English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

One class of solutions to the problem of transparent distributed access to da tabase sys tems cons i s t ing of d i f fe ren t data mode l s (e.g. h ie ra rch ica l , ne twork and relational) involves the p lacement of a uni form layer (e.g. a shell) on top of the DBMSs running each of the databases. This short report proposes an architecture that supports the idea of such a uniform layer. Our foundation of the uniform layer is based on database logic [1,2]. Database logic being an extension of first order logic with the capabili ty to couch relational, network and hierarchical data models in it. The proposed architecture consists o f four levels. The first or lowest level maps the definit ions of the under lying conceptual database structures to the database structures defined in database logic. The languages used as a vehicle for such a mapping are generalizations of SQL and QUEL. Two such languages are Generalized Structured Query Language (GSQL) and Generalized Calculus (GCALC). Both of these languages are discussed in Jacobs [3]. By means of this mapping we interpret the essent ial character is t ics of the di f ferent unde r ly ing conceptua l database s t ructures into a s ingle c o m m o n database structure called cluster. A cluster is comprised of attributes which may either have atomic or non-a tomic domains . A c lus ter s t ructure can be v iewed conceptual ly as tables within tables. The second level of the archi tecture provides site t ransparency of database clusters. At this level one does not interact with the under ly ing DBMSs, the interaction is now managed by a dedicated DBMS such as DAVID [3]. This type of DBMS has among other functions the responsibili ty of performing complex to basic translat ions, external to conceptual t ranslat ions and query decomposi t ion. A query expressed in GSQL may be complex, for example a query in which one query is embedded or nested inside an other query. The input to the complex to basic translation process is a complex query and the output is a tree of s impler or basic queries. In the external to conceptual translation process we replace the external databases in a basic query with their def ini t ions in terms of the under ly ing conceptual databases. In query decomposit ion we take a basic query or set of basic queries and produce a tree of pr imit ive queries. Several min imiz ing considerat ions are used in deciding the order of decomposit ion. The third level of the architecture provides the mapping between the unified schema and the fragment clusters in the system. Each unified schema may be made up of several non-overlapping fragment clusters. At this level of the archi tecture , issues such as name conf l ic ts and data def in i t ions are resolved. If the unified schema is built on pre-existing databases then the type and constraint conflicts are resolved at this level also. The fourth or highest level of the proposed architecture is the interface with the user. This level is described in detail in a paper that is in preparation.

A software architecture for heterogeneous distributed database systems (abstract and references only)