The implementation of cultural heritage archives

Transcription

1 The implementation of cultural heritage archives NICOLE PETERSEN, University of Cape Town April 29, 2015 The rapid growth of technology is changing the way that cultural heritage artifacts are accessed. There are various tools and architectures that exist for the implementation of digital libraries. When selecting one, it is important to consider the goals of the system. This paper identifies the tools, functionalities and architectural requirements of digital libraries. It then describes the aspects of next generation digital libraries, which are moving from monolithic systems to component-based systems, enabling dynamic customization according to the needs of the user. 1. INTRODUCTION Cultural heritage is defined as the legacy of artifacts of a society that are inherited from past generations, maintained by present generations and used by future generations [ICOMOS. 2002]. It brings value to learning, research, documentation and public accountability. The rapid growth of technology is changing the way that cultural heritage artifacts are stored, preserved and accessed. Before the use of technology, researchers were required to physically visit archival repositories and search through large wooden cabinets to find collections that met their needs [Cox. 2007]. Researchers are now able to access information from anywhere at any time by visiting digital libraries, which are defined as managed collections of digitized information, accessible over a network, with services to manipulate the content. Although this brings about many advantages, it also creates new challenges, such as having different metadata elements and retrieval techniques for each different digitized object (for example sound recordings, stories, videos and images), having to allow for the different ways of viewing the information to suit the various needs of the users, and considering the possibility of digitized objects becoming unreadable and therefore inaccessible when technologies become obsolete [Phiri, et al. 2015]. This paper identifies the functionalities, architectures and tools used to implement cultural heritage archives, in an attempt to identify tools that could possibly be used for the implementation of an archive that combines three repositories containing cultural heritage information of Cape Town. 2. FUNCTIONALITIES OF DIGITAL LIBRARIES The core functionalities that should be provided by digital libraries are preservation, accessibility and organization of content [Cleaveland. 1998]. These functionalities are important as they serve as a backbone for other more advanced features that are implemented in modern digital libraries. 2.1 Preservation Preservation of digital objects requires the integration of policy, technology and standards [Jantz, et al. 2005]. This section analyses two aspects of preservation involving technology and standards. Namely, the integrity of objects and the structural design of objects. Author s address: N. Petersen, Computer Science Department, University of Cape Town

2 2.1.1 Structural design of objects The structural design of objects includes the metadata scheme as well as the format that objects are stored in the repository. The Open Archival Information System (OAIS) is a reference model for Open Archives that provide a starting point for implementation and describe how digital objects can be stored in the repository [Santhanagopalan, et al. 2006]. There are three kinds of information packages that the OAIS uses, the Submission Information Package, which contains the information that is sent from the producer to the archive, the Archival Information Package, which is the information stored by the archive, and the Dissemination Information package, which contains the information that is sent to the user [Santhanagopalan, et al. 2006]. The Archival Information Package (AIP) differs from the other two packages as is the only package that is involved in preservation. It contains content that should be preserved as well as a complete set of metadata elements required to preserve the content. The goal of OAIS is to preserve the content that is encapsulated in the Content Data Object and make it available in a form that is understandable [Lavoie. 2004]. Figure 1 illustrates the components of the AIP. Figure 1: Archival information package Object integrity Digital libraries must ensure that objects are not accidently or fraudulently modified during their lifetime. Even single bit changes can dramatically affect the content and function of digital objects [Jantz, et al. 2005]. These changes must therefore be detected, reported and corrected to provide assurance that the digital library is trustworthy. Ways to detect changes in digital objects include using checksums or digital signatures [Jantz, et al. 2005]. Digital signatures can be provided by taking a hash of the digital object and storing the resulting digest in a metadata field of the object. When a user tries to access the object, the system can recalculate the hash of the original object and compare it to the digest stored in the metadata field. If the new digest is not the same as the old digest, then the system knows that the digital object was modified. Checksums are similar to digital signatures in that both recalculates a value and compares it to the original to detect if any inconsistencies are present [Santhanagopalan, et al. 2006]. 2.2 Organization The key process involved in the organization of digital objects involves assigning metadata elements accurately to each digital object such that it describes the

3 attributes or content of the objects effectively. The selection of the metadata scheme will depend on whether it is able to describe all types of digital objects that the digital library is meant to contain. The Metadata can be split into descriptive metadata, which contains data such as the author of the object and administrative metadata, which contains technical data (data about the format of objects), rights metadata and preservation metadata (for example the digital signature of the object) [Gartner. 2008]. The organization of digital objects in the repository is important to consider as it affects their accessibility. For example, a repository architecture design could be centered on the idea of creating a simple repository that should at minimum support the preservation and access of digital content [Phiri, et al. 2015]. This could be implemented by having digital objects organized in a hierarchical structure by making use of a file system as the core infrastructure [Phiri, et al. 2015]. The Bleek and Lloyd collection, described in section 5.2, makes use of this repository architecture. 2.3 Accessibility Digital libraries are often accessed via the Internet, placing no restrictions on physical location and operating hours. To ensure that they are accessible from any location, they should be able to work in different environments. Accessibility can be challenging in developing regions where the digital divide exists. In communities that have limited access to the required Internet bandwidth and computing resources to access digital libraries via the Web, community members will be unable to access cultural heritage artifacts [Suleman. 2008]. The literature surveyed contains few examples of the implementation of digital library projects that are aimed at providing accessibility in poor communities. 3. DIGITAL LIBRARY ARCHITECTURE It is important to consider the architecture for a digital library as it affects what it is able to accomplish and how effective it is [Candela, et al. 2005]. For example, the architecture can affect the interoperability, portability and scalability of the digital library. The literature explores various kinds of architectures, such as service-oriented, peerto-peer and grid-based architectures, each with their own strengths and weaknesses [AGOSTI. 2004]. Peer-to-peer architectures allow for the integration of services and sharing of information. Grid computing enables complex services to be implemented at a reduced cost by distributing computing resources. Service-oriented architectures provide mechanisms to describe the usage of services and to combine services into workflow processes for advanced search services. However, they all share the three basic components that a digital library should have. Namely, the repository layer, which stores and manages digital objects, the service layer, which provides the services required to manipulate digital objects and the interface layer, which is used to display the requests made to the digital objects [Phiri, et al. 2015]. The typical architecture is displayed in figure 2.

4 Figure 2: High level architecture of a typical digital library [Phiri, et al. 2015] 3.1 Interoperable architectures To provide the most effective services for users, digital libraries often work together with other systems to achieve a goal. This means that interoperability of digital libraries is an important aspect to consider when designing the architecture [Suleman. 2002]. The Open Archive Initiative (OAI) was launched to tackle the need for low cost interoperable systems. It encourages a multi-layer approach to the system architecture by separating data from services [Suleman, et al. 2003]. Federated architectures allows for interoperability and information sharing for digital libraries. The basic elements of federated architectures are components, which represent individual systems or services [Heimbigner, et al. 1985]. Interoperability is achieved by integrating the distributed services that communicate using standardized protocols such as OAI-PMH (Open Archives Initiative Protocol for Metadata Harvesting). Europeana, a cultural heritage digital library, implements a federated architecture [Phiri, et al. 2015]. 3.2 Portable architectures Portability refers to the ability of the digital library to be accessed universally [Phiri, et al. 2015]. Since accessibility is a core requirement of current digital libraries, it is important to design for portability. The Bleek and Lloyd collection is an example of a digital library that implements a portable architecture. 3.3 Scalable architectures Scalability refers to the ability of digital library systems to expand, in terms of services offered, types of user communities or information collections. It is an important aspect to consider when designing the architecture due to the likelihood of adding new collections or functionalities to the digital library [Phiri, et al. 2015]. Bondi proposes two ways that scalability can be achieved; vertical and horizontal scalability. Vertical scalability refers to the ability of digital libraries to expand in terms of adding more resources or increasing the capacity of the system, whereas horizontal scalability refers to the ability to grow in terms of adding more components, such as new collections or services [Bondi. 2000]. Horizontal scalability

5 can be implemented by having a component based implementation, such as an Open Digital Library. 3.4 Open digital library Open archives implement the OAI-PMH which is a protocol developed by the Open Archives Initiative to collect metadata elements from objects stored in a repository [Santhanagopalan, et al. 2006]. An Open digital library (ODL) is a network of extended Open Archives, where each node in the network encapsulates data or services [Suleman. 2002]. The Open Digital Library project extends principles of the OAI by creating a set of related protocols for a component-based digital library. It supports inter-component interaction within a digital library, which means that developing digital libraries simply involves inter-connecting components, such that it forms larger digital libraries. These inter-connected components are able to communicate through protocols using XML as the mechanism for data interchange [Suleman. 2002]. Open digital libraries provide an architecture that is both scalable and interoperable. Interoperability is achieved by having a component based design where every service is delivered as an open archive. This allows the reuse of components and interoperability at the level of digital library services [Suleman. 2002]. 4. ANALYSIS OF ARCHIVE BUILDING TOOLS Digital library tools should provide the core functionalities of digital libraries, which includes the organization, preservation and access of digital documents. There are various tools that exist for the implementation of digital libraries. This section describes and compares a selection of four tools; DSpace, Omeka, Fedora and Invenio, each implementing the core functionalities, with some providing additional functionalities that may make for a more usable digital library or make for a more restrictive system. 4.1 DSpace DSpace is an open source digital repository system that provides tools for the storage and management of digital objects [Keats. 2008]. It was designed to operate as a centralized service, building around the idea of having organized communities where each community has a separate area within the system and is able to modify the system to meet their needs. For example, each community may have a different way of submitting content to the repository [Smith, et al. 2003]. Besides the core functionality, additional functionality that is supported by DSpace includes plug in support, collaboration, search, browse, import and export. According to Robert Tansley et al, it is best suited for the use of creating an institutional repository of text-based items as each basic requirement of a digital repository system is addressed in a relatively simple manner [Tansley, et al. 2003]. DSpace provides an easy experience for the user by having a well-designed Web front end, making the process of submitting content easy, having a simple indexing and searching API and accommodating differing submission workflows. Due to the simplistic focus of DSpace, it is bound to have limitations such as having minimal capabilities for batch import of items, having no way to manage complex relationships and not supporting different versions of objects as it assumes all objects are static [Tansley, et al. 2003].

6 4.2 Omeka Omeka is an open source online exhibition tool for archives and libraries. It comes in two versions; Omeka.org and Omeka.net. Omeka.org is an open source software package that is locally stored and managed. In order to use the software package, resources and skills should be available. The resources that are required to use Omeka.org are setting up an operating system, Web server and MySQL database [L. Hardesty. 2014]. Omeka.net is a hosted service where you are able to sign up for an account and upload content. It has exhibit capabilities and the ability to use administrative interfaces to manage content. However, you are restricted in the fact that you will not be in charge of the database and code of Omeka [L. Hardesty. 2014]. Both versions allow for accessing different items in a collective way while maintaining the significance and context of each individual item [L. Hardesty. 2014]. It is therefore used as an alternative to having specialized sites where functionality cannot be generalized across the various archives. It provides batch import, creation of online exhibits and the ability to tag items with keywords, which aids browsing and organizing content that enhances user interaction. Functionality that is not provided by existing plug-ins can be easily developed by making use of the framework provided. Other advantages of Omeka include being able to easily modify a theme. Recent Omeka themes are using responsive designs, which provide an optimal viewing experience on any Web-enabled device. Despite the positive aspects of Omeka, it has limitations. Some attempts at exhibiting content proved to be problematic as it did not work well with the Dublin core metadata standard [L. Hardesty. 2014]. There are also limited bibliographic description capabilities. The most challenging problem that was found was the management of Omeka instances over time as each new collection is created. Hardesty et al suggests that Omeka can be seen as a restrictive software package tool or it can be seen as a solid base from which to provide online access to digital cultural heritage collections [L. Hardesty. 2014]. This could be due to the difficulty of customizing exiting Omeka functionalities, such as searching. 4.3 Fedora Fedora (Flexible Extensible Digital Object Repository architecture) is an open source digital content repository service that is used as a foundation for digital libraries, repositories and archives [L. Hardesty. 2014]. The framework provides for the creation, management and preservation of complex digital objects and is implemented as a set of Web services that provides management of digital objects as well as search and access to multiple representations of objects. Fedora consists of two important frameworks; the service framework and the repository framework. The Fedora service framework consists of a set of services that interact with each other. It is here where digital objects are managed. At the core of this framework is the Fedora repository framework that provides the interfaces for managing and accessing objects from the repository. In comparison to other tools discussed in this section, Fedora only provides the base architecture for the digital library and does not provide complete indexing and management functionalities of digital objects [Keats, 2008]. Fedora has many positive aspects. It stands out from other tools discussed as it has the ability to support both conventional and complex digital objects. It supports the upload of compressed objects and the bulk upload of digital objects along with their metadata. Fedora carries out duplicate checking, allows for adding different versions of a digital document to the repository and provides customizable search and retrieval functionalities [L. Hardesty. 2014]. An important aspect of Fedora is that it

7 was designed from the beginning for extensibility. This allows developers to build customized digital library solutions that meet their needs. Despite the positive aspects of Fedora, it has some limitations. Fedora requires more expertise to implement and use [Keats. 2008]. For example, the interface, FedoraAdmin, used by admin for uploading content into the repository requires users to have experience with the tool. Additionally, there exist limitations to browsing such as being unable to browse by collection or being unable to browse on multiple dimensions, which could be as a result of the system not allowing objects to be grouped in an organized structure, such as a graph structure [Lagoze, et al. 2006]. 4.4 Invenio Invenio is an open source software suite that allows for the creation of a digital library on the Web [Madalli, et al. 2012]. As a result of its flexibility and performance, Invenio serves as a comprehensive solution for the management of repositories of moderate to large sizes. It covers all aspects of digital library management, such as, indexing, curation and dissemination of digital objects. The advantages of Invenio are that it complies with standards such as the OAI metadata harvesting protocol (as does other tools discussed in this section), provides support for Dublin Core and MARC 21 as metadata schemes, is able to check the validity of digital objects by making use of MD5 checksums and has the ability to accept documents in all formats that are specified by the system administrator [Madalli, et al. 2012]. 4.5 Comparison of tools There is currently a wide variety of open-source software systems available for building digital libraries with a lack of consistent standards to evaluate them [Zuccala, et al. 2008]. This was found to be true by the lack of consistency of comparing tools in the literature. This makes the selection process a tough undertaking that will depend mainly on the type of documents you want to upload and display [Madalli, et al. 2012]. Other evaluation criteria that could be considered are metadata support, file features such as size and format, integrity checks, ease of customization and navigation [Madalli, et al. 2012]. This section compares the four tools that were described above to evaluate their effectiveness. When selecting a tool, one must consider the goals of the digital library. If it requires a high degree of customization, it may be more appropriate to select a tool, such as Fedora, that provides a solid base with minimal functionalities, or design a custom base, making use of no tools thereby having no restrictions placed on the design of services. DSpace and Omeka would be more appropriate if the services required by the digital library are more generic. Compared to the other tools discussed, Fedora requires more expertise to implement. For example, Fedora requires the development of a Web-front end, whereas DSpace does not [Keats, 2008]. A trustworthy system must ensure that the integrity of objects are checked. DSpace, Fedora and Invenio support checksums, however they do so differently. In DSpace, the system administrator has the responsibility for ensuring that the integrity of objects are checked, whereas Fedora and Invenio support automatic checksums.

8 All four tools described provide interoperability and ease of access of metadata by conforming to the OAI-PMH. All four are also able to distinguish among different user groups [Andro, et al. 2012]. 5. ANALYSIS OF THE IMPLEMENTATION OF ARCHIVES This section analyses the implementation of two archives, Europeana and the Bleek and Lloyd collection, selected due to their interesting implementations. 5.1 Europeana Europeana is a cultural heritage digital library that aims to make European information resources interesting to use and easier to access by offering access via multilingual interfaces [Valtysson. 2012]. It is centered on participatory use, where users are able to discuss and contribute to the information repository [Valtysson. 2012]. As mentioned in section 3.1, Europeana implements a federated architecture [Purday, 2009]. This requires metadata from data providers to be loaded into the central repository to allow for global access, whereas data collections are able to be stored by the content providers. Europeana makes use of the Europeana Semantic Elements (ESE) metadata scheme that comprises Dublin core elements and a set of 12 elements that are specific to the needs of Europeana [Purday. 2009]. This enables metadata to be harvested using OAI-PMH [Concordia, et al. 2009]. 5.2 Bleek and Lloyd collection The Bleek and Lloyd collection comprises a set of drawings and books that document the language and culture of Khoisan groups in Southern Africa. The implementation avoids the aspects that accompanies a database implementation such as multi operating system support, long term preservation considerations and the use of large collections in areas with limited internet access. As mentioned in section 3, the Bleek and Lloyd collection is an example of a digital library that implements a portable architecture. The implementation is xml centric as it makes use of XML, XSLT and XHTML to generate the static portable library [Suleman. 2007]. 6. NEXT GENERATION DIGITAL LIBRARIES Digital libraries are evolving in terms of their architecture, information, services and interoperability. Next generation digital libraries extend the notion of organizational boundaries by placing more emphasis on user-centered change. This means that users should be able to adapt the library to fit their needs and be able add and share information in the form of comments or annotations [Greenstein. 2002]. Architecture Digital libraries are moving from monolithic systems, which usually serve a single purpose, to component based systems that are able to change dynamically according to the needs of the user [Ioannids, et al. 2005]. The architectures of digital libraries are moving towards being distributed, such that digital objects and services are provided from multiple locations. This removes the responsibility for data providers to create services to access their collections, resulting in more experienced service providers providing the services. Other advantages include being less resource intensive compared to central architectures and being able to provide access to multiple collections, owned by different data providers, from a single system [Suleman. 2012].

9 System interoperability Digital library systems are moving towards interoperable solutions by integrating distributed services that communicate using standardized protocols such as OAI- PMH. They are able to interact with other digital libraries by forwarding search and retrieval requests and by exchanging metadata [Ioannids, et al. 2005]. Information sharing The ability to add annotations to digitized documents in digital libraries can provide a base for online conversations and information sharing. Annotations can be stored together with the artifact or in a separate repository. When it is stored with the artifact it is easier to keep annotations up to date, however when it is stored in a separate repository, it enables shared access and easy search [Agosti, et al. 2003]. 7. CONCLUSIONS Digital libraries are currently undergoing a transition from statically integrated systems to dynamic collections of services, driven by digital library market needs. These needs consists of customizing of content and services offered by digital libraries to the needs of the relevant communities. Future digital libraries should enable any citizen to access information anytime and anywhere, in a highly scalable and customizable way [Agosti, et al. 2004]. This requires the architecture of digital libraries to be designed for portability, interoperability and scalability. A way to achieve this is by having a component-based design, such as the Open Digital Library project and following standards created by the OAI. REFERENCES Agosti, M. And Ferro, N Annotations: Enriching a digital library. In Research and Advanced Technology for Digital Libraries, Anonymous Springer, Agosti, M., Schek, H. And Türker, C Digital Library Architectures: Peer-to-peer, Grid, and Serviceorientation: Pre-proceedings of the Sixth Thematic Workshop of the EU Network of Excellence DELOS: S. Margherita Di Pula, Cagliari, Italy, June, Edizioni Progetto. Andro, M., Asselin, E. And Maisonneuve, M Digital libraries: Comparison of 10 software. Library Collections, Acquisitions, and Technical Services 36, Bondi, A.B Characteristics of scalability and their impact on performance. In Proceedings of the 2nd international workshop on Software and performance, Anonymous ACM, Candela, L., Castelli, D., Pagano, P. And Simi, M Moving digital library service systems to the Grid. In Peer-to-Peer, Grid, and Service-Orientation in Digital Library Architectures, Anonymous Springer, Casey, M.E. And Savastinuk, L.C Service for the next-generation library. Library Journal 131, Cleveland, G. And Dataflow, I.U Digital libraries: definitions, issues and challenges. IFLA, Universal dataflow and telecommunications core programme. Concordia, C., Gradmann, S. And Siebinga, S Not (just) a Repository, nor (just) a Digital Library, nor (just) a Portal: A Portrait of Europeana as an API ).[ ]. Cox, R.J Machines in the archives: Technology and the coming transformation of archival reference. First Monday, 12. Fox, E.A., Suleman, H. And Luo, M Building digital libraries made easy: Toward open digital libraries. In Digital Libraries: People, Knowledge, and Technology, Anonymous Springer, Frommholz, I., Knezevic, P., Mehta, B., Niederée, C., Risse, T. And Thiel, U Supporting Information Access in Next Generation Digital Library Architectures. In DELOS Workshop: Digital Library Architectures, Anonymous, Gartner, R., L'hours, H. And Young, G Metadata for digital libraries: state of the art and future directions. JISC. Greenstein, D Next-generation digital libraries. In JOINT CONFERENCE ON DIGITAL LIBRARIES, Anonymous Citeseer. Dennis Heimbigner and Dennis McLeod A federated architecture for information management. ACM Trans. Inf. Syst. 3, 3 (July 1985), ICOMOS International Committee On Cultural Tourism ICOMOS International Cultural Tourism Charter: Principles and Guidelines for Managing Tourism at Places of Cultural and Heritage Significance. International Council on Monuments and Sites, ICOMOS International Cultural Tourism

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