The function
1078 <function>nmem_total()</function> returns the number of bytes currently
1079 allocated on the handle.
1083 The nibble memory pool is shared amongst threads. POSIX
1084 mutex'es and WIN32 Critical sections are introduced to keep the
1085 module thread safe. Function <function>nmem_init()</function>
1086 initializes the nibble memory library and it is called automatically
1087 the first time the <literal>YAZ.DLL</literal> is loaded. &yaz; uses
1088 function <function>DllMain</function> to achieve this. You should
1089 <emphasis>not</emphasis> call <function>nmem_init</function> or
1090 <function>nmem_exit</function> unless you're absolute sure what
1091 you're doing. Note that in previous &yaz; versions you'd have to call
1092 <function>nmem_init</function> yourself.
1098 <!-- Keep this comment at the end of the file
1103 sgml-minimize-attributes:nil
1104 sgml-always-quote-attributes:t
1107 sgml-parent-document: "yaz.xml"
1108 sgml-local-catalogs: nil
1109 sgml-namecase-general:t