Re: Is it "allowed" to access a database in a BC from the outside?

Hi Atle,

Eric Evans did a couple of talks on his strategies for dealing with legacy
systems. Here's a recording from Skills Matter. The descriptions of the
migration strategies starts somewhere at around 28 minutes:
http://skillsmatter.com/podcast/java-jee/talk-from-eric-evans/mw-3447

Cheers

Dennis


--
Dennis Traub
Software Development Consultancy

Am Bogen 7
33178 Borchen

Phone:  05293/73942-73
Fax:    05293/73942-74
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Mail:   [email protected] <[email protected]>


On Wed, Apr 10, 2013 at 10:18 AM, atle03 <[email protected]> wrote:

> **
>
>
> Hi all,
>
> Anyone out there having experience on integrating a modern, DDD-style app
> with a legacy system?
>
> We are planning to slowly start to replace our legacy system with a set of
> smaller bounded contexts written DDD style. (This also means switching from
> legacy development technology to more modern tools - .NET in this case).
> The legacy system is very DB-centric, and will (because of the business
> value of its code base) be with us for a long time yet. This gradual
> replacement can be seen as a way of using Martin Fowler's strangler
> application pattern (
> http://martinfowler.com/bliki/StranglerApplication.html). An important
> note is that the legacy DB contains (almost) no stored procedures, just
> plain data.
>
> The strategy we have chosen is to let the new bounded contexts use
> (subsets of) the same database as the legacy system. This means that the
> repositories in each "new" BC will work towards a subset of the db tables
> used by the legacy system (they store their data in the same tables).
> Technically this seems to work well, but I am a bit concerned if there are
> more long-term aspects of this that we haven't thought about.
>
> Speaking in DDD terms, I guess we should see the common database as an
> shared kernel upstream to the new bounded contexts, and treat all db
> changes correspondingly. The repositories in the new bounded contexts will
> in addition to being a repository also act as an anti-corruption layer
> towards this shared kernel. But even with an ACL, we still have to pay
> special attention to database changes, since we cannot just compensate for
> everything in the ACL. Over time, more and more logic will be moved into
> the new bounded contexts, but for all foreseeable future the legacy will
> exist and some business processes will be implemented there.
>
> Anyone out there with any experience they want to share?
>
> Regards,
> Atle
>
>  
>