Extensible Metadata Repository for Information Systems - RUN UNL ...

The MDR has some extensibility issues, linked to reusability issues. The major issue with reusability
is that the basic unit in the repository is the XML Schema (as a Concept) and there are no tools or
mechanisms to reuse a Concept (or part of it) to create a new Concept. This means that, in practice,
people designing new Concepts will not try to reuse existing parts, because they will not gain
anything from it and this leads to creating Concepts that have similar meaning but different structure
because no one checked that a similar Concept already existed. In addition, the MDR does not
feature Concept versions; only Instances can have versions, which means there is no explicit support
for temporal evolution of Concepts.
The MDR is a good solution for the management of metadata in the SESS project and provides
several features identified as essential in metadata management earlier in this chapter and chapter
one. However, for a generic information system that needs to integrate external metadata that may
be in very different formats, it is not suitable to the task. The cost of transforming XML documents
and XML Schemas into Instances and Concepts, respectively, is very high. The lack of support for the
use of Concepts (or parts of) to create new Concepts does not promote reutilization and, as such,
people may find themselves redefining Concepts that are very similar (or that should have part of the
same structure) which leads to several conflicting definitions in the same repository.
2.5. Metadata Management Technologies and Repositories
Appreciation
There are several technologies to deal with metadata and two of the most representative ones are
XML and the Semantic Web. Semantic Web would be the most promising technology, but it has a
greater learning curve and some issues are still unresolved and subject to research. XML, although
not delivering some of the very interesting features of the Semantic Web is very stable and
widespread and there is much knowledge available about it, thus, it suits a current metadata
repository better than the Semantic Web. On another hand, current metadata repositories and tools
are limited because they either don’t support different kinds of metadata or, as seen in the SESS
repository, have issues with integration of foreign metadata.
Commercial solutions were left out of the evaluation since the use of metadata is not widespread
and many organizations don’t even grasp the benefits of using it; yet alone pay for a commercial
solution to manage their metadata. In the case of a SME, even if there’s interest in adopting a
solution for metadata management, the cost of a commercial one may simply be prohibitive. There
are some commercial solutions [97, 98] for metadata management, but they are directed to
enterprises of considerable dimension that can afford the high price of such a solution. These
solutions are very complete and provide enterprise wide management of metadata but usually are
deployed in level above the Information System (rather than supporting it) providing document
management, but not having a special focus on technical metadata and its relations with other
metadata. Computer-Aided Software Engineering (CASE) tools are, as the name implies, tools to
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