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.

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 Second set is obsolete and is only provided to ensure backwards compatibility.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

     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 optional an attribute set, an attribute type-value pair and a sub query. The attribute type-value pair is packed in one string: an attribute type, a dash, followed by an attribute value. 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).

Z39.50 version 3 defines various encoding of terms. Use the @term operator to indicate the encoding type: general, numeric, string (for InternationalString), .. If no term type has been given, the general form is used which is the only encoding allowed in both version 2 - and 3 of the Z39.50 standard.

The following are all examples of valid queries in the PQF.

     dylan

     "bob dylan"

     @or "dylan" "zimmerman"

     @set Result-1

     @or @and bob dylan @set Result-1

     @attr 1=4 computer

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

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

     @prox 0 3 1 2 k 2 dylan zimmerman

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

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

     @attr 1=/book/title computer
    

Common Command Language

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 (or 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.

The EUROPAGATE research project working under the Libraries programme of the European Commission's DG XIII has, amongst other useful tools, implemented a general-purpose CCL parser which produces an output structure that can be trivially converted to the internal RPN representation of YAZ (The Z_RPNQuery structure). Since the CCL utility - along with the rest of the software produced by EUROPAGATE - is made freely available on a liberal license, it is included as a supplement to YAZ.

      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

     

      dylan

      "bob dylan"

      dylan or zimmerman

      set=1

      (dylan and bob) or set=1

     

      ti=self portrait

      au=(bob dylan and slow train coming)

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

     

      ti,ranked=knuth computer
     

      ti       u=4 s=1
      au       u=1 s=1
      term     s=105
     

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