Thesaurus have been widely used to provide structured vocabularies to describe books, however, they only provide part of the required knowledge for semantic web contexts. This paper proposes the use of ontologies and standard metadata to model semantic descriptions of image collections that refers to book covers. Ontologies represent keyword-based organizations. The classes and the hierarchical relationships of the ontology allow users to query images by topic with common search engines. The greenBookC collection is used as a test bed. This collection is published and maintained in Greenstone, a suite of software for digital libraries.
Users of digital libraries employ keyword based search engines, browsing
mechanisms or recommendation systems to find relevant information. In these tools,
words are considered as “units of meaning”. However, there is a gap between the
contents and meanings in multimedia data [
Different approaches exist to organize multimedia collections that vary from processing low level features to associate concepts to media. The results of these approaches often require knowledge of experts or specialized users. Most of the users of digital libraries interact with image collections through search engines that allow them to query images by title, date, author, format, publisher or with a feature associated with the file that stores the image. These descriptors are associated with image content.
Frequently, image collections are also described using a set of terms of a
keyword-based organization system or with natural language descriptions. In
order to extend the implicit syntactic level of these descriptions, semantic
descriptions with predefined structures and control vocabularies are considered richer
structures to store background knowledge [
Our interest is focused on describe images that refers to book covers.
Traditionally, thesaurus have been widely used to provide structured vocabularies to
describe books, however, they only provide part of the required knowledge for
semantic web contexts. In semantic digital libraries (SDLs), materials, tools and
meanings are addressed to offer benefits such as: anyone can use it, knowledge
is accessible from the SDL, resources are available with the modality anytime
anywhere, there are friendly and multi-modal interfaces with multiple connected
devises [
This paper explores an alternative to associate background knowledge to image descriptions that refers to book covers. The alternative makes use of ontologies and metadata standards. The classes and the hierarchical relationships of ontologies can be exploited by keyword-based search engines. A collection of images is built as a test bed. The collection is published in Greenstone, a suite of software for digital libraries.
The paper is organized as follows. Section 2 presents brief descriptions of software tools that allow users to construct image collections in the semantic web. Section 3 explains the ontologies and metadata management. Section 4 describes the test bed collection. Section 5 presents preliminary results. Finally, Section 6 includes conclusions and suggests future directions of our work. 2
Open freely distributed software exists around the world to construct image collections for educational, government and commercial institutions. This section describes some of the most common tools used in semantic web applications and depicts some representative collections.
DSpace1 allow users to create repositories of digital content in multiple
formats. This is a widely popular tool that supports the customization of interfaces
to fit different user needs [
Fedora commons repository software3 is a general purpose, open-source
digital object repository system under the Apache License. This is a centered
platform that enables storage, access and management of digital content, although
does not support indexing, discovery and delivery application mechanisms [
http://dspace.nitle.org/handle/10090/1267 3 Fedora home page is available at: http://fedora-commons.org/. This work is licensed under a Creative Commons Attribution-Share Alike 3.0 Unported License and the surrounding region from 1590 to the present. The interface visualizes images and metadata. The Libraries’ Catalog and the ArchivesUM are used to organize this collection.
Greenstone4 is a suite of software to build and construct collection of
semantic digital libraries. This is produced by the New Zealand Digital Library Project
at the University of Waikato, and developed and distributed in cooperation with
UNESCO and the Human Info NGO. This is an open-source, multilingual
software issued under the terms of the GNU General Public License. Greenstone
supports a variety of formats that represents text, images, audio and video [
After analyzing these software tools, we choose Greenstone to implement
the ontology-based alternative to describe image collections. The features of
Greenstone related with the support of semantic descriptions of images are the
following ones [
Protocol for Metadata Harvesting (OAI-PMH) – Export and ingest data from DSpace – Collections can be updated anytime without disturbing users – Dublin Core (DC) is the default metadata format when a new collection is constructed 3
Although thesaurus have been a typical classification system of digital libraries,
they are not able to accomplish the information requirements of the semantic
web. Ontologies have larger representation power than thesaurus [
The steps to construct semantic descriptions based on metadata and ontologies that refers to book covers are the following ones: 1. Construction of a description template for book covers. This template answer questions such as: what kind of information does users want to record for a particular image, how users query an image collection of book covers, what format is appropriate to store images, how can images be organized, 4 Greenstone is available at: http://www.greenstone.org/ 5 The History Campus Arquitecture Project is available at http://puka.cs.waikato.ac.nz/cgi-bin/cic/library what metadata standard is useful to support semantic descriptions, will the descriptions be used locally or a mechanism of information sharing must be considered 2. Linking images to ontology classes in such a way that classes can be used as values for a metadata standard. Hierarchical relationships should be used as a query expansion mechanism 3. Describing additional domain and background knowledge in metadata standard elements
Each case study might use of a different ontology as well as a distinct metadata standard as input. The goal in this work is to exploit ontological characteristics as the basis to improve image descriptions and retrieval mechanisms.
Table 1 shows an excerpt of an ontology that was used to construct semantic descriptions of book covers that form a collection called greenBookC. This collection correspond to book covers of physical books of the library of the UPPuebla. The areas of knowledge proposed by the “Consejo Nacional de Ciencia y Tecnologa” (CONACYT) are used as the main classes of this ontology.
The ontology of Table 1 has 8 main classes and 29 subclasses organized in 3 levels. Each class has a label, a level and one or more instances (images). An additional class is used to hold images of specific types of literature: biographies, dictionaries and novels. The classes were constructed using knowledge of experts. Semantic information is represented by metadata attached to each image; in particular, the dc:subject element is used to support the organization of topics, this means that the names of the classes are used to fill this element. Table 1 shows the DC elements used to form a semantic description. An institutional policy help to maintain a controlled vocabulary for the semantic descriptions.
The hierarchical relationships of the ontology are useful for free text search. For example, a cover book that belongs to the materials class, it is also considered as a member of the industrial engineering class. 4 greenBookC: an image collection with semantic descriptions at Greenstone This section describes the use of the ontology described in Section 3 to enrich an image collection of book covers. GreenBookC collection uses existing legal metadata of Greenstone. Semantic description of images are described with the unqualified Dublin Core (DC) elements of Table 2 as shown in Figure 1. After a metadata standard is added, metadata elements need to be filled as illustrated in Figure 2. These data can be assigned in different languages in order to improve collection accessibility.
According to [
The greenBookC collection is formed by 1504 images of book covers in JPEG
format. JPEG is a standard to represent compressed continuous-tone images [
greenBookC has a web-based interface to search the images. Descriptors such as topic, author or the browse list can be used to query the images. Users can carry traditional keyword-based searches in different DC elements or use the metadata descriptions whose values comes from the ontology. Distinct languages can be used to query the collection. At the date, the work has been address to construct the semantic descriptions and empirically the descriptions have improve collection accessibility. However, a lot of effort is still required to evaluate the proposed approached. 6
The use of lightweight ontologies to enrich metadata standard is a basic but simple policy to organize images by content and an alternative to construct semantic descriptions. Ontologies and metadata enable information sharing between academic communities. Ontologies provide controlled vocabularies that help to reduce ambiguity from natural language or keyword based descriptions.
The visualization of book covers at Greenstone allow users to recognize visual features of book covers. The use of existing legal metadata enables information sharing and improves interoperability in digital libraries. Different metadata standards or additional elements can be used to store relevant information of book covers as the abstract or the synopsis of a book, the publisher and the physical location, respectively.
There are several challenges in the construction of collections for semantic digital libraries, however there are software tools that can help users to develop this task successfully. As future work, we plan to represent the classes, subclasses, individual, properties and restrictions of the ontology formally in order to integrate reasoning capabilities.
We thank to the staff library at the UPPuebla for their help and cooperation in the construction process. This work is partially supported by PROMEP grant Biblioteca Digital Sem´antica de Recursos Educativos /103-5/09/4023.