Net::Z3950::SimpleServer - Simple Perl API for building Z39.50 servers. 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( INIT => \&my_init_handler, CLOSE => \&my_close_handler, SEARCH => \&my_search_handler, FETCH => \&my_fetch_handler); ## Launch server: $z->launch_server("ztest.pl", @ARGV); 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, asbtract 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: - 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 handle. Some of the entries of these hashes are to be considered input and others output parameters. The Perl programmer specifies the event handles for the server by means of the the SimpleServer object constructor my $z = new Net::Z3950::SimpleServer( INIT => \&my_init_handler, CLOSE => \&my_close_handler, SEARCH => \&my_search_handler, PRESENT => \&my_present_handler, SCAN => \&my_scan_handler, FETCH => \&my_fetch_handler); After the custom event handles 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.dk/yaz/yaz-7.php>

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: IMP_NAME => "", ## Z39.50 Implementation name IMP_VER => "", ## Z39.50 Implementation version ERR_CODE => 0, ## Error code, cnf. Z39.50 manual 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 (ie. 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 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.

Search handler
Similarly, the search handler is called with a reference to an anony- mous hash. The structure is the following: $args = { ## Request parameters: 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 data- ## bases to search QUERY => "query", ## The query expression RPN => $obj, ## Blessed reference int the package ## Net::Z3950::APDU::Query ## Response parameters: ERR_CODE => 0, ## Error code (0=Succesful search) ERR_STR => "", ## Error string HITS => 0 ## Number of matches }; 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. The QUERY is a tree-structure of terms combined by operators, the terms being qualified by lists of attributes. The query is presented 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 anymore 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. The RPN member is a blessed reference into the package Net::Z3950::APDU::Query. By means of an augmented type of coding, you can easily construct a parser of the incoming RPN. Take a look at samples/render-search.pl for a sample implementation of such an augmented parser technique.

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 informations exchanged between client and present handle are: $args = { ## Client/server request: HANDLE => ref, ## Reference to datastructure SETNAME => "id", ## Result set ID START => xxx, ## Start position COMP => "", ## Desired record composition NUMBER => yyy, ## Number of requested records ## Respons 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: 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 ## 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 }; 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 (eg. 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 - 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 HANDLE => $ref ## Reference to data structure TERM => 'start', ## The start 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 should be assigned one of two values: Net::Z3950::SimpleServer::ScanSuccess On success (default) Net::Z3950::SimpleServer::ScanPartial Less terms returned than requested The STEP member contains the requested number of entries in the term-list between two adjacent entries in the response.

Close handler
The argument hash recieved by the close handler has one element only: $args = { ## Server provides: 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. Anders Sønderberg (sondberg@indexdata.dk) and Sebastian Hammer (quinn@indexdata.dk). Substantial contributions made by Mike Taylor (mike@tecc.co.uk). perl(1). Any Perl module which is useful for accessing the database of your choice.