multidimensionality);
and they further standardization methods for information and use of
Internet resources for scientific purposes.
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Diann Rusch-Feja
Max Planck Institute for Human Development, Lentzeallee 94
D-14195 Berlin, Germany, e-mail:
ruschfeja@mpib-berlin.mpg.de
Metadata are data about other data and objects. Metadata are used to describe digitized and non-digitized resources located in a distributed system in a networked environment. To be effective, they must be standardized. Traditional metadata include library cataloging rules, schemes, and formats. Due to the expanding electronic information environment, these have been expanded to reflect the needs of information discovery and use of information in such a networked environment and thus, rather than ``electronic cataloging rules'', the term ``metadata'' has been used. This also reflects a movement away from the traditional focus on books and printed works in libraries to a much more expanded focus on all kinds of data and objects, including digitized objects. Thus, metadata can include bibliographic information such as that in traditional library catalogs, subject cataloging, such as descriptors, classification designations, abstracts, etc., structural data on the type and size of resources, as well as technical requirements for their use or necessary for access, relationships (thematic, formal, references, citations, etc.), terms and conditions for obtaining and using the resources, etc.
In a relatively early article, Bearman & Sochats (1994) defined six types of metadata (see http://www.oclc.org:5046/conferences/metadata/requirements.txt), related to
This typology of metadata applies to most of the metadata which could conceivably be used for any digitized or non-digitized resource. Up until now, only the first two sections of the Bearman/Sochats typology have been developed to any degree. The third group of metadata in the Bearman/Sochats typology refers to the structure of the object itself - this may go to the level of arrangement into chapters, sections, data segments, etc. Context metadata give information on the context in which the object being described originated. Content metadata, according to Bearman/Sochats, give a much deeper analysis of the context aspects than the usual context descriptors used for resource discovery (point 1) or in documentational analysis. These and the last type of metadata in the Bearman/Sochats typology have not yet been as developed as the first two - probably because of the fact that these belong to a more sophisticated use of metadata than has thus far been achieved in the networked environment - although working groups are currently developing all areas. In addition to metadata which refer specifically to the object itself, there has also been a need for administrative metadata found by some of the implementers of metadata. These administrative metadata are added locally to distinguish aspects of holdings, individual subscription information, access information, etc.
Metadata are most frequently used in three ways:
In addition to these forms of metadata, based on the wide use of HTML and being accommodated for in HTML Version 4.0, the further development of metadata in RDF (``Resource Description Framework'') by the WWW Consortium and the integration of metadata into XML (EXtensible Markup Language; http://www.w3.org/TR/REC-xml ) structures enhances possibilities for its use. In view of this, the W3 Consortium are working together with the developers of Dublin Core Metadata to implement the use of Dublin Core Metadata into the XML environment. Meetings to this end are currently being held parallel to this conference at the 7th WWW-Conference in Brisbane, Australia. There are various sets of metadata, in fact more than are mentioned here. The major metadata formats include:
TEI and GILS (as well as EAD, WHOIS ++ Templates and other metadata sets prior or parallel to the development of the Dublin Core) are extremely text-oriented. The DOI (http://www.doi.org/ ) was only introduced in October 1997 and has been developed by five publishers or publishing aggregates including the American Publishers' Assocation and the American Medical Association. The DOI has - at the date of this presentation still inofficially - adapted the Dublin Core Metadata Set for the bibliographical and subject-oriented description aspects within the DOI, and will also hold a variety of additional subscription, purchase- and use-oriented metadata necessary for the publishers' purposes. The DOI will also point to metadata indicating the place within the production chain (i.e., whether the text is in the peer review process, whether and when it has been accepted, what issue it will be in, etc.). In the following discussion, this paper will focus on the Dublin Core Metadata, since this set of metadata seems to be developing into a standard for describing all types of Internet resources in various subject domains and geograhical regions of the world.
The Dublin Core Metadata were founded by a group of librarians, information scientists, and other parties interested in describing Internet resources for more precise retrieval than was possible via the universal search engines. They met for the first time in April, 1995, in Dublin, Ohio, (hence the name ``Dublin Core'', or DC) at the invitation of the OCLC organization and the United States' National Science Foundation. The outcome of this first Dublin Core Metadata Workshop was the designation of 13 elements which the participants agreed upon as necessary to meet the requirements of the metadata described in the first point, ``resource discovery'', of the Bearman/Sochats typology. In the ensuing four Dublin Core Workshops (http://purl.org/metadata/dublin_core/workshop.html ), the 13 Dublin Core elements were refined, the overall ``Warwick Framework'' for encorporating various metadata sets was developed, and options of extensibility for Dublin Core Elements were delineated. In December 1996, the set was expanded to 15 elements. The rationale for having only 15 elements was to keep the resource description for purposes of discovery (via search machines and individual Harvester gatherers) to a minimum, although it is recognized that certain detailed and structured information will also be necessary (see below ``Qualifiers''). The 15 DC Metadata Elements (http://purl.org/metadata/dublin_core_elements/ ) are listed here with a short description of each element (more detailed descriptions of the individual elements can be found via the Dublin Core Home Page (http://purl.org/metadata/dublin_core ):
DC.Title Title of the Resource
DC.Creator Author, Creator
DC.Subject Subject, Keyword
DC.Description Annotation, Abstract, etc.
DC.Publisher Publisher (Person or Institution)
DC.Contributor Contributing Person or Institution
DC.Date Date (see separate list of Sub-Elements ``DC.Date'')
DC.Type Resource Type (according to a list of accepted terms)
DC.Format Format, File Type, also Physical Medium
DC.Identifier Resource Identification: URL, URN, ISBN, etc.
DC.Source Resource (physical, digital) from which the
current resource was derived, digitized, etc.
DC.Language Language of the Resource
DC.Relation Relationship to other Works
DC.Coverage Geographic or Temporal Coverage
DC.Rights Rights Management Statement (or Link to), Copyright
In the workshop series, two groups of Dublin Core developers crystallized: the minimalists who maintain that the 15 elements are simple and sufficient enough to be used for resource discovery, and the structuralists who maintain that in order to obtain precision in searching sub-elements and other qualifying aspects are necessary. Thus, since the fourth Dublin Core Workshop, three qualifying aspects have been accepted to enable the Dublin Core to function in an international context and also meet higher level scientific and subject-specific resource discovery needs. These three Dublin Core Qualifiers are:
LANG is important for establishing greater internationality and serving needs of non-English language groups in describing their resources. It not only serves to distinguish specific key words, titles, etc., according to language, but can be used for filtering. For instance, the LANG-field of abstracts for foreign language articles could indicate if an abstract is available in another language. An example of the LANG-Field is given in the following:
<META=DC.Title, CONTENT=``Zeitschrift für Pädagogische Psychologie'' (LANG=de)>
<META=DC.Title, CONTENT=``German Journal of Educational Psychology'' (LANG=en)>
The SCHEME-Qualifier can be used in various ways. It allows distinction of several classification schemes, different abbreviation conventions, different date conventions, etc. The following example shows the differentiation which is possible using the SCHEME-Qualifier:
<META=DC.Title.Alternative, CONTENT=(SCHEME=SCCI Citation Title ISI)``Z PADAGOG P''>
In this example, the alternative title is an abbreviation of the above title used by the Social Sciences Citation Index.
<META=DC.Subject, CONTENT=(SCHEME=DDC)``370.15''>
<META=DC.Subject, CONTENT=(SCHEME=LOC)``LB 1051''>
This example shows how, by using the SCHEME Qualifier, other possibly meaningless or at best indistinguishable numeric or alphanumeric classification numbers can be searched in view of a certain classification system. Using the SCHEME qualifier, notations from various classification systems and thesauri can be used for the same object.
Although in the field of astronomy, internationality has long been achieved, there are still various subject areas which have not achieved this level of internationality. Hence, certain advantages of using metadata for achieving internationality are listed here: Metadata can include various language variations, use language limiters to filter search results, include abstracts in various languages, integrate multilingual thesauri and international classification schemes, provide links to translations, related works, and international cooperation partners, etc.
As an example of the refinement of an individual element through the use of subject elements in order to gain more precision, the example of DC.Date has been chosen. The diversity and the necessity of having sub-elements for certain Dublin Core Elements (but not for all) should be evident. The DC.Date, when not qualified, is considered to be the date of creation or of first publication on the net. However, a vast number of other dates may be relevant for the object. thus, DC.Date can be qualified in the following sub-elements:
DC.Date.Created DC.Date.Available DC.Date.LastModified DC.Date.Verified DC.Date.Published DC.Date.Accepted DC.Date.Expired DC.Date.DataGathered
The additional sub-elements provide additional information which may or may
not necessarily serve as search criteria, but also as filtering criteria.
Using the sub-element DC.Relation.Type, various relationships can be established to other resources. The use of this sub-element provides connections to other works in various relationships far beyond those used previously in the library catalog. For example: A photograph of an original Van Gogh painting object is digitized. The metadata for the digitized image includes a pointer to a metadata set for both the photograph and (if it exists) to the original painting. This is important since the Creator, Date.Created and other information is unique. Such information was being embedded into one HTML-file for the digitized image, but it was found that it was more sensible to hold to the ``one-to-one'' principle: one set of metadata for each digitized or non-digitized object. This means that three sets of metadata would exist, with pointers in the respective DC.Relation field of each metadata set connecting the three. Especially the newly developed Resource Description Framework (RDF) (http://www.w3.org/RDF/ ) and the use of Dublin Core Elements in XML will facilitate bringing together the multifaceted aspects of information on digitized and non-digitized objects in a multidimensional information system. The types of relationships to other resources which can be described using the DC.Relation.Type element are:
Inclusion Relations Reference Relations DC.Relation.IsPartOf DC.Relation.References DC.Relation.HasPart DC.Relation.IsReferencedBy Version Relations Creative Relations DC.Relation.IsVersionOf DC.Relation.IsBasedOn DC.Relation.HasVersionOf DC.Relation.IsBasisFor Mechanical Relations Dependency Relations DC.Relation.IsFormatOf DC.Relation.Requires DC.Relation.HasFormat DC.Relation.IsRequiredBy
The DC.Coverage Element is the one Dublin Core element which requires sub-elements for differentiated use. One aspect of the DC.Coverage is the geographical aspect of being able to use geospatial and geographical coordinates to identify the location or physical coverage limitations of images (and also respective data). This aspect will be an especially important one for use in astronomy. For instance, a digitized image of Saturn might include the following metadata:
<META = DC.Subject, CONTENT = ``Saturn''>
<META = DC.Format, CONTENT = ``.gif 640 x 512 pixel''>
<META = DC.Type, CONTENT = ``Image''>
<META = DC.Date.Created, CONTENT = ``19970623?''>
<META = DC.Coverage.x CONTENT = `` ''>
<META = DC.Coverage.y CONTENT = `` ''>
<META = DC.Coverage.z CONTENT = `` ''>
<META = DC.Coverage.t CONTENT = `` ''>
<META = DC.Identifier, CONTENT = ``http://www.not.iac.es/newwww/photos/images/satnot.gif''>
where coordinates x, y, z give the specific location at the time of creation of the image, and t the duration of the exposure.
The idea behind the Dublin Core and its emphasis on a simple structure was also to enable the creator of the document to submit his or her own metadata with the object itself (in the HMTL-header). Various templates have been developed for this, including the Nordic Metadate Template (DC.Creator by Traugott Koch and Matthias Borell; http://www.lub.lu.se/dgi-bin.nmdc.pl ), My Meta Maker for Theses (http://www.physik.uni-oldenburg.de/EPS/mmm/diss.html ) which is also used not only for theses but with modifications for the German subject servers of the learned societies, the template for the German Educational Resources Server (http://dbs.schule.de/db/inconeue.html ), etc. Ideally, in particular in the case of highly scientific material, the author is the best qualified to submit especially the content-oriented metadata for his or her work. Up until now, no adequate automated indexing service has been able to extract the necessary bibliographic information from HTML-files to fill in the respective metadata fields (even though some search engines purport to be able to do this and various projects to accomplish this have been proposed). In addition to the author/creator, the publisher also can produce and provide metadata, especially in the case of articles, books, etc. (see above ``DOI''). ``Trusted Third Party Metadata'' is a third alternative. Usually, the metadata from a trusted third party refers to more evaluative metadata (such as filtering mechanisms for children to avoid pornography, or evaluation of a certain teaching or learning program with regard to the school grade level, etc.), but may in the future also refer to ``seals of approval'' from certain learned societies or other recognized bodies for certain aspects of the necessary metadata. Librarians and information scientists (as well as information specialists) will still be needed to provide metadata, even if certain metadata are provided by the author/creator and/or publisher. In some cases, it will mean augmenting the metadata provided by these other sources. In other cases, librarians may wish to sell (or provide in another modality) their metadata to publishers, or they may be involved in providing metadata for items for which no metadata are available (i.e., also for earlier works which need to be linked to newer ones - which is already part of retrospective digitization projects). This will also be an important task in order to achieve the ideal goal of metadata in terms of providing precise resource discovery while bringing together all items of related interest. Furthermore, other scientists and researchers can also produce or augment existing metadata for an object.
Currently only a few search engines are capable of ``harvesting'' Dublin Core Metadata, though this number grows if the subject-oriented servers of the learned societies are considered. The Nordic Web Index (http://nwi.ub2.lu.se?lang=eng ) is part of the Nordic Metadata Project and has been harvesting Dublin Core Metadata in HTML-documents for well over a year; the Australian Metadata Search Engine (http://www.dstc.edu.au/dgi-bin/RDU/Harvest/meta_simple_query.cgi) requires users to register their documents at the search engine headquarters so that their metadata can be ``gathered'' into the search engine index.
In Germany, the search engine ``Fireball'' (http://www.fireball.de
) has its
own set of metadata which it generates automatically, but this does not
correspond to the Dublin Core set and is hardly more than the keyword and
data metadata which Alta Vista and HotBot gather. Lycos and InfoSeek have
not yet integrated metadata into their gathering criteria.
The more
universal search engines have the philosophy that metadata are not yet being
used widely enough to merit its integration in their search engines.
Furthermore, the entire idea of for instance, Dublin Core Metadata, was to
conquer the lack of precision of the general search engines and produce
greater precision for resource discovery and retrieval. Hence, the search
engines, which pride themselves on the high number of hits they can
achieve, are logically not interested in reducing the number of hits to a
fine 5-7 items (though the users might indeed truly desire this). However,
this would limit their advertising facility greatly.
In summary, the advantages of metadata, specifically Dublin Core Metadata,
include the fact that they can be integrated into the HTML-document header.
They are easy to implement especially with the use of a template so that
HTML-knowledge is not necessary; they enhance search precision and
filtering; they allow bringing together resources which have formal,
topical, or creative relationships to each other
(multidimensionality);
and they further standardization methods for information and use of
Internet resources for scientific purposes.
The uses of metadata are vast - and perhaps just now being realized
![[*]](foot_motif.gif)
.
The implementation of Dublin Core Metadata has reached an internationally
accepted standardization level. It has been officially accepted and is
being used in the following countries:
Internationally, the Dublin Core is supported by the World Wide Web Consortium (http://www.w3.org/Metadata/ ) and the European Union endorses the Dublin Core in the metadata required by project proposals. The use of Dublin Core (not yet fully officially) in the DOI has already been mentioned. Furthermore, the Dublin Core has submitted an RFC (``Request for Comment''; http://ds.internic.net/internet-drafts/draft-kunze-dc-02.txt ) to the Internet Engineering Task Force for the simple 15 elements without qualifiers, on the basis of an HTML-embedment. A second RFC for the more structured, expanded Dublin Core (15 elements with qualifiers LANG, SCHEME, and sub-elements) is being currently prepared for submission. In addition, an RFC for the use of Dublin Core in XML is in the discussion and development stage and can be expected to be submitted within 1998. Furthermore, an attribute set for Dublin Core for Z 39.50 is being developed. A series of DC Working Groups are working together to precisely define the use and implementation strategies, as well as to give lists of standardized Type and Format categories, prepare a handbook, etc., see http://purl.org/metadata/dublin_core/ . Several metadata registries to serve as reference servers for the Dublin Core are being developed at OCLC, in Germany (http://www.mpib-berlin.mpg.de/dok/metadata/gmr/gmr1e.htm ) and in Thailand. Thus to conclude, metadata, especially Dublin Core, will no doubt increase in use, in particular in the scientific community, in support of improving search and retrieval conditions for information use of the Internet and could serve to be an important indexing tool for the electronic and non-electronic information sources in astrophysics as well.
An extensive reading list on Dublin Core Metadata can be found at
http://www.mpib-berlin.mpg.de/dok/metadata/gmr/dcmdlit.htm
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