Re: Re: Conformist

"Paul Rayner [email protected] [domaindrivendesign]" <[email protected]> Thu, 17 Mar 2016 20:45:45 -0600
Newsgroups	gmane.comp.programming.domain-driven-design
Message-ID	<CAKKp0qg+T1Wrk4c1CHVgkAJH-k5e2RaRVyDandqHiL8P_RJ-Zw@mail.gmail.com>
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Tom,

Conformist is typically conforming to the upstream domain model without
sharing the actual implementation. However, conformist could also include
utilizing the upstream implementation, but purely in a client-only
relationship (not changing the upstream code) and perhaps only making
additive changes. Most teams that start sharing actual code wind up as
shared kernel unless they're really careful, but often without applying the
guidelines and warnings that go along with that happen, and get themselves
in all kinds of difficulties.

Paul.

On Wed, Mar 16, 2016 at 5:03 PM, [email protected]
[domaindrivendesign] <[email protected]> wrote:

>
>
> Tom,
>
> I agree that there is only little advice on how to implement the concepts
> of DDD. Most of the samples one can find are way to simple to be a guidan=
ce
> for the questions arising from real world implementation problems.
>
> Let's for a moment assume that you are right. What are the consequences o=
f
>  A directly using entities and domain services of B? How to they align wi=
th
> some of the more general goals of software architecture and DDD in
> particular?
>
>
> If A directly references entities of B, the B developers are no longer
> free to change their entities without the risk to break something in A.
> That is not only a compile time problem. Usually A starts piling up
> assumptions on the behavior of the B entities nobody outside of A is awar=
e
> of. Changing the behavior of an entity in B could break those assumptions
> causing bugs in A that are hard to find because they show up much later.
> Choosing this path deliberately could be called =E2=80=9EShared Kernel=E2=
=80=9C. Anyway,
> only after some time you will probably call it =E2=80=9EBig Ball Of Mud=
=E2=80=9C.
>
>
> The idea of bounded contexts is to divide the whole system into several
> smaller systems by setting up boundaries between them. There are good
> reasons for that explained in the blue book. One that goes for the
> developers: It gives you more freedom to change your stuff within the
> context without raising the risk to break something outside. But you will
> have to respect the boundaries=E2=80=A6
>
>
> Does that make sense?
>
>
> Rgs,
>
>
> Thomas
>
>=20
>

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<div dir=3D"ltr">Tom,<div><br></div><div>Conformist is typically conforming=
 to the upstream domain model without sharing the actual implementation. Ho=
wever, conformist could also include utilizing the upstream implementation,=
 but purely in a client-only relationship (not changing the upstream code) =
and perhaps only making additive changes. Most teams that start sharing act=
ual code wind up as shared kernel unless they&#39;re really careful, but of=
ten without applying the guidelines and warnings that go along with that ha=
ppen, and get themselves in all kinds of difficulties.=C2=A0</div><div clas=
s=3D"gmail_extra"><br clear=3D"all"><div><div class=3D"gmail_signature"><di=
v dir=3D"ltr"><div class=3D"gmail_signature">Paul.<div><br></div></div></di=
v></div></div><div class=3D"gmail_quote">On Wed, Mar 16, 2016 at 5:03 PM, <=
a href=3D"mailto:[email protected]">[email protected]</a> [doma=
indrivendesign] <span dir=3D"ltr">&lt;<a href=3D"mailto:domaindrivendesign@=
yahoogroups.com" target=3D"_blank">[email protected]</a>&g=
t;</span> wrote:<br><blockquote class=3D"gmail_quote" style=3D"margin:0px 0=
px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);borde=
r-left-style:solid;padding-left:1ex">


<u></u>









=20
<div style=3D"background-color:rgb(255,255,255)">
<span>=C2=A0</span>


<div>
  <div>


    <div>
=20=20=20=20=20=20
=20=20=20=20=20=20
      <p></p><p><span>Tom,</span></p>
<p><span>I agree that there is only little advice on how to implement the c=
oncepts of DDD. Most of the samples one can find are way to simple to be a =
guidance for the questions arising from real world implementation problems.=
=C2=A0</span></p>
<p><span>Let&#39;s for a moment assume that you are right. What are the con=
sequences of =C2=A0A directly using entities and domain services of B? How =
to they align with some of the more general goals of software architecture =
and DDD in particular?</span></p>
<p><span></span><br></p>
<p><span>If A directly references entities of B, the B developers are no lo=
nger free to change their entities without the risk to break something in A=
. That is not only a compile time problem. Usually A starts piling up assum=
ptions on the behavior of the B entities nobody outside of A is aware of. C=
hanging the behavior of an entity in B could break those assumptions causin=
g bugs in A that are hard to find because they show up much later. Choosing=
 this path deliberately could be called =E2=80=9EShared Kernel=E2=80=9C. An=
yway, only after some time you will probably call it =E2=80=9EBig Ball Of M=
ud=E2=80=9C.</span></p>
<p><span></span><br></p>
<p><span>The idea of bounded contexts is to divide the whole system into se=
veral smaller systems by setting up boundaries between them. There are good=
 reasons for that explained in the blue book. One that goes for the develop=
ers: It gives you more freedom to change your stuff within the context with=
out raising the risk to break something outside. But you will have to respe=
ct the boundaries=E2=80=A6</span></p>
<p><span></span><br></p>
<p><span>Does that make sense?</span></p>
<p><span></span><br></p>
<p><span>Rgs,</span></p>
<p><span></span><br></p>
<p><span>Thomas</span></p><div><br></div><p></p>

    </div>
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