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| creator |
Wagner, Ralf
| | date |
2001-04-30
| | | | description |
111 pages
| |
In this work, so-called federated functions are built by
interconnecting function calls to different application systems in a
distributed and heterogeneous environment. These federated functions
are realized as workflows, whereas the activities of the workflows
are responsible for invoking the single functions.
The workflows will be integrated into a federated database system by
means of wrappers, and table functions respectively. For the wrapper
approach, the SQL/MED standard will be utilized, which provides the
notion of foreign tables representing external data, i.e. in this
case the result data of workflows. The standard provides an
interface, which has to be used to implement wrapper executables
that are responsible for supplying the foreign tables with external
data.
In contrast to SQL/MED, the table function approach is not based on
such an elaborated standard because a standardized interface for the
implementation of table function executables is missing. Only the
DDL and DML for defining and accessing table functions is specified.
When the FDBS receives a global SQL query referencing a foreign
table or a table function, the associated wrapper executable or
table function executable respectively are responsible for executing
the correct workflow. The workflow then returns the result data from
its execution and the executable has to convert and transform this
data to correspond with the table format of the foreign table or the
table function respectively.
For every workflow a separate wrapper executable has to be
implemented. Therefore, the wrapper executable will be structured
and divided up into different components. As a result, only some of
the wrapper components have to be reimplemented for each workflow.
Some components of the wrapper can also be used to build the
corresponding table function executable.
In order to further decrease the efforts of implementing wrappers
and table functions, a generation approach will be proposed, which
minimizes the manual portion in implementing a wrapper. A user just
has to specify some information like the format of the table in the
federated database system and the mapping from the corresponding
data structures in the workflow to this table. Using these
specifications the wrapper executable, the table function executable
and their associated definitions can be generated automatically.
| | format |
application/postscript
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