DB-Adapters are responsible for data (queries and answers) flow. Simple input data (in common, unified language) from the front-end interface (GUI) is transferred through the middleware layer to the DB-Adapter where it is combined and converted to form formal SQL statements.
Statements are formed in consideration of the variety of the databases. Queries are sent to the appropriate servers. Data selected by these queries is then transformed into the common, unified form. Finally, they are passed on to the GUI interface.
Architecture of DB-Adapter
The DB-Adapter contains four main units:
- Query Manager
- Daily Cache Manager
The Process queries and forms, using parser module, formal SQL statements, which are executed by Connector unit.
Queries transmitted to the Query Manager have a Google like format, as for instance:
The Parser module cause, that each query, like "Woody Vasulka" is case insensitive and is interprated as the query for Woody AND Vasulka - plus sign ("+") is substituted for space.
In such a case, the search is performed within all fields, unless a query modifier is specified.
If query modifier is “author”:
The WHERE clause is attached - the “author” is a field which should be searched.
If a query contains minus sign ("-"), then the NOT clause is inserted.
The Connector negotiates and opens a connection with the corresponding server with the use of an appropriate driver.
Daily Cache Manager
The Daily Cache Manager creates and manages the Daily Cache table - a part of the DB-Adapter Database (DBA Database). The Daily Cache table contains metadata gathered from the database, to which the DB-Adapter is dedicated.
Metadata are stored in the OASIS unified format. The Daily Cache table is generated once a day by using a special statement specified in the DB-Adapter config file.
An Overview of the → system architecture is depicted in the following figure.
Reference material about OASIS Middleware:
The → Platform forms the Core elements of the OASIS project and presents central aspects of research.
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