<!-- TMPL_INCLUDE NAME="doc-head-open.inc" -->Online Help: System Preferences -- MARC tag structure administration<!-- TMPL_INCLUDE NAME="doc-head-close.inc" -->
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<h1>MARC tag structure administration</h1>
<p>Koha allows you to specify which MARC tags you want to use and which you want to ignore. When you downloaded and installed Koha, you also got the entire list of MARC21 tags and subfields in current use. Now you need to use the administration page to edit this list and tell Koha which tags you want to use and how you want to use them.</p>
<p>You can define as the marc tag structure for each biblio framework you have defined</p>

<p>If you are CERTAIN that you will never use a MARC tag, then you can delete it, but since this will not result in any appreciable improvement in performance, it is probably better to leave it. There will be tags you want to add, however. If you are using older MARC tags that are not in the list of tags supplied with Koha, then use the MARC tag structure administration page to add them. Similarly, you will probably need to add the holdings tag you currently use, or at least check the subfield structure of the 852 tag if you use it for holdings.</p>

<p>Editing the SubFields from the MARC tag structure page is very time-consuming, but also very important; be sure to click the subfield link for each tag in your MARC tag structure.</p>
<p>For each subfield you can set :</p>
<ul>
<li>repeatable : wether it can be repeated or not. If it can be repeated, separate the values by a | in the MARC editor when you want to have the subfield twice</li>
<li>Mandatory : wether the field is mandatory or not. If mandatory, the cataloger can't validate the biblio if the subfield is empty.</li>
<li>Search also : a list of field that Koha will also search on when the user do a search on the subfield</li>
<li>Koha link : <b>very important</b>. Koha is multi-MARC compliant. So, it does not know what the 245$a means, neither what 200$f (those 2 fields being both the title in MARC21 and UNIMARC !). So, in this list you can "map" a MARC subfield to it's meaning. Koha constantly maintains consistency between a subfield and it's meaning. When the user want to search on "title", this link is used to find what is searched (245 if you're MARC21, 200 if you're UNIMARC).</li>
<li>Text for librarian : what appears before the subfield in the librarian interface</li>
<li>Text for OPAC : what appears before the field in the OPAC. If empty, the text for librarian is used instead</li>
<li>Managed in tab : deals with the tab where the subfield is shown. Ignore means that the subfield is not managed. All subfields of a given field must be in the same tab or ignored : 1st it's more logic, 2nd, Koha would be confused to repeat repeatable fields otherwise !!!</li>
<li>hidden : means that the field is managed, but NOT shown in opac. It's usually for internal fields</li>
<li>URL : if checked, the subfield is an URL, and can be clicked</li>
<li>Auth value : means the value is not free, but in the authorised value list of the selected type</li>
<li>thesaurus : means that the value is not free, but can be searched in authority/thesaurus of the selected category</li>
<li>plugin : means the value is calculated or managed by a plugin. Plugins can do almost anything. For example, in UNIMARC there are plugins for every 1xx fields that are coded fields. The plugin is a huge help for cataloger ! There are also two plugins (unimarc_plugin_210c and unimarc_plugin_225a that can "magically" find the editor from an ISBN, and the collection list for the editor)</li>
<li>link : If you enter a field/subfield here (200b), a little glass appears after the subfield. If the user clic on the glass, a search is done on the DB for the field/subfield with the same value. Can be used for 2 main topic : 
	<ul>
		<li>on a field like author (200f in UNIMARC), put 200f here, you will be able to see all biblios with the same author</li>
		<li>on a field that is a link (4xx) to reach another biblio. For example, put 011a in 464$x, will find the serial that was previously with this issn. With the 4xx pligin, you get a powerful tool to manage biblios connected to biblios</li>
	</ul>
</li>
</ul>

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