B2B Integration : A Practical Guide to Collaborative E-commerce

Integration Patterns 63
systems — all of which may run on different platforms and hardware, be
supplied from different vendors, have different data schemas and support
their own dialect of structured query language (SQL). Multi-database
servers provide a single, consolidated view of the data from multiple
sources without physically moving the data from one source to another,
thereby eliminating the need to construct a separate database of redundant
data. An application which interfaces with a multi-database server does
not have to know anything about the underlying data sources, as the
multi-database server provides mapping, type conversion and multi-data
source joins and unions. The server provides full transaction integrity
by using two-phase commit protocol for write operations which spread
across multiple data sources. The server also acts as a storehouse of
views for read-only operations, which may also span across multiple
data sources.
Multi-database servers are one of the emerging solutions for data
oriented integration. Apart from integrating internal data sources, they
can transparently access data from business partners' data sources over
a network, if they are connected to Web gateways, all through the use
of only a single interface and a single SQL dialect. These servers can
work together with replication tools, or may even support replication
functionality implicitly.
For instance, there can be any number of applications connected to
the multi-database server using either ODBC or JDBC APIs. The
individual applications do not have to know about native API or SQL
dialect of each data source. The server interfaces with all the data
sources and invokes operations on them based on the requests received
from the applications.
Several companies, such as Oracle (Transparent Gateway), Sybase
(OmniConnect), DB2 (DataJoiner), Attunity (Connect), provide such a
solution. The support for various data sources differs from product to
product.
Oracle's Transparent Gateway (see Figure 3.15) provides the flexibility
to access transparently more than 40 non-Oracle systems, including
Microsoft SQL Server, IBM DB2 and Sybase.
IBM's product DB2 DataJoiner (see Figure 3.16) supports various
data sources, including all members of the IBM DB2 family, Microsoft
SQL Server, Oracle, Oracle RDB, Sybase, Sybase Anywhere, Informix