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be they technical, bibliographical, or other.What OAI defines is only the manner of how data is
to be transported.This very feature makes OAI most valuable for communities which intend to
share resources via the Web such as bibliographic items and subject information. In other words,
the OAI protocol offers a standardized framework for all kinds of scholarly exchange, while the
establishment of content structures remains up to the user or the particular community of users.
It is possible to illustrate this by some examples: the protocol defines how an electronic archive
must respond when queried by a user. According to OAI, a request must comply to a particular
URL format, e.g., if users wish to know the metadata formats a given repository supports, they
have to issue an OAI compliant request
2
such as the following: http://www.perseus.tufts.edu/cgi-
bin/pdataprov?verb=ListMetadataFormats
In addition to the compulsory DC, a server which provides emblem data could also respond
in the following way:
<metadataFormat>
<metadataPrefix>emblem</metadataPrefix>
<schema>http://diglib.hab.de/rules/schema/emblem.xsd</schema>
<metadataNamespace>
http://diglib.hab.de/rules/schema/emblem.xsd
</metadataNamespace>
</metadataFormat>
The response tells the user which metadata formats may be retrieved from that particular
archive. After having checked the type of supported metadata, one can then retrieve the meta-
data records by issuing the following request:
http://www.perseus.tufts.edu/cgi-bin/pdataprov?verb=GetRecord&identifier=
oai:perseus.tufts.edu:Perseus:text:1999.01.0001&metadataPrefix=perseus
To check which items are available in an archive, one may use the following command:
http://www.perseus.tufts.edu/cgi-bin/pdataprov?verb=ListIdentifiers
All responses are given in XML.This example clearly shows how important exchange stan-
dards are. Procedures of requests and responses must be well defined to share metadata safely.
Processes are conducted automatically and permit simultaneously the searching of various data-
bases and the harvesting of relevant data.The OAI standard not only offers standardized access
models, but also features to update data and means to portion data by, e.g., time stamps. The
latter is an important feature, since users do not want to download all of the data every time,
but may wish to update the database only with the data that have changed in the meantime.
The OAI protocol takes all these cases into account and tremendously facilitates exchange pro-
cedures.
In short, OAI provides a very efficient basis for the interchange and updating of metadata.The
next step is to establish in which form we disseminate emblem metadata. Clearly, a particular
metadata set for emblems is required. Here one can think of two possible approaches.The first is
to apply the Dublin Core metadata set, which an OAI repository will necessarily be able to deliv-
er. Standard DC consists of 15 elements: title, creator, subject, description, publisher, contributor,
date, type, format, identifier, source, language, relation, coverage, rights. Simple DC, however, does
not suffice to deliver all the information required, making it difficult to map the complex meta-
data to these 15 categories. In addition, questions about the meaning of those categories arise, a
problem with which the DC community is not unfamiliar. For instance, what does the element
creator actually mean? If we talk about emblems, one may think of the author of the emblem book.
2
All examples are taken from the
Perseus project, see http://www.
perseus.tufts.edu
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