dArceo is composed of several services which provide functionality for long-term preservation, primarily images, text and a/v documents. One of the most important aspects of the dArceo is the migration function, which has been implemented using the transformation approach of the OAIS model. Migration approach has been selected because of the nature of the content preserved in Polish digital libraries – primarily texts, images and a/v files. The core functions of the dArceo cover:
- Data storage and versioning – each digital object submitted to dArceo is stored and versioned appropriately, so that the user has full access both to the newest version of the digital object as well as the older ones. dArceo can use various storage devices, including hard drive, disk array and SFTP protocols. It can be also easily configured to store data in the PLATON-U4 archiving services developed within the PLATON project and deployed in the Polish nationwide network PIONIER.
- Metadata management – in order to have full information about preserved digital objects, dArceo uses METS format as the metadata container for the metadata related to certain digital object. This main metadata file contains various information, including structural metadata, technical metadata, descriptive metadata as well as administrative metadata. Morveover, metadata can be either provided by the user (along with the content) or extracted by the build-in dArceo mechanism which uses such metadata extraction tools as FITS, FFMpeg or DROID.
- OAI-PMH Repository – provides OAI-PMH interface for digital objects stored in dArceo. Two formats are supported (metadata availability): Dublin Core and METS.
- Data manipulation – the core functionality of dArceo. There are three types of data manipulation functions. The first one is data migration, which play significant role in terms of long-term preservation. It uses transformation approach of the OAIS model. The second type is data conversion, which basically provides lossy conversion and therefore simplify the process of building digital libraries, which primarily provide access to so called presentation versions of digital objects. The third type is advanced data delivery, which provide means to deliver source data (master files) in a personalized way, e.g. streaming/progressive download, text extraction from a/v document, or viewing data on mobile devices.
- Data monitoring – it is possible to monitor preserved data in the context of both integration of the data (SHA-512 checksums) as well as format loss risk calculated based on the information gathered from the UDFR database. As soon as the data is corrupted or the format loss risk is high, the administrator receives appropriate notification.
- Common space of the data manipulation functions – one of the key innovative ideas of the dArceo – this function allows various dArceo deployments to share their data manipulation functions. It means that one institution can provide to other particular migration, conversion or advanced delivery function. Such an approach facilitates the cooperation between digitisation projects and provides means to foster implementation of long-term preservation accross various institutions. Ideally institutions with enough technical potential will provide services, that other, e.g. smaller institutions can also use.