Provided by: libnet-z3950-simpleserver-perl_1.21-1_amd64 bug

NAME

       Net::Z3950::SimpleServer - Simple Perl API for building Z39.50 servers.

SYNOPSIS

         use Net::Z3950::SimpleServer;

         sub my_search_handler {
               my $args = shift;

               my $set_id = $args->{SETNAME};
               my @database_list = @{ $args->{DATABASES} };
               my $query = $args->{QUERY};

               ## Perform the query on the specified set of databases
               ## and return the number of hits:

               $args->{HITS} = $hits;
         }

         sub my_fetch_handler {        # Get a record for the user
               my $args = shift;

               my $set_id = $args->{SETNAME};

               my $record = fetch_a_record($args->{OFFSET});

               $args->{RECORD} = $record;
               if (number_of_hits() == $args->{OFFSET}) {      ## Last record in set?
                       $args->{LAST} = 1;
               } else {
                       $args->{LAST} = 0;
               }
         }

         ## Register custom event handlers:
         my $z = new Net::Z3950::SimpleServer(GHANDLE = $someObject,
                                              INIT   =>  \&my_init_handler,
                                              CLOSE  =>  \&my_close_handler,
                                              SEARCH =>  \&my_search_handler,
                                              FETCH  =>  \&my_fetch_handler);

         ## Launch server:
         $z->launch_server("ztest.pl", @ARGV);

DESCRIPTION

       The SimpleServer module is a tool for constructing Z39.50 "Information Retrieval" servers
       in Perl. The module is easy to use, but it does help to have an understanding of the
       Z39.50 query structure and the construction of structured retrieval records.

       Z39.50 is a network protocol for searching remote databases and retrieving the results in
       the form of structured "records". It is widely used in libraries around the world, as well
       as in the US Federal Government.  In addition, it is generally useful whenever you wish to
       integrate a number of different database systems around a shared, abstract data model.

       The model of the module is simple: It implements a "generic" Z39.50 server, which invokes
       callback functions supplied by you to search for content in your database. You can use any
       tools available in Perl to supply the content, including modules like DBI and WWW::Search.

       The server will take care of managing the network connections for you, and it will spawn a
       new process (or thread, in some environments) whenever a new connection is received.

       The programmer can specify subroutines to take care of the following type of events:

         - Start service (called once).
         - Initialize request
         - Search request
         - Present request
         - Fetching of records
         - Scan request (browsing)
         - Closing down connection

       Note that only the Search and Fetch handler functions are required.  The module can supply
       default responses to the other on its own.

       After the launching of the server, all control is given away from the Perl script to the
       server. The server calls the registered subroutines to field incoming requests from Z39.50
       clients.

       A reference to an anonymous hash is passed to each handler. Some of the entries of these
       hashes are to be considered input and others output parameters.

       The Perl programmer specifies the event handlers for the server by means of the
       SimpleServer object constructor

         my $z = new Net::Z3950::SimpleServer(
                               START   =>      \&my_start_handler,
                               INIT    =>      \&my_init_handler,
                               CLOSE   =>      \&my_close_handler,
                               SEARCH  =>      \&my_search_handler,
                               PRESENT =>      \&my_present_handler,
                               SCAN    =>      \&my_scan_handler,
                               FETCH   =>      \&my_fetch_handler,
                               EXPLAIN =>      \&my_explain_handler,
                               DELETE  =>      \&my_delete_handler,
                               SORT    =>      \&my_sort_handler);

       In addition, the arguments to the constructor may include GHANDLE, a global handle which
       is made available to each invocation of every callback function.  This is typically a
       reference to either a hash or an object.

       If you want your SimpleServer to start a thread (threaded mode) to handle each incoming
       Z39.50 request instead of forking a process (forking mode), you need to register the
       handlers by symbol rather than by code reference. Thus, in threaded mode, you will need to
       register your handlers this way:

         my $z = new Net::Z3950::SimpleServer(
                               INIT    =>      "my_package::my_init_handler",
                               CLOSE   =>      "my_package::my_close_handler",
                               ....
                               ....          );

       where my_package is the Perl package in which your handler is located.

       After the custom event handlers are declared, the server is launched by means of the
       method

         $z->launch_server("MyServer.pl", @ARGV);

       Notice, the first argument should be the name of your server script (for logging
       purposes), while the rest of the arguments are documented in the YAZ toolkit manual: The
       section on application invocation:
       <http://www.indexdata.com/yaz/doc/server.invocation.html>

       In particular, you need to use the -T switch to start your SimpleServer in threaded mode.

   Start handler
       The start handler is called when service is started. The argument hash passed to the start
       handler has the form

         $args = {
                    CONFIG =>  "default-config" ## GFS config (as given by -c)
                 };

       The purpose of the start handler is to read the configuration file for the Generic
       Frontend Server . This is specified by option -c.  If -c is omitted, the configuration
       file is set to "default-config".

       The start handler is optional. It is supported in Simpleserver 1.16 and later.

   Init handler
       The init handler is called whenever a Z39.50 client is attempting to logon to the server.
       The exchange of parameters between the server and the handler is carried out via an
       anonymous hash reached by a reference, i.e.

         $args = shift;

       The argument hash passed to the init handler has the form

         $args = {
                                           ## Response parameters:

                    PEER_NAME =>  "",      ## Name or IP address of connecting client
                    IMP_ID    =>  "",      ## Z39.50 Implementation ID
                    IMP_NAME  =>  "",      ## Z39.50 Implementation name
                    IMP_VER   =>  "",      ## Z39.50 Implementation version
                    ERR_CODE  =>  0,       ## Error code, cnf. Z39.50 manual
                    ERR_STR   =>  "",      ## Error string (additional info.)
                    USER      =>  "xxx"    ## If Z39.50 authentication is used,
                                           ## this member contains user name
                    PASS      =>  "yyy"    ## Under same conditions, this member
                                           ## contains the password in clear text
                    GHANDLE   =>  $obj     ## Global handle specified at creation
                    HANDLE    =>  undef    ## Handler of Perl data structure
                 };

       The HANDLE member can be used to store any scalar value which will then be provided as
       input to all subsequent calls (i.e. for searching, record retrieval, etc.). A common use
       of the handle is to store a reference to a hash which may then be used to store session-
       specific parameters.  If you have any session-specific information (such as a list of
       result sets or a handle to a back-end search engine of some sort), it is always best to
       store them in a private session structure - rather than leaving them in global variables
       in your script.

       The Implementation ID, name and version are only really used by Z39.50 client developers
       to see what kind of server they're dealing with.  Filling these in is optional.

       The ERR_CODE should be left at 0 (the default value) if you wish to accept the connection.
       Any other value is interpreted as a failure and the client will be shown the door, with
       the code and the associated additional information, ERR_STR returned.

   Search handler
       Similarly, the search handler is called with a reference to an anonymous hash. The
       structure is the following:

         $args = {
                                            ## Request parameters:

           GHANDLE             =>  $obj     # Global handle specified at creation
           HANDLE              =>  ref,     # Your session reference.
           SETNAME             =>  "id",    # ID of the result set
           REPL_SET            =>  0,       # Replace set if already existing?
           DATABASES           =>  ["xxx"], # Reference to a list of databases to search
           QUERY               =>  "query", # The query expression as a PQF string
           RPN                 =>  $obj,    # Reference to a Net::Z3950::APDU::Query
           CQL                 =>  $x,      # A CQL query, if this is provided instead of Type-1
           SRW_SORTKEYS        =>  $x,      # XXX to be described
           PID                 =>  $x,      # XXX to be described
           PRESENT_NUMBER      =>  $x,      # XXX to be described
           EXTRA_ARGS          =>  $x,      # XXX to be described
           INPUTFACETS         =>  $x,      # Specification of facets required: see below.

                                            ## Response parameters:

           ERR_CODE            =>  0,       # Error code (0=Successful search)
           ERR_STR             =>  "",      # Error string
           HITS                =>  0,       # Number of matches
           ESTIMATED_HIT_COUNT =>  $x,      # XXX to be described
           EXTRA_RESPONSE_DATA =>  $x,      # XXX to be described
           OUTPUTFACETS        =>  $x       # Facets returned: see below.
         };

       Note that a search which finds 0 hits is considered successful in Z39.50 terms - you
       should only set the ERR_CODE to a non-zero value if there was a problem processing the
       request. The Z39.50 standard provides a comprehensive list of standard diagnostic codes,
       and you should use these whenever possible.

       Query structures

       In Z39.50, the most comment kind of query is the so-called Type-1 _query, a tree-structure
       of terms combined by operators, the terms being qualified by lists of attributes.

       The QUERY parameter presented this tree to the search function in the Prefix Query Format
       (PQF) which is used in many applications based on the YAZ toolkit. The full grammar is
       described in the YAZ manual.

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

               dylan

               "bob dylan"

               @or "dylan" "zimmerman"

               @set Result-1

               @or @and bob dylan @set Result-1

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

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

       You will need to write a recursive function or something similar to parse incoming query
       expressions, and this is usually where a lot of the work in writing a database-backend
       happens. Fortunately, you don't need to support any more functionality than you want to.
       For instance, it is perfectly legal to not accept boolean operators, but you should try to
       return good error codes if you run into something you can't or won't support.

       A more convenient alternative to the QUERY member is the RPN member, which is a reference
       to a Net::Z3950::APDU::Query object representing the RPN query tree.  The structure of
       that object is supposed to be self-documenting, but here's a brief summary of what you
       get:

       ·   "Net::Z3950::APDU::Query" is a hash with two fields:

           "attributeSet"
               Optional.  If present, it is a reference to a "Net::Z3950::APDU::OID".  This is a
               string of dot-separated integers representing the OID of the query's top-level
               attribute set.

           "query"
               Mandatory: a reference to the RPN tree itself.

       ·   Each node of the tree is an object of one of the following types:

           "Net::Z3950::RPN::And"
           "Net::Z3950::RPN::Or"
           "Net::Z3950::RPN::AndNot"
               These three classes are all arrays of two elements, each of which is a node.

           "Net::Z3950::RPN::Term"
               A query term. See below for details.

           "Net::Z3950::RPN::RSID"
               A reference to a result-set ID indicating a previous search.  The ID of the
               result-set is in the "id" element.

       ·   "Net::Z3950::RPN::Term" is a hash with two fields:

           "term"
               A string containing the search term itself.

           "attributes"
               A reference to a "Net::Z3950::RPN::Attributes" object.

       ·   "Net::Z3950::RPN::Attributes" is an array of references to
           "Net::Z3950::RPN::Attribute" objects.  (Note the plural/singular distinction.)

       ·   "Net::Z3950::RPN::Attribute" is a hash with three elements:

           "attributeSet"
               Optional.  If present, it is dot-separated OID string, as above.

           "attributeType"
               An integer indicating the type of the attribute - for example, under the BIB-1
               attribute set, type 1 indicates a ``use'' attribute, type 2 a ``relation''
               attribute, etc.

           "attributeValue"
               An integer or string indicating the value of the attribute - for example, under
               BIB-1, if the attribute type is 1, then value 4 indicates a title search and 7
               indicates an ISBN search; but if the attribute type is 2, then value 4 indicates a
               ``greater than or equal'' search, and 102 indicates a relevance match.

       All of these classes except "Attributes" and "Attribute" are subclasses of the abstract
       class "Net::Z3950::RPN::Node".  That class has a single method, "toPQF()", which may be
       used to turn an RPN tree, or part of one, back into a textual prefix query.

       Note that, apart to "toPQF()", none of these classes have any methods at all: the blessing
       into classes is largely just a documentation thing so that, for example, if you do

               { use Data::Dumper; print Dumper($args->{RPN}) }

       you get something fairly human-readable.  But of course, the type distinction between the
       three different kinds of boolean node is important.

       By adding your own methods to these classes (building what I call ``augmented classes''),
       you can easily build code that walks the tree of the incoming RPN.  Take a look at
       "samples/render-search.pl" for a sample implementation of such an augmented classes
       technique.

       Finally, when SimpleServer is invoked using SRU/SRW (and indeed using Z39.50 if the
       unusual type-104 query is used), the query that is _passed is expressed in CQL, the
       Contextual Query Language. In this case, the query string is made available in the CQL
       argument.

       Facets

       Servers may support the provision of facets -- counted lists of field values which may
       subsequently be be used as query terms to narrow the search.

       In SRU, facets may be requested by the "facetLimit" parameter, as documented in the OASIS
       standard that formalises the SRU specification <http://docs.oasis-open.org/search-
       ws/searchRetrieve/v1.0/os/part3-sru2.0/searchRetrieve-v1.0-os-
       part3-sru2.0.html#_Toc324162453>.  Its value is a string consisting of a comma-separated
       list of facet specifications. Each facet specification consists of of a count, a colon and
       a fieldname. For example, "facetLimit=10:title,5:author" asks for ten title facets and
       five author facets.

       Request format

       The facet request is passed to the search-handler function in the INPUTFACETS parameter.
       Its value is rather complex, due to backwards compatibility with Z39.50:

       ·   The top-level value is a "Net::Z3950::FacetList" array.

       ·   This is an array of "Net::Z3950::FacetField" objects.

       ·   Each of these is an object with two members, "attributes" and "terms".

       ·   "attributes" has type "Net::Z3950::RPN::Attributes" and is a list of objects of type
           "Net::Z3950::RPN::Attribute".

       ·   Each attribute has two elements, "attributeType" and "attributeValue". Each value is
           interpreted according to its type. The meanings of the types are as follows:

           1.  The name of the field to provide values of the facets.

           2.  The order in which to sort the values. (But it's not clear how this is to be
               interpreted: it may be implementation dependent.)

           3.  The number of facets to include for the specified field.

           4.  The first facet to include in the response: for example, if this is 11, then the
               first ten facts should be skipped.

       So for example, the SRU facet specification "facetLimit=10:title,5:author" would be
       translated as a "Net::Z3950::FacetList" list of two "Net::Z3950::FacetField"s. The
       "attributes" of the first would be [1="title", 3=10], and those of the second would be
       [1="author", 3=5].

       It is not clear what the purpose of "terms" is, but for the record, this is how it is
       represented:

       ·   "terms" is a "Net::Z3950::FacetTerms" array.

       ·   This is an array of "Net::Z3950::FacetTerm" objects.

       ·   Each of these is an object with two members, "term" and "count". The first of these is
           an integer, the second a string.

       Response format

       Having generated facets corresponding to the request, the search handler should return
       them in the "OUTPUTFACETS" argument. The structure of this response is similar to that of
       the request:

       ·   The top-level value is a "Net::Z3950::FacetList" array.

       ·   This is an array of "Net::Z3950::FacetField" objects.

       ·   Each of these is an object with two members, "attributes" and "terms".

       ·   "attributes" has type "Net::Z3950::RPN::Attributes" and is a list of objects of type
           "Net::Z3950::RPN::Attribute".

       ·   Each attribute has two elements, "attributeType" and "attributeValue". Each value is
           interpreted according to its type. The meanings of the types are as follows:

           1.  The name of the field for which terms are provided.

           (That is the only type used.)

       ·   "terms" is a "Net::Z3950::FacetTerms" array.

       ·   This is an array of "Net::Z3950::FacetTerm" objects.

       ·   Each of these is an object with two members, "term" and "count". The first of these is
           a string containing one of the facet terms, and the second is an integer indicating
           how many times it occurs in the records that were found by the search.

       The example SimpleServer applicaation server "ztest.pl" includes code that shows how to
       examine the INPUTFACETS data structure and create the OUTPUTFACETS structure.

   Present handler
       The presence of a present handler in a SimpleServer front-end is optional.  Each time a
       client wishes to retrieve records, the present service is called. The present service
       allows the origin to request a certain number of records retrieved from a given result
       set.  When the present handler is called, the front-end server should prepare a result set
       for fetching. In practice, this means to get access to the data from the backend database
       and store the data in a temporary fashion for fast and efficient fetching. The present
       handler does *not* fetch anything. This task is taken care of by the fetch handler, which
       will be called the correct number of times by the YAZ library. More about this below.  If
       no present handler is implemented in the front-end, the YAZ toolkit will take care of a
       minimum of preparations itself. This default present handler is sufficient in many
       situations, where only a small amount of records are expected to be retrieved. If on the
       other hand, large result sets are likely to occur, the implementation of a reasonable
       present handler can gain performance significantly.

       The information exchanged between client and present handle is:

         $args = {
                                           ## Client/server request:

                    GHANDLE   =>  $obj     ## Global handle specified at creation
                    HANDLE    =>  ref,     ## Reference to datastructure
                    SETNAME   =>  "id",    ## Result set ID
                    START     =>  xxx,     ## Start position
                    COMP      =>  "",      ## Desired record composition
                    NUMBER    =>  yyy,     ## Number of requested records

                                           ## Response parameters:

                    HITS      =>  zzz,     ## Number of returned records
                    ERR_CODE  =>  0,       ## Error code
                    ERR_STR   =>  ""       ## Error message
                 };

   Fetch handler
       The fetch handler is asked to retrieve a SINGLE record from a given result set (the front-
       end server will automatically call the fetch handler as many times as required).

       The parameters exchanged between the server and the fetch handler are:

         $args = {
                                           ## Client/server request:

                    GHANDLE   =>  $obj     ## Global handle specified at creation
                    HANDLE    =>  ref      ## Reference to data structure
                    SETNAME   =>  "id"     ## ID of the requested result set
                    OFFSET    =>  nnn      ## Record offset number
                    REQ_FORM  =>  "n.m.k.l"## Client requested format OID
                    COMP      =>  "xyz"    ## Formatting instructions
                    SCHEMA    =>  "abc"    ## Requested schema, if any

                                           ## Handler response:

                    RECORD    =>  ""       ## Record string
                    BASENAME  =>  ""       ## Origin of returned record
                    LAST      =>  0        ## Last record in set?
                    ERR_CODE  =>  0        ## Error code
                    ERR_STR   =>  ""       ## Error string
                    SUR_FLAG  =>  0        ## Surrogate diagnostic flag
                    REP_FORM  =>  "n.m.k.l"## Provided format OID
                    SCHEMA    =>  "abc"    ## Provided schema, if any
                 };

       The REP_FORM value has by default the REQ_FORM value, but can be set to something
       different if the handler desires. The BASENAME value should contain the name of the
       database from where the returned record originates.  The ERR_CODE and ERR_STR works the
       same way they do in the search handler. If there is an error condition, the SUR_FLAG is
       used to indicate whether the error condition pertains to the record currently being
       retrieved, or whether it pertains to the operation as a whole (e.g. the client has
       specified a result set which does not exist.)

       If you need to return USMARC records, you might want to have a look at the MARC module on
       CPAN, if you don't already have a way of generating these.

       NOTE: The record offset is 1-indexed, so 1 is the offset of the first record in the set.

   Scan handler
       A full featured Z39.50 server should support scan (or in some literature browse). The
       client specifies a starting term of the scan, and the server should return an ordered list
       of specified length consisting of terms actually occurring in the data base. Each of these
       terms should be close to or equal to the term originally specified. The quality of scan
       compared to simple search is a guarantee of hits. It is simply like browsing through an
       index of a book, you always find something! The parameters exchanged are:

         $args = {
                                                       ## Client request

                       GHANDLE         => $obj,        ## Global handle specified at creation
                       HANDLE          => $ref,        ## Reference to data structure
                       DATABASES       => ["xxx"],     ## Reference to a list of data-
                                                       ## bases to search
                       TERM            => 'start',     ## The start term
                       RPN             =>  $obj,       ## Reference to a Net::Z3950::RPN::Term

                       NUMBER          => xx,          ## Number of requested terms
                       POS             => yy,          ## Position of starting point
                                                       ## within returned list
                       STEP            => 0,           ## Step size

                                                       ## Server response

                       ERR_CODE        => 0,           ## Error code
                       ERR_STR         => '',          ## Diagnostic message
                       NUMBER          => zz,          ## Number of returned terms
                       STATUS          => $status,     ## ScanSuccess/ScanFailure
                       ENTRIES         => $entries     ## Referenced list of terms
               };

       where the term list is returned by reference in the scalar $entries, which should point at
       a data structure of this kind,

         my $entries = [
                               {       TERM            => 'energy',
                                       OCCURRENCE      => 5            },

                               {       TERM            => 'energy density',
                                       OCCURRENCE      => 6,           },

                               {       TERM            => 'energy flow',
                                       OCCURRENCE      => 3            },

                                       ...

                                       ...
               ];

       The $status flag is only meaningful after a successful scan, and should be assigned one of
       two values:

         Net::Z3950::SimpleServer::ScanSuccess  Full success (default)
         Net::Z3950::SimpleServer::ScanPartial  Fewer terms returned than requested

       The STEP member contains the requested number of entries in the term-list between two
       adjacent entries in the response.

       A better alternative to the TERM member is the the RPN member, which is a reference to a
       Net::Z3950::RPN::Term object representing the scan clause.  The structure of that object
       is the same as for Term objects included as part of the RPN tree passed to search
       handlers.  This is more useful than the simple TERM because it includes attributes (e.g.
       access points associated with the term), which are discarded by the TERM element.

   Close handler
       The argument hash received by the close handler has two elements only:

         $args = {
                                           ## Server provides:

                    GHANDLE   =>  $obj     ## Global handle specified at creation
                    HANDLE    =>  ref      ## Reference to data structure
                 };

       What ever data structure the HANDLE value points at goes out of scope after this call. If
       you need to close down a connection to your server or something similar, this is the place
       to do it.

   Explain handler
       The argument hash received by the explain handler has the following elements:

         $args = {
                                   ## Request parameters:
            GHANDLE   =>  $obj,    # Global handle specified at creation
            HANDLE    =>  ref,     # Reference to data structure
            DATABASE  =>  $dbname, # Name of database to be explained

                                   ## Response parameters:
            EXPLAIN   =>  $zeerex  # ZeeRex record for specified database
         };

       The handler should return a string containing the ZeeRex XML that describes that nominated
       database.

   Delete handler
       The argument hash received by the delete handler has the following elements:

         $args = {
                                           ## Client request:
                    GHANDLE   =>  $obj,    ## Global handle specified at creation
                    HANDLE    =>  ref,     ## Reference to data structure
                    SETNAME   =>  "id",    ## Result set ID

                                           ## Server response:
                    STATUS    => 0         ## Deletion status
                 };

       The SETNAME element of the argument hash may or may not be defined.  If it is, then
       SETNAME is the name of a result set to be deleted; if not, then all result-sets associated
       with the current session should be deleted.  In either case, the callback function should
       report on success or failure by setting the STATUS element either to zero, on success, or
       to an integer from 1 to 10, to indicate one of the ten possible failure codes described in
       section 3.2.4.1.4 of the Z39.50 standard -- see
       http://www.loc.gov/z3950/agency/markup/05.html#Delete-list-statuses1

   Sort handler
       The argument hash received by the sort handler has the following elements:

               $args = {
                                               ## Client request:
                       GHANDLE => $obj,        ## Global handle specified at creation
                       HANDLE => ref,          ## Reference to data structure
                       INPUT => [ a, b ... ],  ## Names of result-sets to sort
                       OUTPUT => "name",       ## Name of result-set to sort into
                       SEQUENCE                ## Sort specification: see below

                                               ## Server response:
                       STATUS => 0,            ## Success, Partial or Failure
                       ERR_CODE => 0,          ## Error code
                       ERR_STR => '',          ## Diagnostic message

               };

       The SEQUENCE element is a reference to an array, each element of which is a hash
       representing a sort key.  Each hash contains the following elements:

       RELATION
           0 for an ascending sort, 1 for descending, 3 for ascending by frequency, or 4 for
           descending by frequency.

       CASE
           0 for a case-sensitive sort, 1 for case-insensitive

       MISSING
           How to respond if one or more records in the set to be sorted are missing the fields
           indicated in the sort specification.  1 to abort the sort, 2 to use a "null value", 3
           if a value is provided to use in place of the missing data (although in the latter
           case, the actual value to use is currently not made available, so this is useless).

       And one or other of the following:

       SORTFIELD
           A string indicating the field to be sorted, which the server may interpret as it sees
           fit (presumably by an out-of-band agreement with the client).

       ELEMENTSPEC_TYPE and ELEMENTSPEC_VALUE
           I have no idea what this is.

       ATTRSET and SORT_ATTR
           ATTRSET is the attribute set from which the attributes are taken, and SORT_ATTR is a
           reference to an array containing the attributes themselves.  Each attribute is
           represented by (are you following this carefully?) yet another hash, this one
           containing the elements ATTR_TYPE and ATTR_VALUE: for example, type=1 and value=4 in
           the BIB-1 attribute set would indicate access-point 4 which is title, so that a sort
           of title is requested.

       Precisely why all of the above is so is not clear, but goes some way to explain why, in
       the Z39.50 world, the developers of the standard are not so much worshiped as blamed.

       The backend function should set STATUS to 0 on success, 1 for "partial success" (don't
       ask) or 2 on failure, in which case ERR_CODE and ERR_STR should be set.

   Support for SRU and SRW
       Since release 1.0, SimpleServer includes support for serving the SRU and SRW protocols as
       well as Z39.50.  These ``web-friendly'' protocols enable similar functionality to that of
       Z39.50, but by means of rich URLs in the case of SRU, and a SOAP-based web-service in the
       case of SRW.  These protocols are described at http://www.loc.gov/standards/sru/

       In order to serve these protocols from a SimpleServer-based application, it is necessary
       to launch the application with a YAZ Generic Frontend Server (GFS) configuration file,
       which can be specified using the command-line argument "-f" filename.  A minimal
       configuration file looks like this:

         <yazgfs>
           <server>
             <cql2rpn>pqf.properties</cql2rpn>
           </server>
         </yazgfs>

       This file specifies only that "pqf.properties" should be used to translate the CQL queries
       of SRU and SRW into corresponding Z39.50 Type-1 queries.  For more information about YAZ
       GFS configuration, including how to specify an Explain record, see the Virtual Hosts
       section of the YAZ manual at http://www.indexdata.com/yaz/doc/server.vhosts.html

       The mapping of CQL queries into Z39.50 Type-1 queries is specified by a file that
       indicates which BIB-1 attributes should be generated for each CQL index, relation,
       modifiers, etc.  A typical section of this file looks like this:

         index.dc.title                        = 1=4
         index.dc.subject                      = 1=21
         index.dc.creator                      = 1=1003
         relation.<                            = 2=1
         relation.le                           = 2=2

       This file specifies the BIB-1 access points (type=1) for the Dublin Core indexes "title",
       "subject" and "creator", and the BIB-1 relations (type=2) corresponding to the CQL
       relations "<" and "<=".  For more information about the format of this file, see the CQL
       section of the YAZ manual at http://www.indexdata.com/yaz/doc/tools.html#cql

       The YAZ distribution includes a sample CQL-to-PQF mapping configuration file called
       "pqf.properties"; this is sufficient for many applications, and a good base to work from
       for most others.

       If a SimpleServer-based application is run without this SRU-specific configuration, it can
       still serve SRU; however, CQL queries will not be translated, but passed straight through
       to the search-handler function, as the "CQL" member of the parameters hash.  It is then
       the responsibility of the back-end application to parse and handle the CQL query, which is
       most easily done using Ed Summers' fine "CQL::Parser" module, available from CPAN at
       http://search.cpan.org/~esummers/CQL-Parser/

AUTHORS

       Anders Sønderberg (sondberg@indexdata.dk), Sebastian Hammer (quinn@indexdata.dk), Mike
       Taylor (indexdata.com).

COPYRIGHT AND LICENCE

       Copyright (C) 2000-2016 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.

SEE ALSO

       Any Perl module which is useful for accessing the data source of your choice.