Template:EPrints Metadata Fields Content

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Metadata Field Types

There are many different types of metadata field. The type controls how a field is rendered, indexed, searched and so forth. A field always has a type and a name property, and usually has several more. Most properties are documented on this page, but some properties are only available to certain types of field, and they are listed on the page for that field.

Some of these subclasses provide very rich features, others very simple. For example the url field works just like the text field except that it's only valid if it looks like a url and when rendered it is a hyper-link.

A metadata field describes one field of data in one type of Data Object. For example the "title" field of an EPrint Object or the "email" field in a User Object.

Every Data Object has system fields (which are set by the system, and not alterable), but the User Object and EPrint Object have additional fields which are configured on a per-repository basis.

These can be customised in the user_fields.pl and eprint_fields.pl files. Note that changing these files does not automatically modify the underlying database so should (generally) only be done before the database is created. Some metadata properties do not affect the database, and are marked as such.

If you add or remove fields, or modify a property which affects the database then you'll need to alter the database to match. In 3.0 this must be done by hand, but we have plans to build a tool to do this for you.

Default values marked *config indicate that the default value for the repository may be modified in the configuration file field_property_defaults.pl


Inheritance

This is the list of useful field types. Under it is listed the other field types which are just included for completeness and are not intended to be used as part of the configuration.

Some field types inherit the properties of another, and then modify them in some way. For example the namedset field works like a set field except that it gets its options from a namedsets file not from the options=>[] in the field properties.

  • Basic metadata field - this is abstract, fields must be one of the types listed below...
    • Boolean - TRUE or FALSE (or can be unset, of course).
    • Compound - virtual field, joins together several "multiple" fields, e.g. author_name and author_email.
      • Dataobjref - references another data object.
      • Multilang - allows language variants of a field, e.g. titles in French, German and/or English.
      • Relation - stores a typed relationship with something represented by a URI.
    • Date - stores a date
      • Time - stores a date and time
    • Float - stores a floating-point value
      • Decimal - stores a decimal number. Specifying the length of number before and after the decimal point.
    • Id - like basic text field but search only finds exact matches
      • Id (case-insensive) - like Id field but search find exact matches ignoring case (use for usernames, email addresses, etc.)
      • Keywords - stores as longtext but searchable as exact individual keyword phrases
      • Recaptcha - virtual field to display a reCAPTCHA to prevent spamming of public input forms.
      • Text - the basic text field. Maximum 255 bytes. nb. uft-8 means some chars take more than one byte.
        • Longtext - like text but allows much longer text (65,000 bytes).
        • Pagerange - a range of page from one number to another.
        • Secret - used to store passwords and other secrets.
        • Set - a limited set of options
          • Namedset - like a normal set, but takes its options from a namedset configuration file.
          • Subject - possible values are taken from the Subject hierarchy.
          • Base64 - stores Base64 encoded data.
            • Image - stores image encoded in Base64 data.
      • Url - stores a URL.
      • Uuid - stores a UUID.
    • Int - an integer value
      • Bigint' - a large integer value (can be greater than 2,147,483,647 or less than -2,147,483.647).
      • Counter' - an auto-incrementing integer value.
      • Itemref - a reference to another Data Object (e.g. a user or other eprint)
      • Pagerange - a pagerange, e.g. 122-130
    • Multipart - Stores a mutiple sub-fields like a person's name.
      • Name - Stores a person's name broken up into logical parts.
    • Subobject - Stores another data object under a parent data object.

Internal-use and Deprecated Field Types

Properties

Note that true/false properties use 1 and 0 to indicate their setting.

Some properties can be temporarily set or overridden by the Workflow Format and Citation Format files.

Core Properties

Name Default Value Required Description Notes
name n/a YES This is the internal name of the field. It should only contain alphanumeric characters and underscores. It will be used to identify this field in scripts, other configuration files, in the database, and in the XML export/import system, etc. This property is not required when defining sub-fields of Compound fields where sub_name should be used. This property affects the database structure. It must be unique within the Data Object (so the EPrint Object cannot have two fields called email but the EPrint Object and User Object can each have a field with the same name.
type n/a YES This sets the type of the metafield, which in turn affects what other properties it may have. This property affects the database structure. The value must be one of the metafield types listed above.
multiple <t>0</t> NO This indicates if this field is a single value or a list of values. E.g. title is only a single Longtext field but creators is a multiple Compound field. This property affects the database structure. In the database a non-multiple field is stored in one (or more) columns in the main object table, but a multiple field gets its own table.
sql_index 1 NO When the database is created this field indicates that an SQL index should be created to speed searching. This property affects the database structure. Different field types override the default value with the sensible option for that type of field. It is not worth putting a SQL index on a field that is only ever searched for words in it (like title or abstract) but it is worth indexing fields who's values are explicitly searched for, or where ranges are searched (e.g. Date fields, Set fields etc.). It is unlikely you will need to set this by hand. You could change it after the database has been created but this will not update the database nor have any other effect.
sub_name undef YES This is a special property which is required instead of the name property for the sub-fields inside Compound fields. This property affects the database structure. The actual name of these fields is then forced to be parent field name + '_' + sub_name. E.g. Compound field creators is a sub-field with sub_name => 'name'. In this case the actual name of the name field in the system, database etc. is creators_name/tt>.

Rendering Properties

These properties affect how values of the metadata in this field are rendered.

Certain of these properties can be turned on temporarily by the Citation Format files - render_magicstop for example.

Name Default Value Required Description Notes
browse_link undef NO This is the name of a view which values of this field should be linked to. E.g. if there was a Browse by Publishers view configured named pubs, then adding browse_link => 'pubs' to the publisher field would cause it to be linked into the browse view page for the named publisher whenever it is rendered.
render_quiet 0 NO Whether to prevent a big ugly UNSPECIFIED being rendered if field is unset. E.g. setting render_quiet => 1 on a field means it just gets rendered as nothing if it is unset.
render_magicstop 0 NO Whether to render a full stop at the end of this field, unless the last character is a dot, question mark or exclamation mark. This helps avoid the ugly World without Cheese?. effect you get when titles end in ? or !.
render_noreturn 0 NO Whether CR (Carriage Return) and LF (Line Feed) characters are turned into normal spaces.
render_dont_link 0 NO Whether rendered field is not encapsulated in a hyperlink. Currently only affects Url fields and Email fields.
render_single_value undef NO The value of this property is the name of a function to call to render individual values from this field. For a multiple field this is called once per value in the list of values. The function should take the following parameters: ($session, $field, $value, $object). It should return a XHTML DOM object of the rendered value.
render_value undef NO The value of this property is the name of a function to call to render the the field as a whole. As with render_single_value, but this gets passed the entire list of values (an array reference) if it is a multiple field. Parameters passed are: ( code>$session, $self, $value, $all_langs, $no_link, $object ). $all_langs indicates that all language variants should be shown and is only really useful for Multilang fields. $no_link being true is a request to place no hyperlinks in the resulting HTML. The function should return an XHTML DOM object of the rendered value.

Input and Validation Properties

name default description
required 0 If this is set to true then the field is always marked as required, no matter what the workflow says.
input_add_boxes 2 *config The number of rows to add when clicking the "more rows" button in a multiple or multilang field.
input_boxes 3 *config The number of input rows to initially show in a multiple field.
input_cols 60 *config The number of columns in a text input field.
input_rows 10 *config For longtext input fields, the number of rows of input to show. For set fields this is the number of items to show in a select menu.
input_lookup_url undef The URL to use for autocompletion. This is generally set using the workflow configuration rather than directly in the field configuration. The URL must be on the same server hostname as the repository.
input_lookup_params undef Additional parameters to pass to the input_lookup_url. For example an indication of which autocomplete file to use.
input_ordered 1 This is true by default. In some multiple fields, such as creators, the order of the values is important and by default numbers are shown to the left of input rows and to the right are "move up" and "move down" arrows. However, with some multiple fields the order is not important in which case you can set this to zero to stop the arrows and numbers being shown.
render_input undef The name of a subroutine which will render the input for this field. This is a bit tricky to use as it must return the same CGI parameters as the default input form would have. It's easiest on simple fields. The subroutine is passed the following parameters ( $field, $session, $current_value, $dataset, $staff, $hidden_fields, $object, $basename ). It should return the XHTML DOM object of the chunk of HTML form.
maxlength 255 This is a limit to the maximum allowed size of a value. It may be useful, for example, as a very simple validation check. Also it may confuse users to be allowed to type in 255 characters in a "postcode/zipcode" field.
toform undef This function is allowed to modify the current value which appears in the form. For example, if your database stores userids in a field, but you want to allow people to edit them as usernames, then this function can be used to take the current value (a userid) and return the associated username. This value is what appears in the field in the search form. It is passed ( $value, $session, $object, $basename ) and returns the user-facing version of $value. **As of version 3.3.13 this only gets passed $value and $session in Metafield.pm**
fromform undef The inverse of toform. This takes the value from the form and converts it into the value that will be stored in the database. It is passed the parameters ( $value, $session) when $value is the value entered on the web form, and the return value is the value to be stored in the database. This function is not called when editing the eprint is cancelled.
help_xhtml undef This can only be set via the Workflow Format configuration not via the metadata field directly. It is used to contain the XHTML to use as the help for this field. This is so that the workflow can conditionally change the help on a field.

Ordering, Indexing and Searching

name default description
text_index 0 If set to true the the indexer considers this field for full text indexing. Otherwise not. Some types of metadata field have a default of true, for example text and longtext.
search_cols 40 *config How many columns (characters) wide the input field for searching this type of field. If one search field searches more than one field then the properties from the first listed field are used.
make_single_value_orderkey undef The orderkey is the (potentially language specific) string used to order by this field. This property allows you to define a method to override the default eprints orderkey generation. This property is passed each value from multiple fields, in turn. It is passed ($field, $value) and returns an ordervalue string.
make_value_orderkey undef As with make_single_value_orderkey but this is passed the array reference for a multiple field rather than just single values. It should return the orderkey string for the entire value. It is passed ( $field, $value, $session, $language_id ).


Other Properties

name default description
can_clone 1 If this is set to false then this field is not copied when the object is

cloned. This is mostly used by system fields such as "dir" or "datestamp".

show_in_fieldlist 1 Set this to false to prevent this field appearing in fields field lists. This is primarily to allow you to remove it from the list of fields in the user configuration which are used to control which fields appear as columns in the Items and Review screens.
show_in_html 1 If set to false then this field is not shown in the Details tab of the eprint control page. This is mostly used to hide confusing internal system fields like "dir".
export_as_xml 1 Set this to false to prevent the field being exported in the XML export. This is handy to supress either confidential or confusing fields, like the fileinfo system field.
import 1 If set to false then new eprints can't be created with this value. For example "eprintid", "dir" and so forth have this set to false. This can also prevent fields being set when import tools are used.


Internal Properties

These are set by the system. Editing them by hand will do strange things.

name default description
parent_name undef On subfields of compound fields this is set automatically to be the name of the parent field.
confid *special This is set to the id of the dataset that this field belongs to and is used to work out what phrase ids etc. it uses.


Deprecated or Buggy Properties

Don't use these!

name default description
input_advice_right undef Do not use.
input_advice_right undef Do not use.
input_assist undef Do not use.
requiredlangs [] Do not use.
allow_null 0 Do not use. Planned for use with compound fields, but not implemented in 3.0.


Required Phrases

These are phrases which you need to define in the local repository phrases file to control how this field renders. Some types of field (eg. set fields) have additional phrases in addition to the ones listed below.

The actual name of the field, as it will appear to users is stored in 

datasetid + "_fieldname_" + fieldname

The default help to display, when the field is being input, is stored in 

datasetid + "_fieldhelp_" + fieldname

For example: 

   <epp:phrase id="eprint_fieldname_abstract">Abstract</epp:phrase>
   <epp:phrase id="eprint_fieldhelp_abstract">A summary of the items content. 
      If the item has a formal abstract then that is what should be entered 
      here. No complicated text formatting is possible.</epp:phrase>


Database

Most fields have a representation in the SQL database using one or more columns. The sub-pages for each field type give the details.


API

When you request (or set) a value of a metadata field, it is usually handled as a perl scalar (which is a string or number).

ALL values passed around in the API should be encoded in utf-8 or BAD THINGS may happen.

For example, 

$eprint->set_value( "title", "For Us, The Living" );

Sets the title to the given string. 

my $foo = $eprint->get_value( "title" );

Sets $foo to the string of the title, eg. "For Us, The Living".

Multiple Fields

If a field is set to multiple, then instead of a single value, a reference to an array of values is used. Eg. 

$eprint->set_value( "corp_creators", [ "Jims Research", "Jones Research ] );

Other Exceptions

See the specific page for the full details.

Examples

Example field definitions that can be copied into an configuration file and edited as appropriates.

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