OAI Provider

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Revision as of 21:03, 20 May 2008

Main Page > Ancillary Resources > OAI Provider

Overview

Below you will find the documentation for using the UMProvider and LoadOai.pl. These tools, along with the OAI Harvester, are open source and available for download from Source Forge. The UMProvider relies heavily on [libxml] (XML::LibXML) for creating and parsing XML data and a database for storage.

• For an overview of the verbs and components of the OAI Protocol for Metadata Harvesting (OAI-PMH), see the Open Archives site.

DLXS also offers an older data provider tool-- broker20, which uses XPAT and collmgr to function.

Basic Setup Steps

Basic steps for setting up an OAI-PMH 2.0 Provider using UMProvider.pm:

1. Create the oai and oaisets tables in MySQL (or other database). See CREATE TABLE examples and explanation below.
2. The hardest part of setting up the OAI Provider is loading your data. There is a script described below to assist you in loading the metadata but there is no way around the fact that you need to generate Dublin Code (DC) metadata for each record. One option is to wrap the oai_dc records in <metadata> tags and put them into the format for loading with the LoadOai.pl (details below). If you have another mechanism for loading the data that you would prefer to use, just create these records and load everything and including the <metadata> element into the oai_dc field of the oai table. For both options you will also need to have a unique identifier for each record as well as the set(s) information.
3. Copy sample_config.xml to config.xml and edit for your setup. Be sure to change: repositoryName, baseURL, adminEmail, repositoryIdentifier, sampleIdentifier, the list of sets and list of possible metadata formats.
4. Place oai (the CGI script), config.xml and UMProvider.pm in a CGI directory on web server.
5. Edit oai (the CGI script) to add database connection settings, pointer to your config.xml and log file location (details below).
6. Test OAI provider:

   http://your.host.org/cgi-bin/oai?verb=Identify
   http://your.host.org/cgi-bin/oai?verb=ListRecords&metadataPrefix=oai_dc

UMProvider

UMProvider: OAI-PMH 2.0 Provider Perl module. UMProvider requires that you have pre-formed oai_dc metadata in a database. The default database is mysql but any DBI.pm supported database should work. The data must be stored in two tables with the following required columns:

  +----+--------------------+
  | table: oai              |
  +----+-----------+--------+
  | id | timestamp | oai_dc |
  +----+-----------+--------+

  +----+-----------+
  | table: oaisets |
  +----+-----------+
  | id | oaiset    |
  +----+-----------+

The second table for OAI set information (oaisets) is optional just like the use of sets in OAI-PMH 2.0.

If you would like to provide additional metadata formats such as marc21 or mods, add these columns after oai_dc in the first (main) table. The column name must match the metadata format. Here are example create table statements:

  CREATE TABLE oai (id VARCHAR(50) PRIMARY KEY,
    timestamp TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
    oai_dc MEDIUMBLOB,
    mods   MEDIUMBLOB,
    marc21 MEDIUMBLOB);

  CREATE TABLE oaisets (id VARCHAR(50), 
    oaiset VARCHAR(32), 
    PRIMARY KEY ('id','oaiset'),
    KEY 'oaiset' (oaiset));

The id values in the oai table and the oaisets tables must match. The id in the oai table must be unique but since an item can exist in multiple oai sets, that id can repeat in the oaisets table. Records do not have to be assigned to a set so it is possible that an item in the oai table does not exist in the oaisets table.

IMPORTANT: If you have hierarchical sets, be sure to have an entry for each unique set name down to the root set for each item. For example, if the item "abc123" is in the set "foo:bar:baz", you must have the following three rows in the oaisets table:

  +--------+-------------+
  | id     | oaiset      |
  +--------+-------------+
  | abc123 | foo:bar:baz |
  | abc123 | foo:bar     |
  | abc123 | foo         |
  +--------+-------------+

The id in the database is only the brief unique identifier and not the full OAI identifier. For the OAI-PMH response, the identifier is created with the host name (repositoryIdentifier) from the XML configuration file (oai:host:id).

Deleted records: If you would like to mark a record as deleted, just set the "oai_dc" field for that record to NULL in the database. The UMProvider will continue to return the header for this record and the header will have the deleted status attribute.

Required perl modules: POSIX, XML::LibXML, DBI, Encode

Synopsis

Here is an example CGI script using UMProvider:

  use OaiProvider;
  use CGI;
  use CGI::Carp;

  my $query  = CGI->new();
  my @params = $query->param();
  my $url    = $query->url();

  my $args = {};
  foreach ( $query->param() ) { $args->{$_} = join($;, $query->param($_)); }

  my $op = new OaiProvider(
      configFile => "oai_provider_conf.xml",
      logFile    => "oai_provider.log",
      url        => $url,
      arguments  => $args);

  if ( $op !~ /OaiProvider/ )
  {
      carp ($op);
      print $query->header(-status => 500);
      exit;
  }

  if ( ! $op->ConnectToDb( $db_user, $db_passwd, $db_name, $db_server ) )
  {
      carp ("failed ConnectToDb: $db_user, $db_passwd, $db_name, $db_server");
      print $query->header(-status => 500);
      exit;
  }

  $op->BuildResponse();
  print $query->header(-type => ’text/xml’, -charset => ’utf-8’, -status => 200);
  print $op->toString();

Public Methods available to CGI scripts using UMProvider:

• new(): Creates a new UMProvider object

  $op->new( hash_ref )
          { configFile => "oai_provider_conf.xml",
            logFile    => "oai_provider.log",
            url        => "http://some.url.org/OAI",
            arguments  => $args, ($args->{verb} = "ListSets")

            ## optional
            maxItems     => 500,                   ## default 100
            tableName    => "my_oai",              ## default "oai"
            setTableName => "my_oaisets",          ## default "oaisets"
            DBDriver     => "SQLite",              ## default "mysql"
            DbUpdate     => "2007-12-25 10:00:01", ## default to check update time of table
          }

Note: When the database table holding the OAI data is altered (Update_time changes for the table), any outstanding resumptionTokens become invalid. If your data is constantly updated, or the OAI table is frequently updated for some reason other than data changes, use the optional DbUpdate time in your CGI script.

• ConnectToDb(): Connect to the database

$op->ConnectToDb( $db_user, $db_passwd, $db_name, $db_server )

• $op->BuildResponse(): Builds a response based on the cgi parameters passed in from new(). If a problem is found, an OAI error node is created and added to the response object.

• $op->toString(): Serialize the response.

• $op->DisconnectDb(): Disconnect from the database. The connection to the DB should be closed when the CGI script terminates. This may be useful if your CGI script is doing something else after getting the response from the UMProvider object.

Configuration

An XML configuration file must be passed to the UMProvider in new(). This file contains the information for the Identify verb, ListSets verb, and all possible metadata formats (for ListMetadataFormats).

Sample config file:

        <?xml version="1.0" encoding="UTF-8"?>
        <oai_config>
          <Identify>
            <repositoryName>Your Repository</repositoryName>
            <baseURL>http://your.host.edu/OAI</baseURL>
            <protocolVersion>2.0</protocolVersion>
            <adminEmail>you@your.edu</adminEmail>
            <earliestDatestamp/>
            <deletedRecord>transient</deletedRecord>
            <granularity>YYYY-MM-DDThh:mm:ssZ</granularity>
            <description>
              <oai-identifier xmlns="http://www.openarchives.org/OAI/2.0/oai-identifier"
                  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                  xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai-identifier
                  http://www.openarchives.org/OAI/2.0/oai-identifier.xsd">
                <scheme>oai</scheme>
                <repositoryIdentifier>your.host.edu</repositoryIdentifier>
                <delimiter>:</delimiter>
                <sampleIdentifier>oai:your.host.edu:000000001</sampleIdentifier>
              </oai-identifier>
            </description>
          </Identify>
          <ListSets>
            <set>
              <setSpec>foo</setSpec>
              <setName>All things of foo</setName>
            </set>
            <set>
              <setSpec>bar</setSpec>
              <setName>All things of bar</setName>
            </set>
          </ListSets>
          <PossibleMetadataFormats>
            <metadataFormat>
              <metadataPrefix>oai_dc</metadataPrefix>
              <schema>http://www.openarchives.org/OAI/2.0/oai_dc.xsd</schema>
              <metadataNamespace>http://www.openarchives.org/OAI/2.0/oai_dc</metadataNamespace>
            </metadataFormat>
            <metadataFormat>
              <metadataPrefix>marc21</metadataPrefix>
              <schema>http://www.loc.gov/standards/marcxml/schema/MARC21slim.xsd</schema>
              <metadataNamespace>http://www.loc.gov/MARC21/slim</metadataNamespace>
            </metadataFormat>
          </PossibleMetadataFormats>
        </oai_config>

LoadOai.pl

This is a generic example script for loading data. The script looks for XML files in the data directory (data dir) and loads each record into the oai and oaisets tables. Before using this script you must change the DB connection settings at the top:

  my $dbUser   = "user";
  my $dbPasswd = "passwd";
  my $dbName   = "foo";
  my $dbServer = "bar";

The available arguments for the script are:

  -d data dir (place to find the XML data)
  -s oai set (optional)
  -h (help: message printed)
  -v (verbose output)

The only required argument is the data dir (-d).

All of the data within and including the <metadata> element is loaded into the DB under the specified format. The script should be able to identify oai_dc and marc21 but any other metadata format may require code modifications. This data is not validated or checked in any way other than to make sure it is well formed XML.

If the oai set option (-s) is used, the setSpec is ignored in the /record/header/ element for all records being loaded.

For the identifier, the script only uses anything after the last ":" (oai:host:id). The "oai:host:" part is added on to the identifier by the UMProvider.

• DB Format (see above under UMProvider)

• XML Format

The XML files must have the OAI record elements wrapped in a <record> element (just like OAI-PMH 2.0). By default, this script will look for record elements wrapped in a <records> tag. If you have the data nested some other way, just change the $recordXpath value in the script to the correct xpath for finding the <record> elements. There can be multiple record elements in a single file as well as multiple XML files in the data directory. Here’s an example XML file:

    <?xml version="1.0" encoding="UTF-8"?>
    <records>
      <record>
        <header>
          <identifier>oai:some.host.edu:id-1234</identifier>
          <setSpec>foo</setSpec>
        </header>
        <metadata> [ ... ]
        </metadata>
      </record>
      <record> [ ... ] </record>
    </records>

Record Loader (PHP)

Lisa Brooks at IssueLab has created an open source PHP script for loading records into a database for the UMProvider. This can be used as an alternative to the Perl script (LoadOai.pl) described above.

The script along with detailed instruction can be found here: http://harvest.issuelab.org/software.php