Chapter 7. Supporting Tools
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## Chapter 7. Supporting Tools

In support of the service API - primarily the ASN module, which provides the pro-grammatic interface to the Z39.50 APDUs, YAZ contains a collection of tools that support the development of applications.

## 1. Query Syntax Parsers

Since the type-1 (RPN) query structure has no direct, useful string representation, every origin application needs to provide some form of mapping from a local query notation or representation to a Z_RPNQuery structure. Some programmers will prefer to construct the query manually, perhaps using `odr_malloc()` to simplify memory management. The YAZ distribution includes three separate, query-generating tools that may be of use to you.

### 1.1. Prefix Query Format

Since RPN or reverse polish notation is really just a fancy way of describing a suffix notation format (operator follows operands), it would seem that the confusion is total when we now introduce a prefix notation for RPN. The reason is one of simple laziness - it's somewhat simpler to interpret a prefix format, and this utility was designed for maximum simplicity, to provide a baseline representation for use in simple test applications and scripting environments (like Tcl). The demonstration client included with YAZ uses the PQF.

### Note

The PQF have been adopted by other parties developing Z39.50 software. It is often referred to as Prefix Query Notation - PQN.

The PQF is defined by the pquery module in the YAZ library. There are two sets of function that have similar behavior. First set operates on a PQF parser handle, second set doesn't. First set set of functions are more flexible than the second set. Second set is obsolete and is only provided to ensure backwards compatibility.

First set of functions all operate on a PQF parser handle:

         #include <yaz/pquery.h>

         YAZ_PQF_Parser yaz_pqf_create(void);

         void yaz_pqf_destroy(YAZ_PQF_Parser p);

         Z_RPNQuery *yaz_pqf_parse(YAZ_PQF_Parser p, ODR o, const char *qbuf);

         Z_AttributesPlusTerm *yaz_pqf_scan(YAZ_PQF_Parser p, ODR o,
                              Odr_oid **attributeSetId, const char *qbuf);

         int yaz_pqf_error(YAZ_PQF_Parser p, const char **msg, size_t *off);

A PQF parser is created and destructed by functions `yaz_pqf_create` and `yaz_pqf_destroy` respectively. Function `yaz_pqf_parse` parses query given by string `qbuf`. If parsing was successful, a Z39.50 RPN Query is returned which is created using ODR stream `o`. If parsing failed, a NULL pointer is returned. Function `yaz_pqf_scan` takes a scan query in `qbuf`. If parsing was successful, the function returns attributes plus term pointer and modifies `attributeSetId` to hold attribute set for the scan request - both allocated using ODR stream `o`. If parsing failed, yaz_pqf_scan returns a NULL pointer. Error information for bad queries can be obtained by a call to `yaz_pqf_error` which returns an error code and modifies `*msg` to point to an error description, and modifies `*off` to the offset within last query were parsing failed.

The second set of functions are declared as follows:

         #include <yaz/pquery.h>

         Z_RPNQuery *p_query_rpn(ODR o, oid_proto proto, const char *qbuf);

         Z_AttributesPlusTerm *p_query_scan(ODR o, oid_proto proto,
                                 Odr_oid **attributeSetP, const char *qbuf);

         int p_query_attset(const char *arg);

The function `p_query_rpn()` takes as arguments an ODR stream (see section The ODR Module) to provide a memory source (the structure created is released on the next call to `odr_reset()` on the stream), a protocol identifier (one of the constants PROTO_Z3950 and PROTO_SR), an attribute set reference, and finally a null-terminated string holding the query string.

If the parse went well, `p_query_rpn()` returns a pointer to a `Z_RPNQuery` structure which can be placed directly into a `Z_SearchRequest`. If parsing failed, due to syntax error, a NULL pointer is returned.

The `p_query_attset` specifies which attribute set to use if the query doesn't specify one by the `@attrset` operator. The `p_query_attset` returns 0 if the argument is a valid attribute set specifier; otherwise the function returns -1.

The grammar of the PQF is as follows:

query ::= top-set query-struct.
top-set ::= [ '@attrset' string ]
query-struct ::= attr-spec | simple | complex | '@term' term-type query
attr-spec ::= '@attr' [ string ] string query-struct
complex ::= operator query-struct query-struct.
operator ::= '@and' | '@or' | '@not' | '@prox' proximity.
simple ::= result-set | term.
result-set ::= '@set' string.
term ::= string.
proximity ::= exclusion distance ordered relation which-code unit-code.
exclusion ::= '1' | '0' | 'void'.
distance ::= integer.
ordered ::= '1' | '0'.
relation ::= integer.
which-code ::= 'known' | 'private' | integer.
unit-code ::= integer.
term-type ::= 'general' | 'numeric' | 'string' | 'oid' | 'datetime' | 'null'.

You will note that the syntax above is a fairly faithful representation of RPN, except for the Attribute, which has been moved a step away from the term, allowing you to associate one or more attributes with an entire query structure. The parser will automatically apply the given attributes to each term as required.

The @attr operator is followed by an attribute specification (`attr-spec` above). The specification consists of an optional attribute set, an attribute type-value pair and a sub-query. The attribute type-value pair is packed in one string: an attribute type, an equals sign, and an attribute value, like this: `@attr 1=1003`. The type is always an integer but the value may be either an integer or a string (if it doesn't start with a digit character). A string attribute-value is encoded as a Type-1 ``complex'' attribute with the list of values containing the single string specified, and including no semantic indicators.

Version 3 of the Z39.50 specification defines various encoding of terms. Use `@term` `type` `string`, where type is one of: `general`, `numeric` or `string` (for InternationalString). If no term type has been given, the `general` form is used. This is the only encoding allowed in both versions 2 and 3 of the Z39.50 standard.

#### 1.1.1. Using Proximity Operators with PQF

### Note

This is an advanced topic, describing how to construct queries that make very specific requirements on the relative location of their operands. You may wish to skip this section and go straight to the example PQF queries.

### Warning

Most Z39.50 servers do not support proximity searching, or support only a small subset of the full functionality that can be expressed using the PQF proximity operator. Be aware that the ability to express a query in PQF is no guarantee that any given server will be able to execute it.

The proximity operator `@prox` is a special and more restrictive version of the conjunction operator `@and`. Its semantics are described in section 3.7.2 (Proximity) of Z39.50 the standard itself, which can be read on-line at http://www.loc.gov/z3950/agency/markup/09.html#3.7.2

In PQF, the proximity operation is represented by a sequence of the form

    @prox exclusion distance ordered relation which-code unit-code

in which the meanings of the parameters are as described in in the standard, and they can take the following values:

- exclusion. 0 = false (i.e. the proximity condition specified by the remaining parameters must be satisfied) or 1 = true (the proximity condition specified by the remaining parameters must not be satisifed).

- distance. An integer specifying the difference between the locations of the operands: e.g. two adjacent words would have distance=1 since their locations differ by one unit.

- ordered. 1 = ordered (the operands must occur in the order the query specifies them) or 0 = unordered (they may appear in either order).

- relation. Recognised values are 1 (lessThan), 2 (lessThanOrEqual), 3 (equal), 4 (greaterThanOrEqual), 5 (greaterThan) and 6 (notEqual).

- which-code. `known` or `k` (the unit-code parameter is taken from the well-known list of alternatives described in below) or `private` or `p` (the unit-code paramater has semantics specific to an out-of-band agreement such as a profile).

- unit-code. If the which-code parameter is `known` then the recognised values are 1 (character), 2 (word), 3 (sentence), 4 (paragraph), 5 (section), 6 (chapter), 7 (document), 8 (element), 9 (subelement), 10 (elementType) and 11 (byte). If which-code is `private` then the acceptable values are determined by the profile.

(The numeric values of the relation and well-known unit-code parameters are taken straight from the ASN.1 of the proximity structure in the standard.)

#### 1.1.2. PQF queries

Example 7.1. PQF queries using simple terms

    	dylan

    	"bob dylan"

Example 7.2. PQF boolean operators

    	@or "dylan" "zimmerman"

    	@and @or dylan zimmerman when

    	@and when @or dylan zimmerman

Example 7.3. PQF references to result sets

    	@set Result-1

    	@and @set seta @set setb

Example 7.4. Attributes for terms

    	@attr 1=4 computer

    	@attr 1=4 @attr 4=1 "self portrait"

    	@attrset exp1 @attr 1=1 CategoryList

    	@attr gils 1=2008 Copenhagen

    	@attr 1=/book/title computer

Example 7.5. PQF Proximity queries

    	@prox 0 3 1 2 k 2 dylan zimmerman

### Note

Here the parameters 0, 3, 1, 2, k and 2 represent exclusion, distance, ordered, relation, which-code and unit-code, in that order. So:

- exclusion = 0: the proximity condition must hold

- distance = 3: the terms must be three units apart

- ordered = 1: they must occur in the order they are specified

- relation = 2: lessThanOrEqual (to the distance of 3 units)

- which-code is ``known'', so the standard unit-codes are used

- unit-code = 2: word.

So the whole proximity query means that the words `dylan` and `zimmerman` must both occur in the record, in that order, differing in position by three or fewer words (i.e. with two or fewer words between them.) The query would find ``Bob Dylan, aka. Robert Zimmerman'', but not ``Bob Dylan, born as Robert Zimmerman'' since the distance in this case is four.

Example 7.6. PQF specification of search term type

    	@term string "a UTF-8 string, maybe?"

Example 7.7. PQF mixed queries

    	@or @and bob dylan @set Result-1

    	@attr 4=1 @and @attr 1=1 "bob dylan" @attr 1=4 "slow train coming"

    	@and @attr 2=4 @attr gils 1=2038 -114 @attr 2=2 @attr gils 1=2039 -109

### Note

The last of these examples is a spatial search: in the GILS attribute set, access point 2038 indicates West Bounding Coordinate and 2030 indicates East Bounding Coordinate, so the query is for areas extending from -114 degrees to no more than -109 degrees.

### 1.2. CCL

Not all users enjoy typing in prefix query structures and numerical attribute values, even in a minimalistic test client. In the library world, the more intuitive Common Command Language - CCL (ISO 8777) has enjoyed some popularity - especially before the widespread availability of graphical interfaces. It is still useful in applications where you for some reason or other need to provide a symbolic language for expressing boolean query structures.

#### 1.2.1. CCL Syntax

The CCL parser obeys the following grammar for the FIND argument. The syntax is annotated by in the lines prefixed by `--`.

          CCL-Find ::= CCL-Find Op Elements
                    | Elements.

          Op ::= "and" | "or" | "not"
          -- The above means that Elements are separated by boolean operators.

          Elements ::= '(' CCL-Find ')'
                    | Set
                    | Terms
                    | Qualifiers Relation Terms
                    | Qualifiers Relation '(' CCL-Find ')'
                    | Qualifiers '=' string '-' string
          -- Elements is either a recursive definition, a result set reference, a
          -- list of terms, qualifiers followed by terms, qualifiers followed
          -- by a recursive definition or qualifiers in a range (lower - upper).

          Set ::= 'set' = string
          -- Reference to a result set

          Terms ::= Terms Prox Term
                 | Term
          -- Proximity of terms.

          Term ::= Term string
                | string
          -- This basically means that a term may include a blank

          Qualifiers ::= Qualifiers ',' string
                      | string
          -- Qualifiers is a list of strings separated by comma

          Relation ::= '=' | '>=' | '<=' | '<>' | '>' | '<'
          -- Relational operators. This really doesn't follow the ISO8777
          -- standard.

          Prox ::= '%' | '!'
          -- Proximity operator

Example 7.8. CCL queries

The following queries are all valid:

           dylan

           "bob dylan"

           dylan or zimmerman

           set=1

           (dylan and bob) or set=1

           righttrunc?

           "notrunc?"

           singlechar#mask

Assuming that the qualifiers `ti`, `au` and `date` are defined we may use:

           ti=self portrait

           au=(bob dylan and slow train coming)

           date>1980 and (ti=((self portrait)))

#### 1.2.2. CCL Qualifiers

Qualifiers are used to direct the search to a particular searchable index, such as title (ti) and author indexes (au). The CCL standard itself doesn't specify a particular set of qualifiers, but it does suggest a few short-hand notations. You can customize the CCL parser to support a particular set of qualifiers to reflect the current target profile. Traditionally, a qualifier would map to a particular use-attribute within the BIB-1 attribute set. It is also possible to set other attributes, such as the structure attribute.

A CCL profile is a set of predefined CCL qualifiers that may be read from a file or set in the CCL API. The YAZ client reads its CCL qualifiers from a file named `default.bib`. There are four types of lines in a CCL profile: qualifier specification, qualifier alias, comments and directives.

##### 1.2.2.1. Qualifier specification

A qualifier specification is of the form:

`qualifier-name` [`attributeset``,`]`type``=``val` [`attributeset``,`]`type``=``val` ...

where `qualifier-name` is the name of the qualifier to be used (eg. `ti`), `type` is attribute type in the attribute set (Bib-1 is used if no attribute set is given) and `val` is attribute value. The `type` can be specified as an integer or as it be specified either as a single-letter: `u` for use, `r` for relation,`p` for position, `s` for structure,`t` for truncation or `c` for completeness. The attributes for the special qualifier name `term` are used when no CCL qualifier is given in a query.

Table 7.1. Common Bib-1 attributes

Type | Description
--- | ---
`u=``value` | Use attribute (1). Common use attributes are 1 Personal-name, 4 Title, 7 ISBN, 8 ISSN, 30 Date, 62 Subject, 1003 Author), 1016 Any. Specify value as an integer.
`r=``value` | Relation attribute (2). Common values are 1 <, 2 <=, 3 =, 4 >=, 5 >, 6 <>, 100 phonetic, 101 stem, 102 relevance, 103 always matches.
`p=``value` | Position attribute (3). Values: 1 first in field, 2 first in any subfield, 3 any position in field.
`s=``value` | Structure attribute (4). Values: 1 phrase, 2 word, 3 key, 4 year, 5 date, 6 word list, 100 date (un), 101 name (norm), 102 name (un), 103 structure, 104 urx, 105 free-form-text, 106 document-text, 107 local-number, 108 string, 109 numeric string.
`t=``value` | Truncation attribute (5). Values: 1 right, 2 left, 3 left& right, 100 none, 101 process #, 102 regular-1, 103 regular-2, 104 CCL.
`c=``value` | Completeness attribute (6). Values: 1 incomplete subfield, 2 complete subfield, 3 complete field.

Refer to Bib-1 Attribute Set(7) or the complete list of Bib-1 attributes

It is also possible to specify non-numeric attribute values, which are used in combination with certain types. The special combinations are:

Table 7.2. Special attribute combos

Name | Description
--- | ---
`s=pw` | The structure is set to either word or phrase depending on the number of tokens in a term (phrase-word).
`s=al` | Each token in the term is ANDed. (and-list). This does not set the structure at all.
`s=ol` | Each token in the term is ORed. (or-list). This does not set the structure at all.
`s=ag` | Tokens that appears as phrases (with blank in them) gets structure phrase attached. Tokens that appers as words gets structure phrase attached. Phrases and words are ANDed. This is a variant of s=al and s=pw, with the main difference that words are not split (with operator AND) but instead kept in one RPN token. This facility appeared in YAZ 4.2.38.
`r=o` | Allows ranges and the operators greather-than, less-than, ... equals. This sets Bib-1 relation attribute accordingly (relation ordered). A query construct is only treated as a range if dash is used and that is surrounded by white-space. So `-1980` is treated as term `"-1980"` not `<= 1980`. If `- 1980` is used, however, that is treated as a range.
`r=r` | Similar to `r=o` but assumes that terms are non-negative (not prefixed with `-`). Thus, a dash will always be treated as a range. The construct `1980-1990` is treated as a range with `r=r` but as a single term `"1980-1990"` with `r=o`. The special attribute `r=r` is available in YAZ 2.0.24 or later.
`t=l` | Allows term to be left-truncated. If term is of the form `?x`, the resulting Type-1 term is `x` and truncation is left.
`t=r` | Allows term to be right-truncated. If term is of the form `x?`, the resulting Type-1 term is `x` and truncation is right.
`t=n` | If term is does not include `?`, the truncation attribute is set to none (100).
`t=b` | Allows term to be both left&right truncated. If term is of the form `?x?`, the resulting term is `x` and trunctation is set to both left&right.
`t=x` | Allows masking anywhere in a term, thus fully supporting # (mask one character) and ? (zero or more of any). If masking is used, trunction is set to 102 (regexp-1 in term) and the term is converted accordingly to a regular expression.
`t=z` | Allows masking anywhere in a term, thus fully supporting # (mask one character) and ? (zero or more of any). If masking is used, trunction is set to 104 (Z39.58 in term) and the term is converted accordingly to Z39.58 masking term - actually the same truncation as CCL itself.

Example 7.9. CCL profile

Consider the following definition:

    	ti       u=4 s=1
    	au       u=1 s=1
    	term     s=105
    	ranked   r=102
    	date     u=30 r=o

`ti` and `au` both set structure attribute to phrase (s=1). `ti` sets the use-attribute to 4. `au` sets the use-attribute to 1. When no qualifiers are used in the query the structure-attribute is set to free-form-text (105) (rule for `term`). The `date` sets the relation attribute to the relation used in the CCL query and sets the use attribute to 30 (Bib-1 Date).

You can combine attributes. To Search for "ranked title" you can do

    	 ti,ranked=knuth computer

which will set relation=ranked, use=title, structure=phrase.

Query

    	 date > 1980

is a valid query. But

    	 ti > 1980

is invalid.

##### 1.2.2.2. Qualifier alias

A qualifier alias is of the form:

`q` `q1` `q2` ..

which declares `q` to be an alias for `q1`, `q2`... such that the CCL query `q=x` is equivalent to `q1=x or q2=x or ...`.

##### 1.2.2.3. Comments

Lines with white space or lines that begin with character `#` are treated as comments.

##### 1.2.2.4. Directives

Directive specifications takes the form

`@``directive` `value`

Table 7.3. CCL directives

Name | Description | Default
--- | --- | ---
truncation | Truncation character | `?`
mask | Masking character. Requires YAZ 4.2.58 or later | `#`
field | Specifies how multiple fields are to be combined. There are two modes: `or`: multiple qualifier fields are ORed, `merge`: attributes for the qualifier fields are merged and assigned to one term. | `merge`
case | Specifies if CCL operators and qualifiers should be compared with case sensitivity or not. Specify 1 for case sensitive; 0 for case insensitive. | `1`
and | Specifies token for CCL operator AND. | `and`
or | Specifies token for CCL operator OR. | `or`
not | Specifies token for CCL operator NOT. | `not`
set | Specifies token for CCL operator SET. | `set`

#### 1.2.3. CCL API

All public definitions can be found in the header file `ccl.h`. A profile identifier is of type `CCL_bibset`. A profile must be created with the call to the function `ccl_qual_mk` which returns a profile handle of type `CCL_bibset`.

To read a file containing qualifier definitions the function `ccl_qual_file` may be convenient. This function takes an already opened `FILE` handle pointer as argument along with a `CCL_bibset` handle.

To parse a simple string with a FIND query use the function

    struct ccl_rpn_node *ccl_find_str(CCL_bibset bibset, const char *str,
                                      int *error, int *pos);

which takes the CCL profile (`bibset`) and query (`str`) as input. Upon successful completion the RPN tree is returned. If an error occur, such as a syntax error, the integer pointed to by `error` holds the error code and `pos` holds the offset inside query string in which the parsing failed.

An English representation of the error may be obtained by calling the `ccl_err_msg` function. The error codes are listed in `ccl.h`.

To convert the CCL RPN tree (type `struct ccl_rpn_node *`) to the Z_RPNQuery of YAZ the function `ccl_rpn_query` must be used. This function which is part of YAZ is implemented in `yaz-ccl.c`. After calling this function the CCL RPN tree is probably no longer needed. The `ccl_rpn_delete` destroys the CCL RPN tree.

A CCL profile may be destroyed by calling the `ccl_qual_rm` function.

The token names for the CCL operators may be changed by setting the globals (all type `char *`) `ccl_token_and`, `ccl_token_or`, `ccl_token_not` and `ccl_token_set`. An operator may have aliases, i.e. there may be more than one name for the operator. To do this, separate each alias with a space character.

### 1.3. CQL

CQL - Common Query Language - was defined for the SRU protocol. In many ways CQL has a similar syntax to CCL. The objective of CQL is different. Where CCL aims to be an end-user language, CQL is the protocol query language for SRU.

### Tip

If you are new to CQL, read the Gentle Introduction.

The CQL parser in YAZ provides the following:

- It parses and validates a CQL query.

- It generates a C structure that allows you to convert a CQL query to some other query language, such as SQL.

- The parser converts a valid CQL query to PQF, thus providing a way to use CQL for both SRU servers and Z39.50 targets at the same time.

- The parser converts CQL to XCQL. XCQL is an XML representation of CQL. XCQL is part of the SRU specification. However, since SRU supports CQL only, we don't expect XCQL to be widely used. Furthermore, CQL has the advantage over XCQL that it is easy to read.

#### 1.3.1. CQL parsing

A CQL parser is represented by the `CQL_parser` handle. Its contents should be considered YAZ internal (private).

    #include <yaz/cql.h>

    typedef struct cql_parser *CQL_parser;

    CQL_parser cql_parser_create(void);
    void cql_parser_destroy(CQL_parser cp);

A parser is created by `cql_parser_create` and is destroyed by `cql_parser_destroy`.

To parse a CQL query string, the following function is provided:

    int cql_parser_string(CQL_parser cp, const char *str);

A CQL query is parsed by the `cql_parser_string` which takes a query `str`. If the query was valid (no syntax errors), then zero is returned; otherwise -1 is returned to indicate a syntax error.

    int cql_parser_stream(CQL_parser cp,
                          int (*getbyte)(void *client_data),
                          void (*ungetbyte)(int b, void *client_data),
                          void *client_data);

    int cql_parser_stdio(CQL_parser cp, FILE *f);

The functions `cql_parser_stream` and `cql_parser_stdio` parses a CQL query - just like `cql_parser_string`. The only difference is that the CQL query can be fed to the parser in different ways. The `cql_parser_stream` uses a generic byte stream as input. The `cql_parser_stdio` uses a `FILE` handle which is opened for reading.

#### 1.3.2. CQL tree

The the query string is valid, the CQL parser generates a tree representing the structure of the CQL query.

    struct cql_node *cql_parser_result(CQL_parser cp);

`cql_parser_result` returns the a pointer to the root node of the resulting tree.

Each node in a CQL tree is represented by a `struct cql_node`. It is defined as follows:

    #define CQL_NODE_ST 1
    #define CQL_NODE_BOOL 2
    #define CQL_NODE_SORT 3
    struct cql_node {
        int which;
        union {
            struct {
                char *index;
    	    char *index_uri;
                char *term;
                char *relation;
    	    char *relation_uri;
                struct cql_node *modifiers;
            } st;
            struct {
                char *value;
                struct cql_node *left;
                struct cql_node *right;
                struct cql_node *modifiers;
            } boolean;
            struct {
                char *index;
                struct cql_node *next;
                struct cql_node *modifiers;
                struct cql_node *search;
            } sort;
        } u;
    };

There are three node types: search term (ST), boolean (BOOL) and sortby (SORT). A modifier is treated as a search term too.

The search term node has five members:

- `index`: index for search term. If an index is unspecified for a search term, `index` will be NULL.

- `index_uri`: index URi for search term or NULL if none could be resolved for the index.

- `term`: the search term itself.

- `relation`: relation for search term.

- `relation_uri`: relation URI for search term.

- `modifiers`: relation modifiers for search term. The `modifiers` list itself of cql_nodes each of type `ST`.

The boolean node represents `and`, `or`, `not` + proximity.

- `left` and `right`: left - and right operand respectively.

- `modifiers`: proximity arguments.

The sort node represents both the SORTBY clause.

#### 1.3.3. CQL to PQF conversion

Conversion to PQF (and Z39.50 RPN) is tricky by the fact that the resulting RPN depends on the Z39.50 target capabilities (combinations of supported attributes). In addition, the CQL and SRU operates on index prefixes (URI or strings), whereas the RPN uses Object Identifiers for attribute sets.

The CQL library of YAZ defines a `cql_transform_t` type. It represents a particular mapping between CQL and RPN. This handle is created and destroyed by the functions:

    cql_transform_t cql_transform_open_FILE (FILE *f);
    cql_transform_t cql_transform_open_fname(const char *fname);
    void cql_transform_close(cql_transform_t ct);

The first two functions create a tranformation handle from either an already open FILE or from a filename respectively.

The handle is destroyed by `cql_transform_close` in which case no further reference of the handle is allowed.

When a `cql_transform_t` handle has been created you can convert to RPN.

    int cql_transform_buf(cql_transform_t ct,
                          struct cql_node *cn, char *out, int max);

This function converts the CQL tree `cn` using handle `ct`. For the resulting PQF, you supply a buffer `out` which must be able to hold at at least `max` characters.

If conversion failed, `cql_transform_buf` returns a non-zero SRU error code; otherwise zero is returned (conversion successful). The meanings of the numeric error codes are listed in the SRU specifications at http://www.loc.gov/standards/sru/resources/diagnostics-list.html

If conversion fails, more information can be obtained by calling

    int cql_transform_error(cql_transform_t ct, char **addinfop);

This function returns the most recently returned numeric error-code and sets the string-pointer at `*addinfop` to point to a string containing additional information about the error that occurred: for example, if the error code is 15 (``Illegal or unsupported context set''), the additional information is the name of the requested context set that was not recognised.

The SRU error-codes may be translated into brief human-readable error messages using

    const char *cql_strerror(int code);

If you wish to be able to produce a PQF result in a different way, there are two alternatives.

    void cql_transform_pr(cql_transform_t ct,
                          struct cql_node *cn,
                          void (*pr)(const char *buf, void *client_data),
                          void *client_data);

    int cql_transform_FILE(cql_transform_t ct,
                           struct cql_node *cn, FILE *f);

The former function produces output to a user-defined output stream. The latter writes the result to an already open `FILE`.

#### 1.3.4. Specification of CQL to RPN mappings

The file supplied to functions `cql_transform_open_FILE`, `cql_transform_open_fname` follows a structure found in many Unix utilities. It consists of mapping specifications - one per line. Lines starting with `#` are ignored (comments).

Each line is of the form

`CQL pattern``=` `RPN equivalent`

An RPN pattern is a simple attribute list. Each attribute pair takes the form:

[`set`] `type``=``value`

The attribute `set` is optional. The `type` is the attribute type, `value` the attribute value.

The character `*` (asterisk) has special meaning when used in the RPN pattern. Each occurrence of `*` is substituted with the CQL matching name (index, relation, qualifier etc). This facility can be used to copy a CQL name verbatim to the RPN result.

The following CQL patterns are recognized:

`index.``set``.``name`

  This pattern is invoked when a CQL index, such as dc.title is converted. `set` and `name` are the context set and index name respectively. Typically, the RPN specifies an equivalent use attribute.

  For terms not bound by an index the pattern `index.cql.serverChoice` is used. Here, the prefix `cql` is defined as `http://www.loc.gov/zing/cql/cql-indexes/v1.0/`. If this pattern is not defined, the mapping will fail.

  The pattern, `index.``set``.*` is used when no other index pattern is matched.

`qualifier.``set``.``name` (DEPRECATED)

  For backwards compatibility, this is recognised as a synonym of `index.``set``.``name`

`relation.``relation`

  This pattern specifies how a CQL relation is mapped to RPN. `pattern` is name of relation operator. Since `=` is used as separator between CQL pattern and RPN, CQL relations including `=` cannot be used directly. To avoid a conflict, the names `ge`, `eq`, `le`, must be used for CQL operators, greater-than-or-equal, equal, less-than-or-equal respectively. The RPN pattern is supposed to include a relation attribute.

  For terms not bound by a relation, the pattern `relation.scr` is used. If the pattern is not defined, the mapping will fail.

  The special pattern, `relation.*` is used when no other relation pattern is matched.

`relationModifier.``mod`

  This pattern specifies how a CQL relation modifier is mapped to RPN. The RPN pattern is usually a relation attribute.

`structure.``type`

  This pattern specifies how a CQL structure is mapped to RPN. Note that this CQL pattern is somewhat to similar to CQL pattern `relation`. The `type` is a CQL relation.

  The pattern, `structure.*` is used when no other structure pattern is matched. Usually, the RPN equivalent specifies a structure attribute.

`position.``type`

  This pattern specifies how the anchor (position) of CQL is mapped to RPN. The `type` is one of `first`, `any`, `last`, `firstAndLast`.

  The pattern, `position.*` is used when no other position pattern is matched.

`set.``prefix`

  This specification defines a CQL context set for a given prefix. The value on the right hand side is the URI for the set - not RPN. All prefixes used in index patterns must be defined this way.

`set`

  This specification defines a default CQL context set for index names. The value on the right hand side is the URI for the set.

Example 7.10. CQL to RPN mapping file

This simple file defines two context sets, three indexes and three relations, a position pattern and a default structure.

           set.cql  = http://www.loc.gov/zing/cql/context-sets/cql/v1.1/
           set.dc   = http://www.loc.gov/zing/cql/dc-indexes/v1.0/

           index.cql.serverChoice = 1=1016
           index.dc.title         = 1=4
           index.dc.subject       = 1=21

           relation.<             = 2=1
           relation.eq            = 2=3
           relation.scr           = 2=3

           position.any           = 3=3 6=1

           structure.*            = 4=1

With the mappings above, the CQL query

            computer

is converted to the PQF:

            @attr 1=1016 @attr 2=3 @attr 4=1 @attr 3=3 @attr 6=1 "computer"

by rules `index.cql.serverChoice`, `relation.scr`, `structure.*`, `position.any`.

CQL query

            computer^

is rejected, since `position.right` is undefined.

CQL query

            >my = "http://www.loc.gov/zing/cql/dc-indexes/v1.0/" my.title = x

is converted to

            @attr 1=4 @attr 2=3 @attr 4=1 @attr 3=3 @attr 6=1 "x"

Example 7.11. CQL to RPN string attributes

In this example we allow any index to be passed to RPN as a use attribute.

           # Identifiers for prefixes used in this file. (index.*)
           set.cql  = info:srw/cql-context-set/1/cql-v1.1
           set.rpn  = http://bogus/rpn
           set      = http://bogus/rpn

           # The default index when none is specified by the query
           index.cql.serverChoice     = 1=any

           index.rpn.*                = 1=*
           relation.eq                = 2=3
           structure.*                = 4=1
           position.any               = 3=3

The `http://bogus/rpn` context set is also the default so we can make queries such as

            title = a

which is converted to

            @attr 2=3 @attr 4=1 @attr 3=3 @attr 1=title "a"

Example 7.12. CQL to RPN using Bath Profile

The file `etc/pqf.properties` has mappings from the Bath Profile and Dublin Core to RPN. If YAZ is installed as a package it's usually located in `/usr/share/yaz/etc` and part of the development package, such as `libyaz-dev`.

#### 1.3.5. CQL to XCQL conversion

Conversion from CQL to XCQL is trivial and does not require a mapping to be defined. There three functions to choose from depending on the way you wish to store the resulting output (XML buffer containing XCQL).

    int cql_to_xml_buf(struct cql_node *cn, char *out, int max);
    void cql_to_xml(struct cql_node *cn,
                    void (*pr)(const char *buf, void *client_data),
                    void *client_data);
    void cql_to_xml_stdio(struct cql_node *cn, FILE *f);

Function `cql_to_xml_buf` converts to XCQL and stores result in a user supplied buffer of a given max size.

`cql_to_xml` writes the result in a user defined output stream. `cql_to_xml_stdio` writes to a a file.

#### 1.3.6. PQF to CQL conversion

Conversion from PQF to CQL is offered by the two functions shown below. The former uses a generic stream for result. The latter puts result in a WRBUF (string container).

    #include <yaz/rpn2cql.h>

    int cql_transform_rpn2cql_stream(cql_transform_t ct,
                                     void (*pr)(const char *buf, void *client_data),
                                     void *client_data,
                                     Z_RPNQuery *q);

    int cql_transform_rpn2cql_wrbuf(cql_transform_t ct,
                                    WRBUF w,
                                    Z_RPNQuery *q);

The configuration is the same as used in CQL to PQF conversions.

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