Object oriented interface to Pica+ records, fields, and subfields
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PicaRecord – Object oriented interface to Pica+ records

About

PicaRecord provides an object oriented interface to Pica+ records, fields, and subfields. It does not provide the means to read or write Pica+ records. In order to do so you need to install the packages PicaReader and PicaWriter that are available as dedicated composer packages.

PicaRecord is copyright (c) 2012-2016 by Herzog August Bibliothek Wolfenbüttel and released under the terms of the GNU General Public License v3.

Installation

You can install PicaRecord via Composer.

composer require hab/picarecord

Usage

Records, Fields, and Subfields

Subfields

Subfields are represented by the Subfield class. A Pica+ subfield is a cons (pair) of an alphanumeric case-sensitive ASCII character and a non-empty string value. The code of a subfield is considered to be immutable and the value must not be the empty string.

Fields

Field are represented by the Field class. A Pica+ field is an ordered list of subfields and partially identified[1] by two properties, the field tag and the field occurrence. Both properties are set on instantiation and considered to be immutable.

In the following text the field shorthand refers to a string consisting of the field tag, followed by a forward slash (ASCII 47) followed by two digits denoting the field occurrence. For example the field shorthand of the field 021A with an occurrence of 0 is 021A/00.

Retrieving subfields

Field::getSubfields() returns all subfields of a field when called with no arguments. To retrieve specific subfields you can pass an arbitrary number of arguments each representing a subfield code. If you do so the returned array will be constructed as follows:

Each element of the returned array corresponds to a subfield code in the argument list. If the field has a subfield with the specified code the element of the returned array contains the subfield. If the field does not have a subfield with the specified code the element of the returned array contains NULL. In order to retrieve multiple subfields with the same subfield code you need to repeat the subfield code in the argument list. The first occurrence of the code in the argument list refers to the first subfield with the specified code, the second occurrence to the second subfield and so on.

Because Field::getSubfields() when called with subfield codes as arguments returns an array with a known size (as much elements as arguments were passed to the function) you can conveniently use PHP’s list() operation.

Example: To retrieve the first and last name of the author encoded in the Pica+ field 028A/00 you can call Field::getSubfields() as follows:

list($firstName, $lastName, $personalName) = $field->getSubfields('d', 'a', '5');

Manipulating the subfield list

You can use Field::addSubfield() to add a field to the end of the subfield list. If the subfield is already part of the subfield list an InvalidArgumentException is thrown. For more sophisticated manipulations of a field’s subfield list you can use Field::setSubfields() to replace the subfield list of a field.

A subfield can be deleted using Field::removeSubfield() which takes the subfield to delete as sole argument and throws an InvalidArgumentException if the field does not contain the subfield.

Records

Record classes

PicaRecord provides classes for the four record types of title records, authority records, local records, and copy records. The relationship of title, local, and copy records is as follows: A title record may contain zero or more local records. Each local record may contain up to 99 copy records.

Local records can be identified by the internal library number (ILN) of the library they belong to and retrieved either by TitleRecord::getLocalRecord(), which returns an array of all local records, or TitleRecord::getLocalRecordByILN() which retrieves a single local record identifed by its first argument.

Copy records hold information about particular items (exemplars) and are identified by the number of the item in the local record. You can use LocalRecord::getCopyRecords() or LocalRecord::getLocalRecordByItemNumber() to retrieve an array with all copy records or a single copy record with a specified item number respectively.

All record classes implement the two methods Record::isEmpty() which returns TRUE if a record is empty (does not contain any fields) and Record::isValid() which performs a preliminary validation of the record.

Selecting and deleting fields

Record::getFields() returns all fields of the record when called without arguments. If you call it with the body of a regular expression as argument it will only return the fields whose shorthand is matched by the regular expression.

Record::select() provides a more generic access to a record’s fields. It takes a predicate function as argument and returns all fields that fullfill the predicate. A predicate function can be any valid PHP callback that takes a Field as argument and return TRUE if the field fullfills the predicate or otherwise FALSE.

Record::delete() deletes all fields that match a predicate function (see above).

If a record contains other records, i.e. if a record is a title or local record, Record::delete(), Record::select(), and Record::getFields() operate on all fields of the record, including the fields of the contained records.

Appending fields to a record

Append fields to an existing record is not as straightforward as selecting or deleting fields. Each record class has its own restrictions when it comes to appending a field to it via the Record::append() function:

  • you can only append fields with a level of 0 to title and authority records
  • you can append fields with a level of 1 to local records
  • you can only append fields with a level of 2 to copy records; as an additional restriction the occurrence value of the field must be equal to the item number of the copy record
Record classAllowed field level in append()
TitleRecordLevel 0
AuthorityRecordLevel 0
LocalRecordLevel 1
CopyRecordLevel 2

The attempt to add a field with a different level then the allowed level results in an InvalidArgumentException to be thrown.

Acknowledgments

Large parts of this package would not have been possible without studying the source of Pica::Record, an open source Perl library for handling Pica+ records by Jakob Voß, and the practical knowledge of our library’s catalogers.

Footnotes

[1] E.g. a title record may contain zero or more fields with tag 101@ and occurrence 00; fields with this shorthand indicate the start of a local record.