Databases Reference
In-Depth Information
With BPEL 1.1, you can only create variables based on global elements,
NOT global types.
When reusing components from other namespaces, refer to the
element
that is
defined against the type (as highlighted previously), rather than using the type
directly. Otherwise, the namespace of the top element will take on the namespace
of the schema that is reusing the type.
Finally, we recommend that you use different names for elements and complex
types. Although the XML Schema specification allows for an element and a type to
have the same name, this can cause issues for some tools. So for our purposes, we
prefix all types with a lower case "
t
" to indicate that it's a type.
Partitioning the canonical model
When building your first SOA application, it's very easy to fall into the trap of
defining a single schema that meets the specific needs of your current set of services.
However, as each project develops its own schema, it will often redesign its own
version of common elements. This not only reduces the opportunity for reuse, but
makes interoperability between applications more complicated as well as increases
the maintenance burden.
The other common pitfall is to design a single, all encompassing schema that defines
all your business objects within an organization. There are two issues with this
approach. First, you could end up "boiling the ocean", that is, you set out to define
every single business object with the organization and the project never starts
because it's waiting for the model to be completed.
Even if you take a more iterative approach, only defining what's required upfront
and extending this schema as new applications come on line, you very quickly end
up with the situation where every application will become dependent on this single
schema. Change often becomes very protracted, as a simple change could potentially
impact many applications. The end result is a strict change control being required,
often resulting in protracted time frames for changes to be implemented, which is
not exactly an agile solution.
