| Metadata is usually defined as data about data, and semantics is the meaning of meaning. The most significant and difficult requirement for digital libraries (usually considered as distributed information systems on the web to provide resources and services to users) is to achieve a high level of "semantic interoperability". When computing involves with semantics, metadata and ontologies are becoming more and more significantly important to be the semantic building blocks for all kinds of information systems including digital libraries. But metadata or ontology itself, without some sort of mechanism, including term selection, profile composition, encoding formalization, ontology annotation, vocabulary mapping, authority controlling and service allocation etc., will not realize its full potential to implement semantics. In the dissertation, we call such a mechanism the "semantic architecture".We can never imagine that digital library applications will be developed with a uniformed data model or conformed to just a few metadata sets, such as Dublin Core, IEEE-LOM, EAD, VRA Core etc. There will be emerging numerous domain specific metadata sets continuously, while at the same time the sharing of metadata standards becomes widely accepted and popular. We have to set up an explicit tier to formalize the semantic description of the entities and establish a dynamic SOA services (with Web Services technology) within digital library systems. That's the best way to deal with the heterogeneous problem and to integrate the diversity information systems for digital libraries into a consolidated semantic view.The ideas in the dissertation were inspired by a lot of early digital library projects and contributions. Chapter 2 gives a brief retrospectation to these projects such as Infobus, Dienst, FEDORA, and especially to those interoperation protocol or architecture like Z39.50, STARTS, SDLIP and SDARTS, as well as some well-established and widely distributed interoperability solutions like OAI, OpenURL, and SRU/SRW. A semantic interoperation quadrant was introduced to examine the suitability of a series of W3C markup languages for encoding semantics, which consist of standard metadata element set mentioned above and knowledge organizingsystems (KOS). Semantic Web as a significant movement about Web technologies, which aims to move from syntactic interoperability to semantic interoperability and relies on machine interpretable semantic descriptions, is also a technical input to the designing of Semantic Architecture for digital libraries.Semantic interoperability is a major challenge in resources and services integration. Semantic heterogeneity comes from the mismatch in meanings with different tags represented by different terms from different vocabularies, when expressed with different schemas conformed to different guidelines. There are various kinds of conflicts that cause semantic inconsistencies with naming, data structure, attributes, granularity, types of values, etc. We think an integrity semantic architecture can help a lot to facilitate the semantic interoperability between systems.The research and experiments concluded that the semantic architecture is crucial for a digital library application especially in a distributed system environment. It can provide various approaches to overcome semantic interoperability problems, including the metadata profiles, encoding consistence, authority control, ontology functioning, semantic integration, etc. An articulated layered semantic architecture is established in a prototype for Chinese Cultural Celebrity Manuscripts Digital Library of Shanghai Library to provide semantic services with a wide range of standards and protocols.
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