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NAME

       ZOOM - Perl extension implementing the ZOOM API for Information
       Retrieval

SYNOPSIS

        use ZOOM;
        eval {
            $conn = new ZOOM::Connection($host, $port,
                                         databaseName => "mydb");
            $conn->option(preferredRecordSyntax => "usmarc");
            $rs = $conn->search_pqf('@attr 1=4 dinosaur');
            $n = $rs->size();
            print $rs->record(0)->render();
        };
        if ($@) {
            print "Error ", $@->code(), ": ", $@->message(), "
";
        }

DESCRIPTION

       This module provides a nice, Perlish implementation of the ZOOM
       Abstract API described and documented at http://zoom.z3950.org/api/

       the ZOOM module is implemented as a set of thin classes on top of the
       non-OO functions provided by this distribution's "Net::Z3950::ZOOM"
       module, which in turn is a thin layer on top of the ZOOM-C code
       supplied as part of Index Data's YAZ Toolkit.  Because ZOOM-C is also
       the underlying code that implements ZOOM bindings in C++, Visual Basic,
       Scheme, Ruby, .NET (including C#) and other languages, this Perl module
       works compatibly with those other implementations.  (Of course, the
       point of a public API such as ZOOM is that all implementations should
       be compatible anyway; but knowing that the same code is running is
       reassuring.)

       The ZOOM module provides two enumerations ("ZOOM::Error" and
       "ZOOM::Event"), three utility functions "diag_str()", "event_str()" and
       "event()" in the "ZOOM" package itself, and eight classes:
       "ZOOM::Exception", "ZOOM::Options", "ZOOM::Connection", "ZOOM::Query",
       "ZOOM::ResultSet", "ZOOM::Record", "ZOOM::ScanSet" and "ZOOM::Package".
       Of these, the Query class is abstract, and has four concrete
       subclasses: "ZOOM::Query::CQL", "ZOOM::Query::PQF",
       "ZOOM::Query::CQL2RPN" and "ZOOM::Query::CCL2RPN".  Finally, it also
       provides a "ZOOM::Query::Log" module which supplies a useful general-
       purpose logging facility.  Many useful ZOOM applications can be built
       using only the Connection, ResultSet, Record and Exception classes, as
       in the example code-snippet above.

       A typical application will begin by creating an Connection object, then
       using that to execute searches that yield ResultSet objects, then
       fetching records from the result-sets to yield Record objects.  If an
       error occurs, an Exception object is thrown and can be dealt with.

       More sophisticated applications might also browse the server's indexes
       to create a ScanSet, from which indexed terms may be retrieved; others
       might send ``Extended Services'' Packages to the server, to achieve
       non-standard tasks such as database creation and record update.
       Searching using a query syntax other than PQF can be done using an
       query object of one of the Query subclasses.  Finally, sets of options
       may be manipulated independently of the objects they are associated
       with using an Options object.

       In general, method calls throw an exception if anything goes wrong, so
       you don't need to test for success after each call.  See the section
       below on the Exception class for details.

UTILITY FUNCTIONS

   ZOOM::diag_str()
        $msg = ZOOM::diag_str(ZOOM::Error::INVALID_QUERY);

       Returns a human-readable English-language string corresponding to the
       error code that is its own parameter.  This works for any error-code
       returned from "ZOOM::Exception::code()", "ZOOM::Connection::error_x()"
       or "ZOOM::Connection::errcode()", irrespective of whether it is a
       member of the "ZOOM::Error" enumeration or drawn from the BIB-1
       diagnostic set.

   ZOOM::diag_srw_str()
        $msg = ZOOM::diag_srw_str(18);

       Returns a human-readable English-language string corresponding to the
       specified SRW error code.

   ZOOM::event_str()
        $msg = ZOOM::event_str(ZOOM::Event::RECV_APDU);

       Returns a human-readable English-language string corresponding to the
       event code that is its own parameter.  This works for any value of the
       "ZOOM::Event" enumeration.

   ZOOM::event()
        $connsRef = [ $conn1, $conn2, $conn3 ];
        $which = ZOOM::event($connsRef);
        $ev = $connsRef->[$which-1]->last_event()
            if ($which != 0);

       Used only in complex asynchronous applications, this function takes a
       reference to a list of Connection objects, waits until an event occurs
       on any one of them, and returns an integer indicating which of the
       connections it occurred on.  The return value is a 1-based index into
       the list; 0 is returned if no event occurs within the longest timeout
       specified by the "timeout" options of all the connections.

       See the section below on asynchronous applications.

CLASSES

       The eight ZOOM classes are described here in ``sensible order'': first,
       the four commonly used classes, in the he order that they will tend to
       be used in most programs (Connection, ResultSet, Record, Exception);
       then the four more esoteric classes in descending order of how often
       they are needed.

       With the exception of the Options class, which is an extension to the
       ZOOM model, the introduction to each class includes a link to the
       relevant section of the ZOOM Abstract API.

   ZOOM::Connection
        $conn = new ZOOM::Connection("indexdata.dk:210/gils");
        print("server is '", $conn->option("serverImplementationName"), "'
");
        $conn->option(preferredRecordSyntax => "usmarc");
        $rs = $conn->search_pqf('@attr 1=4 mineral');
        $ss = $conn->scan('@attr 1=1003 a');
        if ($conn->errcode() != 0) {
           die("somthing went wrong: " . $conn->errmsg())
        }
        $conn->destroy()

       This class represents a connection to an information retrieval server,
       using an IR protocol such as ANSI/NISO Z39.50, SRW (the Search/Retrieve
       Webservice), SRU (the Search/Retrieve URL) or OpenSearch.  Not all of
       these protocols require a low-level connection to be maintained, but
       the Connection object nevertheless provides a location for the
       necessary cache of configuration and state information, as well as a
       uniform API to the connection-oriented facilities (searching, index
       browsing, etc.), provided by these protocols.

       See the description of the "Connection" class in the ZOOM Abstract API
       at http://zoom.z3950.org/api/zoom-current.php#3.2

       Methods

       new()

        $conn = new ZOOM::Connection("indexdata.dk", 210);
        $conn = new ZOOM::Connection("indexdata.dk:210/gils");
        $conn = new ZOOM::Connection("tcp:indexdata.dk:210/gils");
        $conn = new ZOOM::Connection("http:indexdata.dk:210/gils");
        $conn = new ZOOM::Connection("indexdata.dk", 210,
                                      databaseName => "mydb",
                                      preferredRecordSyntax => "marc");

       Creates a new Connection object, and immediately connects it to the
       specified server.  If you want to make a new Connection object but
       delay forging the connection, use the "create()" and "connect()"
       methods instead.

       This constructor can be called with two arguments or a single argument.
       In the former case, the arguments are the name and port number of the
       Z39.50 server to connect to; in the latter case, the single argument is
       a YAZ service-specifier string of the form

       When the two-option form is used (which may be done using a vacuous
       second argument of zero), any number of additional argument pairs may
       be provided, which are interpreted as key-value pairs to be set as
       options after the Connection object is created but before it is
       connected to the server.  This is a convenient way to set options,
       including those that must be set before connecting such as
       authentication tokens.

       The server-name string is of the form:

       ·   [scheme:]host[:port][/databaseName]

       In which the host and port parts are as in the two-argument form, the
       databaseName if provided specifies the name of the database to be used
       in subsequent searches on this connection, and the optional scheme
       (default "tcp") indicates what protocol should be used.  At present,
       the following schemes are supported:

       tcp Z39.50 connection.

       ssl Z39.50 connection encrypted using SSL (Secure Sockets Layer).  Not
           many servers support this, but Index Data's Zebra is one that does.

       unix
           Z39.50 connection on a Unix-domain (local) socket, in which case
           the hostname portion of the string is instead used as a filename in
           the local filesystem.

       http
           SRU connection over HTTP.

       If the "http" scheme is used, the particular SRU flavour to be used may
       be specified by the "sru" option, which takes the following values:

       soap
           SRU over SOAP (i.e. what used to be called SRW).  This is the
           default.

       get "SRU Classic" (i.e. SRU over HTTP GET).

       post
           SRU over HTTP POST.

       If an error occurs, an exception is thrown.  This may indicate a
       networking problem (e.g. the host is not found or unreachable), or a
       protocol-level problem (e.g. a Z39.50 server rejected the Init
       request).

       create() / connect()

        $options = new ZOOM::Options();
        $options->option(implementationName => "my client");
        $options->option(implementationId => 12345);
        $conn = create ZOOM::Connection($options)
        # or
        $conn = create ZOOM::Connection(implementationName => "my client",
                                        implementationId => 12345);

        $conn->connect($host, 0);

       The usual Connection constructor, "new()" brings a new object into
       existence and forges the connection to the server all in one operation,
       which is often what you want.  For applications that need more control,
       however, these two methods separate the two steps, allowing additional
       steps in between such as the setting of options.

       "create()" creates and returns a new Connection object, which is not
       connected to any server.  It may be passed an options block, of type
       "ZOOM::Options" (see below), into which options may be set before or
       after the creation of the Connection.  Alternatively and equivalently,
       "create()" may be passed a list of key-value option pairs directly.
       The connection to the server may then be forged by the "connect()"
       method, which accepts hostname and port arguments like those of the
       "new()" constructor.

       error_x() / errcode() / errmsg() / addinfo() / diagset()

        ($errcode, $errmsg, $addinfo, $diagset) = $conn->error_x();
        $errcode = $conn->errcode();
        $errmsg = $conn->errmsg();
        $addinfo = $conn->addinfo();
        $diagset = $conn->diagset();

       These methods may be used to obtain information about the last error to
       have occurred on a connection - although typically they will not been
       used, as the same information is available through the
       "ZOOM::Exception" that is thrown when the error occurs.  The
       "errcode()", "errmsg()", "addinfo()" and "diagset()" methods each
       return one element of the diagnostic, and "error_x()" returns all four
       at once.

       See the "ZOOM::Exception" for the interpretation of these elements.

       exception()

        die $conn->exception();

       "exception()" returns the same information as "error_x()" in the form
       of a "ZOOM::Exception" object which may be thrown or rendered.  If no
       error occurred on the connection, then "exception()" returns an
       undefined value.

       check()

        $conn->check();

       Checks whether an error is pending on the connection, and throw a
       "ZOOM::Exception" object if so.  Since errors are thrown as they occur
       for synchronous connections, there is no need ever to call this except
       in asynchronous applications.

       option() / option_binary()

        print("server is '", $conn->option("serverImplementationName"), "'
");
        $conn->option(preferredRecordSyntax => "usmarc");
        $conn->option_binary(iconBlob => "foobar");
        die if length($conn->option_binary("iconBlob") != 7);

       Objects of the Connection, ResultSet, ScanSet and Package classes carry
       with them a set of named options which affect their behaviour in
       certain ways.  See the ZOOM-C options documentation for details:

       Connection options are listed at
       http://indexdata.com/yaz/doc/zoom.tkl#zoom.connections

       These options are set and fetched using the "option()" method, which
       may be called with either one or two arguments.  In the two-argument
       form, the option named by the first argument is set to the value of the
       second argument, and its old value is returned.  In the one-argument
       form, the value of the specified option is returned.

       For historical reasons, option values are not binary-clean, so that a
       value containing a NUL byte will be returned in truncated form.  The
       "option_binary()" method behaves identically to "option()" except that
       it is binary-clean, so that values containing NUL bytes are set and
       returned correctly.

       search() / search_pqf()

        $rs = $conn->search(new ZOOM::Query::CQL('title=dinosaur'));
        # The next two lines are equivalent
        $rs = $conn->search(new ZOOM::Query::PQF('@attr 1=4 dinosaur'));
        $rs = $conn->search_pqf('@attr 1=4 dinosaur');

       The principal purpose of a search-and-retrieve protocol is searching
       (and, er, retrieval), so the principal method used on a Connection
       object is "search()".  It accepts a single argument, a "ZOOM::Query"
       object (or, more precisely, an object of a subclass of this class); and
       it creates and returns a new ResultSet object representing the set of
       records resulting from the search.

       Since queries using PQF (Prefix Query Format) are so common, we make
       them a special case by providing a "search_pqf()" method.  This is
       identical to "search()" except that it accepts a string containing the
       query rather than an object, thereby obviating the need to create a
       "ZOOM::Query::PQF" object.  See the documentation of that class for
       information about PQF.

       scan() / scan_pqf()

        $rs = $conn->scan(new ZOOM::Query::CQL('title=dinosaur'));
        # The next two lines are equivalent
        $rs = $conn->scan(new ZOOM::Query::PQF('@attr 1=4 dinosaur'));
        $rs = $conn->scan_pqf('@attr 1=4 dinosaur');

       Many Z39.50 servers allow you to browse their indexes to find terms to
       search for.  This is done using the "scan" method, which creates and
       returns a new ScanSet object representing the set of terms resulting
       from the scan.

       "scan()" takes a single argument, but it has to work hard: it specifies
       both what index to scan for terms, and where in the index to start
       scanning.  What's more, the specification of what index to scan
       includes multiple facets, such as what database fields it's an index of
       (author, subject, title, etc.) and whether to scan for whole fields or
       single words (e.g. the title ``The Empire Strikes Back'', or the four
       words ``Back'', ``Empire'', ``Strikes'' and ``The'', interleaved with
       words from other titles in the same index.

       All of this is done by using a Query object representing a query of a
       single term as the "scan()" argument.  The attributes associated with
       the term indicate which index is to be used, and the term itself
       indicates the point in the index at which to start the scan.  For
       example, if the argument is the query "@attr 1=4 fish", then

       @attr 1=4
           This is the BIB-1 attribute with type 1 (meaning access-point,
           which specifies an index), and type 4 (which means ``title'').  So
           the scan is in the title index.

       fish
           Start the scan from the lexicographically earliest term that is
           equal to or falls after ``fish''.

       The argument "@attr 1=4 @attr 6=3 fish" would behave similarly; but the
       BIB-1 attribute 6=3 mean completeness=``complete field'', so the scan
       would be for complete titles rather than for words occurring in titles.

       This takes a bit of getting used to.

       The behaviour is "scan()" is affected by the following options, which
       may be set on the Connection through which the scan is done:

       number [default: 10]
           Indicates how many terms should be returned in the ScanSet.  The
           number actually returned may be less, if the start-point is near
           the end of the index, but will not be greater.

       position [default: 1]
           A 1-based index specifying where in the returned list of terms the
           seed-term should appear.  By default it should be the first term
           returned, but "position" may be set, for example, to zero
           (requesting the next terms after the seed-term), or to the same
           value as "number" (requesting the index terms before the seed
           term).

       stepSize [default: 0]
           An integer indicating how many indexed terms are to be skipped
           between each one returned in the ScanSet.  By default, no terms are
           skipped, but overriding this can be useful to get a high-level
           overview of the index.

           Since scans using PQF (Prefix Query Format) are so common, we make
           them a special case by providing a "scan_pqf()" method.  This is
           identical to "scan()" except that it accepts a string containing
           the query rather than an object, thereby obviating the need to
           create a "ZOOM::Query::PQF" object.

       package()

        $p = $conn->package();
        $o = new ZOOM::Options();
        $o->option(databaseName => "newdb");
        $p = $conn->package($o);

       Creates and returns a new "ZOOM::Package", to be used in invoking an
       Extended Service.  An options block may optionally be passed in.  See
       the "ZOOM::Package" documentation.

       last_event()

        if ($conn->last_event() == ZOOM::Event::CONNECT) {
            print "Connected!
";
        }

       Returns a "ZOOM::Event" enumerated value indicating the type of the
       last event that occurred on the connection.  This is used only in
       complex asynchronous applications - see the sections below on the
       "ZOOM::Event" enumeration and asynchronous applications.

       destroy()

        $conn->destroy()

       Destroys a Connection object, tearing down any low-level connection
       associated with it and freeing its resources.  It is an error to reuse
       a Connection that has been "destroy()"ed.

   ZOOM::ResultSet
        $rs = $conn->search_pqf('@attr 1=4 mineral');
        $n = $rs->size();
        for $i (1 .. $n) {
            $rec = $rs->record($i-1);
            print $rec->render();
        }

       A ResultSet object represents the set of zero or more records resulting
       from a search, and is the means whereby these records can be retrieved.
       A ResultSet object may maintain client side cache or some, less, none,
       all or more of the server's records: in general, this is supposed to an
       implementaton detail of no interest to a typical application, although
       more sophisticated applications do have facilities for messing with the
       cache.  Most applications will only need the "size()", "record()" and
       "sort()" methods.

       There is no "new()" method nor any other explicit constructor.  The
       only way to create a new ResultSet is by using "search()" (or
       "search_pqf()") on a Connection.

       See the description of the "Result Set" class in the ZOOM Abstract API
       at http://zoom.z3950.org/api/zoom-current.php#3.4

       Methods

       option()

        $rs->option(elementSetName => "f");

       Allows options to be set into, and read from, a ResultSet, just like
       the Connection class's "option()" method.  There is no
       "option_binary()" method for ResultSet objects.

       ResultSet options are listed at
       http://indexdata.com/yaz/doc/zoom.resultsets.tkl

       size()

        print "Found ", $rs->size(), " records
";

       Returns the number of records in the result set.

       record() / record_immediate()

        $rec = $rs->record(0);
        $rec2 = $rs->record_immediate(0);
        $rec3 = $rs->record_immediate(1)
            or print "second record wasn't in cache
";

       The "record()" method returns a "ZOOM::Record" object representing a
       record from result-set, whose position is indicated by the argument
       passed in.  This is a zero-based index, so that legitimate values range
       from zero to "$rs->size()-1".

       The "record_immediate()" API is identical, but it never invokes a
       network operation, merely returning the record from the ResultSet's
       cache if it's already there, or an undefined value otherwise.  So if
       you use this method, you must always check the return value.

       records()

        $rs->records(0, 10, 0);
        for $i (0..10) {
            print $rs->record_immediate($i)->render();
        }

        @nextseven = $rs->records(10, 7, 1);

       The "record_immediate()" method only fetches records from the cache,
       whereas "record()" fetches them from the server if they have not
       already been cached; but the ZOOM module has to guess what the most
       efficient strategy for this is.  It might fetch each record, alone when
       asked for: that's optimal in an application that's only interested in
       the top hit from each search, but pessimal for one that wants to
       display a whole list of results.  Conversely, the software's strategy
       might be always to ask for blocks of a twenty records: that's great for
       assembling long lists of things, but wasteful when only one record is
       wanted.  The problem is that the ZOOM module can't tell, when you call
       "$rs->record()", what your intention is.

       But you can tell it.  The "records()" method fetches a sequence of
       records, all in one go.  It takes three arguments: the first is the
       zero-based index of the first record in the sequence, the second is the
       number of records to fetch, and the third is a boolean indication of
       whether or not to return the retrieved records as well as adding them
       to the cache.  (You can always pass 1 for this if you like, and Perl
       will discard the unused return value, but there is a small efficiency
       gain to be had by passing 0.)

       Once the records have been retrieved from the server (i.e. "records()"
       has completed without throwing an exception), they can be fetched much
       more efficiently using "record()" - or "record_immediate()", which is
       then guaranteed to succeed.

       cache_reset()

        $rs->cache_reset()

       Resets the ResultSet's record cache, so that subsequent invocations of
       "record_immediate()" will fail.  I struggle to imagine a real scenario
       where you'd want to do this.

       sort()

        if ($rs->sort("yaz", "1=4 >i 1=21 >s") < 0) {
            die "sort failed";
        }

       Sorts the ResultSet in place (discarding any cached records, as they
       will in general be sorted into a different position).  There are two
       arguments: the first is a string indicating the type of the sort-
       specification, and the second is the specification itself.

       The "sort()" method returns 0 on success, or -1 if the sort-
       specification is invalid.

       At present, the only supported sort-specification type is "yaz".  Such
       a specification consists of a space-separated sequence of keys, each of
       which itself consists of two space-separated words (so that the total
       number of words in the sort-specification is even).  The two words
       making up each key are a field and a set of flags.  The field can take
       one of two forms: if it contains an "=" sign, then it is a BIB-1
       type=value pair specifying which field to sort (e.g. "1=4" for a title
       sort); otherwise it is sent for the server to interpret as best it can.
       The word of flags is made up from one or more of the following: "s" for
       case sensitive, "i" for case insensitive; "<" for ascending order and
       ">" for descending order.

       For example, the sort-specification in the code-fragment above will
       sort the records in $rs case-insensitively in descending order of
       title, with records having equivalent titles sorted case-sensitively in
       ascending order of subject.  (The BIB-1 access points 4 and 21
       represent title and subject respectively.)

       destroy()

        $rs->destroy()

       Destroys a ResultSet object, freeing its resources.  It is an error to
       reuse a ResultSet that has been "destroy()"ed.

   ZOOM::Record
        $rec = $rs->record($i);
        print $rec->render();
        $raw = $rec->raw();
        $marc = new_from_usmarc MARC::Record($raw);
        print "Record title is: ", $marc->title(), "
";

       A Record object represents a record that has been retrived from the
       server.

       There is no "new()" method nor any other explicit constructor.  The
       only way to create a new Record is by using "record()" (or
       "record_immediate()", or "records()") on a ResultSet.

       In general, records are ``owned'' by their result-sets that they were
       retrieved from, so they do not have to be explicitly memory-managed:
       they are deallocated (and therefore can no longer be used) when the
       result-set is destroyed.

       See the description of the "Record" class in the ZOOM Abstract API at
       http://zoom.z3950.org/api/zoom-current.php#3.5

       Methods

       error() / exception()

        if ($rec->error()) {
            my($code, $msg, $addinfo, $dset) = $rec->error();
            print "error $code, $msg ($addinfo) from $dset set
";
            die $rec->exception();
        }

       These functions test for surrogate diagnostics associated with a
       record: that is, errors pertaining to a particular record rather than
       to the fetch-some-records operation as a whole.  (The latter are known
       in Z39.50 as non-surrogate diagnostics, and are reported as exceptions
       thrown by searches.)  If a particular record can't be obtained - for
       example, because it is not available in the requested record syntax -
       then the record object obtained from the result-set, when interrogated
       with these functions, will report the error.

       "error()" returns the error-code, a human-readable message, additional
       information and the name of the diagnostic set that the error is from.
       When called in a scalar context, it just returns the error-code.  Since
       error 0 means "no error", it can be used as a boolean has-there-been-
       an-error indicator.

       "exception()" returns the same information in the form of a
       "ZOOM::Exception" object which may be thrown or rendered.  If no error
       occurred on the record, then "exception()" returns an undefined value.

       render()

        print $rec->render();
        print $rec->render("charset=latin1,utf8");

       Returns a human-readable representation of the record.  Beyond that, no
       promises are made: careful programs should not make assumptions about
       the format of the returned string.

       If the optional argument is provided, then it is interpreted as in the
       "get()" method (q.v.)

       This method is useful mostly for debugging.

       raw()

        use MARC::Record;
        $raw = $rec->raw();
        $marc = new_from_usmarc MARC::Record($raw);
        $trans = $rec->render("charset=latin1,utf8");

       Returns an opaque blob of data that is the raw form of the record.
       Exactly what this is, and what you can do with it, varies depending on
       the record-syntax.  For example, XML records will be returned as, well,
       XML; MARC records will be returned as ISO 2709-encoded blocks that can
       be decoded by software such as the fine "Marc::Record" module; GRS-1
       record will be ... gosh, what an interesting question.  But no-one uses
       GRS-1 any more, do they?

       If the optional argument is provided, then it is interpreted as in the
       "get()" method (q.v.)

       get()

        $raw = $rec->get("raw");
        $rendered = $rec->get("render");
        $trans = $rec->get("render;charset=latin1,utf8");
        $trans = $rec->get("render", "charset=latin1,utf8");

       This is the underlying method used by "render()" and "raw()", and which
       in turn delegates to the "ZOOM_record_get()" function of the underlying
       ZOOM-C library.  Most applications will find it more natural to work
       with "render()" and "raw()".

       "get()" may be called with either one or two arguments.  The two-
       argument form is syntactic sugar: the two arguments are simply joined
       with a semi-colon to make a single argument, so the third and fourth
       example invocations above are equivalent.  The second argument (or
       portion of the first argument following the semicolon) is used in the
       "type" argument of "ZOOM_record_get()", as described in
       http://www.indexdata.com/yaz/doc/zoom.records.tkl This is useful
       primarily for invoking the character-set transformation - in the
       examples above, from ISO Latin-1 to UTF-8 Unicode.

       clone() / destroy()

        $rec = $rs->record($i);
        $newrec = $rec->clone();
        $rs->destroy();
        print $newrec->render();
        $newrec->destroy();

       Usually, it's convenient that Record objects are owned by their
       ResultSets and go away when the ResultSet is destroyed; but
       occasionally you need a Record to outlive its parent and destroy it
       later, explicitly.  To do this, "clone()" the record, keep the new
       Record object that is returned, and "destroy()" it when it's no longer
       needed.  This is only situation in which a Record needs to be
       destroyed.

   ZOOM::Exception
       In general, method calls throw an exception (of class
       "ZOOM::Exception") if anything goes wrong, so you don't need to test
       for success after each call.  Exceptions are caught by enclosing the
       main code in an "eval{}" block and checking $@ on exit from that block,
       as in the code-sample above.

       There are a small number of exceptions to this rule: the three record-
       fetching methods in the "ZOOM::ResultSet" class, "record()",
       "record_immediate()", and "records()" can all return undefined values
       for legitimate reasons, under circumstances that do not merit throwing
       an exception.  For this reason, the return values of these methods
       should be checked.  See the individual methods' documentation for
       details.

       An exception carries the following pieces of information:

       error-code
           A numeric code that specifies the type of error.  This can be
           checked for equality with known values, so that intelligent
           applications can take appropriate action.

       error-message
           A human-readable message corresponding with the code.  This can be
           shown to users, but its value should not be tested, as it could
           vary in different versions or under different locales.

       additional information [optional]
           A string containing information specific to the error-code.  For
           example, when the error-code is the BIB-1 diagnostic 109 ("Database
           unavailable"), the additional information is the name of the
           database that the application tried to use.  For some error-codes,
           there is no additional information at all; for some others, the
           additional information is undefined and may just be an human-
           readable string.

       diagnostic set [optional]
           A short string specifying the diagnostic set from which the error-
           code was drawn: for example, "ZOOM" for a ZOOM-specific error such
           as "ZOOM::Error::MEMORY" ("out of memory"), and "BIB-1" for a
           Z39.50 error-code drawn from the BIB-1 diagnostic set.

       In theory, the error-code should be interpreted in the context of the
       diagnostic set from which it is drawn; in practice, nearly all errors
       are from either the ZOOM or BIB-1 diagnostic sets, and the codes in
       those sets have been chosen so as not to overlap, so the diagnostic set
       can usually be ignored.

       See the description of the "Exception" class in the ZOOM Abstract API
       at http://zoom.z3950.org/api/zoom-current.php#3.7

       Methods

       new()

        die new ZOOM::Exception($errcode, $errmsg, $addinfo, $diagset);

       Creates and returns a new Exception object with the specified error-
       code, error-message, additional information and diagnostic set.
       Applications will not in general need to use this, but may find it
       useful to simulate ZOOM exceptions.  As is usual with Perl, exceptions
       are thrown using "die()".

       code() / message() / addinfo() / diagset()

        print "Error ", $@->code(), ": ", $@->message(), "
";
        print "(addinfo '", $@->addinfo(), "', set '", $@->diagset(), "')
";

       These methods, of no arguments, return the exception's error-code,
       error-message, additional information and diagnostic set respectively.

       render()

        print $@->render();

       Returns a human-readable rendition of an exception.  The "" operator is
       overloaded on the Exception class, so that an Exception used in a
       string context is automatically rendered.  Among other consequences,
       this has the useful result that a ZOOM application that died due to an
       uncaught exception will emit an informative message before exiting.

   ZOOM::ScanSet
        $ss = $conn->scan('@attr 1=1003 a');
        $n = $ss->size();
        ($term, $occ) = $ss->term($n-1);
        $rs = $conn->search_pqf('@attr 1=1003 "' . $term . "'");
        assert($rs->size() == $occ);

       A ScanSet represents a set of candidate search-terms returned from an
       index scan.  Its sole purpose is to provide access to those term, to
       the corresponding display terms, and to the occurrence-counts of the
       terms.

       There is no "new()" method nor any other explicit constructor.  The
       only way to create a new ScanSet is by using "scan()" on a Connection.

       See the description of the "Scan Set" class in the ZOOM Abstract API at
       http://zoom.z3950.org/api/zoom-current.php#3.6

       Methods

       size()

        print "Found ", $ss->size(), " terms
";

       Returns the number of terms in the scan set.  In general, this will be
       the scan-set size requested by the "number" option in the Connection on
       which the scan was performed [default 10], but it may be fewer if the
       scan is close to the end of the index.

       term() / display_term()

        $ss = $conn->scan('@attr 1=1004 whatever');
        ($term, $occurrences) = $ss->term(0);
        ($displayTerm, $occurrences2) = $ss->display_term(0);
        assert($occurrences == $occurrences2);
        if (user_likes_the_look_of($displayTerm)) {
            $rs = $conn->search_pqf('@attr 1=4 "' . $term . '"');
            assert($rs->size() == $occurrences);
        }

       These methods return the scanned terms themselves.  "term()" returns
       the term is a form suitable for submitting as part of a query, whereas
       "display_term()" returns it in a form suitable for displaying to a
       user.  Both versions also return the number of occurrences of the term
       in the index, i.e. the number of hits that will be found if the term is
       subsequently used in a query.

       In most cases, the term and display term will be identical; however,
       they may be different in cases where punctuation or case is normalised,
       or where identifiers rather than the original document terms are
       indexed.

       option()

        print "scan status is ", $ss->option("scanStatus");

       Allows options to be set into, and read from, a ScanSet, just like the
       Connection class's "option()" method.  There is no "option_binary()"
       method for ScanSet objects.

       ScanSet options are also described, though not particularly
       informatively, at http://indexdata.com/yaz/doc/zoom.scan.tkl

       destroy()

        $ss->destroy()

       Destroys a ScanSet object, freeing its resources.  It is an error to
       reuse a ScanSet that has been "destroy()"ed.

   ZOOM::Package
        $p = $conn->package();
        $p->option(action => "specialUpdate");
        $p->option(recordIdOpaque => 145);
        $p->option(record => content_of("/tmp/record.xml"));
        $p->send("update");
        $p->destroy();

       This class represents an Extended Services Package: an instruction to
       the server to do something not covered by the core parts of the Z39.50
       standard (or the equivalent in SRW or SRU).  Since the core protocols
       are read-only, such requests are often used to make changes to the
       database, such as in the record update example above.

       Requesting an extended service is a four-step process: first, create a
       package associated with the connection to the relevant database;
       second, set options on the package to instruct the server on what to
       do; third, send the package (which may result in an exception being
       thrown if the server cannot execute the requested operations; and
       finally, destroy the package.

       Package options are listed at http://indexdata.com/yaz/doc/zoom.ext.tkl

       The particular options that have meaning are determined by the top-
       level operation string specified as the argument to "send()".  For
       example, when the operation is "update" (the most commonly used
       extended service), the "action" option may be set to any of
       "recordInsert" (add a new record, failing if that record already
       exists), "recordDelete" (delete a record, failing if it is not in the
       database).  "recordReplace" (replace a record, failing if an old
       version is not already present) or "specialUpdate" (add a record,
       replacing any existing version that may be present).

       For update, the "record" option should be set to the full text of the
       XML record to added, deleted or replaced.  Depending on how the server
       is configured, it may extract the record's unique ID from the text
       (i.e. from a known element such as the 001 field of a MARCXML record),
       or it may require the unique ID to passed in explicitly using the
       "recordIdOpaque" option.

       Extended services packages are not currently described in the ZOOM
       Abstract API at http://zoom.z3950.org/api/zoom-current.php They will
       be added in a forthcoming version, and will function much as those
       implemented in this module.

       Methods

       option()

        $p->option(recordIdOpaque => "46696f6e61");

       Allows options to be set into, and read from, a Package, just like the
       Connection class's "option()" method.  There is no "option_binary()"
       method for Package objects.

       Package options are listed at http://indexdata.com/yaz/doc/zoom.ext.tkl

       send()

        $p->send("create");

       Sends a package to the server associated with the Connection that
       created it.  Problems are reported by throwing an exception.  The
       single parameter indicates the operation that the server is being
       requested to perform, and controls the interpretation of the package's
       options.  Valid operations include:

       itemorder
           Request a copy of a nominated object, e.g. place an ILL request.

       create
           Create a new database, the name of which is specified by the
           "databaseName" option.

       drop
           Drop an existing database, the name of which is specified by the
           "databaseName" option.

       commit
           Commit changes made to the database within a transaction.

       update
           Modify the contents of the database by adding, deleting or
           replacing records (as described above in the overview of the
           "ZOOM::Package" class).

       xmlupdate
           I have no idea what this does.

       Although the module is capable of making all these requests, not all
       servers are capable of executing them.  Refusal is indicated by
       throwing an exception.  Problems may also be caused by lack of
       privileges; so "send()" must be used with caution, and is perhaps best
       wrapped in a clause that checks for execptions, like so:

        eval { $p->send("create") };
        if ($@ && $@->isa("ZOOM::Exception")) {
            print "Oops!  ", $@->message(), "
";
            return $@->code();
        }

       destroy()

        $p->destroy()

       Destroys a Package object, freeing its resources.  It is an error to
       reuse a Package that has been "destroy()"ed.

   ZOOM::Query
        $q = new ZOOM::Query::CQL("creator=pike and subject=unix");
        $q->sortby("1=4 >i 1=21 >s");
        $rs = $conn->search($q);
        $q->destroy();

       "ZOOM::Query" is a virtual base class from which various concrete
       subclasses can be derived.  Different subclasses implement different
       types of query.  The sole purpose of a Query object is to be used in a
       "search()" on a Connection; because PQF is such a common special case,
       the shortcut Connection method "search_pqf()" is provided.

       The following Query subclasses are provided, each providing the same
       set of methods described below:

       ZOOM::Query::PQF
           Implements Prefix Query Format (PQF), also sometimes known as
           Prefix Query Notation (PQN).  This esoteric but rigorous and
           expressive format is described in the YAZ Manual at
           http://indexdata.com/yaz/doc/tools.tkl#PQF

       ZOOM::Query::CQL
           Implements the Common Query Language (CQL) of SRU, the
           Search/Retrieve URL.  CQL is a much friendlier notation than PQF,
           using a simple infix notation.  The queries are passed ``as is'' to
           the server rather than being compiled into a Z39.50 Type-1 query,
           so only CQL-compliant servers can support such querier.  CQL is
           described at http://www.loc.gov/standards/sru/cql/ and in a slight
           out-of-date but nevertheless useful tutorial at
           http://zing.z3950.org/cql/intro.php

       ZOOM::Query::CQL2RPN
           Implements CQL by compiling it on the client-side into a Z39.50
           Type-1 (RPN) query, and sending that.  This provides essentially
           the same functionality as "ZOOM::Query::CQL", but it will work
           against any standard Z39.50 server rather than only against the
           small subset that support CQL natively.  The drawback is that,
           because the compilation is done on the client side, a configuration
           file is required to direct the mapping of CQL constructs such as
           index names, relations and modifiers into Type-1 query attributes.
           An example CQL configuration file is included in the ZOOM-Perl
           distribution, in the file "samples/cql/pqf.properties"

       ZOOM::Query::CCL2RPN
           Implements CCL by compiling it on the client-side into a Z39.50
           Type-1 (RPN) query, and sending that.  Because the compilation is
           done on the client side, a configuration file is required to direct
           the mapping of CCL constructs such as index names and boolean
           operators into Type-1 query attributes.  An example CCL
           configuration file is included in the ZOOM-Perl distribution, in
           the file "samples/ccl/default.bib"

           CCL is syntactically very similar to CQL, but much looser.  While
           CQL is an entirely precise language in which each possible query
           has rigorously defined semantics, and is thus suitable for transfer
           as part of a protocol, CCL is best deployed as a human-facing UI
           language.

       See the description of the "Query" class in the ZOOM Abstract API at
       http://zoom.z3950.org/api/zoom-current.php#3.3

       Methods

       new()

        $q = new ZOOM::Query::CQL('title=dinosaur');
        $q = new ZOOM::Query::PQF('@attr 1=4 dinosaur');

       Creates a new query object, compiling the query passed as its argument
       according to the rules of the particular query-type being instantiated.
       If compilation fails, an exception is thrown.  Otherwise, the query may
       be passed to the "Connection" method "search()".

        $conn->option(cqlfile => "samples/cql/pqf.properties");
        $q = new ZOOM::Query::CQL2RPN('title=dinosaur', $conn);

       Note that for the "ZOOM::Query::CQL2RPN" subclass, the Connection must
       also be passed into the constructor.  This is used for two purposes:
       first, its "cqlfile" option is used to find the CQL configuration file
       that directs the translations into RPN; and second, if compilation
       fails, then diagnostic information is cached in the Connection and be
       retrieved using "$conn->errcode()" and related methods.

        $conn->option(cclfile => "samples/ccl/default.bib");
        # or
        $conn->option(cclqual => "ti u=4 s=pw
ab u=62 s=pw");
        $q = new ZOOM::Query::CCL2RPN('ti=dinosaur', $conn);

       For the "ZOOM::Query::CCL2RPN" subclass, too, the Connection must be
       passed into the constructor, for the same reasons as when client-side
       CQL compilation is used.  The "cclqual" option, if defined, gives a CCL
       qualification specification inline; otherwise, the contents of the file
       named by the "cclfile" option are used.

       sortby()

        $q->sortby("1=4 >i 1=21 >s");

       Sets a sort specification into the query, so that when a "search()" is
       run on the query, the result is automatically sorted.  The sort
       specification language is the same as the "yaz" sort-specification type
       of the "ResultSet" method "sort()", described above.

       destroy()

        $p->destroy()

       Destroys a Query object, freeing its resources.  It is an error to
       reuse a Query that has been "destroy()"ed.

   ZOOM::Options
        $o1 = new ZOOM::Options();
        $o1->option(user => "alf");
        $o2 = new ZOOM::Options();
        $o2->option(password => "fruit");
        $opts = new ZOOM::Options($o1, $o2);
        $conn = create ZOOM::Connection($opts);
        $conn->connect($host); # Uses the specified username and password

       Several classes of ZOOM objects carry their own sets of options, which
       can be manipulated using their "option()" method.  Sometimes, however,
       it's useful to deal with the option sets directly, and the
       "ZOOM::Options" class exists to enable this approach.

       Option sets are not currently described in the ZOOM Abstract API at
       http://zoom.z3950.org/api/zoom-current.php They are an extension to
       that specification.

       Methods

       new()

        $o1 = new ZOOM::Options();
        $o1and2 = new ZOOM::Options($o1);
        $o3 = new ZOOM::Options();
        $o1and3and4 = new ZOOM::Options($o1, $o3);

       Creates and returns a new option set.  One or two (but no more)
       existing option sets may be passed as arguments, in which case they
       become ``parents'' of the new set, which thereby ``inherits'' their
       options, the values of the first parent overriding those of the second
       when both have a value for the same key.  An option set that inherits
       from a parent that has its own parents also inherits the grandparent's
       options, and so on.

       option() / option_binary()

        $o->option(preferredRecordSyntax => "usmarc");
        $o->option_binary(iconBlob => "foobar");
        die if length($o->option_binary("iconBlob") != 7);

       These methods are used to get and set options within a set, and behave
       the same way as the same-named "Connection" methods - see above.  As
       with the "Connection" methods, values passed to and retrieved using
       "option()" are interpreted as NUL-terminated, while those passed to and
       retrieved from "option_binary()" are binary-clean.

       bool()

        $o->option(x => "T");
        $o->option(y => "F");
        assert($o->bool("x", 1));
        assert(!$o->bool("y", 1));
        assert($o->bool("z", 1));

       The first argument is a key, and the second is a default value.
       Returns the value associated with the specified key as a boolean, or
       the default value if the key has not been set.  The values "T" (upper
       case) and 1 are considered true; all other values (including "t" (lower
       case) and non-zero integers other than one) are considered false.

       This method is provided in ZOOM-C because in a statically typed
       language it's convenient to have the result returned as an easy-to-test
       type.  In a dynamically typed language such as Perl, this problem
       doesn't arise, so "bool()" is nearly useless; but it is made available
       in case applications need to duplicate the idiosyncratic interpretation
       of truth and falsehood and ZOOM-C uses.

       int()

        $o->option(x => "012");
        assert($o->int("x", 20) == 12);
        assert($o->int("y", 20) == 20);

       Returns the value associated with the specified key as an integer, or
       the default value if the key has not been set.  See the description of
       "bool()" for why you almost certainly don't want to use this.

       set_int()

        $o->set_int(x => "29");

       Sets the value of the specified option as an integer.  Of course, Perl
       happily converts strings to integers on its own, so you can just use
       "option()" for this, but "set_int()" is guaranteed to use the same
       string-to-integer conversion as ZOOM-C does, which might occasionally
       be useful.  Though I can't imagine how.

       set_callback()

        sub cb {
            ($udata, $key) = @;
            return "$udata-$key-$udata";
        }
        $o->set_callback(\&cb, "xyz");
        assert($o->option("foo") eq "xyz-foo-xyz");

       This method allows a callback function to be installed in an option
       set, so that the values of options can be calculated algorithmically
       rather than, as usual, looked up in a table.  Along with the callback
       function itself, an additional datum is provided: when an option is
       subsequently looked up, this datum is passed to the callback function
       along with the key; and its return value is returned to the caller as
       the value of the option.

       Warning.  Although it ought to be possible to specify callback function
       using the "\&name" syntax above, or a literal "sub { code }" code
       reference, the complexities of the Perl-internal memory management
       system mean that the function must currently be specified as a string
       containing the fully-qualified name, e.g. "main::cb".>

       Warning.  The current implementation of the this method leaks memory,
       not only when the callback is installed, but on every occasion that it
       is consulted to look up an option value.

       destroy()

        $o->destroy()

       Destroys an Options object, freeing its resources.  It is an error to
       reuse an Options object that has been "destroy()"ed.

ENUMERATIONS

       The ZOOM module provides two enumerations that list possible return
       values from particular functions.  They are described in the following
       sections.

   ZOOM::Error
        if ($@->code() == ZOOM::Error::QUERY_PQF) {
            return "your query was not accepted";
        }

       This class provides a set of manifest constants representing some of
       the possible error codes that can be raised by the ZOOM module.  The
       methods that return error-codes are "ZOOM::Exception::code()",
       "ZOOM::Connection::error_x()" and "ZOOM::Connection::errcode()".

       The "ZOOM::Error" class provides the constants "NONE", "CONNECT",
       "MEMORY", "ENCODE", "DECODE", "CONNECTION_LOST", "ZINIT", "INTERNAL",
       "TIMEOUT", "UNSUPPORTED_PROTOCOL", "UNSUPPORTED_QUERY",
       "INVALID_QUERY", "CQL_PARSE", "CQL_TRANSFORM", "CCL_CONFIG",
       "CCL_PARSE", "CREATE_QUERY", "QUERY_CQL", "QUERY_PQF", "SORTBY",
       "CLONE", "PACKAGE", "SCANTERM" and "LOGLEVEL", each of which specifies
       a client-side error.  These codes constitute the "ZOOM" diagnostic set.

       Since errors may also be diagnosed by the server, and returned to the
       client, error codes may also take values from the BIB-1 diagnostic set
       of Z39.50, listed at the Z39.50 Maintenance Agency's web-site at
       http://www.loc.gov/z3950/agency/defns/bib1diag.php

       All error-codes, whether client-side from the "ZOOM::Error" enumeration
       or server-side from the BIB-1 diagnostic set, can be translated into
       human-readable messages by passing them to the "ZOOM::diag_str()"
       utility function.

   ZOOM::Event
        if ($conn->last_event() == ZOOM::Event::CONNECT) {
            print "Connected!
";
        }

       In applications that need it - mostly complex multiplexing applications
       - The "ZOOM::Connection::last_event()" method is used to return an
       indication of the last event that occurred on a particular connection.
       It always returns a value drawn from this enumeration, that is, one of
       "NONE", "CONNECT", "SEND_DATA", "RECV_DATA", "TIMEOUT", "UNKNOWN",
       "SEND_APDU", "RECV_APDU", "RECV_RECORD", "RECV_SEARCH" or "ZEND".

       See the section below on asynchronous applications.

LOGGING

        ZOOM::Log::init_level(ZOOM::Log::mask_str("zoom,myapp,-warn"));
        ZOOM::Log::log("myapp", "starting up with pid ", $$);

       Logging facilities are provided by a set of functions in the
       "ZOOM::Log" module.  Note that "ZOOM::Log" is not a class, and it is
       not possible to create "ZOOM::Log" objects: the API is imperative,
       reflecting that of the underlying YAZ logging facilities.  Although
       there are nine logging functions altogether, you can ignore nearly all
       of them: most applications that use logging will begin by calling
       "mask_str()" and "init_level()" once each, as above, and will then
       repeatedly call "log()".

   mask_str()
        $level = ZOOM::Log::mask_str("zoom,myapp,-warn");

       Returns an integer corresponding to the log-level specified by the
       parameter.  This is a string of zero or more comma-separated module-
       names, each indicating an individual module to be either added to the
       default log-level or removed from it (for those components prefixed by
       a minus-sign).  The names may be those of either standard YAZ-logging
       modules such as "fatal", "debug" and "warn", or custom modules such as
       "myapp" in the example above.  The module "zoom" requests logging from
       the ZOOM module itself, which may be helpful for debugging.

       Note that calling this function does not in any way change the logging
       state: it merely returns a value.  To change the state, this value must
       be passed to "init_level()".

   module_level()
        $level = ZOOM::Log::module_level("zoom");
        ZOOM::Log::log($level, "all systems clear: thrusters invogriated");

       Returns the integer corresponding to the single log-level specified as
       the parameter, or zero if that level has not been registered by a prior
       call to "mask_str()".  Since "log()" accepts either a numeric log-level
       or a string, there is no reason to call this function; but, what the
       heck, maybe you enjoy that kind of thing.  Who are we to judge?

   init_level()
        ZOOM::Log::init_level($level);

       Initialises the log-level to the specified integer, which is a bitmask
       of values, typically as returned from "mask_str()".  All subsequent
       calls to "log()" made with a log-level that matches one of the bits in
       this mask will result in a log-message being emitted.  All logging can
       be turned off by calling init_level(0).

   init_prefix()
        ZOOM::Log::init_prefix($0);

       Initialises a prefix string to be included in all log-messages.

   init_file()
        ZOOM::Log::init_file("/tmp/myapp.log");

       Initialises the output file to be used for logging: subsequent log-
       messages are written to the nominated file.  If this function is not
       called, log-messages are written to the standard error stream.

   init()
        ZOOM::Log::init($level, $0, "/tmp/myapp.log");

       Initialises the log-level, the logging prefix and the logging output
       file in a single operation.

   time_format()
        ZOOM::Log::time_format("%Y-%m-%d %H:%M:%S");

       Sets the format in which log-messages' timestamps are emitted, by means
       of a format-string like that used in the C function "strftime()".  The
       example above emits year, month, day, hours, minutes and seconds in
       big-endian order, such that timestamps can be sorted lexicographically.

   init_max_size()
       (This doesn't seem to work, so I won't bother describing it.)

   log()
        ZOOM::Log::log(8192, "reducing to warp-factor $wf");
        ZOOM::Log::log("myapp", "starting up with pid ", $$);

       Provided that the first argument, log-level, is among the modules
       previously established by "init_level()", this function emits a log-
       message made up of a timestamp, the prefix supplied to "init_prefix()",
       if any, and the concatenation of all arguments after the first.  The
       message is written to the standard output stream, or to the file
       previous specified by "init_file()" if this has been called.

       The log-level argument may be either a numeric value, as returned from
       "module_level()", or a string containing the module name.

ASYNCHRONOUS APPLICATIONS

       Although asynchronous applications are conceptually complex, the ZOOM
       support for them is provided through a very simple interface,
       consisting of one option ("async"), one function ("ZOOM::event()"), one
       Connection method ("last_event()" and an enumeration ("ZOOM::Event").

       The approach is as follows:

       Initialisation
           Create several connections to the various servers, each of them
           having the option "async" set, and with whatever additional options
           are required - e.g. the piggyback retrieval record-count can be set
           so that records will be returned in search responses.

       Operations
           Send searches to the connections, request records, etc.

       Event harvesting
           Repeatedly call "ZOOM::event()" to discover what responses are
           being received from the servers.  Each time this function returns,
           it indicates which of the connections has fired; this connection
           can then be interrogated with the "last_event()" method to discover
           what event has occurred, and the return value - an element of the
           "ZOOM::Event" enumeration - can be tested to determine what to do
           next.  For example, the "ZEND" event indicates that no further
           operations are outstanding on the connection, so any fetched
           records can now be immediately obtained.

       Here is a very short program (omitting all error-checking!) which
       demonstrates this process.  It parallel-searches three servers (or more
       of you add them the list), displaying the first record in the result-
       set of each server as soon as it becomes available.

        use ZOOM;
        @servers = ('z3950.loc.gov:7090/Voyager',
                    'z3950.indexdata.com:210/gils',
                    'agricola.nal.usda.gov:7190/Voyager');
        for ($i = 0; $i < @servers; $i++) {
            $z[$i] = new ZOOM::Connection($servers[$i], 0,
                                          async => 1, # asynchronous mode
                                          count => 1, # piggyback retrieval count
                                          preferredRecordSyntax => "usmarc");
            $r[$i] = $z[$i]->search_pqf("mineral");
        }
        while (($i = ZOOM::event(\@z)) != 0) {
            $ev = $z[$i-1]->last_event();
            print("connection ", $i-1, ": ", ZOOM::event_str($ev), "
");
            if ($ev == ZOOM::Event::ZEND) {
                $size = $r[$i-1]->size();
                print "connection ", $i-1, ": $size hits
";
                print $r[$i-1]->record(0)->render()
                    if $size > 0;
            }
        }

SEE ALSO

       The ZOOM abstract API, http://zoom.z3950.org/api/zoom-current.php

       The "Net::Z3950::ZOOM" module, included in the same distribution as
       this one.

       The "Net::Z3950" module, which this one supersedes.
       http://perl.z3950.org/

       The documentation for the ZOOM-C module of the YAZ Toolkit, which this
       module is built on.  Specifically, its lists of options are useful.
       http://indexdata.com/yaz/doc/zoom.tkl

       The BIB-1 diagnostic set of Z39.50,
       http://www.loc.gov/z3950/agency/defns/bib1diag.php

AUTHOR

       Mike Taylor, <mike@indexdata.com>

COPYRIGHT AND LICENCE

       Copyright (C) 2005-2014 by Index Data.

       This library is free software; you can redistribute it and/or modify it
       under the same terms as Perl itself, either Perl version 5.8.4 or, at
       your option, any later version of Perl 5 you may have available.



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