Provided by: libnet-z3950-zoom-perl_1.30-2_amd64 bug

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(), "\n";
        }

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"), "'\n");
        $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.html#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:

       ยท   [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"), "'\n");
        $conn->option(preferredRecordSyntax => "usmarc");
        $conn->option_binary(iconBlob => "foo\0bar");
        die if length($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!\n";
        }

       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.html#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\n";

       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\n";

       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(), "\n";

       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.html#3.5

       Methods

       error() / exception()

        if ($rec->error()) {
            my($code, $msg, $addinfo, $dset) = $rec->error();
            print "error $code, $msg ($addinfo) from $dset set\n";
            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.html#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(), "\n";
        print "(addinfo '", $@->addinfo(), "', set '", $@->diagset(), "')\n";

       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.html#3.6

       Methods

       size()

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

       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.html 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(), "\n";
            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.html

       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.html#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\nab 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.html 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");
        $o->option_binary(iconBlob => "foo\0bar");
        die if length($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.html

       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!\n";
        }

       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), "\n");
            if ($ev == ZOOM::Event::ZEND) {
                $size = $r[$i-1]->size();
                print "connection ", $i-1, ": $size hits\n";
                print $r[$i-1]->record(0)->render()
                    if $size > 0;
            }
        }

SEE ALSO

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

       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.html

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.