WCF: Best way to get data from Oracle 10g, MySQL and SQL Server 2008 databases?

I am designing a simple C# WCF service using ASP.NET 4.0 and hosted on IIS7, which will be used by .NET and Java web applications and desktop applications to extract data stored in various databases (both local and remote). I am starting to learn how to use VS2010 and WCF after working for a few years on VS2005 and asp.net web services, so am somewhat of a noob to WCF but know a bit about web servi开发者_Python百科ces and Visual Studio.

Does anyone have opinions on what the best approach would be in terms of project/class/file setup in Visual Studio 2010 to do this, seeing as how I want to maximize code re-use and minimize development time yet still have the ability to connect to the different databases? I have a WCF Service Application project for the service, and have generated a WCF Client to use for testing using svcutil.exe, but now I'm at the point where I need to start writing database access layer code (or "model" code for MVC if that's the design route I need to go down).

Any help appreciated, thanks!

Each of the databases will have their set of nuisances while integration.
The first thing you need to start with would be to design your model in more of OO (Object Oriented) fashion than relation DB way.
Once such a model is created, you need to implement mapper layer/classes that would map data from a relational form to a OO format.
Then for each DB you need to write some data access code. The amount of code you write for data access may well depend upon the tools\technologies you use. You could look into Entity Framework or NHibernate or other such ORMs to decrease the code required to access data.
But keep in mind these ORM mappers may require their own set of tweaks to work well with MySQL, Oracle, SQL Server.